Positive Displacement Pumps Summary

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# The flow delivered by a centrifugal pump during one revolution of the impeller depends upon the head against which the pump is operating. The positive displacement pump delivers a definite volume of fluid for each cycle of pump operation regardless of the head against which the pump is operating.

# Positive displacement pumps may be classified in the following ways:
Reciprocating piston pump

# As the viscosity of a liquid increases, the maximum speed at which a reciprocating positive displacement pump can properly operate decreases. Therefore, as viscosity increases, the maximum flow rate through the pump decreases.

# The characteristic curve for a positive displacement pump operating at a certain speed is a vertical line on a graph of head versus flow.

# Slippage is the rate at which liquid leaks from the discharge of the pump back to the pump suction.

# Positive displacement pumps are protected from over pressurization by a relief valve on the upstream side of the pump discharge valve.