HYDRAULICS

PREPARED BY : MISS TAJ NESHA

2012

• 5.1 Explain arrangement of components • 5.1 .1 Show the arrangement of components in hydraulic basis circuit. • 5.2 Explain basic circuit of hydraulic system • 5.2.1 Design the basic circuit of hydraulic system: • a. Sterling hydraulic • b. Electro-hydraulic

• 5.2.2 Explain the advantages and disadvantages of hydraulic system’s

basic circuit: • a. Opened cynosure system • b. Closed cynosure system

• 5.3 Explain pressure and flow control at hydraulic system’s actuators.

5.3.1 Sketch and explain the methods of pressure and flow control at hydraulic system’s actuators:

• a. Metering in • b. Metering out • c. Metering off

COURSE LEARNING OUTCOMES

Hydraulics hy·drau·lics [h drólliks ] noun

study of fluids: the study of water or other fluids at rest or in motion,

especially with respect to engineering applications

A hydraulic drive system is a drive or transmission

system that uses pressurized hydraulic fluid to drive

hydraulic machinery.

APPLICATION

Hydraulic Theory

• Hydraulics

• Covers the physical behavior of liquids in motion

• Pressurized oil used to gain mechanical advantage and perform work

• Important Properties

• Shapelessness

• Incompressibility

• Transmission of Force

Important Properties • “Shapelessness”

• Liquids have no neutral form

• Conform to shape of container

• Easily transferred through piping from one location to another

• Incompressibility • Liquids are essentially incompressible

• Once force is removed, liquid returns to original volume (no permanent distortion)

• Transmission of Force • Force is transmitted equally & undiminished

in every direction -> vessel filled with pressure

Hydraulic Theory

• Pascal’s Law

• Magnitude of force transferred is in direct proportion to the surface area (F = P*A)

• Pressure = Force/Area

• Liquid properties enable large objects (rudder, planes, etc) to be moved smoothly

Hydraulic Mechanical Advantage F2 =

F1 = 20 lbf

A1 = 2 in2

A1 = 20 in2

Basic Hydraulic System

• Hydraulic Fluid • Usually oil (2190 TEP)

• Pressure Source • Hydraulic pump (A-end of system)

• Pressure user • Hydraulic motor (B-end of system)

• Piping system (w/ valves, tanks, etc) • Get fluid from A-end to B-end

Advantages Of Hydraulics:

• Transmission of large forces using small components, i.e. great power intensity

• Precise positioning

• Start-up under heavy load

• Even movements independent of load, since liquids are scarcely compressible and flow control valves can be used

• Smooth operation and reversal

• Good control and regulation

• Favourable heat dissipation

Disadvantages Of Hydraulics:

• Pollution of the environment by waste oil (danger of fire or accidents)

• Sensitivity to dirt

• Danger resulting from excessive pressures (severed lines)

• Temperature dependence (change in viscosity)

• Unfavourable efficiency factor

FUNCTIONS OF BASIC COMPONENTS IN A HYDRAULIC SYSTEM

• Valve - to adjust the pressure in a circuit and control flow of oil.

• Motor – supply power to do work for rotary movement

• Filter – filter the hydraulic oil free from dirt/contamination

• Pump – to distribute quantity of hydraulic oil to the whole system.

• Cylinder – can provide power to do work for linear movement.

• Accumulator – to store system pressure, absorb vibration and stabilize system pressure.

• Tank – contain hydraulic oil and cools it.

Basic hydraulic circuit

D.A CYLINDER

4/3 dcv close centre

Relieve valve

Motor

Tank

Filter

Check valve

accumulator

Pump

Flow control valve

Basic Circuit Of Hydraulic System • Sterling circuit – figure 8.4- unit 8 page 5

Untuk Gerudi Untuk Pengapit

A B

3

2

4 1

Electro hydraulic circuit ?(figure 8.5)- unit 8 page 6

Types of pump

• Gear

• Ram

• Piston

• Screw

Gear Pump

Ram pump

Hydraulic Pump (A-End)

• Pumps can be positive displacement or centrifugal

•Waterbury pump

•Variable-stroke piston pump

•Tilting box can tilt fwd/aft while pump rotates

•Angle of tilting box determines capacity and direction of oil flow

Hydraulic Pump (A-End) •Variable-stroke piston pump

•Tilting box can tilt fwd/aft while pump rotates

•Angle of tilting box determines capacity and dir. of flow

Cylinder/Motor (B-end) • Piston/cylinder used if desired motion is

linear

• Hydraulic pressure moves piston & ram

• Load is connected to ram (rudder, planes, masts, periscopes)

Piston Cylinder

RAM

Hydraulic Fluid Supply/Return Ports

Seal

Cylinder/Motor (B-end)

• Motor used if desired motion is rotary

• Essentially a variable-stroke pump in reverse

• Used for capstan, anchor windlass, etc

Piping System

• Has to withstand excessive pressure

• Valves, filters, & HX’s all necessary

• Accumulators

• Holds system under pressure (w/out contin. pump)

• Provides hydraulics when pump off/lost

• Compensates for leakage/makeup volume

• Types: piston, bladder, & direct contact

Accumulator Types

• Piston

• Most common

• Bladder

• Gun mounts

• Steering systems

• Direct contact

• Least common

Advantages • Convenient power transfer

• Few moving parts

• Low losses over long distances

• Little wear

• Flexibility

• Distribute force in multiple directions

• Safe and reliable for many uses

• Can be stored under pressure for long periods

• Variable speed control

• Quick response (linear and rotary)

Disadvantages

• Requires positive confinement (to give shape)

• Fire/explosive hazard if leaks or ruptures

• Filtration critical - must be free of debris

• Manpower intensive to clean up

Electrohydraulic Drive System

• Uses hydraulics to transfer power from electric motor to load

• Rotary: Waterbury pump connected to rotary piston hydraulic motor (speed gear)

• Tilting box of A-end controls direction/speed of B-end

• Adv: high starting torque, reversibility, high power-to-weight ratio

• ex: Electrohydraulic Speed Gear or Steering Gear

• capstan, anchor windlass, cranes, elevator, ammo hoist

Electrohydraulic Speed Gear

Electrohydraulic Steering Gear

• Same as speed gear except B-end is a hydraulic cylinder to produce linear motion

• Waterbury pumps connected by piping to hydraulic ram cylinder

• Various methods for connecting rams to tillers

• Two pumps for redundancy & reliability

• Movement of steering wheel through hydraulic system moves rudder

Control of System

• Remote control

• Normal method

• Control from bridge

• Emergency

• Take local control

• Manually position control surface/rudder

2005/2006 I. Hydraulic and

Pneumatic Systems

31

A typical hydraulic system

1 – pump

2 – oil tank

3 – flow control valve

4 – pressure relief valve

5 – hydraulic cylinder

6 – directional control valve

7 – throttle valve

The Hydraulic System

• The basic hydraulic system has seven parts

• Pump

• Lines and connectors

• Cylinder or Motor

• Check valve

• Reservoir

• Control Valve

• Relief Valve

Hydraulic pump

• The pump moves the hydraulic fluid

• Pumps create flow not pressure

• Come in positive fixed displacement and variable displacement

• Fix displacement – Moves the same amount of fluid every rotation

• Variable displacement – The amount of fluid discharged can be changed and controled.

Lines and Connections

• Carry the fluid from the pump to where the work will be done and back.

• Come in various sizes and shapes

• Are a major source of repair

Cylinders and motors

• Do the work the system was designed for.

• Convert hydraulic force into mechanical motion.

• Cylinders

• Convert hydraulic force into recipricating motion

• Can be single acting or double acting

• Motors

• Convert hydraulic force into rotary motion

The Check Valve

• A simple one way valve which uses a poppet to control fluid flow.

• Can be used to control

• Fluid direction

• Circuit pressures

The Reservoir

• Is the storage container for the hydraulic fluid

• Maintains constant supply of fluid to the pump

• Helps in fluid filtration

• Acts as a heat sink and is a major part of the fluid heat dissipation system.

Control Valves

• Control valves are used to control the pressure, direction and volume of oil flow in hydraulic systems.

• There are three types of control valves

• Pressure control

• Direction control

• Volume Control

Relief Valves

• Hydraulic systems are designed to operate at certain pressures. Relief valves are built into the system as a protection device.

Opened cynosure system (UNIT 8/PAGE 9/ FIGURE 8.10)

Opened cynosure system

Disadvantages-

• Low pressure

• Reduce vibration

• waste electrical energy

• slow start for actuator

Advantages-

• Not Easily leaking/wear/tear

• Rarely maintained except the motor

Closed cynosure system

Pressure switch

Closed cynosure system

Advantages-

• High pressure

• saves electrical energy

• Fast start for actuator

Disadvantages-

• Easily leaking/wear/tear

• Need frequent maintenance

• Explain pressure and flow control at hydraulic system’s actuators. 5.3.1 Sketch and explain the methods of pressure and flow control at hydraulic system’s actuators:

• a. Metering in

• b. Metering out

• c. Metering off

a) Metering – in – UNIT 9/PAGE 3. FIGURE 9.1

b) Meter-Out

c) Bleed-Off / Meter off

6.0 CONSTRUCTION AND LIMITATION OF

HYDRAULIC SYSTEM

• 6.1 Apply practical construction.

• 6.1.1 Design the construction of hydraulic system in a practical way.

• 6.2 Apply construction with the help of computerized software/simulation.

• 6.2.1 Design the construction of hydraulic circuit with the help of computerized software/simulation.

• 6.3 Identify main problems in hydraulic system.

• 6.3.1 Determine these main problems:

a. Effects of overload burden

b. Effects of flow rate exchanger

c. Hollowing

d. Leaking in the system

e. Other problems