FLUID POWER HANDBOOK
WWW.MOBILEHYDRAULICTIPS.COM
HYDRAULIC
CYLINDERS
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Few things represent a fluid power system the way a hydraulic cylinder does. These true workhorses operate in industrial and mobile applications. When compared with pneumatic, mechanical or electric systems, hydraulics can be simpler, more durable and also offer greater power density. For example, a hydraulic cylinder has about ten times the power density of an electric linear actuator of similar size. Selecting the right cylinder for an application is critical to attaining maximum performance and reliability, which means taking into consideration several design and performance parameters. Fortunately, an assortment of cylinder types, mounting methods and “rules of thumb” are available to help select the appropriate cylinder. CYLINDER TYPES The three most common types of cylinders are tie-rod, welded and ram, the latter of which is single acting, meaning it is powered in one direction only.
Tie-rod cylinders can be single acting, although they are most often powered in both directions. They have machined, square caps and heads being forced together against the barrel by high-tensile steel tie rods fastened by nuts, making them easy to disassemble and repair in the field. Welded cylinders employ a steel barrel with a cap welded to the bottom and the end treatment subsequently welded to the cap. The rod and piston assembly then has to be assembled around the head — which uses a buttress thread for strength — and is tightened into the barrel. Finally, the single-acting ram is typically just a rod inside a barrel with a single port and requires either a spring or mass to retract. For all cylinders, the critical measurements include stroke length and bore and rod diameter. Stroke lengths vary from less than an inch to several feet or more, depending on the requirement of the machine. Bore diameters can range from 1 in. up to more than 24 in., and piston rod diameters range from 1-2 in. to more than 20 in. In practice, however, the choice of stroke, bore and rod dimensions may be limited by environmental or design conditions.
IMAGE COURTESY OF PRINCE MANUFACTURING
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FLUID POWER WORLD
Hydraulic Cylinders 7-19_FPW Vs3.indd 18
7 • 2019
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7/15/19 9:28 AM
