Positive displacement pump pdf

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What is pump?

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• Pumps are used to any substance which flows or which can be made to flow.

• When we thinking of pumping we ordinarily think of moving water, oil, air steam and other common liquids and gases. How ever such substance as molten metal and sludge.

The positive displacement pump displaces forcibly specific volumes of liquid

against the system resistance. The system resistance directly affects the pump

delivery pressure which will keep on rising until the delivery pressure matches 

the system or until the driver or the pump is overloaded. For this reason these

pumps must be provided with relief valves either in the pump or directly after 

the pump in the delivery line to provide the necessary protection.

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The forcible displacement of specific volumes makes the flow rate dependent theoretically on the pump speed and geometry. In practice there is always leakage through the necessary clearances between the moving and stationary 

wetted components. Thus the head capacity curve is a substantially flat line showing a small capacity reduction with increasing differential pressure or head rise.

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