Rated flow of and minimum re-circulation line of centrifugal pump
Rated flow of and minimum re-circulation line of centrifugal pump
(OP)
Hi All,
1. I have been preparing some centrifugal pump datasheets and in this context I want to clarify the difference between the 'Maximum operating flow of the pump' and the 'Rated Flow of the pump'.
2. Can someone please explain the real purpose behind having a minimum re-circulation line in a centrifugal pump. I have read that there are different schemes involved in designing the re-circulation line for a pump(e.g. having an FO, Control Valve, ARC etc). Also any help/advice as to how the selection of the re-circulating scheme is made would be useful.
3. Can someone explain how the Minimum Continuous Stable Flow (MCSF) would compare with the minimum re-circulation flow for a centrifugal pump?
Kind Regards,
Vinayak
1. I have been preparing some centrifugal pump datasheets and in this context I want to clarify the difference between the 'Maximum operating flow of the pump' and the 'Rated Flow of the pump'.
2. Can someone please explain the real purpose behind having a minimum re-circulation line in a centrifugal pump. I have read that there are different schemes involved in designing the re-circulation line for a pump(e.g. having an FO, Control Valve, ARC etc). Also any help/advice as to how the selection of the re-circulating scheme is made would be useful.
3. Can someone explain how the Minimum Continuous Stable Flow (MCSF) would compare with the minimum re-circulation flow for a centrifugal pump?
Kind Regards,
Vinayak





RE: Rated flow of and minimum re-circulation line of centrifugal pump
The "rated flow" is the normal design flow to achieve the requested application duty, whereas the "Maximum operating flow" is the flow that may need to be met at various times during operation without causingel any pump hydraulic upsets.
A centrifugal pump is not designed to operate at zero flow a maximum head or near minimum flow approaching maximum head, hence the need to by-pass some of the flow to waste or back to the source, how to achieve this is really beyond normal in discussion here.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Rated flow of and minimum re-circulation line of centrifugal pump
RE: Rated flow of and minimum re-circulation line of centrifugal pump
RE: Rated flow of and minimum re-circulation line of centrifugal pump
RE: Rated flow of and minimum re-circulation line of centrifugal pump
Johnny Pellin
RE: Rated flow of and minimum re-circulation line of centrifugal pump
10% of rated flow at BEP for intermittent duties
20% of rated flow at BEP for continuous duties
A lot of our kit is magnetic drive which adds to heat generation in the pump/magnet assembly (through eddy currents). It is also important to mention that vibration, hydraulic thrusts etc are also a big concern when operating at this point of the curve too, especially when you get to larger API style pumps etc so really needs some consideration adn advice when selecting or sizing up plant.
www.cdrpumps.co.uk
Ash Fenn
www.cdrpumps.co.uk
RE: Rated flow of and minimum re-circulation line of centrifugal pump
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RE: Rated flow of and minimum re-circulation line of centrifugal pump
RE: Rated flow of and minimum re-circulation line of centrifugal pump
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Rated flow of and minimum re-circulation line of centrifugal pump
The reason you can't find a single scheme for designing re-circulation lines is because there isn't one. You need to design the recirculation pipe and flows based on the main use of the fluid. Pump and circulation requirements for a closed-loop heating/cooling system are different than that of an open-loop potable hot water system.
Ideally you want your pump operating at peak efficiency, which is something that is included on the afore mentioned pump curves.
Generally speaking, you will want the minimum flow rate through the pump to be no less than ~20% of peak flow. This isn't because it can't go slower, but you have to take into consideration the accuracy of your flow measuring device, which (for the most part) start to loose accuracy below ~20% peak flow. With variable speed drives, the efficiency of the pump drops off as well.
RE: Rated flow of and minimum re-circulation line of centrifugal pump
RE: Rated flow of and minimum re-circulation line of centrifugal pump
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)