Design and analysis of hydraulic circuits

Dr. TJS JothiAssistant Professor

Mechanical Engineering DepartmentNIT Calicut

Hydraulic circuit

• Hydraulic circuit – consist group of components to perform useful task

– pumps

– Actuators

– Control valves and others

• Hydraulic circuits should be

– Safe to operate

– Performing the desired functions efficiently

Examples of hydraulic circuits

• Can be highly complex – such as actuating more than 500 cylinders at various time sequence.

• Simple examples –

– Control of single cylinder/double cylinder

– Regenerative circuit and so on

Control of single acting hydraulic cylinder

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DCV used - ___ way,___ position

Actuation mode – extension Spring offset mode - retraction

Control of double acting hydraulic cylinder

Spring Centered DCV• Neutral positions is adjusted by springsDCV type - ____way

____ position

At Spring centered position• Cylinder is hydraulically lockedAt position 1 – ExtensionAt position 2 - Retraction

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Worked exampleA double acting cylinder is hooked up to reciprocate. Therelief valve setting is 70 bars. The piston area is 0.016 m2 andthe rod area is 0.0045 m2. If the pump flow is 0.0013m3/s, findthe cylinder speed and load-carrying capacity for theExtending stroke and Retracting stroke

Extending Stroke

Cylinder speed, Vp,ext = Qp / AP = ____

Load carrying capacity, Fload = P x AP = ____

Retraction Stroke

Cylinder speed, Vp,ext = Qp / (AP - Ar) = ____

Load carrying capacity, Fload = P x (AP - Ar) = ____

0.0813 m / s

112 kN

0.113 m / s

80.5kN

Regenerative circuit

• To Speed up the extension speed of double acting hydraulic cylinder.

• Retraction at regular speed as double acting cylinder

• Total flow during extension = pump flow + flow from rod end of cylinder (regenerative flow)

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On solving

Ratio of extending to retraction speed

Speed during retraction

Speed during extension

Ratio of speeds

When two speeds become equal?When piston area equals two times the rod area

Load-Carrying Capacity during Extension

• load-carrying capacity of a regenerativecylinder during extension is less than thatobtained from a regular double-acting cylinder

Application of Regenerative circuit –Drilling machine

At tandem neutral, spring centered position• extension – rapid spindle rotation

At position 1• Extension with lower feed

At position 2•Piston retraction

Worked example-1• A double acting cylinder is hooked up in the regenerative circuit. The relief

valve setting is 70 bars. The piston area is 0.016 m2 and the rod area is 0.0045 m2. If the pump flow is 0.0013m3/ s, find the cylinder speed and load- carrying capacity for the Extending stroke and Retracting stroke.

• Extending Stroke:

Retracting Stroke

Worked example - 2

• A double acting cylinder is hooked up in the regenerative circuit. The relief valve setting is 105 bars and the pump flow is 0.0016 m3 / s. If the regenerative and retracting speed are equal to 0.25 m/ s, find the piston and rod area and also load- carrying capacity for the Extending stroke and Retracting stroke.