PumpsDOE-HDBK-1018/1-93POSITIVE DISPLACEMENT PUMPSFigure 20 Diaphragm PumpPositiveDisplacementPumpCharacteristicCurvesPositive displacement pumps deliver a definite volume ofFigure 21 Positive Displacement Pump Characteristic Curveliquid for each cycle of pump operation. Therefore, theonly factor that effects flow rate in an ideal positivedisplacement pump is the speed at which it operates. Theflow resistance of the system in which the pump isoperating will not effect the flow rate through the pump.Figure 21 shows the characteristic curve for a positivedisplacement pump.The dashed line in Figure 21 shows actual positivedisplacement pump performance. This line reflects thefact that as the discharge pressure of the pump increases,some amount of liquid will leak from the discharge of thepump back to the pump suction, reducing the effectiveflow rate of the pump. The rate at which liquid leaksfrom the pump discharge to its suction is called slippage.Rev. 0ME-03Page 27
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