hydraulic circuit design

1MEL334: Low Cost Automation 1

Hydraulic Circuit Design & Analysis

Dr. Sunil Jha

MEL334: Low Cost Automation 2

Design Considerations

Safety of OperationPressure and Temperature ratings Interlocks for sequential operationsEmergency shutdown featuresPower failure locksOperation speedEnvironment conditions



Meet functional requirementsMeet required performance specificationLife expectancy same as machineFacilitate good maintenance practiceCompatibility with electrical and mechanical

componentsWithstand operational hazards



Efficiency of OperationKeep system Simple, Safe and FunctionalAccess to parts need repair or adjustmentDesign to keep min operational costDesign to prevent and remove contamination.


Linear Circuits Simple reciprocating circuit

Reservoir Strainer Pump Flexible coupling Electric Motor Connectors Relief valve DCV 4 way Hyd. Cylinder


Circuit Design Approach

What are the specifications of the job?Force requirement 8 kNLength of work stroke 15 cmSpeed of piston and rod assembly 0.5 sec

What Size of Cylinder is needed?Force known. Cylinder Area & Operating

Pressure must be selected. F = PAF = PAStandard bore and rod size cylinders


Circuit Design Approach Cylinder Selection Reasoning Large Diameter Cylinder

Operates at Low Pressure Requires Bigger pump for speed

Small Diameter Cylinder Operates at High Pressure Smaller pump give speed

Cylinder selected = 50 mm bore Find Pressure and then select suitable pump



What Capacity Pump is needed?Max Cylinder Speed requiredFlow rate = (Cyl Area)x(Stroke)/(time)Pump selection

What size of Electric Motor needed?Calculate power required to run PumpConsider efficiency of pumpShaft size, type and electric source



What Size reservoir should be used?2.5-3.0 times the pump capacity

What size of Electric Motor needed?Calculate power required to run PumpConsider efficiency of pumpShaft size, type and electric source


Circuit Design Approach Size of pump inlet? Inlet flow velocity = 60-150 cm/sec

Size of Discharge tubing?Outlet flow velocity = 200 450 cm/sec

Relief valve selectionPressure rangeValve port size

Direction Control valveBased on function


Control of a Single Acting Hydraulic Cylinder

Two PositionThree WayManually ActuatedSpring OffsetDCV


Control of a Double Acting Hydraulic Cylinder

Three PositionFour WayManually ActuatedSpring CenteredDCV


Regenerative Circuit

Pressurized fluid discharge returned to system

Speed up extending speed

Retraction bypass DCV

Extend Retract

Qt

Qr

Qp

Qt = Qp + Qr


Drilling Machine Application

Spring centered position Rapid spindle advance

Left envelope Slow feed

Right envelope Retracts piston


PUMP Unloading circuit

Unloading valve unloads the pumpat the ends of extending and retracting strokes

As well as in spring centered position of DCV


Double Pump Hydraulic System

Punch Press Initial Low

Pressure high flow rate req.

When punching operation begins, increased pressure opens unloading valve to unload low pressure pump.

Unload Valve

Relief Valve


Counterbalance Valve

To keep vertically mounted cylinder in upward position while pump is idling.

Counterbalance valve is set to open at slightly above the pressure required to hold the piston up.


Hydraulic Cylinder Sequence Circuit Left Env: Left Cyl

extends completely and then Right Cylextend.

Right Env: Right Cylretracts fully and then Left Cylretracts.

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Automatic Cylinder Reciprocating System Two sequence

valve sensing strokes completion by corresponding pressure build up.


Locked Cylinder using Pilot Check Valves Lock Cylinder so that

piston can not move by external load.

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Cylinder Synchronizing Circuit

Cylinders connected in parallel Loads identical Moves in exact synchronization Loads Not exactly Identical (practical situation) Cylinders also not exactly identical (packing Friction)



Cylinders connected in Series For two cylinder to be synchronized Piston Area of Cyl 2 = Piston Area of Cyl 1-

Rod area

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Pump pressure should overcome load acting on both cylinders.

P1Ap1- P2(Ap1-Ar1) = F1P2Ap2- P3(Ap2-Ar2) = F2



Ap2 = Ap1-Ar1P3 = 0P1Ap1 = F1+F2

Q. For the Cylinder Synchronizing Circuit, what pumppressure is required if the cylinder loads are 22kNeach and cylinder 1 has a piston area of 65 cm2?

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Fail Safe Circuit Designed to prevent injury to operator or

damage to equipment. Prevent Cylinder from

accidentally falling on an Operator in the event of: Hydraulic line ruptures Person inadvertently operates

manual override on Pilot actuated DCV when pump not operating


Fail Safe Circuit with Overload Protection

DCV-1 controlled by Push button valve-2.

When Overload Valve -3 is in spring offset mode, it drains the pilot line of valve 1.

If Cyl experience excessive resistance, Valve-4 actuates overload valve -3. This drains pilot line of Valve1, causing it to return to spring offset mode.

Nothing happen if push button 2 pressed unless overload valve shifted manually into blocked configuration.

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Two hand Safety Circuit

Designed to protect an operator from injury.

For circuit to function, operator must depress both manually actuated valves.

Any one button prevents operation.


Speed Control of a Hydraulic Motor

Hydraulic Motor Rotary Motion Spring Center Position Motor hydraulically locked

Left EnvelopRotates Clockwise

Right EnvelopRotates Anticlockwise

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Speed Control of a Hydraulic Motor


Hydraulic Motor Braking System

Hydraulic motor may be driving Machine having a large inertia.

Creates Flywheel effect. Stopping motor, acts as a pump. Circuit is designed to provide fluid to the motor

while it is pumping. Provisions should be made for discharge fluid

from motor to be returned to Tank. This would stop motor without damaging.

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Hydraulic Motor Braking System


Hydrostatic Transmission

Open Circuit DrivesPump draws fluid from reservoirPump output directed to Hydraulic MotorDischarge from Motor into reservoir

Closed Circuit DriveExhaust oil from the motor returned directly to

pump inlet.

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Closed Circuit One-Direction Hydrostatic Transmission Closed Circuit that

allows only one direction of motor rotation.

Motor speed varied by changing pump displacement.

Torque capacity of motor adjusted by pressure setting of the relief valve.


Closed Circuit Reversible Direction Hydrostatic Transmission

hydraulic circuit design

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