fluid power devices circuits

HYDRAULIC CONTROL DEVICES &

CIRCUITS

1

FLUID POWER DEVICES & CIRCUITS


RANA SAHA

DEPARTMENT OF MECHANICAL ENGINEERING

JADAVPUR UNIVERSITY

KOLKATA 700 032

[email protected]


ELECTRIC

MOTORPUMP

CONTROL

DEVICESACTUATOR

ACCESSORIES

LOAD

EHP IHP HHP HHP OHP

Voltage rpm lpm lpm

rpmor

m/s

Torque/ForcePressurePressureTorqueCurrent

RESERVOIR

AUTOMATIC CONTROL

Power Supply

Controller

Sensors

DAS

PC Interface

THE SYSTEM


CIRCUITS

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Hydraulic fluids


Reservoir

In addition to holding the supply of fluid needed

to ensure that all lines and components are

completely filled with fluid at all times, the

reservoir has four other functions:

1. It separates entrained air. Dwell time in the

reservoir provides opportunity for air bubbles in

the fluid to rise to the top and burst on the surface.

2. It dissipates pressure pulses. Circuits with

several actuators and random actuation of these

actuators can have significant pressure pulses in

the return line. Off-line filtration eliminates the

influence of these pulses on the filter, because

they are dissipated by the reservoir.

3. It provides cooling.

4. It traps contaminant. If the reservoir has to trap

contaminant, the filtration is not working

correctly. The reservoir does trap contaminant

when the filter bypasses.


CIRCUITS

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Fixed

Screw

Piston

Vane

Gear

Variable

Pumps

Vane

Positive DisplacementNon Positive Displacement

AxialRadial

Bent Axis Swash Plate

Unbalanced

Balanced

Piston

Axial

Radial

Swash Plate Bent Axis

Centrifugal

Axial Propeller

Mixed Flow

Classification of Pumps

Internal

(Crescent)ExternalInternal

(Gerotor)

Rotating Swash Plate

Rotating Cylinder Block


For relatively low level of pressure (about 140 to 180 bar or 14 to 18 MPa)

Very simple, reliable, relatively cheap and less dirt sensitive

In order to prevent cavitation, the pressure at the suction side of the pump

should not exceed 0.1 to 0.2 bar (10 to 20 kPa) below atmospheric pressure

(minimim absolute pressure: 0.8 bar or 80 kPa).

GEAR PUMP


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GEAR PUMP DETAILS


VANE PUMP

Maximum pressure: about 200 bar.

Pulse free delivery and low level of noise.

The amount of eccentricity determines the displacement of the pump.

In order to prevent cavitation, the pressure at the suction side of the pump

should not exceed 0.1 to 0.2 bar (10 to 20 kPa) below atmospheric pressure

(minimim absolute pressure: 0.8 bar or 80 kPa).

FixedVariable


CIRCUITS

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AXIAL PISTON PUMP

Rotating Swash Plate

Rotating Barrel

Workingpressure above

aprox. 250 bar.

This type of pump can be

driven in both directions.

Can operate without valves

because the rotating barrel has a

determined suck and pressure

zone.

Normally this pump has 5, 7, 9

or 11 pistons.

Fixed


AXIAL PISTON PUMP CYLINDER

VALVE PLATE DETAILS


CIRCUITS

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The angle of the swashplate determines the stroke of the pistons and therefore

the amount of displacement of the pump.

Normally the swashplate is adjusted by a hydraulic cilinder built inside the

pumphousing.

Variable


Pressure Control

Unloading

Sequence

Pressure Relief

Pressure Reducing

Flow Control Direction Control

Counterbalance

Check Valve

Valves

Variable

Fixed

Pressure Compensated

Deceleration

Shuttle

Two Way

Three Way

Four Way

Valve Functions Classification


CIRCUITS

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PRESSURE RELIEF VALVE

Single Stage


Pilot Operated (2 Stage)



CIRCUITS

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AS AN UNLOADING VALVE

The pilot operated pressure relief valve is applied in systemswith a considerable amount of flow. It's task is to limit the

pressure in the system on an acceptable value.

The pilot valve is adjusted at 150 bar. The pressure below themain valve is equal to the pressure above the main valve, for

example 100 bar (determined by the load on the hydraulic motor).

The spring on the main valve (about 1 to 5 bar) keeps the valve in

the closed position. As long as the pressure in the system does not

increase the adjusted pressure, the pump flow goes to the

hydraulic motor. When the hydraulic motor is overloaded, the

pressure will increase and the pilot valve will open. From that

moment on the pressure above the main valve is limited on 150

bar.

However, the pump flow cannot be drained by the small throttlein the by-pass canal, so the pressure below the main valve will

increase with the spring pressure of about 1 to 5 bar (the pressure

below the main valve will increase to 151...155 bar). Then the

main valve opens and the majority of the pump flow will be

drained by the main valve.


SEQUENCE VALVE


CIRCUITS

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COUNTER BALANCE VALVE


FLOW CONTROL

Fixed


CIRCUITS

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PRESSURE COMPENSATED FLOW CONTROL VALVE


CHECK VALVES

Pilot operated check valve


CIRCUITS

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SHUTTLE VALVE


DIRECTION CONTROL VALVE

Method of actuation:

Manual

Electrical

- Solenoid

- Force/Torque Motor


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Limited rotation

Piston

Vane

Continuous rotation

Actuators

RotaryLinear

Piston

Vane

Gear

Symmetric

Asymmetric

Single Acting

Classification of Actuators and their Symbols

Double Acting

Unidirectional Bidirectional

Fixed

Variable


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A typical linear actuator details


ACCUMULATORS

An accumulator is a container in which fluid is stored under pressure as a

source of power.

Functions:

1.Auxiliary power source to supplement the pump

2.Emergency power source in case of power failure to operate critical circuit

functions

3.Hydraulic shock absorber for circuits where sudden impact loads, quick

stops, or reversals with heavy loads are a characteristic of the system


CIRCUITS

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Converts low-pressure fluid power into higher-pressure fluid power.

Intensifiers (also called boosters) are used to multiply forces when a great force is needed through a relatively short distance.

Hydraulic presses, riveting machines, and spot welders are typical applications.

INTENSIFIERS


Some Basic Hydraulic Circuits

Basic Hydraulic Circuit

- Linear

- Rotary

Regenerative Circuit

Counterbalance Circuit

Hydraulic Circuit with Speed Control

- Meter-In

- Meter-Out

Sequence Circuit

Accumulator Circuit

Intensifier Circuit


CIRCUITS

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RETRACT

A B

P T

EXTEND

BASIC HYDRAULIC CIRCUIT-1

Pump

Pressure Relief Valve

Directional Control Valve

Linear Actuator (Hydraulic Cylinder)

Pressure Gauge

Suction Strainer

Reservoir


A B

P T

BASIC HYDRAULIC CIRCUIT-2

Rotary Actuator (Hydraulic Motor)


CIRCUITS

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RETRACT

A B

P T

EXTEND

REGENERATIVE CIRCUIT

(Extension stroke)


COUNTERBALANCE CIRCUIT

Counter balance Valve


CIRCUITS

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SPEED CONTROL CIRCUIT

(METER-IN)

Pressure Compensated Flow Control Valve


SPEED CONTROL CIRCUIT

(METER-OUT)

Pressure Compensated Flow Control Valve


CIRCUITS

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SEQUENCING CIRCUIT

Sequence Valve


ACCUMULATOR CIRCUIT

(AUXILIARY POWER SOURCE)

Accumulator

2 way, Solenoid operated DCV4 way, Solenoid operated DCV


CIRCUITS

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INTENSIFIER CIRCUIT

(High speed, low pressure approach followed by low speed high pressure piercing operation)

Intensifier (Booster Cylinder)


A TYPICAL ELECTROHYDRAULIC CONTROL SYSTEM


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Suggested Reading:

Pease, D.A. Basic Fluid Power. Prentice Hall.

Merritt, H. E. (1967), Hydraulic Control Systems. Wiley, New York.

Esposito, A.; Fluid Power (with Application). 2003

Sullivan, James A., 1998, Fluid Power Theory and Applications, Fourth

Edition, Prentice-Hall International

Yeaple, Frank, 1996, Fluid Power Design Handbook, Third Edition,

Marcel Dekker, Inc., N.Y.

Thank You

fluid power devices circuits

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