sump pump 4

Flow rate

Flow rate

The flow rate (Q) of a centrifugal pump is the useful volume flow delivered by the pump via its outlet cross-section (see Pump discharge nozzle). Volume flow rates which are tapped upstream of the pump's outlet cross-section for other purposes (e.g. bypass) must be taken into account when calculating the pump's flow rate.

If the fluid handled is compressible, a conversion must be made based on the condition prevailing in the pump suction nozzle the arithmetic mean (Q s+ Q d)/2 may have to be applied.

The unit of the flow rate is m 3/s; in centrifugal pump engineering the units m 3/h and l/sare more common. Various measuring methods are used for flow rate measurement (see Flow velocity measurement). Various types of flow rate are distinguished in conjunction with the H/Q curve (see Characteristic curve).

Flow rates and their significance

Flow rate at BEP (Q opt): flow rate at the best efficiency point at the rotational speed and for the fluid handled specified in the supply contract

Nominal flow rate (Q N): flow rate for which the pump has been designed

Supply contract flow rate (Qcontract): the flow rate agreed in the supply contract (order confirmation)

Minimum flow rate (Q min): minimum permissible flow rate at which the pump can be continuously operated without suffering any damage at the rotational speed and with the fluid specified in the supply contract

Maximum flow rate (Q max): maximum permissible flow rate at which the pump can be continuously operated without suffering any damage at the rotational speed and with the fluid specified in the supply contract

Peak flow rate (Q peak): flow rate at the apex (relative maximum of H/Q curve) of an unstable H/Q curve(see Characteristic curve)

Balancing flow (Q ba l)

Leakage flow(Q Leak)

Suction-side volume flow rate (Q s): volume flow entering the pump suction nozzle

Inlet volume flow rate (Q e): volume flow entering the system's inlet cross-section

Discharge-side volume flow rate (Q d): volume flow leaving the pump discharge nozzle

Outlet volume flow rate (Q a): volume flow leaving the system's outlet cross-section.

Occasionally, a so-called pump flow rate (Q/Q opt) and a system flow rate (Q/Q contract) are defined, where Q contract is the flow rate specified in the supply contract.

A centrifugal pump's mass flow rate (ṁ) is: