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Pump H-Q Curve

Centrifugal pumps are classified as self-priming if they have the capability to handle liquids, gases and liquid/gas mixtures. The pump suction pipe is then air-evacuated without any special external suction devices.

Centrifugal pumps without external or internal suction devices can be operated with a suction lift if the pump body is filled with water before starting the actual fluid displacement. Due to the function of a non-return valve the fluid will be retained within the pump body after switch-off.

The construction required for self priming capability has a negative effect on the pump efficiency.

Each change of head effects a consequential variation in the rate of flow.

  • Higher rate of flow -> lower head
  • Lower rate of flow -> higher head

Though it is the installed pipe system exclusively which determines, by its frictional resistance, which rate of flow exists at a given pump capacity, the respective pump can always take up only one Duty Point on its curve. This duty point is the intersection of pump H-Q curve with the system H-Q curve.

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