Collection of slides for Hydraulic and Pneumatic systems

7/28/2019 Collection of slides for Hydraulic and Pneumatic systems

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2005/2006 I. Hydraulic and Pneumatic Systems 1

A typical hydraulic system

1 – pump

2–

oil tank3 – flow control valve

4 – pressure relief valve

5 – hydraulic cylinder

6 – directional control valve

7 – throttle valve

,,



What is Fluid Power?

• Fluid power is energy transmitted and controlled bymeans of a pressurized fluid, either liquid or gas. Theterm fluid power applies to both hydraulics andpneumatics.

• Hydraulics uses pressurized liquid, for example, oil orwater;

• Pneumatics uses compressed air or other neutralgases.

•Fluid power can be effectively combined with othertechnologies through the use of sensors, transducersand microprocessors.

From: http://www.nfpa.com/OurIndustry/OurInd_AboutFP_WhatIsFluidPower.asp

http://www.nfpa.com/OurIndustry/OurInd_AboutFP_WhatIsFluidPower.asp

http://www.nfpa.com/OurIndustry/OurInd_AboutFP_WhatIsFluidPower.asp



© Goodheart-Willcox Co., Inc. Permission granted to reproduce foreducational use only.

3

Reservoir

• The primary purpose of the reservoir is tohold the system fluid not currently in use inthe system

• Other important functions of the reservoirare:

– Remove heat

–

Separate solid particles – Release air from fluid

– Separate water from fluid




4

Reservoir

• The reservoir serves many functions




5

Reservoir

• Baffles are used in the interior of reservoirs to

direct flow to maximize the distance the fluid

must travel between the return line and the

pump inlet line

– Slows the movement of the fluid

– Increases cooling

– Increases separation of solid particles, air, andwater




6

Reservoir

• Typical reservoir construction




7

Conductors

• Pipe, tubing, and flexible hose are considered

basic conductors in a hydraulic system




8

Conductors

• Conductors must have:

– Adequate strength to withstand high system

pressures

– Low flow resistance to assure low energy loss

during system operation

– A design that allows economic installation and low

maintenance




9

Conductors

• Conductors must not only withstand normal

system operating pressure, but also hydraulic

shock pressures

• Shock pressures result from kinetic energy in

the system when:

– Directional control valves are shifted to reverse

the movement of a load or heavy machinemember

– Actuators encounter sudden load changes




10

Conductors

• Future maintenance must be carefully

considered when designing and installing

hydraulic system conductors to assure minimal

difficulty in removing components for service




11

Conductors

• Tubing:

– Is a relatively thin-walled, semirigid conductor

– Can be bent and shaped into lines that provide

good flow characteristics with a minimum of

visual clutter




12

Conductors

• Tubing can be bent, unlike pipe

Used with permission of CNH America LLC




13

Conductors

• Hose is a flexible conductor made up of:

– Inner tube to conduct the fluid

– Middle layer of reinforcing material for strength

– Outer protective coating to withstand abrasion

and abuse




14

Conductors

• Hose provides

flexibility

Used with permission of CNH America LLC




Hydraulic fluids - tasks

They have the following primary tasks:

o Power transmission (pressure and motion

transmission)o Signal transmission for control

Secondary tasks:

o Lubrication of rotating and translatingcomponents to avoid friction and wear

o Heat transport, away from the location of heat

generation, usually into the reservoiro Transport of particles to the filter

o Protection of surfaces from chemical attack,especially corrosion




Hydraulic fluids - requirements

Functional

o Good lubrication characteristics

o Viscosity should not depend strongly ontemperature and pressure

o Good heat conductivity

o Low heat expansion coefficient

o Large elasticity modulus

Economic

o Low price

o Slow aging and thermal and chemical stability long life cycle




Hydraulic fluids - requirements (contd.)

Safety

o High flash point or in certain cases not

inflammable at all

o Chemically neutral (not aggressive at allagainst all materials it touches)

o Low air dissolving capability, not inclined tofoam formation

Environmental friendliness

o No environmental harmo No toxic effect




Hydraulic Accumulators

Constructions and

tasks in the hydraulic system Tasks:

The hydropneumatic accumulators

perform different tasks in the hydraulic

systems, e.g.:

Constructions

• reserve energy

• store fluid

• emergency operate

• force compensating

• damp mechanical shocks

• absorb pressure oscillations

• compensate leakage losses

• springs in vehicles

• recover of braking energy

• stabilize pressure

• compensate volumetric flow rate

(expansion reservoir)

With springWith weight With gas(hydropneumatic accumulator)

Separating part between gas and fluid

Piston Bladder Membrane



Properties of Compressed Air

• Availability

• Easily stored in large volumes

•

Simplicity in design and control• Provides linear and rotary movement

• Installation

• Low system cost due to low component cost



• Components have long working life

resulting in longer system reliability

• Environmentally friendly

• Safety issues are minimized e.g.. Fire

hazards; unaffected by overloads (actuators

stall or slip)• Pneumatic actuators in a system do not

produce heat (except for friction)

Properties of Compressed Air



Pressure SwitchCompressor DrainCheck Valve

A Basic Pneumatic SystemAir Production and Distribution System

Motor

Tank

Pressure GaugeRefrigerated Air Dryer Line Filter



Directional Valve

A Basic Pneumatic SystemAir Consumption System

Air Line Take-off DrainConditioning Unit Actuator



Air Receiver

A pressure Vessel (Tank) normally made of metal and installed

either horizontally or vertically. This vessel provides a volume of air

to be utilized by the system and reduced the loading and unloading

of the compressor.

Air Receiver (Tank)



Air Treatment

All atmospheric air carries both moisture and dust

Inlet Filter •Used to remove large particle dirt from

entering the system.

•Used to prevent excessive

wear of cylinder, piston rings

and other moving parts in theinitial stage of the system



Regulating and Conditioning

The compressed air to be used in a system needs to be treated

because of contamination inside the system. An example of this could

be the scaling of piped or worn seal material. A line filter is used to

collect water and solid impurities. A Lubricator is used to vaporize oil

into the air stream to lubricate moving parts in the system such as air

tools

A regulator is used to adjust the

line pressure to a lower usable

pressure needed for some tool

applications.



Air Dryer

Compressed air cannot hold the same amount of moisture as noncompressed air. Once the air is compressed, some of the moisture

condenses in the tank and is removed through a drain valve. The remaining

moisture will rust internal components of the system and must be removed.

One way this is done by sending the air through an air conditioned chamber

which will condense more of the moisture which is present.



Control Valves

Double Pressure Operated5 Port Valve

3 Port Pilot Valve 3 Port Pilot Valve



Actuators

The work done by a pneumatic actuator can be linear or rotary.

There are two basic types of linear cylinders

•Single-acting

•Double-acting

Documents

Collection of slides for Hydraulic and Pneumatic systems