Pump Handbook

Minimum Continuous Flow

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There are three factors which must be looked at with respect to minimum flow. These are:

  1. Mechanical ability - this is the ability of the pump to withstand all of the forces (side thrust, axial thrust, vibration, etc. ) associated with operating the pump at low flows.


  2. Hydraulic stability - this is the stability of the pump to operate at flow rates other than the Best Efficiency Point (or nearby), particularly low flow rates as a percentage of the BEP, without detrimental internal recirculation, hydraulic instabilities, etc. that can cause pump damage.


  3. Thermal stability - has to with the properties of the particular liquid being pumped and the effects of heat (temperature) rise to liquid. See HEAT INPUT above for a discussion of temperature rise. A commonly accepted conservative temperature rise through a pump is 15 deg. F. For a 15 deg. F rise, the minimum flow can be calculated as follows:

It is important to understand that a catastrophic failure of any pump can occur if the liquid within the pump casing is allowed to vaporize. To prevent flashing, a flow must be maintained through the pump which will keep the liquid below its saturation temperature.

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