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UNIT-5

POSITIVE DISPLACEMENT MACHINES

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Reciprocating Pumps

It is a positive displacement pump It uses a piston and cylinder

arrangement with suction and deliveryvalves integrated with the pump.

It can be single acting and double acting

There may be single or multi cylindersalso.

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Reciprocating Pumps

It is a positive displacement pump

It sucks and raises the liquid by actually

displacing it with a piston/plunger thatexecutes a reciprocating motion in a closely

fitting cylinder.

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Working of single acting ReciprocatingPump

Single Acting Reciprocating Pump

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Working of single acting ReciprocatingPump

During suction stroke the piston moves tothe left, causing the inlet valve to open.

Water is admitted into the cylinder throughthe inlet valve.

During the discharge stroke the piston

moves to the right closes the suction valve andopens the out let valve.

Through the outlet valve the volume ofliquid moved out of the cylinder.

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Double Acting Reciprocating pump

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Double Acting Reciprocating Pump -Working

Each cycle consists of two strokes.

Both the strokes are effective, hence it is knownas double acting pump

Liquid is filled at one end and discharged atother end during forward stroke.

During the return stroke, end of cylinder justemptied is filled and the end just filled is

emptied.

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Advantages of reciprocating pump

Relatively compact design High viscosity performance

Ability to handle high differentialpressure.

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Discharge of reciprocating pump

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Double acting reciprocating pump

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Problems

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Air Vessels

Air vessel is a closed

chamber containing

compressed air in the

upper part and liquid

being pumped in the

lower part.

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Purpose of using an Air Vessel

To get continuous supply of liquid at auniform rate.

To save the power required to drive the

pump (By using an air vessel the accelerationand friction heads are considerably reduced)

To run the pump at much higher speed

without any danger of separation.

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