Positive Displacement Pump Characteristic Curves:

Positive displacement pumps deliver a definite volume of liquid for every cycle of pump operation. Thus, an only factor which affects flow rate in an ideal positive displacement pump is the speed at that it operates. A flow resistance of the system in that the pump is operating will not effect the flow rate by the pump. Figure displays the features curve for a positive displacement pump.

The dashed line in Figure displays actual positive displacement pump performance. That line reflects the actual which as the discharge pressure of the pump increases, a few amount of liquid will leak from the discharge of the pump back to the pump suction, decreasing the effective flow rate of the pump. A rate at that liquid leaks from the pump discharge to its suction is known as slippage.

Figure: Positive Displacement Pump Characteristic Curve