Hydraulics

Hydraulics

An area of engineering science that deals with

liquid flow and pressure

Hydraulic Fluids Liquid pumped through a hydraulic system Petroleum-based or synthetic oil Serve four major functions:

1. Power transmission

2. Lubrication of moving parts

3. Sealing of spaces between moving parts

4. Heat removal Relatively Incompressible!

Two Types or Conditions of Hydraulic Systems

Hydrostatic

Hydrodynamic

Hydrostatics -a “No Flow” Scenario “Static” means “stationary” or “non flowing” in

a hydraulic system Hydraulic systems are considered static when

there is no flow Pascal’s Law (for hydrostatics):

a pressure applied to a confined hydrostatic fluid is transmitted with equal intensity throughout the fluid

Same pressure all throughout!

Hydrodynamics – a “Flow” scenario

“Dynamic” means “moving” or “flowing” in a hydraulic system

Hydraulic systems are considered dynamic when there is flow

Pascal’s Law does not apply! Pressure does not have equal intensity in a

flowing dynamic system Pressure drops along the length of a hydraulic line

in flowing systems

Flow and Pressure Flow, Q

volume flow rate amount of fluid moving through system per

unit time Pressure, P

force per unit area of fluid moving through a system

Area

ForcePressure

A

FP

Mechanical Advantage Ideal mechanical advantage (IMA)

Assumes no frictional losses Calculated as ratio of output force to input force

Actual mechanical advantage (AMA) always less than ideal difficult to calculate

FF

input

outputIMA

Application of Pascal’s Law in a Simple Hydrostatic System

How much force must you exert on piston A to lift a load on piston B of 500 lbs? What is the ideal mechanical advantage of this system?

Problem SolvingStep 1: Determine the pressure in the system using information about piston B

Known Unknown

A = 500 in2 P=?

F = 500 lb

Equation No algebra needed

Substitution & Solution

STEP 2: Use the pressure calculated in STEP 1 and information about piston A to calculate force

Known UnknownA = 1.0 in2 F=?

Equation and algebra:

Substitution & Solution

1psiin

lb1

500in

500lbP

22

(A)A

F(A)P

A

FP PAF

2in

lb1psi1P

1.0lb1.0inin

lb1PAF 2

2

A

FP

Problem SolvingStep 3: Determine the ideal mechanical advantage (IMA) of the system using information from STEPS 1 & 2

Known UnknownF(input) = 1 lb IMA=?F(output) = 500 lb

Equation No algebra needed

Substitution & Solution

5001.0lb

500lbIMA

F(input)

F(output)IMA

A Hydraulic System

Tank/Reservoir Storage device which is open and not

pressurized

Filter

Pumps Positive displacement

pump (Gear Pump): a specific amount of fluid passes through the pump for each rotation

Centrifugal pump (Vane Pump): no specific amount of fluid flow per rotation; flow depends on speed of blades

Accumulators Storage device which is closed and is

under pressure

Valves Check Valve Directional Control

Linear ActuatorsUse hydraulic power to move linearly

Single Acting Double Acting

Rotary ActuatorsUse hydraulic power to rotate

Single-Vane Double-Vane

Applications Robotics Oil systems in vehicles (e.g. brakes) Presses Heavy equipment Wood splitter Aircraft control systems

The Hydraulic Trainer

Motor

Pump

Return linefrom reservoir

Pressure line

Pressure RegulatorIn-line Pressure

Gauge

Flow Control Valve

Check Valve

Actuators

Directional Control Valve

Inline-Tee

Return lineConnections

Supply lineConnections