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HYDRAULIC CIRCUITS

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BASIC HYDRAULIC

COMPONENTS

RESERVOIR

PUMP + ELECTRIC MOTOR

DIRECTION + PRESSURE + FLOWCONTROL VALVES

ACTUATORS

PIPE LINES

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HYDRAULIC CIRCUITS

SINGLE ACTING

CYLINDER CIRCUIT

DOUBLE ACTING

CYLINDER CIRCUIT

RECIPROCATING

CIRCUIT

REGENERATIVE

CIRCUIT

SEQUENCING CIRCUIT

SYNCHRONISING

CIRCUIT

ACCUMULATOR

CIRCUITS

SAFETY SIRCUITS

PUNCHING PRESS DRILLING AND

CLAMPING

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SINGLE ACTING CYLINDER

CIRCUIT

Control of a single acting

hydraulic cylinder

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SINGLE ACTING CYLINDER

CIRCUIT It has a reservoir, pump, two position- three way manual operated

direction control valve, a pressure relief valve and a single actingcylinder.

In its normal position, the fluid is diverted back to the tank through

the pressure relief valve.

When the direction control valve is manually pushed to left envelop,flow enters the piston side of the single acting cylinder.

At the end of extension stroke, DCV is pushed to right envelop

resulting in the pump flow diverted through the PRV to the tank.

The fluid in the cylinder is pushed by the spring on the rod side toretract and the flow goes to the tank

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DOUBLE ACTING CYLINDER

CIRCUIT

Control of a double-acting hydraulic cylinder

F Load

A B

P T

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CIRCUIT It has a reservoir, a pump, a pressure relief valve,

manual operated three position four way DCV (tandemposition), and a double acting cylinder

In its spring centered position, the cylinders arehydraulically locked and the flow without any increase inpressure is diverted back to the tank (advantage oftandem position)

When shifted to left envelop position of the DCV, flowenters the piston side of the cylinder and extensionstroke takes place against the load

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CIRCUIT At the end of extension stroke, the DCV can be shifted to the right

envelop in which case the flow is directed to the rod side of theactuator and retraction takes place.

In the double acting cylinder both extension and retraction is by the

fluid.

The extension of the cylinder is slow as they act against the load butcan carry large load as the area on the piston side is more

The retraction in double acting cylinder is fast as the area on the rod

side is less and the same pump flow enters the side.

At the end of extension and return strokes if the flow is not stoppedthere is increase in pressure and flow is diverted through the PRV.

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RECIPROCATION CIRCUIT

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RECIPROCATING CIRCUIT

This circuit has a reservoir, a pump, a pressure reliefvalve, pilot operated spring centered four way threeposition DCV, pair of Sequence Valves, a pair of checkvalves, and a double acting cylinder.

In its neutral position, the pump flow is diverted throughthe PRV at high pressure.

When the DCV is shifted to any position, the pump flowis diverted either to rod side or piston side

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If flow enters the piston side, then extension takes placeand at the end of the stroke, the pressure is increasedand the flow is diverted through the sequence valvewhich shift the DCV to its left envelop.

In this position, the flow is diverted to the rod side of theactuator and retraction occurs. At its end similarly theincrease in pressure is sensed by the sequence valveand shifts the DCV to its right envelop

Thus the continuous reciprocation takes place as longthe flow is stopped.

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The check valves and their correspondingpilot line prevent shifting of the four wayvalve until particular stroke is completed.

The check valves are needed to allow pilotoil to leave either end of the DCV while

pilot pressure is applied to the oppositeend which will permit the shifting of thespool of the DCV

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REGENERATIVE CIRCUIT

Regenerative circuit

F Load

Blocked

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This circuit is used to speed up the extending speed ofthe double acting actuator.

In this circuit the pipelines to the cylinder are connected

in parallel and one of the ports of the DCV is blocked.

In the left envelop of the DCV, the flow from the pumpand the flow from the rod side (regeneration) joins andthis results in the increased speed of extension.

When shifted to the right envelop of the DCV, the flowbypasses the DCV and enters the rod side and the fluidin the piston side drains through the DCV.

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Total flow to the piston side

QT=QP+QR

Pump Flow QP=QT-QR

Total flow rate AP X VP exti.e. (area of piston) X (speed of extension)

Regenerative flow rate = (AP AR) X VPextTherefore, QP= AP X VP ext- (AP AR) X VPext

VP ext = QP/ AR (this gives the large velocity of

extension)

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Ratio of Extending and Retracting Speeds

Retracting Speed VP ret= QP/ AP-AR

VP ext

/ VP ret

= (QP/ AR )/ QP/ AP-AR

=AP-AR/ AR= AP/AR-1

When Piston area= 2 X Rod area

VP ext= VP ret

Drawback: Load carrying capacity during extension in a Regenerative

circuit is less than the regular double acting cylinder

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APPLICATION OF


Drilling machine application

A B

P T

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DRILLING MACHINE

The increase in extension speed iscompensated by reduction in load bearingcapacity of the regenerative circuits.

This is overcome by having a regeneratedconnection in its central position of the

drilling circuit and the other positions (left,right) act as a simple double actingcylinder.

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SYNCHRONISING CIRCUIT

Synchronization is the technique of

operating two cylinders to do identical

strokes

There are two ways to make the cylinders

operate in synchronization

i) Connecting the cylinders parallel

ii) Connecting the cylinders in series

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Synchronization by connecting

cylinders in Parallel

F load

F load

Cylinders hooked in parallel will not operate in synchronization

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cylinders in Parallel

The piping to two cylinders are parallel

The two cylinders cannot operate insynchronization if connected in parallel because:

Loads on cylinders are not identical

No two cylinders are exactly identical

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cylinders in Series

P1

P2

F1

F2

CYLINDER 1

CYLINDER 2A-P1

A-P2

A-R1

A-R2

Cylinders hooked in series will operate in synchronization

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cylinders in Series

This is the simplest, accurate and easiest way ofachieving synchronization.

The fluid from pump is connected to piston side ofcylinder 1 and fluid from rod side of cylinder 1 isconnected to piston side of cylinder 2 and fluid from rodside of cylinder 2 is directed to tank via DCV.

For synchronization the piston area of cylinder 2 must beequal to the difference between the areas of the pistonand rod for cylinder 1.

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cylinders in Series

The pump flow should have the pressure rating equal to thatrequired for both the cylinders.

As per Pascals law,

P1AP1 P2(AP1-AR1)=F1P2AP2 P3(AP2-AR2)=F2

Adding both these equations and also note

AP2=AP1-AR1 and P3=0;

P1AP1= F1+ F2

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ACCUMULATOR CIRCUITS

Accumulators are devices that stores the potentialenergy of the compressible fluid under pressure by anexternal source against some dynamic force. The storedenergy is used to do useful work.

The Accumulators are used as

Auxiliary power source

As a leakage compensator As a emergency power source

As a shock absorber

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ACCUMULATOR AS AN

AUXILIARY POWER SOURCE

Accumulator as an auxiliary power source

ACCUMULATOR

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ACCUMULATOR AS AN

AUXILIARY POWER SOURCE

The oil delivered by pump is stored by theaccumulator

The accumulator then delivers the stored oil ondemand

Useful to systems which has intermittentoperations

The oil flows form the pump as well as from the

accumulator to the cylinder and at the end ofstrokes the oil from the pump is stored in theaccumulator.

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ACCUMULATOR AS A LEAKAGE

COMPENSATOR

Accumulator as a leakage compensator

PRESSURESWITCH

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ACCUMULATOR AS A LEAKAGE

COMPENSATOR

This is used for systems which operate for long period oftime.

The pump charges the accumulator to the maximumpressure and when it reaches the pressure switch closesthe operation and pump. The further operation ismanaged by the flow from the accumulator and when thepressure reduces, the pressure switch once again startsthe pump and thus it prevents the functioning of pumpfor a long period and also supplies the fluid as and whenrequired.

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ACCUMULATOR AS AN

EMERGENCY POWER SOURCE

Accumulator as an

emergency power source

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ACCUMULATOR AS AN

EMERGENCY POWER SOURCE

The accumulators are used to retract thecylinders in case of power failures.

In the circuit, the fluid is passed to blank side,rod side and through the check valve to theaccumulator. In any case the power fails, the

solenoid DCV is pushed to spring offset modeand the accumulator supplies fluid towards theretraction of the cylinder.

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ACCUMULATOR AS A

HYDRAULIC SHOCK ABSORBER

Accumulator as a hydraulic

shock absorber

TO SYSTEM

EMERGENCYSHUT-OFF

VALVE

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ACCUMULATOR AS A

HYDRAULIC SHOCK ABSORBER

The hydraulic shocks are due to sudden

stoppage, deceleration of flow etc.. The shock

creates compression waves and travels at thespeed of sound and travels up and down until

their energy is lost as friction. This causes

damage to the components and if an

accumulator is placed near the rapidly closingvalve, the pressure pulsations are suppressed

and thus serves as a shock absorber.

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SAFETY CIRCUITS

Fail Safe circuits are designed to prevent

injury to the operator or damage to

equipment.

In general it prevents the system from free

falling on the operator and prevent the

system from overloading.

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FAIL SAFE CIRCUIT TO PROTECT FROM

CYLINDER FALLING

Fail-safe circuit

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FAIL SAFE CIRCUIT TO PROTECT FROM

CYLINDER FALLING

In this circuit, the lowering of the cylinder will occur onlywhen the pilot pressure from the blank side of thecylinder pushes the pilot operated check valve to allowthe flow from the rod side to pass through the DCV.

This is helpful in those places where inadvertent pushingof the DCV takes place or rupture in the flow line occurs.

To insure safety the push button will be used to give thepilot pressure to operate the DCV or only when manualoperation of the DCV is done the flow is passed to theblank side.

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FAIL SAFE CIRCUIT FOR OVERLOAD

PROTECTION

Valve 2

Valve 3Valve 4

Valve 1

Fail-safe circuit with overloadprotection

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FAIL SAFE CIRCUIT FOR OVERLOAD

PROTECTION

Valve 1 is controlled by Valve 2.

Valve 3 drains Valve 2 in its spring offset mode

Valve 4 is operated when an increase in pressure due to overload is felt in theupward line to the cylinder

When Valve 2 is operated, it pushes the Valve 1(DCV)

This transfers oil to the blank side and any increase in pressure operates Valve 4 andthis Valve 4 pilot operates Valve 3 and this drains Valve 1 and results in flow to therod side and prevents from further downward motion against load.

Any motion of Valve 2 now will not do anything and only at the retraction of Valve 4 ormanual pushing of Valve 3 only will result in downward motion of the cylinder.

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TWO HANDED SAFETY SYSTEM

Two-hand safety circuit

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TWO HANDED SAFETY SYSTEM

In this circuit the extension of cylinder will

occur only when both the push buttons are

pushed down In this circuit the retraction will occur only

when both the push buttons are released

In any case, if one button is pressed there will

be no operation.

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PUNCHING PRESS- DOUBLE PUMP CIRCUIT

Double pump hydraulic system

High pressure pump Low pressure pump

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PUNCHING PRESS- DOUBLE PUMP CIRCUIT

In this circuit there is a low pressure, high flow pump and highpressure low flow pump, an unloading valve, a check valve, apressure relief valve and a double acting cylinder.

The high flow low pressure pump is used for rapid extension andhigh pressure low flow pump delivers during the actual punching

operation.

The high flow pump during high pressure is protected by the checkvalve and during punching, the flow is diverted through theunloading valve back to the tank at low pressure.

This eliminates the need of a large high pressure, high flow pump.

An alternate circuit for punching is the pressure intensifier circuit.

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PUNCHING PRESS-PRESSURE

INTENSIFIER CIRCUIT

F load

int

Pressure intensifier circuit

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PUNCHING PRESS-PRESSURE

INTENSIFIER CIRCUIT

This circuit has a pilot operated check valve ,a pressureintensifier placed close to the cylinder in the loadapplication direction and a sequence valve.

Once the flow is passed through the check valve, thecylinder extends and when the pressure is required theflow is passed to the intensifier through the sequencevalve that deliver the required pressure.

The return flow is through the pilot check valve

This eliminates the need of two pumps in a circuit.

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SEQUENCING CIRCUIT

Hydraulic cylinder sequence circuit

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SEQUENCING CIRCUIT

In this circuit if the DCV is shifted to the left, the leftcylinder extends completely and the right cylinderextend.

If the DCV is shifted to its right, the right cylinder retractscompletely and then the left cylinder retract.

If Cylinder on left is clamping cylinder and Cylinder onright is drilling, it can be taken for a clamp and drillcircuit.

This procedure can be adopted to all the machiningoperations.

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