Hydraulics

BASIC PRINCIPLES OF HYDRAULICS i) Definition ii) Conversion of energy in hydraulics iii) Special characteristic iv) Measuring and controlling parameters v) Basic laws vi) Loss of energy by friction vii) Flow configuration viii) Basic form of a hydraulic system ix) Basic Diagram of Hydraulic Circuit x) Application of Hydraulic System

HYDRAULICS: The transmission and control of forces and movement by means of fluid is known as hydraulics.

Fluid mechanics (Hydromechanics)

Hydrostatics

Hydrodynamics

(Mechanics of Still fluid) (Mechanics of moving fluid)

CONVERSION OF ENERGY IN A HYDRAULIC UNIT Drive Elec. Motor I/C Engine

El. Energy or Thermal energy

Hyd. Pump

Mechanical energy

Hydraulic energy

Hydraulic Control & Regulating unit

User Hyd. Cylinder Hyd. Motor

Hydraulic energy

Operating element to be actuated

Mechanical energy

OTHER FORM OF CONVERSION: Mechanical – Gear, shaft, crank mechanism etc.

Electrical - rotating field motor, line motor or moving field motor, torque motor Electronic - Amplifier Pneumatic - Similar to hydraulic air is used as medium.

SPECIAL CHARACTERISTICS OF HYDRAULICS: i) High power density. (High force/torque with compact size) ii) Movement from stand still possible with full load. iii) Control or regulation of speed, torque, stroke, force can be achieved simply. iv) Simple overload protection. v) Suitable for controlling fast movement process and for extremely slow precision movements. vi) Self lubrication vii) Relatively simple accumulation of energy by means of gas (accumulators).

Pressure and Flow are two measuring / controlling parameters similar to electrical systems Voltage and Current.

P = F/A, N/m², kg/cm², Pascal – 1 N/m² Q = m³/sec.

Patm = 1.013 bar Gauge Pressure (Pg) = Pabs - Patm Case 1: Pg = 0, Pabs = Patm , 0% Vaccum Case 2: Pabs = 0, Pg = -1.013,100% Vaccum (Not Possible)

BASIC LAWS: i) Hydrostatic force (gravity force) Hydraulics ii) Pascal Law iii) Energy Law (Bernaulli’s Equation) Hydro iv) Flow Equation (Continuity Equation) dynamics HYDROSTATIC FORCE: Pressure occurs due to the weight of the fluid mass over a determined area. This is related to height of the liquid, the density and gravity. p = ρgh

PRESSURE BY EXTERNAL FORCE (Pascal’s Law), year 1605:

When force acts on enclosed fluid via surface area A, pressure (F/A) occurs in the fluid. It acts on all sides equally and simultaneously.

F1 A1

F2 A2

F2 = A2 X S1A1 = S2A2,

F1 A1 S2 = (S1A1) A2

FLOW LAW (CONTINUITY EQUATION): For a steady flow, the flow (discharge) of fluid in pipes with different diameter will be same.

Q = AV = Const.

A= Sectional area of pipe.

V = Velocity of fluid

ENERGY LAW (BERNAULLI’S EQUATION): The total energy of a flow of fluid doesn’t change as long as energy is not supplied from the outside or drained to the outside. ρgh = potential energy related to height of the head of fluid. p = pressure of static pressure, (External force) ρv²/2 = movement energy (pressure head related to flow) For hydraulic system, pressure energy (þ ) is the main decisive factor.

LOSS OF ENERGY BY FRICTION: Hydraulic energy can not be transferred without loss. The amount of friction loss depends on i) ii) iii) iv) v)

Pipe length.

Roughness of pipe wall.

No. of pipe bends.

Pipe diameter.

Flow speed.

FLOW CONFIGURATION: i) Laminar flow Re < Re critical 2300 ii) Turbulent flow Re > Re critical LAMINAR FLOW: Individual particles move up to certain speed in uniform layer along side each other without disturbing / influencing each other.

TURBULENT FLOW: Flow speed increases when pipe diameter decreases and the flow characteristic changes after certain speed (critical speed). Flow becomes whirling and turbulent.

Reynold’s Number (Re) = V.dH ‫ע‬ V = Velocity dH = hydraulic diameter ‫ע‬ = kinematic viscosity

BASIC FORM OF A HYDRAULIC SYSTEM

USES OF HYDRAULICS: 1)

2)

3) 4)

5)

Industrial Hydraulics

– Plastic machining - Press - Heavy machine - Machine Tools Steel works & Civil Engg.

- Lock gates & Dams - Bridge operating - Turbine - Nuclear Power Station Mobile Hydraulics - Hydra, Forklift, Brake Hydraulics in special Technical – Telescopes, Application – Antenna operation, - Rudder control of air craft Hydraulic for marine - Rudder control