Does MCSF vary with pump speed?

[TimboGMO]

Does MCSF vary with the speed of the pump? I have seen the definition below for MCSF from a Pumps and Systems article, but it doesn't adress a change in speed. I have a boiler feed pump that has a MCSF line with the supplied pump curve, wondering if this line would move to the left with a reduction in speed. Thank you, -Tim

http://www.pump-zone.com/pumps/pumps/working-with-minimum-flow.html

"Minimum Continuous Stable Flow (MCSF) is defined as flow below which the pump should not be operated continuously. It can operate there for a short time (such as start-up), but not too long. The main reasons are unstable operation, high radial and axial thrust, vibrations and noise - all of which ultimately deflect the shaft; damage the seal, bearings, and couplings; and reduce reliability significantly. The value MCSF is established by the pump manufacturer and guided by several factors, including pump type, pump energy level, pump Ns and Nss and onset of recirculation, guiding specifications, and experience."

 

[GPRnD]

The short answer is: "Usually but it depends"

The MCSF is determined by a number of things, many of which you mentioned. One noticeable omission however is the allowable temperature rise through the pump.

Slowing down a pump will result in less energy lost in the pump but at the same time a lower flowrate. In addition as you slow down the pump, the efficiency will drop. It is therefore possible that for a small number of pumps, the MSCF will not really change with reducing speed.

However this generally only occurs on v low specific speed designs with low efficiences.


For the vast majority of centrifugal pumps, the MCSF will reduce with reducing speed. Your boiler feed pump would fall into that majority.