WHAT IS THE DIFFERENCE BETWEEN POSITIVE DISPLACEMENT AND NON-POSITIVE DISPLACEMENT PUMP

PUMP *Pump is a mechanical device which converts mechanical energy into hydraulic energy. *pump add energy into liquid by means of external ...

PUMP

*Pump is a mechanical device which converts mechanical energy into hydraulic energy.

*pump add energy into liquid by means of external work by virtue of which liquid can be rise from

lower level to higher level.

There is an increase in

-pressure head/energy

-kinetic head/energy

-potential head/energy

CLASSIFICATION OF PUMP

Pump is broadly classified into 2 types

1-Positive displacement pump

2-Non positive displacement pump

Positive displacement pump

*A positive displacement pump is one that displace same amount of liquid for each  rotating cycle of the pumping element, that means the amount  liquid entering the pump per unit time must be equal with the amount of liquid coming out of the pump per unit time.

*Constant delivery is possible because of positive seal and close tolerance fit between the pumping element and casing of pump.

*The delivery per cycle almost remain constant, even if the pressure changes.

*If the delivery port is plugged the pressure will rise instantaneously and will damage/fail the entire pump.

*Efficiency will rise with increase in pressure.

*Positive displacement pump can handle fluid with higher viscosity very easily. 

Ex- of positive displacement pump-Reciprocating pump, gear pump,vane pump.

Non-positive displacement pump

*A non-positive displacement pump is one whose flow rate is not constant, that means the the amount of liquid entering the pump per unit time is not equal with the amount of liquid coming out of the pump per unit time.

*Delivery is not constant because positive seal is not there in case of non-positive displacement pump.

*The delivery  per cycle changes if the pressure varries.

*If the delivery port is plugged the pressure will rise and flow rate at delivery side will be zero but it will not damage/fail the pump.

*Pump is suitable for low pressure range so it can handle liquid having lower viscosity.

*EX-of non positive displacement pump-Centrifugal pump.