Fluid Power Journal October 2020

OCTOBER 2020

www.fluidpowerjournal.com

Building

A Sports Mech THE TOP

PROPER CHECK VALVE SIZING P.12

REASONS

CYLINDERS

FAIL HIGH-PRESSURE HYDRAULIC CYLINDERS P.24

The World's Largest Exoskeleton P. 28

Innovative Designs & Publishing • 3245 Freemansburg Avenue • Palmer, PA 18045-7118

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ton. Weighted accumulators are appealing from the perspective of c usually practical for mobile applications. They must be mounted atively large, and they are heavy. Spring-loaded and gas-charged s, take up less space, and can be mounted horizontally, although it OCTOBER 2020 tically.

VOLUME 27 • ISSUE 9

IN THIS ISSUE

Features 6 The Top Three Reasons Cylinders Fail 12 Proper Check Valve Sizing Can Avoid Costly Problems

24

16

Fig. 1.BBa Weighted Accumulator

14 Eliminating Water Hammer: Check Valves Prevent Hydraulic Shock 16 Understanding the Function of Accumulators

Fig. 1.BBb Spring-Loaded Accumulator 24 Bringing Reliability to High-Pressure Hydraulic

s accumulators are sometimes referred to as having a gas spring Cylinders re are six main types: •

Piston

•

Bladder

72 • Mobile 28 Hydraulic Mechanic Certification

28 Cover Story: Building a Sports Mech

Departments 4

Publisher’s Note: The information provided in this publication is for informational purposes only. While all efforts have been taken to ensure the technical accuracy of the material enclosed, Fluid Power Journal is not responsible for the availability, accuracy, currency, or reliability of any information, statement, opinion, or advice contained in a third party’s material. Fluid Power Journal will not be liable for any loss or damage caused by reliance on information obtained in this publication.

CELEBRATING 60 YEARS

Notable Words

8

IFPS Update

18

Product Spotlight

23

Figure It Out

31

Classifieds

•

Bello

•

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N OTA B L E WO R D S

Hydrostatic Gear Drives and Evolving Electrohydraulic Applications

PUBLISHER Innovative Designs & Publishing, Inc. 3245 Freemansburg Avenue, Palmer, PA 18045-7118 Tel: 800-730-5904 or 610-923-0380 Fax: 610-923-0390 • Email: Art@FluidPowerJournal.com www.FluidPowerJournal.com

Founders: Paul and Lisa Prass

Associate Publisher: Bob McKinney Editor: Michael Degan

Technical Editor: Dan Helgerson, CFPAI/AJPP, CFPS, CFPECS, CFPSD, CFPMT, CFPCC - CFPSOS LLC

Art Director: Quynh Fisher Eastern Region Acct Executive: Norma Abrunzo Director of Creative Services: Erica Montes Accounting: Donna Bachman, Sarah Varano

Circulation Manager: Andrea Karges

By Jon Frey, Head of Engineering Systems and Solutions, Bosch Rexroth

»

WHEN FACED WITH the opportunity to develop a circuit or system design, application engineers can choose from a mechanical, electric, or hydraulic solution.

But what if the desired outcome does not fit neatly in one of these three options, or if the application requires linear movement?

Combining electric drive content with mechanical or hydraulic components has been accomplished successfully for many years. However, evolving requirements for compactness, energy efficiency, dynamics, accuracy, load-carrying ability, and other application-specific demands may necessitate more than bundling existing components to achieve a classic ball-screw/planetary-screw drive or power unit-satellite manifold-actuator solution.

These three independent technologies offer attractive solutions for state-of-the-art applications – and there are champions and advocates for each. However, hydrostatic gear drives combine the strengths and unique attributes of electrics and hydraulics to achieve a broader solution for the circuit or system designer.

The hydrostatic gear drive or self-contained hydraulic actuator combines existing technologies into unique, compact, dynamic, efficient configurations that can be designed for a singular application or a serialized solution. A hydrostatic gear drive may offer unique attributes that would be more difficult to achieve applying electromechanical drives alone.

One such attribute may be found within the definitions of hydrostatic gear drives and primary controlled actuators.

A fundamental precondition begins with an electrical drive – one where electrical energy input is converted to rotational output. A second condition is a method to convert rotational output into a linear movement, thereby determining a primary controlled actuator.

Using these two preconditions alone, the resulting solution could be either electromechanical or electrohydraulic and help to serve the application’s purpose. Either result could be described as a gear drive by converting rotary into linear movement.

However, other specific attributes become significant differentiators for a hydrostatic gear drive in their ability to offer a variable transmission via a differential actuator ratio and varying pump displacement. Application of a mechanical drive requires selection of pitch, diameter, and length, to name a few.

The electromechanical drive manufacturer prescribes data on the individual limits of these three attributes, and the circuit designer/solution provider elects the most relevant compromise to achieve the desired function. Enter the hydrostatic gearbox.

Differential cylinders can be used in regenerative mode to achieve equal extend or retract speeds; they can also opt out of regeneration mode and have full piston area available to generate force. This can result in a hi-low transmission of sorts, speed, or force and changeable, as necessary, in the circuit. (Continued on page 5)

4

OCTOBER 2020

INTERNATIONAL FLUID POWER SOCIETY 1930 East Marlton Pike, Suite A-2, Cherry Hill, NJ 08003-2141 Tel: 856-489-8983 • Fax: 856-424-9248 Email: AskUs@ifps.org • Web: www.ifps.org 2020 BOARD OF DIRECTORS

President: Jeff Kenney, CFPMHM, CFPIHM, CFPMHT - Dover Hydraulics South

Immediate Past President: Timothy White, CFPAI/AJPP, CFPS, CFPECS, CFPMIH, CFPMMH, CFPMIP, CFPMT, CFPMM - The Boeing Company

First Vice President: Rocky Phoenix, CFPMMH - Open Loop Energy, Inc.

Treasurer: Jeff Hodges, CFPAI/AJPP, CFPMHM - Altec Industries, Inc. Vice President Certification: Denis Poirier, Jr., CFPAI/AJPP, CFPHS, CFPIHM, CFPCC - Eaton Corporation

Vice President Marketing: Scott Sardina, PE, CFPAI, CFPHS Waterclock Engineering

Vice President Education: Kenneth Dulinski, CFPAI/AJPP, CFPECS, CFPHS, CFPMIH, CFMMH, CFPMT - Macomb Community College

Vice President Membership: John Bibaeff, PE, CFPAI, CFPE, CFPS DIRECTORS-AT-LARGE Chauntelle Baughman, CFPHS - OneHydraulics, Inc. Stephen Blazer, CFPE, CFPS, CFPMHM, CFPIHT, CFPMHT Altec Industries, Inc. Randy Bobbitt, CFPAI, CFPHS - Danfoss Power Solutions Cary Boozer, PE, CFPE - Motion Industries, Inc. Lisa DeBenedetto, CFPS - Argo-Hytos Daniel Fernandes, CFPECS, CFPS - Sun Hydraulics Brandon Gustafson, PE, CFPE, CFPS, CFPIHT, CFPMHM - Graco, Inc. Garrett Hoisington, CFPAI/AJPP, CFPS, CFPMHM Open Loop Energy Brian Kenoyer, CFPHS - Five Landis Corp.

James O’Halek, CFPAI/AJPP, CFPMIP, CMPMM The Boeing Company Mohaned Shahin, CFPS - Parker Hannifin Randy Smith, CFPHS - Northrop Grumman Corp.

HONORARY DIRECTORS-AT-LARGE AND EX-OFFICIO Ex-Officio: Donna Pollander, ACA, Executive Director Elizabeth Rehfus, CFPE, CFPS Paul Prass, Fluid Power Journal Robert Sheaf, CFPAI/AJPP, CFC Industrial Training

IFPS STAFF Executive Director: Donna Pollander, ACA Communications Director: Adele Kayser Technical Director: Thomas Blansett, CFPS, CFPAI Assistant Director: Stephanie Coleman Certification Coordinator: Kyle Pollander Bookkeeper: Diane McMahon Administrative Assistant: Beth Borodziuk

Fluid Power Journal (ISSN# 1073-7898) is the official publication of the International Fluid Power Society published monthly with four supplemental issues, including a Systems Integrator Directory, Off-Highway Suppliers Directory, Tech Directory, and Manufacturers Directory, by Innovative Designs & Publishing, Inc., 3245 Freemansburg Avenue, Palmer, PA 18045-7118.

All Rights Reserved. Reproduction in whole or in part of any material in this publication is acceptable with credit. Publishers assume no liability for any information published. We reserve the right to accept or reject all advertising material and will not guarantee the return or safety of unsolicited art, photographs or manuscripts.

WWW.FLUIDPOWERJOURNAL.COM • WWW.IFPS.ORG

Custom Modular Fittings (Continued from page 4) Conversely, an electromechanical drive may necessitate selecting a diameter and a pitch to achieve the most appropriate compromise.

Beyond the actuator, the hydrostatic gear drive may also incorporate a variable displacement pump in addition to the variable speed electric drive.

Using a variable displacement pump allows electric motor rotation to remain within desirable power bands through varying pump output flow to achieve actuator speed. Hydrostatic gear drives offer additional variants, since pumps can be combined to achieve greater flow outputs and conserve installation space requirements.

Pumps can be fixed, variable, or a combination of displacements.

Actuators can be single-rod, double-rod, tandem, multiarea, or even a motor if, for example, the linear output is a conveyor belt.

Hydrostatic gear drives offer greater load-holding ability in applications where a force dwell time is required for setting, curing, or clamping. The attributes of differential area actuators combined with variable displacement pump(s) provide circuit and system designers with an effective hydrostatic gear drive capability not easily matched with only electric or electromechanical drives.

Bundling hydrostatic gear technology within a self-contained hydraulic actuator can provide a fluid power solution that is scalable, configurable, dynamic, efficient, space-saving, and not easily displaced via other traditional solutions.

Hydrostatic gear drives can be integrated.

For example, drive packaging can minimize fluid volume, connections, tube lengths, and so on. They can also be distributed via a hydraulic pump and manifold being separated from the hydraulic cylinder.

In either scenario, integrated or distributed, the designer eliminates unnecessary fluid volumes, seeks to reduce size, and enhances efficiency while the hydraulic circuit is closed with no atmospheric tank. A truly self-contained hydraulic actuator or hydrostatic gear drive requires no external fluid connections.

From the user’s perspective it may be a complex electrical device, since it has hydraulic fluid in it, and the only external connections are electrical. As hydroelectric applications evolve, the hydrostatic gear drive offers circuit and systems designers a powerful tool to create successful solutions. 

WWW.IFPS.ORG • WWW.FLUIDPOWERJOURNAL.COM

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OCTOBER 2020

5

THE TOP

REASONS

CYLINDERS

FAIL

By Ryan Roberts, Market Specialist, Parker Hannifin Cylinder Division

Cylinders can fail for a number of reasons, from wrong specifications to operator error. However, in this day and age with a number of engineering tools available to help reduce spec errors and strong expertise within the fluid power industry, one of the leading causes of cylinder failure is still seals. Whether the seals are sized wrong, incorrect material is spec’d, or just installed wrong, error in sealing can have a major effect on the entire cylinder operation.

Cylinder operation is based on precise fluid pressure to both sides of the piston. If a seal breaks down and allows fluid to leak from one side of the piston to the other, or out of the cylinder all together, the pressures change, and your cylinder will no longer operate as intended. With over 100 years in the fluid power industry, Parker engineers have seen countless examples of how seal issues can escalate into much larger problems for a hydraulic system.

Seal issues tend to fall into three main categories: hardening, bad installation, and erosion.

the seal used in a cylinder is not specified to the appropriate pressure, pressure can get trapped underneath the seal and push it against the cylinder body, causing wear.

Recently, Parker cylinder engineers identified an issue of a piston seal getting blow by and causing the cylinder to drift in a hydraulic press application. They were able to identify that the seal thickness varied from about 1/32 of an inch under to almost 1/16 of an inch under print dimensions and that there was a slight amount of extrusion on the side of the seal facing toward the cap end of the cylinder. This would indicate higher pressure on the rod end of the cylinder that was getting trapped underneath the seal and pushing it against the cylinder body, causing wear.

Parker recommended switching from the KP piston seal to the HP, which is made of polyurethane, a tougher material, with reliefs molded into the sides of the seal to allow venting excess pressure underneath. This helped the customer identify an issue early that could have grown into a much bigger problem.

HARDENING

The Parker HP energized bidirectional piston seal improves on the low friction and long wear of lipseals by including excellent low-pressure sealing performance. Specially formulated polyurethane is long wearing and abrasion resistant with running friction comparable to lipseals. An O-ring energizer ensures virtually zero leakage in low-pressure applications. Also, pressure trapping that can result in energized lipseals is not possible with a single energized seal.

Parker’s HP piston seal is an excellent choice for most industrial applications operating with mineral-based hydraulic oil and is available in seal classes 1 and 4.

Seal hardening is exactly what it sounds like. The seal can solidify and dry out, making it hard and brittle. The most common reason for this is exposure to temperatures that are too high for the seal to handle. Be warned this is not just ambient temperature around the cylinder. The piston itself can generate substantial heat through motion and friction, causing wear to the seal.

This heat can be monitored by measuring the temperature of the hydraulic fluid entering and exiting the cylinder. There are several methods to combat hardening, including insulation and cooling, but the best way is to use materials that are suited for the temperature requirements for your application.

BAD INSTALLATION SEAL THICKNESS ISSUE

Seal thicker Seal thinner

While cylinder operation may seem simple on its surface, it takes precise installation of several parts to ensure that the cylinder will operate correctly for its entire life cycle. The seals are an integral part of this, and if they are misaligned it can allow hydraulic fluid to leak past the seals. This can cause problems in cylinder operation that lead to major failures and result in costly downtime.

EROSION Erosion can occur from three main sources. One cause is the general wear from the normal back-and-forth motion of the cylinder. Another source of erosion is pressure buildup. If

SEAL CLASS CHART

HP POLYURETHANE PISTON SEAL

KP FILLED PTFE PISTON SEAL The Parker KP bronze filled PTFE seal ring material has low-running friction for accurate positioning in closed loop servo applications.

When combined with a fluorocarbon energizing ring, the Parker KP seal is rated for 400° F and will increase service intervals in high-temperature applications when compared to fluorocarbon lipseals.

By combining the Parker KP seal with other energizer O-ring compounds and wear ring materials, the KP seal offers excellent service in all seal-class environments.

The final main source of erosion is use with an incompatible fluid. Hydraulic systems use a relatively incompressible fluid, and, given the application environment, different types of hydraulic fluids may be required. For example, use of synthetic hydraulic fluid may be used for highly flammable applications.

That is why you must keep in mind that not every seal will work with every application. If your job calls for a particular type of hydraulic fluid, evaluate the compatibility of the seal material to the fluid to ensure the seal will withstand the chemical properties of that fluid.

The Parker Sealing Technology Bulletin provides information on a variety of actuation sealing options and can help you choose the right seal for your application. 

6

OCTOBER 2020

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OCTOBER 2020

7

I F P S U P D AT E

»

On-demand Web Seminars

ACTUATORS • Hydraulic

Cylinder Fundamentals and Failure Modes • Increase

the Life of a Cylinder • Proper

Sizing of Conductors when using Single Rod Cylinders HYDRAULIC VALVES • Load

Sens, Pressure Compensation Application • Counterbalance

Valves • Flow

Dividers • Slip-In

Cartridge Valves • Industrial

Directional Control Valve Common Spools and Actuation • Load

Sensing Valves in Mobile Hydraulic Systems • Don’t

Be A Knob Turning Idiot!

8

CELEBRATING 60 YEARS

ATTENTION IFPS MEMBERS - Earn 1 professional development point toward your recertification by expanding your knowledge with our archived, on-demand web seminars. Log into ifps.org/web-seminars.

OCTOBER 2020

ELECTROHYDRAULICS • Closed

Loop Hydraulic Circuits • Hydromechanical

vs.

Electrohydraulic Solutions • Controller

Area Network (CANBUS) • Proportional

Valves - Wiring, Tuning, Troubleshooting • Proportional

Directional Control Valve Systems for Mobile Hydraulics • Part

1 and Part 2 • CANBus

for Mobile Proportional Valve Systems • Proportional

Valves • Troubleshooting

Electrohydraulic Amplifier Systems

HYDRAULICS GENERAL • Basic

Hydraulic Troubleshooting • Selecting

and Sizing Accumulators • High-Pressure

Hydraulics • Accumulators

in Hydraulic Systems

• PSIA

& PSIG – What’s the Difference?

• Rules

of Thumb – Thumbs Down CONTAMINATION CONTROL • Fluid

Maintenance • Contamination

Study of a Hydraulic System Using a Variable Volume Reservoir • Fluids

and Filtration Basics • Cavitation

and Aeration • Causes

and Cures • Filter

Sizing ENERGY SAVINGS • Pressure

Controls Factors to Predict Setting in Applications • Designing

& Building a Machine for Energy Conservation • The

Use and Misuse of Energy in Fluid Power Systems • How

to Fix an Air Leak So It Stays Fixed

• Energy

Savings in Pneumatic Systems • Transforming

Fluid Power • Hydraulics

• Applications

• Pneumatics

PUMPS • Hydraulic

Pump Modeling for Application Engineers • Pumps,

Controls & Where to Set the Relief PNEUMATICS • Pneumatic

Filtration • IO Link High Level Basic Functionality • Machine

Safety Overview • Vacuum

Basic Concepts

WWW.FLUIDPOWERJOURNAL.COM • WWW.IFPS.ORG

I F P S U P D AT E

Newly Certified Accredited Instructors

»

CONGRATULATIONS TO OUR new certified fluid power Accredited Instructors (AI) and Authorized Job Performance Proctors (AJPP.) The approved applicants, who must hold at least one certification, conducted a planned presentation and were evaluated by a panel of subject-matter experts and peers during a recent instructor training workshop in Detroit.

MARK FIORI, CFPMIH, CFPAI, CFPJPP, CFPJPCC MICHAEL O’CONNOR, CFPHS, CFPAI, CFPJPP, CFPJPCC BRADLEY WAGNER, MMH, CFPHS, CFPAI, CFPJPP, CFPJPCC

To become an AI or AJPP, register for the upcoming instructor training workshop in Kansas City, Missouri, Nov. 30-Dec. 2. Register at www.ifps.org or call 800-308-6005.

CELEBRATING 60 YEARS

ACCREDITED INSTRUCTOR

Certification for Today's Mobile Hydraulic Mechanic

»

IN 2021, IFPS WILL RELEASE a n upgraded Mobile Hydraulic Mechanic Certification Study Manual that reflects the knowledge and skills needed for today’s mobile hydraulic mechanic. It aligns more closely with the European Fluid Power Committee and CETOP.

ADDED AND IMPROVED AREAS OF THE MANUAL: • Principles

of operation explained for commonly found components within a mobile hydraulic system – pumps, valves, actuators, and accessories • Color-coded

cutaway illustrations of hydraulic components to aid in understanding operation • Symbology

updated to conform to ISO 1219 • Expanded

content on troubleshooting to include decision-tree aids • Detailed

content on pressure, flow, and directional control valves • Improved

graphics throughout and many real-life photos to assist in visualization • Basic

hydraulic calculations useful in troubleshooting • Safety

tips • Basic

principles of electrohydraulic control – open loop and closed loop • Electrohydraulic

valves • Sensors

used in electrohydraulic systems

WWW.IFPS.ORG • WWW.FLUIDPOWERJOURNAL.COM

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OCTOBER 2020

9

I F P S U P D AT E

Certification Testing Locations ndividuals wishing to take any IFPS written certification tests can select from convenient locations across the United States and Canada. IFPS is able to offer these locations through its affiliation with The Consortium of College Testing Centers provided by National College Testing Association.

I

TENTATIVE TESTING DATES FOR ALL LOCATIONS: November 2020 Tuesday 11/3 • Thursday 11/19 December 2020 Tuesday 12/1 • Thursday 12/17 January 2021 Tuesday 1/12 • Thursday 1/28 February 2021 Tuesday 2/2 • Thursday 2/25

ALABAMA Auburn, AL Birmingham, AL Calera, AL Decatur, AL Huntsville, AL Jacksonville, AL Mobile, AL Montgomery, AL Normal, AL Tuscaloosa, AL ALASKA Anchorage, AK Fairbanks, AK ARIZONA Flagstaff, AZ Glendale, AZ Mesa, AZ Phoenix, AZ Prescott, AZ Scottsdale, AZ Sierra Vista, AZ Tempe, AZ Thatcher, AZ Tucson, AZ Yuma, AZ ARKANSAS Bentonville, AR Hot Springs, AR Little Rock, AR CALIFORNIA Aptos, CA Arcata, CA Bakersfield, CA Dixon, CA Encinitas, CA Fresno, CA Irvine, CA Marysville, CA Riverside, CA Salinas, CA San Diego, CA San Jose, CA San Luis Obispo, CA Santa Ana, CA Santa Maria, CA Santa Rosa, CA Tustin, CA Yucaipa, CA COLORADO Aurora, CO Boulder, CO Springs, CO Denver, CO Durango, CO Ft. Collins, CO Greeley, CO Lakewood, CO Littleton, CO Pueblo, CO DELAWARE Dover, DE Georgetown, DE Newark, DE FLORIDA Avon Park, FL Boca Raton, FL Cocoa, FL Davie, FL Daytona Beach, FL Fort Pierce, FL Ft. Myers, FL Gainesville, FL Jacksonville, FL Miami Gardens, FL Milton, FL New Port Richey, FL Ocala, FL Orlando, FL Panama City, FL Pembroke Pines, FL Pensacola, FL Plant City, FL Riviera Beach, FL Sanford, FL

10

OCTOBER 2020

Tallahassee, FL Tampa, FL West Palm Beach, FL Wildwood, FL Winter Haven, FL GEORGIA Albany, GA Athens, GA Atlanta, GA Carrollton, GA Columbus, GA Dahlonega, GA Dublin, GA Dunwoody, GA Forest Park, GA Lawrenceville, GA Morrow, GA Oakwood, GA Savannah, GA Statesboro, GA Tifton, GA Valdosta, GA HAWAII Laie, HI IDAHO Boise, ID Coeur d ‘Alene, ID Idaho Falls, ID Lewiston, ID Moscow, ID Nampa, ID Rexburg, ID Twin Falls, ID ILLINOIS Carbondale, IL Carterville, IL Champaign, IL Decatur, IL Edwardsville, IL Glen Ellyn, IL Joliet, IL Malta, IL Normal, IL Peoria, IL Schaumburg, IL Springfield, IL University Park, IL INDIANA Bloomington, IN Columbus, IN Evansville, IN Fort Wayne, IN Gary, IN Indianapolis, IN Kokomo, IN Lafayette, IN Lawrenceburg, IN Madison, IN Muncie, IN New Albany, IN Richmond, IN Sellersburg, IN South Bend, IN Terre Haute, IN IOWA Ames, IA Cedar Rapids, IA Iowa City, IA Ottumwa, IA Sioux City, IA Waterloo, IA KANSAS Kansas City, KS Lawrence, KS Manhattan, KS Wichita, KS KENTUCKY Ashland, KY Bowling Green, KY Erlanger, KY Highland Heights, KY Louisville, KY Morehead, KY

LOUISIANA Bossier City, LA Lafayette, LA Monroe, LA Natchitoches, LA New Orleans, LA Shreveport, LA Thibodaux, LA MARYLAND Arnold, MD Bel Air, MD College Park, MD Frederick, MD Hagerstown, MD La Plata, MD Westminster, MD Woodlawn, MD Wye Mills, MD MASSACHUSETTS Boston, MA Bridgewater, MA Danvers, MA Haverhill, MA Holyoke, MA Shrewsbury, MA MICHIGAN Ann Arbor, MI Big Rapids, MI Chesterfield, MI Dearborn, MI Dowagiac, MI East Lansing, MI Flint, MI Grand Rapids, MI Kalamazoo, MI Lansing, MI Livonia, MI Mount Pleasant, MI Sault Ste. Marie, M Troy, MI University Center, MI Warren, MI MINNESOTA Alexandria, MN Brooklyn Park, MN Duluth, MN Eden Prairie, MN Granite Falls, MN Mankato, MN MISSISSIPPI Goodman, MS Jackson, MS Mississippi State, MS Raymond, MS University, MS MISSOURI Berkley, MO Cape Girardeau, MO Columbia, MO Cottleville, MO Joplin, MO Kansas City, MO Kirksville, MO Park Hills, MO Poplar Bluff, MO Rolla, MO Sedalia, MO Springfield, MO St. Joseph, MO St. Louis, MO Warrensburg, MO MONTANA Bozeman, MT Missoula, MT NEBRASKA Lincoln, NE North Platte, NE Omaha, NE NEVADA Henderson, NV Las Vegas, NV North Las Vegas, NV Winnemucca, NV

CELEBRATING 60 YEARS

NEW JERSEY Branchburg, NJ Cherry Hill, NJ Lincroft, NJ Sewell, NJ Toms River, NJ West Windsor, NJ NEW MEXICO Albuquerque, NM Clovis, NM Farmington, NM Portales, NM Santa Fe, NM NEW YORK Alfred, NY Brooklyn, NY Buffalo, NY Garden City, NY New York, NY Rochester, NY Syracuse, NY NORTH CAROLINA Apex, NC Asheville, NC Boone, NC Charlotte, NC China Grove, NC Durham, NC Fayetteville, NC Greenville, NC Jamestown, NC Misenheimer, NC Mount Airy, NC Pembroke, NC Raleigh, NC Wilmington, NC NORTH DAKOTA Bismarck, ND OHIO Akron, OH Cincinnati, OH Cleveland, OH Columbus, OH Fairfield, OH Findlay, OH Kirtland, OH Lima, OH Maumee, OH Newark, OH North Royalton, OH Rio Grande, OH Toledo, OH Warren, OH Youngstown, OH OKLAHOMA Altus, OK Bethany, OK Edmond, OK Norman, OK Oklahoma City, OK Tonkawa, OK Tulsa, OK OREGON Bend, OR Coos Bay, OR Eugene, OR Gresham, OR Klamath Falls, OR Medford, OR Oregon City, OR Portland, OR White City, OR PENNSYLVANIA Bloomsburg, PA Blue Bell, PA Gettysburg, PA Harrisburg, PA Lancaster, PA Newtown, PA Philadelphia, PA Pittsburgh, PA Wilkes-Barre, PA York, PA

SOUTH CAROLINA Beaufort, SC Charleston, SC Columbia, SC Conway, SC Graniteville, SC Greenville, SC Greenwood, SC Orangeburg, SC Rock Hill, SC Spartanburg, SC TENNESSEE Blountville, TN Clarksville, TN Collegedale, TN Gallatin, TN Johnson City, TN Knoxville, TN Memphis, TN Morristown, TN Murfreesboro, TN Nashville, TN TEXAS Abilene, TX Arlington, TX Austin, TX Beaumont, TX Brownsville, TX Commerce, TX Corpus Christi, TX Dallas, TX Denison, TX El Paso, TX Houston, TX Huntsville, TX Laredo, TX Lubbock, TX Lufkin, TX Mesquite, TX San Antonio, TX Victoria, TX Waxahachie, TX Weatherford, TX Wichita Falls, TX UTAH Cedar City, UT Kaysville, UT Logan, UT Ogden, UT Orem, UT Salt Lake City, UT VIRGINIA Daleville, VA Fredericksburg, VA Lynchburg, VA Manassas, VA Norfolk, VA Roanoke, VA Salem, VA Staunton, VA Suffolk, VA Virginia Beach, VA Wytheville, VA WASHINGTON Auburn, WA Bellingham, WA Bremerton, WA Ellensburg, WA Ephrata, WA Olympia, WA Pasco, WA Rockingham, WA Seattle, WA Shoreline, WA Spokane, WA WEST VIRGINIA Ona, WV WISCONSIN La Crosse, WI Milwaukee, WI Mukwonago, WI

WYOMING Casper, WY Laramie, WY Torrington, WY CANADA ALBERTA Calgary, AB Edmonton, AB Fort McMurray, AB Lethbridge, AB Lloydminster, AB Olds, AB Red Deer, AB BRITISH COLUMBIA Abbotsford, BC Burnaby, BC Castlegar, BC Delta, BC Kamloops, BC Nanaimo, BC Prince George, BC Richmond, BC Surrey, BC Vancouver, BC Victoria, BC MANITOBA Brandon, MB Winnipeg, MB NEW BRUNSWICK Bathurst, NB Moncton, NB NEWFOUNDLAND AND LABRADOR St. John’s, NL NOVA SCOTIA Halifax, NS ONTARIO Brockville, ON Hamilton, ON London, ON Milton, ON Mississauga, ON Niagara-on-the-Lake, ON North Bay, ON North York, ON Ottawa, ON Toronto, ON Welland, ON Windsor, ON QUEBEC Côte Saint-Luc, QB Montreal, QB SASKATCHEWAN Melfort, SK Moose Jaw, SK Nipawin, SK Prince Albert, SK Saskatoon, SK YUKON TERRITORY Whitehorse, YU UNITED KINGDOM Elgin, UK GHAZNI Kingdom of Bahrain, GHA Thomasville, GHA EGYPT Cairo, EG JORDAN Amman, JOR NEW ZEALAND Taradale, NZ

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I F P S U P D AT E

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OCTOBER 2020

11

CHECK VALV E S 12

OCTOBER 2020

PROPER CHECK VALVE

S Z NG

CAN AVOID COSTLY PROBLEMS

By Sheila Kennedy, CMRP, Additive Communications Managing Director Brian Strait, Business Development Manager, Check-All Valve Mfg. Co.

IT IS SURPRISINGLY common for check valve sizing to be an afterthought in the flow-control and fluid-process industries. Often marketed together with gate and globe valves, check valves are such a small part of the gate, globe, and check valve market that many engineers in the field don’t even think about their sizing. It is usually check valve failure that prompts engineers to seek technical support. Even then, they may not consider that sizing is the underlying issue.

Check valves serve essential functions. They’re primarily used to prevent the reverse flow of media – liquid, gases, and steam, typically – but can also be used for vacuum breaking, low-pressure relief, line isolation, manifolding, media injection, and many other applications.

By allowing flow in one direction only, check valves prevent damaging backflow, and some styles can prevent hydraulic shock, otherwise known as water hammer. (See article page 14.)

There are different items to consider when sizing media-actuated check valves versus other types of flow-control valves that utilize externally actuated methods.

Systems operate more effectively and reliably when check valves are properly sized.

Correctly sizing valves protects them from preventable problems such as wearing prematurely or breaking apart, which can disrupt processes and cause damage to other equipment and components.

WHY OVERSIZING IS A PROBLEM Valves that are oversized can experience a significantly shorter lifespan due to premature wear, potentially leading to complete failure. If they come apart, they can damage or destroy more expensive components upstream or downstream – normally downstream of the check valve – resulting in costs that are far greater than a simple valve replacement. A telltale sign of oversizing is when the check mechanism rattles and chatters because it is not opening and closing properly.

WHY UNDERSIZING IS A PROBLEM Undersized check valves can create a choked flow condition, which means a process doesn’t get the flow of media or pressure it needs downstream of the check valve. When the valve is too small, it will interfere with the performance of the intended function.

Because the system can’t operate effectively, it can put more strain and stress on the source of the flow, such as a pump. Furthermore, when a check valve is undersized or the spring is too heavy, the checking mechanism may not perform as desired.

Even if the valve size matches the line size, the flow capacity is less than required for the application, causing choked flow. As a result, it will not produce the flow of media needed downstream to accomplish the intended function.

For example, a system requiring 100 gallons per minute of flow and 50 pounds per square inch of pressure to operate effectively may fall short with undersized check valves or improperly selected springs.

INCENTIVES FOR ACCURACY A common adage says the final cost of a valve is much more important than the first cost of a valve. In other words, an inexpensive commodity valve that must be replaced frequently will likely cost more in parts and labor than using a performance check valve made to meet the application needs. Paying a little more for a valve that’s going to last a long time and have few issues will cost much less over time.

Properly sizing check valves improves valve operation, promoting a longer life cycle; minimizes the frequency, costs, and duration of valve maintenance, repair, and replacement; reduces downtime from valve failure and consequential equipment damage or destruction; and enables adequate flow and pressure to operate at optimum performance.

HOW TO GET SIZING RIGHT Sizing is highly dependent on the type of valve. For most flow-control valves, including gate valves, globe valves, and ball valves, it is simply based on the size of the line. Also, these valve types

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are manually throttled. With the turn of a handle, a ball or gate valve’s opening mechanism can be manipulated as much as needed to achieve the desired pressure loss or flow coefficient (Cv). Because of this capability, using these valve types with a flow capacity well in excess of what is needed for the application is oftentimes desired.

For example, if a valve Cv of 100 is required for an application to achieve the desired flow and pressure drop of the media, then it is okay to use a valve that is 150 Cv capable if it can be throttled down to 100 Cv by turning the handle. Manually operated valves, such as ball valves, are much less sensitive to varying flow conditions.

On the other hand, a check valve is automatic, whereby it is activated by flow conditions. This makes accurate valve sizing more important. For spring-loaded check valves specifically, proper spring selection is essential for optimum valve performance.

When it comes to spring-loaded check valves, or any sort of check valve that is operated by the media, the media’s function is what opens the valve; no external controls are involved. Whether the media is gas or liquid is important in sizing. With gas sizing, pressures and temperatures must be considered. With liquid sizing, temperature has little effect because it doesn’t affect the compressibility. Pressure cannot compress liquid, but it can compress or expand gas.

The cracking pressure is equal to the minimum pressure differential it takes to initially open the valve. Some additional amount of pressure differential and flow is needed to open a valve fully, but if the spring is too heavy, it will not fully open and ultimately will rattle, chatter, and may wear out prematurely.

With the points we’ve discussed in mind, here are the basic steps to properly size a check valve: the line size, media, and tem• Determine

perature of the application. the flow and pressure of the system.

• Determine

• Calculate

the required Cv based on the application flow conditions.

• Choose

the right spring and valve style and size with proper Cv to make sure the valve operates properly in the system.

Industry-standard sizing formulas are available to assist with the calculations.

It is highly important to make sure the media can fully open and fully close the valve by flow and pressure differential. Normally, you want to get the minimum setting to make sure it opens fully and yet takes as little pressure away as possible. An exception is when

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an application requires the check valve to hold back a certain amount of pressure to make a pump operate more effectively, for example.

IMPORTANCE OF AN EFFECTIVE SUPPLY PARTNER The time lost to correct a problem depends on how fast the valve provider can supply properly selected product for the application. Expert advice is another quality sought in valve partners, whether for troubleshooting or specification advice. 

LOOK FOR A PROVIDER WHO CAN HELP YOU FIND PROPERLY SELECTED AND SIZED CHECK VALVES SO YOUR SYSTEMS WILL OPERATE AS EFFICIENTLY AND ECONOMICALLY AS THEY CAN.

OCTOBER 2020

13

CHECK VALV E S 14

OCTOBER 2020

CHECK VALVES PREVENT HYDRAULIC SHOCK

BY DESIGN

By Sheila Kennedy, CMRP, Additive Communications Managing Director Brian Strait, Business Development Manager, Check-All Valve Mfg. Co.

WATER HAMMER CAN be so damaging to machinery and dangerous to human health that every effort should be taken to prevent this hazard. Also called hydraulic shock, water hammer sounds like a mechanical noise and is sometimes perceived to be a valve slamming closed. In reality, it is a phenomenon that occurs in piping systems when fast-moving fluid stops instantly, or reverse flow begins. The sudden change in momentum or direction induces the hydraulic shock wave, creating what sounds like a loud bang.

The jarring water-hammer noise is a recognizable symptom of a serious problem. Though short-lived, the pressure or shock wave will reverberate all the way through the fluid-handling system until it eventually dissipates. The banging or hammering sound is a result of the pressure spike traveling through the media, bouncing back and forth against the pipe walls, valves, and other obstacles in its path – putting them at risk of damage or destruction. OSHA accident reports detailing water-hammer incidents illustrate the potentially harrowing nature of its effects.

Because of its risks to equipment reliability, process performance, and safety, it is essential to prioritize the elimination of hydraulic shock and its costly consequences. Proper valve selection and sizing can help avert the damaging

effects of water hammer. Spring-loaded check valves, designed primarily to prevent the reverse flow of media, are uniquely effective at minimizing if not eliminating the phenomenon.

UNDERSTANDING THE PROBLEM Compared to industrial systems, the water hammer heard in household plumbing probably won’t do much damage. When a kitchen-sink faucet running at full force is shut off suddenly, or a washing machine finishes filling, the abrupt stop causes the surge of water to slam against the pipes.

Recurrences over time can loosen a pipe’s connections or joints, potentially causing a water leak. To mitigate further hydraulic shock, the pipes can be tightened and secured, and devices such as pressure reducers or water hammer arrestors can be installed.

In industrial fluid processes, where the hydraulic shock is more powerful, the system is more extensive, and the components are more sensitive, the risks of water hammer are greater.

Usually a liquid is involved, but it can also occur with a gas, steam, slurry, or multiphase fluid. When a forced stop of fluid or abrupt change in fluid direction creates hydraulic shock, the transient

pressure spike and shaking effects could destroy anything from pressure sensors and flow meters to pumps, boilers, and entire piping systems. For instance, pressure spikes can travel into a pump and damage its impeller and drive.

Water hammer can destroy equipment, even knocking pumps off their moorings. The degree of damage caused by the momentary spike in fluid pressure depends on the intensity of the shock wave. But even mild water hammer can gradually degrade a system. It is best to assume there is no “safe” level of water hammer and to work toward its elimination.

OPERATIONAL AND HUMAN COSTS Failures arising from water hammer are extremely costly, not only in terms of repairs, replacements, and process downtime, but also due to the serious health, safety, and regulatory repercussions.

Significant operational effects may include cracked, ruptured, or burst pipes; blown gaskets; fractured fittings; damaged valves; leaking joints; compromised supports and pipe racks; destroyed expansion joints; collapsed structures; and disabled process equipment such as pumps, boilers, and steam systems.

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Severe injury or death can result for people in the vicinity if steam or hot condensate forcefully escapes, fluid-carrying hazardous chemicals are released, or equipment fragments are forcefully propelled into the air.

TACKLING THE CAUSE Properly designed pipeline systems won’t experience water hammer. Choosing the right valve type and components for the given media and application is essential to an efficient, effective, noise-minimizing fluid system. Valve styles that stop reverse flow or backflow before the flow direction changes will significantly minimize if not eliminate water hammer.

Earlier check valve designs were subject to hydraulic shock. For example, traditional swing check valves depend on flow reversal and gravity from the weight of the disc to fully close. The swing check valve’s disc, a moveable flapper, sits on a hinge pin, and forward fluid flow pushes it open. Reverse flow causes it to slam shut, returning it to its seat, though it doesn’t always close quickly enough to completely prevent backflow; or, when it does close, it can do so very rapidly.

Both conditions induce the damaging presFinally, silent check valves are engisure and shock wave of water hammer. neered to operate silently by closing On the other hand, modern spring- quickly and smoothly. They utilize a spring loaded check valves tackle the cause of water to assist the poppet in closing the check hammer by design. Inline spring-assisted valve before fluid flow reversal. check valves allow media (typically liquids, When selecting a spring-loaded check gases, and steam) to flow in one direction. valve, its style, size, flow coefficient, Media flow and pressure drop cause the cracking pressure, seat material, and temspring to collapse, allowing the valve to perature rating are among the important open. The spring closes the valve quickly and considerations. Ideal designs ensure that smoothly as the forward velocity of the fluid the media flows over smooth, contoured TM slows down or stops, preventing flow reversal. surfaces with a minimum change of direcThe most effective check valve style tion to minimize pressure drop. The orifice combines three characteristics. First, spring- size will be engineered to give a minimum loaded check valves incorporate a spring to pressure drop over the full flow range of Part number Part description Applicable machines Number of parts assist in closing the check valve before fluid the valve. Also, the valve will ensure posSWINGFLGLCK2062 Swing hose FlangeLock kit EX3600,by EX5600, EX8000 16 x 2062U - red FlangeLock flow reversal, thus avoiding water hammer. itive sealing inducing turbulence on They function equally well in vertical or horisurfaces just before16the SWINGCAP2062 Swing circuitthe cap kitseating EX3600, EX5600, EX8000 x 2062valve - cap zontal positions with proper spring selection. closes, helping to remove any minute forEX3600, EX5600, EX8000 16 x 2462U - purple FlangeLock TRAVELFLGLCK2462 Travel hose FlangeLock kit Secondly, poppet-style check valves are eign particles suspended in the fluid. spring-loaded to help close the valve priorTravel to circuit capWhen designing to avoid water TRAVELCAP2462 kit EX3600, EX5600, EX8000 16 hammer, x 2462 - cap fluid flow reversal, preventing water hammer. other factors are at play, such as avoiding 14 x 3262U - black FlangeLock Front attachment EX3600, EX5600, EX8000 FRONTATTFLGLCK326162 4 x 3261U - black & silver FlangeLock FlangeLock kit They incorporate a disc as the checking having pumps output into vertical lines; 14 x 3262 - cap FRONTATTCAP326162 Front attachment cap kit EX3600, EX5600, EX8000 pumps feed into a mechanism, normally at the end of a sleeve avoiding having multiple 4 x 3261 - cap Boom archcommon hose or stem. Designed to reduce maintenance header; and identifying the optimal EX3600, EX5600, EX8000 20 x 3262U - black FlangeLock BOOMARCHFLGLCK3262 FlangeLock kit costs, the seating surfaces are parallel to each valve locations within a piping system. Also be BOOMARCHCAP3262 Boom arch hose cap kit EX3600, EX5600, EX8000 20 x 3262 - cap other, thereby preventing the excessive wear aware of industry standards and regulations that can occur in plug, cone, and ball seats. regarding water hammer’s hazards. 

HITACHI FLANGELOCK AND CAP KITS AVAILABLE TM

Weight (kg)

TM

TM

6.7 4.5

TM

7.7 6.4

TM

TM

TM

TM

TM

8.9 9.5 9.9 11.3

CONTAMINATION CONTROL

Routine and scheduled maintenance of hydraulic systems are vital to getting the most out of your Hitachi Mining Excavator. While maintenance plays the largest role in the prevention of unnecessary machine downtime, it can also expose the hydraulic system to high levels of contamination rapidly decreasing component longevity. The importance of contamination control is sometimes overlooked when performing maintenance due to incorrect practices being used.

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CONTAMINATION CONTROL EASY sealing of open SAE code 61, 62 your hydraulic It allows for the simple Hitachi have packaged FlangeLock™ tool and caps specifically for Hitachi mining excavators. The Hitachi customised & make CAT-Style hydraulic without Constructed from lightweight aluminum. kits sure no matter whichflanges component routine tools. maintenance is being performed on, you will always have the exact Easyofon, easy off.™*Offers to hydraulic system and environmental number FlangeLocks and capsatoleakproof help reducesolution contamination. cleanliness. FlangeLock™ Tools stop the mess! ™ *Note: FlangeLocks are not to be used under pressure

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OCTOBER 2020

15

of energy energy whenever of energy working with whenever or with around or working around hydraulic with hydraulic accumulators. or around accumulators. hydraulic The energy accumulators.

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to an accumulator. to an accumulator.

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Understanding the Function of

also must also relieved be relieved must or isolated. also or be isolated. relieved or isolated.

There are several ways in which accumulators are used to absorb energy. The must returning flowbe from a large bore cylinder may be greater than should be conducted by the plumbing. A low-pressure accumulator can Accumulators Accumulators areHydraulic pre-loaded Accumulators are fluid pre-loaded so that are so there pre-loaded thatwill there be will so a minimum that be athere minimum pressure will be pressure afor minimum anyfor available any pressure available for any available receive a portion of the flow and then discharge it at an appropriate rate for the plumbing. has a relatively high rate of thermal expansion. If a volume of fluid is confined and unable to expand or fluid.

The fluid. three Thetypes three fluid. of types pre-loading The ofthree pre-loading are types weights, of are pre-loading weights, springs,springs, are andweights, gas. and The gas. springs, symbol The symbol and for agas. fluid forThe a fluid symbol for a fluid contract due to temperature changes, there could be very high pressure that could damage equipment or energy energy storagestorage or absorption energy or absorption storage device is device or the absorption extended is the extended device oval shown is oval the extended in shown Fig. 1.AA. in oval Fig.The 1.AA. shown specific The in Fig. specific 1.AA. The specific low pressure that could cause air bubbles to appear in the hydraulic fluid. Accumulators can be used to type of type accumulator of accumulator istype shown ofisaccumulator by shown the additional by the isadditional shown symbols by symbols the within additional the within oval, symbols the asoval, shown within as Fig.1.BBa, shown the oval, Fig.1.BBa, as shown Fig.1.BBa, absorb the expanding fluid and/or supply the contracting fluid. They also absorb and dissipate energy when used to dampen pressure pulses, reducing noise and vibration.

1.BBb, 1.BBb, and 1.BBc. and Of 1.BBc. 1.BBb, the three Of and thetypes three 1.BBc. oftypes Of accumulators, the of three accumulators, types onlyof the accumulators, only weighted the weighted oneonly hasone the constant has weighted constant one has constant

ACCUMULATORS

*

pressure. pressure.

The pressure The pressure. pressure is produced is The produced pressure by the by weight is the produced weight dividedby divided bythe theweight by area theof divided area the supporting ofby the the supporting area of the supporting

Safety Tip: Accumulators store energy. There is the potential for the sudden, uncontrolled release piston. piston.

Weighted accumulators accumulators Weighted are appealing are accumulators appealing from the from are perspective appealing the perspective from of circuit the of perspective design circuit but design are of but circuit are are of energy whenever working with or around hydraulic accumulators.

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This relatively relatively large, and large, relatively and are they heavy. large, are heavy.

Spring-loaded and they Spring-loaded are heavy. and gas-charged Spring-loaded and gas-charged accumulators andaccumulators gas-charged weigh weigh accumulators weigh must also be relieved or isolated.

A

ccumulators come in a

less, take less, up take less up space, less less,and space, take can up and be less can mounted space, be mounted horizontally, and canhorizontally, be mounted although although horizontally, it is preferred it is preferred although to mount it toisaccumulators mount preferred accumulators to mount Accumulators are

Accumulators are pre-loaded so that there will be a minimum pressure for any available vertically. vertically. vertically. fluid. The three types variety of pre-loading are weights, springs, and gas. The symbol a fluid preloaded so thatforthere of forms and have energy storage or absorption device is the extended oval shown in Fig. 1.AA. The specific be asashown minimum important functions insymbols many type of accumulator is shown by the additional withinwill the oval, Fig.1.BBa, 1.BBb, and 1.BBc. Of the three types of accumulators, only the weighted one has constant They are used pressure any availpressure. Thehydraulic pressure is circuits. produced by the weight divided by the area for of the supporting piston. Weighted accumulators are appealing from the perspective of circuit The designthree but are Fig. to store or absorb hydraulic energy. able fluid.

Fig.1.AA 1: not usually practical for mobile applications. They must be mounted vertically, they are Extended Oval Extended relatively large, When and they are heavy.

Spring-loaded and gas-charged accumulators weigh storing energy, they receive types of preloading are less, take up less space, and can be mounted horizontally, although it is preferred to mount accumulators oval pressurized hydraulic fluid for later weights, springs, and vertically.

use. Sometimes accumulator flow gas. The symbol for a fluid energy is added to pump flow to speed up storage or absorption device is the a process. Other times the stored extended oval shown in figure 1. energy is kept in reserve until it is The specific type of accumulator 1.BBa Fig.symbols Weighted 1.BBa Weighted Fig. 1.BBa Weighted Fig. 1.BBb Fig. Spring-Loaded 1.BBb Spring-Loaded Fig. 1.BBb Spring-Loaded Fig. 1.BBc Fig.Gas-Charged 1.BBc Gas-Charged Fig. 1.BBc Gasneeded and may be independent of is shown by theFig. additional Fig. 4:Accumulator Gas-charged Fig. 2: Weighted Accumulator Fig. 3: Accumulator Accumulator Accumulator Accumulator Accumulator Accumulator Accumula pump flow. This could be for emer- within the oval, as shown in figures accumulator Spring-loaded accumulator Gas accumulators Gas accumulators are Gas sometimes accumulators are sometimes referred are referred to sometimes as having to as referred having a gas spring. a to gas as spring. having In the a In gas gas the accumulator spring. gas accumulator In the category, gas category, accumul accumulator gency power when pump flow is not 2, 3, and 4. Of the three types of accuthere are there six are main sixtypes: main theretypes: are six main types: available.

It could be Fig. used to hold mulators, only the weighted one has Fig. 1.BBa Weighted 1.BBb Spring-Loaded Fig. 1.BBc Gas-Charged • Piston • Piston • Piston • Bellows • Bellows • Bellows Accumulator Accumulator pressure in a system whenAccumulator pump constant pressure.

The pressure is A hydraulic mechanic may be amount of hydraulic fluid), the • Bladder • Bladder • Bladder • Noise • Suppressor Noise Suppressor • Noise Suppressor Gas accumulators are sometimes referred to as having a gas spring. In the gas accumulator category, has stopped by providing fluid produced by the weight divided by required to check the gas pressure maximum system pressure readthere are six flow main types: 1 of - 72 •1supporting Mobile - 72 •Hydraulic Mobile 1 Hydraulic -Mechanic 72 • Mobile Certification Hydraulic Certification Mechanic StudyisManual Study •Manual 07/01/20 • Study 07/01/20 Ma • Bellows to compensate•forPiston leakage. the area the piston. inMechanic an accumulator.

ThreeCertification different ing is p2. If this reading too high • Bladder • Noise Suppressor There are several ways in which Weighted accumulators are appeal- pressures are considered when or too low, the controlling relief 1 - 72 • Mobile Hydraulic Mechanic Certification Study Manual • 07/01/20 Study Manual • 07/01/20 Mobile Hydraulic Mechanic Certificati accumulators are used to absorb ing from the perspective of circuit working with gas-charged accu- valve or pressure compensator energy. The returning flow from a design but are not usually practical mulators. These pressures are not may need to be adjusted. During large-bore cylinder may be greater for mobile applications. They must always described in the literature operation, the minimum system than should be conducted by the be mounted vertically, they are rel- and may simply have the designa- pressure (p1) should be noted. plumbing. A low-pressure accumu- atively large, and they are heavy. tion of p0, p1, and p2.

Then the precharge (p0) is tested lator can receive a portion of the flow Spring-loaded and gas-charged p0 = Precharge pressure: The original to be sure it is at the specified presand then discharge it at an appropri- accumulators weigh less, take up gas pressure before any hydraulic sure below p1. Over time, some of ate rate for the plumbing. Hydraulic less space, and can be mounted fluid is stored in the accumulator. the gas may escape, reducing the fluid has a relatively high rate of ther- horizontally, although it is preferred p1 = Minimum pressure: The lowest precharge. If this happens too fremal expansion. If a volume of fluid to mount accumulators vertically. hydraulic pressure requirement of quently, it indicates that the barrier is confined and unable to expand Gas accumulators are some- the system. has failed, and the accumulator or contract due to temperature times referred to as having a gas p2 = Maximum pressure. The high- must be repaired or replaced. changes, there could be very high spring. In the gas accumulator est pressure that the accumulator When an accumulator loses its pressure that could damage equip- category, there are six main types: will see. precharge, it will no longer store ment or low pressure that could • Piston Each of these pressures provides energy. The accumulator can be • Noise suppressor cause air bubbles in the hydraulic • Bellows information about the hydraulic filled to full system pressure, but • Diaphragm fluid. Accumulators can be used to • Bladder system. If the accumulator is fully there would be no energy stored in • Air-over-oil absorb the expanding fluid and/or Like a compressed spring that charged (is holding the maximum the gas spring to push the fluid out. supply the contracting fluid. They wants to push toward its extended also absorb and dissipate energy position, a compressed gas wants to SIZING GAS ACCUMULATORS: Gas accumulators are not described when used to dampen pressure push toward its decompressed state. pulses, reducing noise and vibration. The gas used is incombustible, usuby how much hydraulic fluid they can hold. They are described by ally nitrogen, unless the pressure is the volume of gas they hold. A 1-liter accumulator will hold 1 liter of very low. Even though there is usucompressed gas. As hydraulic fluid enters the accumulator, it comSAFETY TIP: Accumulators store energy. There ally a separating element between presses the gas, increasing its pressure and reducing its volume. is the potential for the sudden, uncontrolled release of energy whenever working with or the gas being used and the hydrauThe amount of stored hydraulic fluid is the difference between the around hydraulic accumulators. The energy lic fluid, using a gas that contains original gas volume and the new compressed volume. A 1-liter gas must be released or isolated before any work is done on an accumulator or on components oxygen, such as air, can result in an accumulator half-filled with hydraulic fluid would have ½ liter of that may be connected to an accumulator. compressed gas and ½ liter of stored hydraulic fluid. explosion. As the air is compressed, When hydraulic pressure is relieved, there is it is heated, and if the heated oxygen still stored energy in the gas. This must also be relieved or isolated. interacts with the hydraulic fluid, it may cause ignition. *The material in this article is included in the upgraded Mobile Hydraulic Mechanic Certification Study Manual to be released in 2021.

16

OCTOBER 2020

WWW.FLUIDPOWERJOURNAL.COM • WWW.IFPS.ORG

(p0) at a pressure (p0) (p at 0a) that pressure at a is pressure below thatthe that is below minimum is below minimum hydraulic the minimum pressure hydraulic pressure This (p is 1so This that ). This is hydraulic isthat so that hydraulic will pressu 1). pressure 1 UNDERalways S TAUNDER ND Hthe Y DR S TA UNDER AUL ND IC Hpiston S Y COMP TA DRthe ND AUL ONEN HIC Yout.

DR COMP Tout.

AUL Shydraulic A(p ND ONEN IC COMP T HEIR T).S(p ONEN A ND F so UNC T THEIR Spressure T ION Ahydraulic NDF UN Tpr H prevent always always prevent piston prevent the from piston the bottoming fromfrom bottoming out.bottoming

PISTON ACCUMULATORS: These are made of cylinders with pistons. the that bladder high, may the extrude bladder high,under the maybladder extrude the poppet may under extrude andthe bepoppet pinched under and the andbe poppet torn pinched as and theand be poppet pinched torn as closes. and the poppet torn as ct The seals on the pistons are the separationhigh, elements isolate the gas from the liquid. Like all gas accumulators, they are precharged (p0) at a pressure that is below the minimum hydraulic pressure (p1). This is so UNDER TA ND UNDER H Y DRSAUL TA ND IC UNDER COMP H Y DR S TA ONEN AUL ND ICTHS COMP Y DR A ND AUL ONEN T HEIR IC TCOMP S FAUNC ND ONEN T TION HEIR T S AFN U that hydraulic pressure will always prevent the piston fromSbottoming out.

Fig. 1.DDa Bladder Fig. 1.DDa Accumulator Fig. Bladder 1.DDa Accumulator Bladder Fig. 1.DDb Accumulator Bladder Fig. 1.DDb Accumulator Fig. Bladder 1.DDb Accumulator Bladder Fig. 1.DDc Accumulator Bladder Fig. 1.DDc Accumulator, Fig. Bladder 1.DDc BLADDER ACCUMULATORS: A metal or composite bottle Precharge pressure, Maximum accumulator pressure, Minimum system pressure, Fig. is 1.CCaFig. Pre-Charge 1.CCa Fig. 1.CCa Pre-Charge Pressure, Pre-Charge Pressure, Fig. Pressure, 1.CCbFig. Minimum 1.CCb Fig. 1.CCb Minimum System Minimum System Fig. System 1.CCcFig. Maximum 1.CCc Fig. 1.CCc Maximum Accumulator Maximum Accumu Acc Before Pre-Charge Before Pre-Charge Before With Pre-Charge Pre-Charge, With Poppet Pre-Charge, With Closed Pre-Charge, Poppet Closed Poppet Fully-Charged Closed Fully-Char noStored stored energy maximum stored energy minimal stored energy high, the bladder high, may extrude the bladder under high, may the the extrude poppet bladder under and may be the extrude pinched poppet under and and torn be the pinched as poppet the poppet and be torn closes. pinched as the and popp tF No Stored No Energy Stored No Energy Energy Pressure, Pressure, Minimal Pressure, Stored Minimal Minimal Energy Stored Stored Pressure, Energy Energy Pressure, Maximum Pressure, Maximum Stored Maximum Energy Stored Stor En fitted with an expandable bladder used to store pressurized gas Diaphragm Accumulators: Diaphragm Accumulators: Diaphragm accumulators Diaphragm useis a rubber accumulators use disc awith to rubber isolate use abladder disc rubber to used isolate disc to isola Accumulators: Bladder Bladder Accumulators: Accumulators: AAccumulators: metal or ADiaphragm composite metal A metal or composite bottle oraccumulators composite fitted bottle bottle with is fitted an is fitted expandable with an expandable an expandable bladder to bladder store used use to and keep it separated from the hydraulic fluid.Diaphragm A chargingBladder valve the gas frompressurized the the gas liquid. from the This gas thedisc from liquid. is the positioned This liquid. disc is between positioned disc two positioned between spherical between two shells that are spherical shells that are that pressurized gas pressurized and keep gas it and gas separated keep and keep it separated from itThis separated the hydraulic fromis from the fluid. hydraulic the hydraulic A charging fluid. fluid.

Aspherical valve charging A two charging is connected valve valve is connected toisshells the connected bladder to the toa bt is connected to the bladder at the top of the bottle.

At welded the Tbottom at the top atof the the at top the bottle. of top the At of bottle. the bottom At the At ofbottom the the bottom bottle, ofabove the there of bottle, the isbottle, adiaphragm there spring-loaded there is a the spring-loaded is above aisspring-loaded poppet valve poppet that poppet valve is invalve that the tha is either either or screwed welded either together. orwelded screwed The or bottle. screwed together. compartment together.

The compartment The the compartment above diaphragm filledthe diaphragm is filled is fille UNDER S TA ND H Y DR AUL IC COMP ONEN T S A ND T HEIR F UNC ION it stretches it 0stretches and ),hydraulic it completely stretches and completely and fills completely thethe bottle, fills the fills closing bottle, the bottle, the closi position. open open When position. position. thecompartment When bladder When theis bladder pre-charged the bladder is pre-charged is(p (p (p of the bottle, there is a spring-loaded poppet valve that is open in the 0), 0), with nitrogen. with The nitrogen. compartment with nitrogen.

The below The iscompartment directly below connected ispre-charged directly below to is connected the directly connected to the circuit. hydraulic to hydraulic circuit. circu poppet.

The poppet. poppet poppet.

The prevents poppet The poppet the prevents bladder prevents the from bladder the being bladder from destroyed from being being destroyed by extruding destroyed by extruding into

by Accumulator extruding the Fig. piping. into 1.DDc the into piping. the piping.

Fig. 1.DDa Bladder Fig. 1.DDa Accumulator Bladder Fig. 1.DDa Accumulator Fig. Bladder 1.DDb Accumulator Bladder Fig. 1.DDb Accumulator Bladder Fig. 1.DDb Accumulator Fig. Bladder 1.DDc Bladder Accumulator, Bladder Fig. 1.

There is a poppet There that is a There prevents poppet is a that the poppet prevents diaphragm that prevents the from diaphragm extruding the diaphragm from into extruding the from piping. extruding into Some the piping. into the Some piping.

Som open position. When the bladder is precharged (p0), it stretches adder may extrude under the poppet and be pinched and torn as the closes. ofpoppet the diaphragm of Before the accumulators diaphragm ofPre-Charge the diaphragm accumulators are not serviceable accumulators are not so serviceable are that not if the serviceable so disc that ruptures if so the that disc or if the ruptures the disc ruptures or the or th Before Pre-Charge Before With Pre-Charge, Pre-Charge With Poppet Pre-Charge, Closed With Pre-Charge, Poppet Closed Poppet Fully-Charged Closed Fully-Cha When the When accumulator When the accumulator the is accumulator filled with is filled the is filled maximum with with the maximum the volume maximum of volume hydraulic volume of hydraulic fluid, of hydraulic the fluid, gas is fluid, the compressed gas the is gas compressed is to compres the Fig. 1.EE Diaphragm Fig. 1 and completely fills the bottle, closing the poppet. The poppet prepre-charge is pre-charge lost, they pre-charge must is lost, be they replaced. is lost, must they be must replaced. be replaced. maximum maximum pressure maximum pressure (p (p (p Just as Just ). Just as piston inasthe accumulator, in piston the piston accumulator, the accumulator, pre-charge the pre-charge the is pre-charge lower than is lower is thelower than minimum than the min the 2).pressure 2).in 2the Accumulator A Diaphragm Accumulators: Diaphragm Diaphragm Accumulators: Diaphragm Accumulators: accumulators Diaphragm use accumulators Diaphragm a rubber accumulators disc use to a rubber isolate use disc a rubber to isolate disc to i vents the bladder from being destroyed by extruding into the piping. system pressure. system system pressure.

In this pressure. way, In the this Inbladder way, this way, thedoes bladder thenot bladder bottom doesdoes not out bottom not against bottom out the against out poppet. against theIfpoppet. the poppet. pre-charge If theIfpre-charge the is too pre-ch the gas from the the liquid. gas from This the the disc gas liquid. is from positioned This the disc liquid. between is positioned This disc two is spherical between positioned shells two between spherical that are two shells spherical that are shells th tification chanic c Mechanic Certification Certification Study Manual Study • Study 07/01/20 Manual Manual • 07/01/20 • 07/01/20 Study Manual Study • Study 07/01/20 Manual Manual • 07/01/20 • 07/01/20 Mobile Hydraulic Mobile Mobile Mechanic Hydraulic Hydraulic Certification Mechanic Mechanic Certification • 1 Certificat 73 • When the accumulator is filled with the maximum volume of hydraulic either pressure welded (p or either welded either or screwed welded The compartment together. or screwed The together. above compartment the Thediaphragm compartment above the is filled diaphragm above the isdiaphragm filled is fluid, the gas is compressed to the maximum ).screwed Just as together.

2 with nitrogen. with The compartment nitrogen. with The nitrogen. below compartment isThe directly compartment below connected is directly below to the connected ishydraulic directlytoconnected circuit. the hydraulic to the circuit. hydraulic c in the piston accumulator, the precharge is lower than the minimum There is a poppet There that is prevents a poppet Therethe that is adiaphragm poppet prevents that the from prevents diaphragm extruding thefrom diaphragm into extruding the piping. from into Some extruding the piping. intoSome the piping. system pressure. In this way, the bladderof does bottomof out against thenot diaphragm the accumulators diaphragm of theare accumulators diaphragm not serviceable accumulators are not so serviceable thatare if Bladder the notdisc so serviceable that ruptures if theso or disc that theruptures ifaccumulator, the disc or the ruptures Bladder accumulator Bladder accumulator Fig. 1.EE Diaphragm Fig. 1.DDa Bladder Fig. 1.DDa Bladder Fig. Fig. 1.DDa 1.DDb Bladder Bladder Fig. Accumulator Accumulator 1.DDb Bladder Fig. Fig. Accumulator 1.DDb 1.DDc Bladder Bladder Accumulator Fig. Accumulator, 1.DDc Blad1 the poppet. If the precharge is Fig. too high, the bladder may extrude under before precharge fully charged withreplaced. precharge, poppet closed pre-charge isAccumulator lost, pre-charge they must is pre-charge lost, beAccumulator replaced. they is must lost, be they replaced. must be Accumulator Pre-Charge With Pre-Charge, Before Pre-Charge With Poppet Pre-Charge, Closed With Poppet Pre-Charge, Closed Fully-Charged Poppet Closed Fully-A the poppet and be pinched and torn asBefore the poppet closes. Before Pre-Charge

a Bladder Accumulator ore Pre-Charge

Fig. 1.DDb Bladder Accumulator Fig. 1.DDc Bladder Accumulator, With Pre-Charge, Poppet Closed Fully-Charged Diaphragm Accumulators: Diaphragm Diaphragm Accumulators: Diaphragm accumulators Accumulators: Diaphragm useaccumulators a rubber Diaphragm discuse to accumulators isolate a rubber disc usetoaisolate rubber

d

DIAPHRAGM Diaphragm accumulathea gas from the the liquid. gasThis from disc theis the liquid. positioned gas This fromdisc between the is liquid. positioned two This spherical disc between is positioned shells twothat spherical between are shells two that spherical are s m Accumulators: Diaphragm ACCUMULATORS: accumulators use rubber disc to isolate m the liquid. This between two spherical are torsdisc useis apositioned rubber disc to isolate the welded gas shells from that the liquid.

Fig. 1.FFa Diaphragm 1.FFa Fig. Diaphragm 1.FFa Fig. 1.FFb Diaphragm Fig.diaphragm 1.FFb Fig. Diaphragm 1.FFb Diaphragm Fig. 1.DDc Diaphragm Fig. 1.DDc Fig. Dia 1 either or screwed either welded together. orFig. either screwed The welded compartment together. orDiaphragm screwed The above compartment together. the The above compartment is the filled diaphragm above isthe filled diaph ed or screwed together. The compartment above the diaphragm is filled Accumulator Accumulator Before Pre-Charge Accumulator Before Pre-Charge Before Accumulator Pre-Charge Accumulator Pre-charged Accumulator Pre-charged Pre-charged Accumulator, Fullyto Charged Accumu Ful This disc is positioned between two spherical shells that nitrogen. with with compartment The below with compartment nitrogen. is directly The connected below compartment is directly to thebelow connected hydraulic is directly circuit. toAccumulator, theconnected hydraulic circuit. the hyd en. The compartment below is directly connected to nitrogen. the hydraulic The circuit. poppet that prevents the diaphragm extruding into piping.

Some There isthe a poppet There that prevents isAccumulator: a Bellows poppet the There that diaphragm prevents a Accumulator: poppet from the that extruding diaphragm prevents the the diaphragm extruding piping.

Some into from the extruding piping.

Some into are either welded or from screwed together.

The compartment Bellows Bellows Accumulator: A is less common A less accumulator common A less into common accumulator isfrom the bellows accumulator is type. the bellows It is consists the type. bellows ofIt an consists type. expandab Itthe con of hragm accumulators are not serviceable so that if the disc ruptures ormetal the chamber metal inside chamber metal a housing. chamber inside The a inside housing. metal a chamber housing.

The metal is The precharged chamber metal chamber is with precharged nitrogen, is precharged with and nitrogen, the with housing nitrog and of the diaphragm of accumulators the diaphragm are of accumulators not the serviceable diaphragm are accumulators so not that serviceable if the disc are so not ruptures that serviceable if the or the disc so ruptures that if the or disc the ru Fig. 1.EE Diaphragm above the diaphragm is filled with nitrogen. The compartis lost, they must be replaced.

Fig. 1.EE Diaphragm Ft then exposed then to the exposed high-pressure then exposed to must the is high-pressure hydraulic to the high-pressure fluid. hydraulic The walls fluid. of the Thefluid. expandable wallsThe of the walls container expandable of the expandable do container not touchcon d Accumulator pre-charge is lost, pre-charge they must isbe lost, replaced. pre-charge they be lost, replaced. they must behydraulic replaced.

ment below is directly connected to the hydraulicwalls circuit.

There is a of the of the housing, walls therefore walls housing, of the there housing, therefore is no frictional therefore there is wear no there frictional as is the no frictional bellows wear asexpand the wear bellows asand theretract. expand bellowsThey and expand retra do na Accumulator useinto elastomeric use bladders, elastomeric use elastomeric diaphragms, bladders,bladders, diaphragms, or pistondiaphragms, seals. or piston Therefore or seals. piston they Therefore seals. are not Therefore they subject are to they notthe subject are limitatio not to su poppet that prevents the diaphragm from extruding the piping. of elastomers. of elastomers.

Metal of bellows elastomers.

Metal operate bellows Metal reliably operate bellows in high-temperature, operate reliably in reliably high-temperature, in extremely high-temperature, abrasive, extremely extremel and abrasi har Some of the diaphragm accumulators are not serviceable so that if the Diaphragm accumulator, Diaphragm accumulator Diaphragm accumulator environments. environments.

The1.FFa welded environments. bellows The welded are The hermetically bellows welded are bellows hermetically sealed areand hermetically can sealed operate and sealed can reliably and operate without canFig. reliably operate servicing witho relia Fig. 1.FFa Diaphragm Fig. Diaphragm Fig. 1.FFa Fig. Diaphragm 1.FFb Diaphragm Fig. 1.FFb Diaphragm Fig. 1.FFb Fig. Diaphragm 1.DDc Diaphragm 1.DDc Di F fully charged precharged before precharge disc ruptures or the precharge is lost, theyAccumulator must be replaced. maintenance. maintenance. maintenance.

Before Accumulator Pre-Charge Accumulator Before Pre-Charge Accumulator Before Pre-Charge Pre-charged AccumulatorAccumulator Pre-charged Accumulator, Pre-charged Fully Accumulator, ChargedAccu Fu

UNDER S TA ND Bellows Accumulator: Bellows ABellows less common Accumulator: A accumulator less common A less isaccumulator the common bellowsaccumulator istype. the bellows It consists is the type. of bellows It an consists expandab type. of It BELLOWS ACCUMULATOR: A less common accumulator is the bel-Accumulator: metal chambermetal inside chamber a housing. metal inside chamber Thea metal housing. inside chamber The a housing. metal is precharged chamber The metal is with chamber precharged nitrogen, is precharged with and nitrogen, the housing withand ni lows type. It consists of an expandable metal chamber inside athe housing.

Fig. 1.GGa Bellows Accumul then exposed to then exposed high-pressure then to the exposed high-pressure hydraulic to the fluid. high-pressure hydraulic The wallsfluid. ofhydraulic the The expandable walls fluid. of The the container walls expandable of do the not expandable container touch thd Any Gas or Hydrau The metal chamber is precharged with walls nitrogen, and housing, thewalls housing is walls of the oftherefore the housing, there of the therefore ishousing, no frictional there therefore iswear no frictional there as theisbellows no wear frictional as expand the wear bellows andBefore as retract. the expand bellows They and do expa retra no Pressure 1.FFa Diaphragm Fig. 1.FFb Diaphragm Fig. 1.DDc Diaphragm use elastomeric bladders, elastomeric diaphragms, elastomeric bladders,ordiaphragms, piston bladders, seals. diaphragms, orTherefore piston seals. or they piston Therefore are seals. not subject they Therefore are to not the they subject limitation are no to then exposedAccumulator to the high-pressure fluid. The use walls of the use tor Before Pre-Charge Pre-charged hydraulic Accumulator, Fully Charged of elastomers. of Metal elastomers. bellows of elastomers.

Metal operate bellows reliably Metal operate bellows in high-temperature, reliably operate in reliably high-temperature, extremely in high-temperature, abrasive, extremely andMost abras extre hars UNDER S TA ND H Y DR AUL IC COMP ONEN T S A ND T HEIR F UNC T ION Noise Suppressor: hy expandable container do not touch the walls of the housing, therefore ccumulator: A less common accumulator is the bellowsenvironments. type. It consists environments. of an welded expandable The environments. bellows The welded are hermetically The bellows welded aresealed bellows hermetically and arecan hermetically sealed operate andreliably can sealed without and can reliably servicing operate withor as operate the individual chambers mber inside a there housing.

The metal chamber precharged with nitrogen, and the housing is is no frictional wear asisthe bellowsmaintenance. expand and retract.

They do maintenance. maintenance. produce vibration and noise ed to the high-pressure hydraulic fluid. The walls of the expandable container do not touch the dampen sound and reduce not use elastomeric bladders, diaphragms, or piston seals; therefore e housing, Fig. therefore there is no frictional wear as the bellows expand and retract.

They do not 1.GGa Bellows Accumulator Fig. 1.FFa Diaphragm Fig. 1.FFa Diaphragm Fig. Fig.1.FFa 1.FFbDiaphragm Diaphragm Fig. 1.FFb Diaphragm Fig. Fig. 1.FFb 1.DDc Diaphragm Diaphragm Fig. 1.DDc in-line device equipped with meric bladders,they diaphragms, or piston seals.

Therefore they are not subject to the limitations Fig. 1.GGb Bellows Expanded Fig. 1.GGc Bellows Compressed at areAny not Gas subject the limitations of elastomers.

Metal bellowsBefore tube.

The bladder is charged ortoHydraulic Accumulator Before Accumulator Pre-Charge Accumulator Pre-Charge Accumulator Before Pre-charged Pre-Charge Accumulator Pre-charged Accumulator Accumulator, Pre-charged Fully Accumulator Charged ers. Metal Before bellows operate reliably in high-temperature, extremely abrasive, and harsh Pre-charge ) Full-Charge (p2) system pressure. As the fluid operate in high temperature, extremely abrasive, and servicing harsh(p0or nts. The welded bellowsreliably are hermetically sealed and can operateAfter reliably without Pressure Bellows accumulator Bellows at Bellows expanded of the compressed energy pulse is absor ce.

Bellows Accumulator: Bellows A Accumulator: less common Bellows accumulator A Accumulator: less common is the A accumulator less bellows common type. is the accumulator It consists bellows type. of is an theItexpandab bellows consists environments. The welded bellows are hermetically sealed and can before any gas or hydraulic pressure full charge (p2) after precharge (p0) noise. metal chamber inside metal a chamber housing. metal inside The metal chamber a housing. chamber inside The is a metal precharged housing. chamber The with metal is precharged nitrogen, chamber and with is the precharged nitrogen, housing operate reliably without servicing or maintenance.

Noise Suppressor: Most hydraulic pumps produce energy pulses

Air-Ove then exposed to the then to•then the hydraulic high-pressure exposed fluid. to the The hydraulic high-pressure walls ofCertification fluid. the expandable The hydraulic walls of fluid. container the The expandable walls do Manual not of touch the contain exp th - 74high-pressure •exposed Mobile1 Hydraulic - 74 Mobile 1 Mechanic - 74 Hydraulic • Mobile Certification Hydraulic Mechanic Mechanic Certification Study Study • 07/01/ M as the individual chamberswalls discharge fluid.1walls These pulses of the housing, therefore of energy the housing, there wallsistherefore ofnothe frictional housing, there wear therefore is no as frictional the there bellows wear is expand noas frictional theand bellows retract. wearexpand as They the simple bellow and do nrv it has s produce and Most noise.

A type ofproduce accumulator is used to NOISEvibration SUPPRESSOR: hydraulic pumps pulses use elastomeric bladders, use energy elastomeric diaphragms, use bladders, elastomeric or piston diaphragms, seals. bladders, Therefore or diaphragms, piston they seals.are or Therefore piston not subject seals. theyto are Therefore thenot limitation subjec they mounted dampen sound and reduce vibration in hydraulic lines.

It is an as the individual chambers discharge fluid. TheseMetal energy pulses pro- operate of elastomers. of elastomers. bellows of Metal elastomers. bellows reliably operate Metal in high-temperature, bellows reliablyoperate in high-temperature, extremely reliably inabrasive, high-temperature extremely and hars ab become in-line device equipped a of bladder that surrounds a diffusing illustratio The environments. welded bellows The environments. are welded hermetically bellows The sealed welded are hermetically and bellows can are operate sealed hermetically and reliably can without sealed operateand servicing reliably can ow duce vibration and noise.with A environments. type accumulator is used to dampen is no bar tube.sound The and bladder isvibration charged gas,lines. typically ½ device the hydraulic maintenance. maintenance. maintenance. reduce in with hydraulic It is an at inline lot of mo system pressure.

As the fluid passes through the suppressor, much fluid, pro equipped with a bladder that surrounds a diffusing tube. The bladder of the energy pulse is absorbed, providing reduced vibration and is charged with gas, typically at ½ the hydraulic system pressure. As noise.

the fluid passes through the suppressor, much of the energy pulse is 1 -noise.

74 • Mobile Hydraulic 1 - 74 • Mobile Mechanic 1 -Hydraulic 74 Certification • Mobile Mechanic Hydraulic Certification Mechanic Certification absorbed, providingAir-Over-Oil: reduced vibration and Noise suppressor An air-over-oil system is a

bile Hydraulic Mechanic Certification

Study Manual • 07/01/20

Study Manual • 07/01/20

Fig. 3.HH Noise Suppressor

simple version of an accumulator. However,

Study Manual • Study 07/01/2 M Fig. 4.II Air-Over-Oil Air-over-oil accumulator Mobile Hydraulic Me Accumulator

AIR-OVER-OIL: An it air-over-oil systemserious is a simple version of an accuhas some limitations.

It must be TEST YOUR SKILLS mulator. However, it mounted has some serious limitations. must mounted low-pressure vertically andItbe a be relatively system.areHigh-pressure The airadvantage can Accumulators of the vertically and be a relatively High-pressure becomelow-pressure very hot system. and could cause air ignition of theused hydraulic fluid. As seenweighted in theaccumulator is that: to: a. compress a. it can there be mounted horizontally. illustration, the ignition hydraulic pressure as the nitrogen. air pressure. Because can become very hot and could cause of the hydraulic will fluid.be the same b. compress hydraulic fluid. b. it is lighter is no barrier between the air and the hydraulic fluid, the unit should not be subject to in a weight.

As seen in the illustration, the hydraulic pressure will be the same as c. accumulate particulates. c. it takes up less space. lot of there motion. and vibration mixing of the air with the hydraulic the air pressure. Because is no Movement barrier between the air and themay caused.astore or absorb energy. d. it can be charged with shop air. fluid, producing a sponginess in the system. hydraulic fluid, the unit should not be subject to a lot of motion. Movee. reduce flow. e. it has a constant pressure. ment and vibration may cause a mixing of the air with the hydraulic See page 31 for the correct solutions. fluid, producing a sponginess in the system.  1 - 74 • Mobile Hydraulic 1 - 74 Mechanic • Mobile Hydraulic Certification 1 - 74 • Mechanic Mobile Hydraulic Certification Mechanic Certification Study Manual Stu OCTOBER 2020 17 • 07/01/

1

Fig. 4.II Air-Over-Oil

2

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When you need a valve, fast, call Aignep USA. We have the valves you need to get your machine up and running quickly and for a great price. Our wide range of inline valves and manifolds come with an extensive array of operators including manual, mechanical, solenoid and air pilot, all in the most common sizes.

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OCTOBER 2020

Modular Hydraulic Solutions Adaconn® and Inserta® combine to eliminate leaks and bulk associated with line mounted components by removing pipe, tube, and hose connections. Flange mounted modular fittings, ball valves, diverter valves, check valves, relief valves, connectors and adapters can be used to obtain a compact integrated hydraulic system. Made-to-order custom modular fittings, with a variety of ports and port sizes, can be combined to make custom manifolds unique for a particular application, with a savings of space, labor, and potential leakage points. Components can ship assembled.

Send us a sketch of your requirements for a proposed solution.

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Cordis Electronic Proportional Pressure Controls Known for reliability, innovation and focus on miniature pneumatics, Clippard’s new revolutionary micro-controllers utilize the proven EVP and DVP lines of Clippard proportional valves allowing for steady, repeatable downstream pressure as demand or processes change. The result, a precise, linear digital pressure control within a closed-loop system with ultra high resolution (≤5 mV) and repeatability. Made in the USA.

The TL Automatic Control Valve For Steam Systems The model TL valve is designed for temperature control of steam systems. Typical applications are temperature control for winterization protection of process lines, steam tracing, instrument tracing or other systems requiring control based on ambient temperature. Set points are available from 35-240°F. The TL is available in Bronze or 304 Stainless Steel construction, from ½ inch to 2 inch NPT, and carries an 18-month warranty.

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3-A Certification for Hose Assemblies GENUINE KAWASAKI K3VL UNITS & PARTS AVAILABLE We can supply factory new genuine Kawasaki® K3VL series service parts and units—all priced very competitively. This includes 28, 45, 60, 80, 112, 140 and 200 frame sizes with splined or keyed shafts, as well as the common wear parts associated with these units such as rotating groups, shafts, swash plates, bearings, seal kits and more.

Hydraulex For more information, call us at 1-800-323-8416 or visit www.hydraulex.com

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Texcel recently received 3-A certification for hose assemblies.

Six hoses from our FDA product line are certified and we partner with two fitting manufacturers to provide couplings. Clean and precise procedures are used throughout the entire process. When complete, the assembly is tagged, recorded as 3-A certified and shipped anywhere in the USA.

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OCTOBER 2020

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Valve + Actuator: Compact Automated On/Off Valve Filtration Solutions for Low-Flow Applications Anodized aluminum housings with all stainless steel filter elements for flow rates up to 15 gpm and 3000 psi.

Pipe sizes ranging from ¼” to 1” npt and SAE straight threads, too. You choose your level of filtration from 5 to 595 microns. Positive o-ring seal and cleanable element. In stock.

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Optimicron® Pulp & Paper Element with Exclusive Micro Glass Media HYDAC Optimicron Pulp & Paper element technology is designed specifically to meet the demanding requirements of paper machine applications, including paper machine oil compatibility. With our exclusive anti-hydrolysis micro glass media and innovative pleat geometry, we are able to increase free flow surface area while maintaining an exceptionally stable mesh pack, for optimized filtration efficiency and high flow volume performance. ®

The VA Series is a compact, pneumatic on-off coaxial valve, available in 3/8” to 2”. Nickel plated brass body, Buna-N, Viton or EPDM seals make it ideal for hydraulic, pneumatic and vacuum control. Operating life has been tested to well over 1,000,000 cycles.

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CAT-Style Split Flanges, Split Flange Adapters & Flange Plugs Anchor Fluid Power now offers split flanges (PTXO), JIC threaded split flange adapters (609) & flange plugs (COPX) for use with Caterpillar's thicker, Code 62 flange head connections.

These are in addition to the complete line of Code 61 and Code 62 flanges and one-piece, no-braze adapters that we have historically offered.

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21

HITACHI MAKING CONTAMINATION CONTROL EASY

Hitachi have packaged FlangeLock™ tool and caps specifically for Hitachi mining excavators. The Hitachi cus kits make sure no matter which component routine maintenance is being performed on, you will always have th number of FlangeLocks™* and caps to help reduce contamination.

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OCTOBER 2020

Starcyl Canada Inc. 2340 Michelin St., Laval Quebec, Canada H7L 5C3 www.Starcyl.ca

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FIGURE IT OUT

New Problem

Electric Motor Blowing Overloads

By Robert Sheaf, CFPAI/AJPP, CFPE, CFPS, CFPECS, CFPMT, CFPMIP, CFPMMH, CFPMIH, CFPMM, CFC Industrial Training

Âť

WE WERE CALLED out to trouble shoot a problem on a heat-treating system's hydraulic unit in which the electric motor was reading twice the nameplate amperage and causing the overloads to fail. The customer had the motor checked out by a reliable motor-repair house and they felt the problem was with the hydraulic system.

The system had an overhead vertically mounted cylinder with the rod end attached to a large basket. The rod would extend lowering the basket into the hot quenching fluid, where it would sit for hours and then would be raised to the unloading position by retracting the cylinder.

When we arrived, we found the that the overload problem would happen every so often when the cylinder was lowered by the weight of the basket pulling on the rod. When the machine would cycle normally, our amp meter never exceeded the maximum nameplate amp rating of 20 amp, but when the problem popped up, the amps would exceed 108 inrush and drop to 40 amps and trip the overloads all within 1 to 2 seconds. We could not find any mechanical malfunctions, so it had to be a hydraulic problem.

Any idea what the problem turned out to be?

S

Robert Sheaf has more than 45 years troubleshooting, training, and consulting in the fluid power field. Email rjsheaf@cfc-solar.com or visit his website at www.cfcindustrialtraining.com.

Solution to September 2020 problem:

Banging Damages Pipes and Fittings

Large noise, the big bang that happens when a directional valve shifts, is caused by oil under high pressure that is suddenly released to the tank line. A simple system with a 30-GPM pump and a large cylinder could have a 300-GPM discharge rate that only lasts for 20 to 40 milliseconds causing the damaging banging noise. Slowing the directional valve shifting speed from 20 ms to 40 ms would reduce the discharge rate in half to 150 GPM. Pilot pressure orifices will slow the main spool shifting speed on three-position valves from the center position to the fully shifted position. However, they have little or no control when the spool shifts from the fully shifted position to the center position. The centering springs shift the spool quickly to the center position, and the pilot orifice takes control at the center to the fully shifted position. We had the customer install meter-out pilot chokes under the pilot valve to control the main spool shifting speed through the entire stroke, from fully extended position to fully retracted. This greatly reduced the shock banging but extended the cycle time by about 100 ms, which was not a problem on this machine.

Visit www.fluidpowerjournal.com to view previous problems.

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OCTOBER 2020

23

AS HYDRAULIC SYSTEM WORKING PRESSURES INCREASE, COMPONENT DESIGN DETAILS BECOME MORE IMPORTANT.

By Ed Danzer, 6K Products

igh system pressure, defined as 6,000 psi (41,000 kPa or 410 bar), is the pressure setting on some newer excavator functions.

A system that operates at 6,000 psi will see short pressure spikes that are two to three times the working pressure. This means the components need to handle 12,000 to 18,000 psi (82,737 to 124,105 kPa or 827 to 1,241 bar) pressure spikes for a reasonable service life of 8,000 hours, or four years, and should not fail in less than 2,000 hours, or one year of service.

CYLINDER DESIGN CONSIDERATIONS When a machine or attachment is being designed, the designer has an idea of what the unit should do and how it should be done. As soon as you hand the machine to a different operator, the application, duty cycle, and operating parameters have changed. In some cases the change is enough that things start to fail. Frequently, the cylinder will be subjected to a work-induced load that is much greater than what is possible by direct control.

Both counterbalance valves and pilot-operated check valves are used to hold a cylinder in position, 24

OCTOBER 2020

and both valves can produce additional loads on the cylinder components when in operation.

Some load-holding valve settings are increased by back pressure on the pilot port.

A short-stroke cylinder does not typically need to be concerned with buckling load design. A longstroke cylinder will require running a buckling load calculation. Use standard NFPA/T3.6.37 R1-2010 for buckling calculations.

The speed the cylinder will move, or the flow going into the cylinder, must be considered to determine port and plumbing size. This speed is also important when designing cushions if they are required.

Choosing the correct bore and rod size can be the single most difficult aspect of the cylinder to determine because of the forces required when extending and retracting, the stroke required, and the pin centers distance needed to be met. If the cylinder needs cushioning, this could change the bore or rod size requirements. Sometimes a larger bore and rod will be required to meet all the design needs. One side of the piston may need to run at a lower pressure to meet the force requirements as well

as structural requirements, such as the piston-to-rod interface, the piston fastening needs, and buckling of the rod.

It may be difficult to determine the load, or load vectors, for a highly accurate model, but it is important to determine this data if you expect to create a robust design. Some designs will require enough mounting flexibility that either adequate side clearance, self-alignment capabilities, or both need to be incorporated into the anchor and pin-joint design. If possible, do a finite element analysis of the structure to determine its deflection.

Pin-joint design needs to be applied to both the cylinder ends and the pin anchors being actuated by the cylinder. For boom pivot joints you will need to look at not only the loads created by the cylinder, but also by other loads of the system such as torsion loading. For cylinder pins, you need to design for the maximum load the cylinder will see, which may be the work-induced loads. We use 6,000 psi projected area loading on the bushing or bushings.

We recommend using a bushing length that is about two times

longer than the pin diameter if possible. The fixed pin-holes widths should be .75 to 1.25 times the pin diameter. Longer, smaller diameter pins and bushings tend to bend more than shorter, larger diameter pins and will make the manufacturing and maintenance more expensive over the life of the cylinder.

For many applications, slowing the cylinder at the end of stroke is not required. If the application has high inertia loads and no speed control feedback, building deceleration cushions into the cylinder can be an inexpensive solution. Designing an adequate cushion will require a good understanding of the application and loads to be controlled.

To cushion a cylinder there has to be a way to meter the oil going out of the cylinder. There are several methods of metering the oil flow and controlling cushion pressure. We typically use the piston to close the port to increase the area decelerating the load. The pressure on the side of the piston opposite to the side being cushioned is additive to the mass being decelerated and must be considered during design.

WWW.FLUIDPOWERJOURNAL.COM • WWW.IFPS.ORG

1

2

Cylinder parts

3

4

COMMON FAILURES Piston-to-rod interface is one area of high-pressure cylinder design that seems to be the most difficult to manage well. Many times the bore and rod size are chosen from a prior lower-pressure design.

This can get the designer into trouble if the fastener is too small, or if the piston-to-rod interface area is too small. Figures 1, 2, and 3 are all 5-inch bore by 3-inch long rod, log-grapple cylinder piston designs.

Figure 1 is the 5K design I developed in 1985. It uses a 1½-inch NF nut to hold the piston in place.

Figure 2 is my 6K design, developed in the late 1990s, with a 1¾-inch NF nut. Figure 3 is a competitive design, developed in the early 2000s, with a threaded-on piston.

This cylinder is a shorter-stroke cylinder that does not have extreme side load, but it does have a pilot-operated check valve hard plumbed to the barrel, so if a hose fails the cylinder cannot drop the

load. There will be times when the operator will hit the grapple in such a way that the cylinder will see high extension forces acting against the threads. Sometimes the operators will use the grapple to pull stumps so the blind end of the cylinder will see pressures up to about 20,000 psi before there is a catastrophic failure.

The 5K piston design did not have a large enough thread, allowing the rod to break at the end of the threads. Also, the rod-bearing area was not large enough so the piston would cold form over the rod.

Figure 4 shows the area that was cold forming over the rod on a 5K cylinder. When the rod and piston bearing area are loaded above the yield point of the material, there will be material movement, and this will allow the piston to come loose causing further damage.

In figure 3 the internal thread piston has an even smaller rod-bearing area. There must be clearance in the thread for assembly. This clearance, and the clamping force of tightening the piston, will allow the piston to cold form over the rod even sooner than other designs. The deflection in the threads when the piston loosens can cause breakage in the rod, as shown. The 6K piston in figure 2 has the larger fastener, and to get a larger bearing area a tapered interface is used. We have upgraded the piston to 4150 HT on the 6K design for additional

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protection from pressure spikes.

We have customers that have used all three cylinder designs and have never had a 6K piston-to-rod interface failure. The limitations of the current 6K design are at about 18,000 psi when the barrel will yield, or the pilot-operated check valve will fail.

MATERIAL CHOICE With the highly concentrated force on the rod and piston, the materials used for the rod and piston should have a similar hardness, a high-impact capability, and may require a high Charpy impact value at low temperatures. This is required if the cylinder is being used at low temperatures. The barrel should be made from a material with a highyield strength, good weldability, and adequate impact capabilities.

Do not use materials that contain free-machining elements in parts that will be welded. These free-machining elements include, sulfur, lead, manganese, calcium, selenium, tellurium, and bismuth. The wall thickness choice should be thick enough to keep barrel swell low to reduce seal failure. The graph shows barrel swell in inches and psi for a 4-inch ID barrel with a 5-inch OD. Barrel swell can reduce seal life by increasing the gap between the piston and barrel. This increases the diameter of the element or elements contacting the barrel, causing an increased seal-groove volume.

There are many different methods to attach the head gland to the barrel. The most reliable design will handle the maximum load the cylinder sees when extended by pressure in the blind end, plus the stopping load. If the cylinder has an extension hard stop, then the stopping load is 0. If the cylinder has to stop the movement of the structure it is driving, it must be calculated and added to the extend force. In the case of excavator boom and bucket cylinders, this can be a large force. I do not recommend screwing the head into the barrel.

As the pressure swells the barrel, it increases the thread clearance, which allows movement that will cause thread wear and reduce the service life of the cylinder. Barrel or gland nuts work if properly sized for wall thickness. It also helps to use Acme or square threads.

Buttress threads have a sharp, thin cross section, so they can be weaker than other thread forms.

Using a ring of cap screws is a common method that works well if properly designed. The thickness of the flange that the fasteners clamp must be thick enough to not deflect during loading. The 5K-cylinder design had flanges that were marginally thick enough, so in an application where there were high forces at the end of the cylinder travel, the deflection caused the head and cap screws to fail sooner than in other applications. Using a flange that is twice as thick as the bolt diameter will usually be adequate for most applications.

Welding failures are common in high-pressure hydraulic cylinders for many reasons. Let’s look at the more common ones and some repair information.

WELD CHAMFER. The weld chamfer needs to allow for correct wire stick out and shield gas control, but no larger than necessary as this will increase welding time and weld generated distortion.

FILLER MATERIAL. Early in the development of high-pressure cylinders, one of the weld failures came from using the incorrect yield strength filler materials. Most tubing for high-pressure cylinders will need a yield strength greater than 70,000 psi.

(Continued on page 26) OCTOBER 2020

25

(Continued from page 25) This will require a filler material that is 80,000 psi yield or higher. E80 wire is typically a good choice.

WELD BEAD SIZE. To ensure the weld does not have too much stress from welding, I recommend using a multipass pulsed-spray weld procedure. This will also reduce distortion of the parts. There should be a small contact area where the barrel tube and the blind end connect, so if the barrel needs to be replaced, the barrel pilot and locating shoulder machined on the blind end will still exist after weld removal. This does require the weld to be larger in diameter than the barrel, which may not work in some applications.

WELD REPAIR. Weld repair in hydraulic cylinders can be a challenge because of oil saturation. Lowhydrogen welding materials will not seal oil-contaminated metals. The first pass should be done with a 6010 or 6011 stick rod using a whipping motion. Cover passes using higherstrength filler materials are required for structural integrity.

The materials chosen for sealing and guiding the rod and piston can be the single most difficult portion of high-pressure cylinder design.

Many designs are based on using existing seals that work acceptably in lower-pressure applications.

Some designs use low-cost products, so repairs are less expensive.

For the end user, in most cases, the cost of downtime far exceeds the cost of a properly designed and installed seal kit.

Every cylinder needs to have guide bearings in the form of wear rings or plain bearings. This is to guide the rod in the head gland and the piston in the barrel. These guiding components will have to accept the side load the cylinder sees, hold the running clearance, and must be included in the repair seal kit.

Finally, the seal kit should include all the parts to make the cylinder like new.

Do not use pipe threads for anything operating over 100 psi if possible. Do not weld on commercial hydraulic adaptors, as they are manufactured from free-machining steels and will crack near or in the weld area.

Barrel swell in inches and psi for a 4-inch ID barrel with a 5-inch OD.

5

7

6

8

9

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OCTOBER 2020

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Try to not have right- and left-handed cylinders. Determining the correct hand can be difficult for the customer and will increase the cost of inventory of spare parts.

Use thicker wall tubing, or pipe, when there is the possibility of being hit during operation. If the tubes need to be removed and if it’s possible, have some part of the tube attachment system welded to the barrel. Clamps will come loose from pressure expansion of the barrel and can allow the tube to rotate enough that the tube, hose, or cylinder barrel will be damaged.

HIGH-PRESSURE SEALING CHALLENGES Pressure and velocity (P/V) capability of the sealing material is an important consideration in high-pressure sealing. When the piston and rod assembly are moving, the seal surface becomes a bearing that has no running clearance and must run almost dry to stop fluid bypass. Every sealing material will have a different P/V value relative to different contacting materials. Most published P/V values are not correct for sealing applications, and correct P/V information may not exist.

If there is too much space for movement in the seal groove, it can reduce seal life. Filled seal materials tend to break down under high pressure, scratch components, and contaminate the hydraulic oil. Glass-filled material tends to be brittle where the glass bonds to the parent material and will deposit glass into the hydraulic system as they fail.

Off-highway equipment cylinders can see high pressure spikes during operation that will reduce seal life. Proper use of step-cut or lap-cut wear rings, zero-split clearance bushings, or wear rings can be a better solution than buffer seals.

Buffer seals can trap high-pressure oil against the rod seal, causing premature rod-seal failure. A backup ring behind the rod seal to reduce extrusion is a good option for all cylinders.

Extrusion, nibbling, and breakage are common failures. Figure 5 is an example of extrusion in less than 300 hours of operation from too much pressure for a urethane seal.

Figure 6 is seal extrusion from honing a cylinder to clean it up during repair without increasing the diameter of the piston. Figures 7 and 8 are examples of nibbling. Nibbling can be caused by barrel swell, axial movement of the seal in the groove, or incorrect groove dimensions. Figure 9 is an example of a filled material breaking, and the sides of the expander show evidence of axial movement in the groove.

When assembling hydraulic components, use oils or greases that are compatible with the hydraulic oil used in the machine. Do not use materials that contain mineral-based additives or thickeners. We use a polyurea-based grease to meet these requirements.

If you are faced with the task of redesigning a cylinder to handle higher working pressures, use finite element analysis or other simulation tools to reverse engineer failed components and to qualify new designs. Remember that just because component design, material choice, seal choice, or assembly method worked at 5,000 psi does not guarantee it will perform well at 6,000 psi. 

EVERY Part Matters!

PENINSULAR CYLINDER CO. ®

EFFECTS OF TEMPERATURE ON SEAL PERFORMANCE We have found that most elastomers have increased compression set when cooled below freezing and raised to operating temperature daily.

Many O-ring grooves do not have dimensions to allow for the cyclic temperature compression set.

If you see O-rings damp enough to collect dust in static applications, this leak is probably from cyclic temperature compression set.

Elastomers have a higher coefficient of thermal expansion than steel. This means the seal will shrink more when cold than steel does and expand more when hot. When looking at seal groove dimensions, it is important to consider the size the elastomer will be during the lowest and highest operating temperatures. Too little or too much volume can reduce seal life.

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Hydraulic • Air • Custom Cylinders

Let’s Talk Cylinders

800-526-7968 www.peninsularcylinders.com

OCTOBER 2020

27

F

ourteen years ago I had vision for a global came back with a much more agile and aggressive mech racing league that would pit multiple worldsuit when we saw the advanced mobility platform suit class athletes in head-to-head competitions in 2009’s “Avatar.” While these were both inspirational through complex technical obstacle courses wearing giant pieces of technology, they had one key thing in common powered exoskeletons, or mech suits. that limited their utility: they were not real. This would At that point, such machines were only ever depicted in make using them to develop a large-scale mech racing science fiction, such as the legendary power loader in the league fairly challenging. There appeared to be only one solution: I had to develop the technology myself. timeless 1986 James Cameron classic “Aliens.” Cameron

Building a

By Jonathan Tippett, CEO, Cofounder, and Test Pilot, Furrion Exo-Bionics

Defining a mech The first thing to do was to define a mech and then establish the qualities of a sports mech. We had many design constraints and criteria.

It was to have legs only; no wheels would be allowed. No external part of the machine could rotate more than 360 degrees continuously; that is what makes it a mech. It had to be 100% human piloted, using the pilot’s arms and legs; that is also integral to what makes it a mech.

It should be fun. That’s what makes it a sport. Fun can involve serious engineering that translates to comfortable, learnable, 28

OCTOBER 2020

stable, and responsive. If it has automation, that’s not fun. If it is an untameable beast, that is also not fun. Achieving that balance between challenging and rewarding is at the heart of what defines a good sport.

It had to be lightweight, which is not something that usually figures heavily in off-highway hydraulic equipment. But in a sport machine, dynamic loads become more significant and weight is king. It needed to be 100% electric powered. It required high efficiency. Solving inefficiency by adding more radiators and power would add weight,

particularly when batteries are used, offering diminishing returns.

The machine needed to be simple, which should be a criterion for any design. But when it comes to learning to walk, we knew we’d already be challenged, so the fewer degrees of freedom the better. We had to make sure it was safe. Anyone who’s ever learned a new sport knows that falling is an inevitable part of the learning process. The machine had to be able to fall over with zero damage and injury to the pilot. Finally, it had to be an all-terrain machine capable of covering ground that a similarly sized 4x4 or tracked vehicle could not.

With the basic design parameters established, we began developing the hydraulics and motion controls. Over the course of 10 years I assembled a community of volunteers, students, and industry sponsors who believed in the project. We were based in the lab space of the Energy Awareness Through ART (eatART) Foundation, an educational charity I cofounded in 2007. The foundation supports the creation of large-scale, technically sophisticated projects used to educate people about the role of energy and to raise questions about its social and environmental impact.

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Within the creative crucible of the eatART laboratory, our team was able to develop a fully functional, ridable 2:3 scale prototype leg mounted on a tower. It was called the Alpha Leg. This prototype validated the core assumption that a pilot could control a giant limb with an exoskeletal interface while being hurled around by that same limb.

It also yielded a first-generation exoskeletal control system, electrohydraulic power plant, and leg architecture that would become the foundation for the full-sized mech.

It is often said that we make great steps forward in technology standing on the shoulders of giants. The giants were the millennia of technological innovation that brought us to the current state of the art. Perhaps more literally, the giants in this case are giant excavators and other large-scale articulated hydraulic machinery. But the giants on whose shoulders you stand must be headed in the right direction. When it came time to scale the technology in the Alpha Leg and put it on a mobile, dynamically balancing, untethered mech and create a hydraulic sports machine, we still needed to make substantial upgrades.

From Alpha Leg to sports mech The next stage was designing the mech itself, which was done from the pilot outward. It started with an ergonomic exoskeletal control system on the pilot’s body to pick up the movements of his limbs.

That exoframe was then suspended on a three-degree-of-freedom suspension system to cushion the pilot from any impacts. Around that, a robust, CrMo steel cage and chassis were designed to hold the pilot, batteries, and hydraulic power plant. The chassis sported four massive, impact-absorbing bumper bars, two at the front and two at the rear, mounted on dual air shocks to soak up the impact when the machine fell over. The legs came next. They were simple and identical for ease of manufacture. The knee joint was placed halfway up the limb, incorporating multiple high-end King racing shocks to provide 50 cm (19 in.) of suspension travel. The four legs pivoted on a shared hip axis. The legs were sized proportionally with the chassis, which allowed for a 4.3-m (14-foot) stride. To move the 400-kg (1,000-pound) steel limbs and make this behemoth walk, we custom engineered a 96-volt battery pack that used 350 kg (770 pounds) of lithium ion batteries to run twin AC electric motors. The motors drove two hydraulic pumps for a total power output of approximately 200 hp.

With core technology in place and a mech design based on 10 years of development and testing, we attracted investment from global technology leader Furrion and in 2016 formed Furrion Exo-Bionics, which provided the resources to build our flagship prototype mech, Prosthesis:

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The Anti-Robot. The result was a 4,000-kg (8,818-pound), all-terrain mech suit capable of stepping onto objects as high as 1.2 m (4 feet). In fact, it was so large it was named the world’s largest quadrupedal exoskeleton and appears in the 2020 “Guinness World Records.”

One of the differences between the Alpha Leg and the full-sized mech was it had to carry its power plant. Carried on a two-story experimental waking machine operated by a rookie pilot, it was thrown around a lot. The mech would regularly go from face-plant to face-up in seconds. A conventional, rigid, vented fluid-reservoir tank was out of the question; keeping the outlet under the oil line was by no means a sure thing. The solution was a pair of Smart Reservoirs. This ingenious device uses an expandable bladder to account for the volume changes produced by cylinder movements and thermal expansion, allowing a sealed hydraulic system with no air to be pulled into pump inlets.

It had the additional advantage of providing 1-5 psi positive inlet pressure to the pumps, allowing them to run at max flow without risk of cavitation.

Learning to walk With the pumps well fed and the pilot safely strapped in, the process of learning to walk began. This was the crux of the whole project. Prosthesis has no autonomy or gyro stabilization; it relies entirely on the pilot’s movements.

The first thing that became apparent was that walking produced a wildly varying duty cycle for the pumps. One solution would be larger variable-flow axial piston pumps, which would have created an upgrade cascade effect through the powertrain resulting in substantial weight increases. A more weight-efficient solution to meeting spikes in power demand was accumulators, but standard steel accumulators are also heavy.

(Continued on page 30)

OCTOBER 2020

29

(Continued from page 29) So we found ultra-lightweight carbon-fiber accumulators made by a company called Steelhead Composites that were one-quarter the weight of their traditional steel counterparts.

After about two years of intensive field trials that were equal parts engineering and pilot training, we had a reliable machine that followed the pilot’s movements accurately. But we were still having difficulty achieving a smooth, dynamic gait. The hydraulic circuit we were using to control cylinder movement was developed with valuable input from the applications team at Hydraforce and drew on decades of knowledge and leading valve technology. It took hundreds of hours in the pilot seat, however, to realize that the state of the art was not going to work for this new breed of machine. Traditional heavy-duty hydraulic circuits favor strength and precision, with an emphasis on minimizing operator fatigue.

Sports machines are different.

They have a more visceral relationship to their operators. Rather than the operator just moving the machine where he wants it, an athlete wants to feel the machine more directly and appreciate the momentum and kinematics of the machine. This allows the pilot and the machine system to benefit from the human nervous system, 30

OCTOBER 2020

shock loading as the pilot pushes the limits of the leg travel in a quest for more speed.

These cylinders represent a major step forward in the evolution of mech technology.

High-accuracy positional awareness will open up a spectrum of performance improvements, such as cylinder travel limit endpoint control and nonlinear pilot input mapping that takes into account mech position to produce a more consistent piloting experience throughout the full range of motion.

It will also enable the gathering of valuable data for the calculation of joint velocities, joint-specific duty cycles, efficiency, and the development of a simulator for training or even remote operation.

Despite mech suits being fantasized about for decades, Prosthesis is the first and only mech suit of this scale and with this level of power and agility. But it is just the beginning. It is essentially the Kitty Hawk of mech development, and the potential for this technology is just beginning to be appreciated.

There is still a long journey ahead, and there is still lots of room for improvement, particularly with lightweight higher-efficiency components and systems. 

one of the most sophisticated motion-control speeds and forces at play were subsystems around. stantial. If we had mechanical-limit Through some bold and stops on our joints, the mass of the unconventional innovations, structures would have been excessive, we eventually developed a and even the most skilled pilot could proprietary valve circuit and not be relied on to bring each of the motion-control code that, at first, eight joints to a gentle stop in both seemed to turn the mech into a wild directions all the time. We needed animal. It was so wild, in fact, that a smarter machine, something that the first time we tried it we wrote it would let the pilot focus on speed and off as unusable and returned to our agility without holding back. original technology. It wasn’t until I had gained many more hours of Smart cylinders piloting experience that I was able This brings us to the next chapter to harness intense and immediate in the evolution of the sports mech control over the machine. To new – smart cylinders. We chose internal pilots it still seems wild and at times MTS sensors because we needed the alarming, but to me it just feels like 100 μm accuracy and durability they a sporty mech suit. provide, and we had new hip and With 200 hp, ultraresponsive con- knee cylinders custom engineered trols, and a 4,082-kg (9,000-pound) by Edmonton-based RHK Hydraulic mech to balance, the massive legs Cylinder Services. Not only do the started making fast moves. We were new cylinders incorporate the MTS seeing linear motions in 50-mm sensors, but they have massively (2-in.) bore cylinders on the order of oversized ports placed to opti254cm/sec (100 in./sec). The basic mize hose routing and minimize utility cylinders we used up to this flow restrictions. They also have point were heating up and being integrated hydraulic cushions at torn in half on a regular basis. The the extension limit to mitigate the DWG.#

MF03D-1508

IF IN DOUBT. . . . ASK! CYLINDER INFORMATION:

MAGNET 400 533

SNAP RING

CONE POINT SETSCREW

1. BORE = 2" 2. ROD = 1 1/4" 3. STROKE = 17 5/16" 4. PORT SIZE = #10 ORB / #8 ORB 5. PIN SIZE = 1" 6. MAX. W.P. = 3,500 PSI 7. TEST PRESSURE = 4,000 PSI 8. PUSH @ 3,500 PSI = 10,996 LBS 9. PULL @ 3,500 PSI = 6,700 LBS 10. MAX. COMPRESSIVE LOAD @ FULL EXTENSION = 9,020 LBS (S.F.=2) 11. EST. EMPTY CYL. WEIGHT = 27.5 lbmass

SPACER

DETAIL A SNAP RING

M12 SENSOR CONNECTOR

MAGNET 400 533

4 - M4 x 10 SCHS

DETAIL B

SPACER

A

B

MS F 0485M

SENSOR DETAILS

NOTES: 1. ALL DIMENSIONS ARE IN INCHES UNLESS NOTED OTHERWISE. 2. BREAK ALL SHARP EDGES.

3. IF IN DOUBT, ASK! UNLESS STATED OTHERWISE, ALL DIMENSIONS IN INCHES. TOLERANCES: .X = `.030 .XX = `.010

NO.

DATE:

REVISIONS

DESCRIPTION

.XXX = `.002

ISO9001:2015 REGISTERED

13111-159 ST EDMONTON, AB T5V 1H6 PHONE (780)452-2876 FAX (780)451-4664 rhk@rhkhydraulics.com www.rhkhydraulics.com

X = `1/16 X~ = `1~

This drawing and the design shown therein is the property of RHK Hydraulic Cylinder Services Inc. and use of or copies thereof can not be made without written authorization.

KW

CUSTOMER: FURRION EXO-BIONICS

DRAWN BY:

CUSTOMER P.O.#:

CHECKED BY: SR

DATE: 7/02/20

CUSTOMER PART#:

APPROVED BY: DR

DATE: 7/02/20

W.O.#: TITLE:

SCALE: N.T.S

2" BORE x 1 1/4" ROD x 17 5/16" STR. KNEE CYLINDER

DESIGN BY: DRG.#

KW

MF03D-1508

DATE: 7/02/20

DATE: 7/02/20 REV.

QTY.

0

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HYDRAULIC FLANGES and COMPONENTS THE “SPECIAL” YOU WANT IS PROBABLY ON OUR SHELVES MAIN Mfg. Products, Inc. 800.521.7918 fax 810.953.1385 www.MAINMFG.com/fpj

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ADVERTISER INDEX Company.................................................Page.................................Phone....................................................... Web Aggressive Hydraulics...................Back cover, 21........................ 866-406-4100...............www.AggressiveHydraulics.com Aignep USA................................................... 23, 18........................ 615-771-6650.................................. www.aignepusa.com Anchor Fluid Power....................................... 7, 20........................ 513-527-4444 ................................anchorfluidpower.com Assured Automation.......................................... 20........................ 800-899-0553 ............................ assuredautomation.com Bimba Manufacturing Company.........................1........................ 800-442-4622............................... www.bimba.com/airos CFC Industrial Training...................................... 31.....................1-513-874-3225............................cfcindustrialtraining.com Clippard Instrument Lab Inc............................. 19........................ 877-245-6247.......................................www.clippard.com Doering Company.......................................... 7, 22.....................1-320-743-2276................................................. doering.com Festo Corp.....................................Inside back, 18.....................1-800-993-3786............................................... www.festo.us Flange Lock.................................................. 15, 22........................ 203-861-9400.................................. www.flangelock.com Flow Ezy Filters Inc............................................ 20....................... 1-88-237-1165............................. www.flowezyfilters.com Fluidyne Fluid Power................................... 13, 21........................ 586-296-7200 ................................... www.fluidynefp.com Hydac International Inc................Inside front, 20........................ 610-266-0100.....................................www.hydac-na.com Hydraulex........................................................ 9, 19.....................1-800-323-8416....................................www.hydraulex.com Hydraulics, Inc.............................................. 19, 26........................ 817-923-1965..............................www.hydraulicsinc.com Inserta Products............................................. 5, 18........................ 215-643-0192 ........................................ www.inserta.com Main Manufacturing Products Inc................... 21.....................1-800-521-7918...............................www.mainmfg.com/fpj Ogontz Corporaton........................................ 5, 19.....................1-800-523-2478........................................ www.ogontz.com Peninsular Cylinder Co. Inc............................... 27.....................1-800-526-7968...................www.peninsularcylinders.com RHK Hydraulics.............................................. 8, 21.....................1-800-406-3111............................. www.rhkhydraulics.com Spir Star Inc.................................................. 26, 18.....................1-800-890-7827........................................www.spirstar.com Starcyl Cylinders Corp................................. 22, 20.....................1-877-782-7295.........................................www.Starcyl.com Texcel.............................................................. 3, 19.....................1-800-231-7116............................... www.texcelrubber.com WWW.IFPS.ORG • WWW.FLUIDPOWERJOURNAL.COM

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