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Pumps and pressure differences

Pumps set up pressure differences, and fluid flows pass through them. The relation between pump pressure difference and current of liquid is called the pump characteristic (Figure 1). This is how continuous flow pumps are represented. Intermittently working pumps, such as the heart, may be represented by an appropriate pressure-volume characteristic.

Interpretation

A simple model of a pump is one in which the pressure difference across the pump is constant. Real pumps commonly have a more complicated type of characteristic (Figure 1). The pressure difference is lower when the flows are stronger because of increasing effects of flow resistance. Put differently, a part of the pressure difference set up by the pump is needed to force the fluid through the pump. As a result, the fluid exits at a lower pressure than otherwise expected.