Centrifugal pump minimum flow protection 1

[learn123]

Hi everybody,

Can anybody please make me aware the importance of the minimim flow circulation required for the centrifugal pump. In which scenario we go for the minimum flow protection.
Is the minimum flow and the recycle flow is same terms for the pump ?
If we have the process requirement of 100 m3/hr and the pump minimum flow is 20m3/hr, then should the pump be 120m3/hr atleast ?


thanks

 

[25362]

There are various factors that determine the minimum flow rate (MFR) of a centrifugal pump, among them: fluid temperature rise, NPSH rise due to internal recirculation, and, as well, possible increases in vibration, pressure fluctuations and thrusts.

As a long-time pump user my impression is that the MFR is the lowest pump delivery that can be maintained continuously without sustaining damage. Thus the answer would be no, any flow rate greater than the minimum indicated by the manufacturer, would be admissible.

For a lively discussion on the subject of a spillback line see thread407-195091.

 

[Valvecrazy]

If the recirculating line is running all the time, then the pump must be large enough to supply the recirculating amount plus the process requirement at the same time. If you have a way of closing off the recirculating line when the process is using the water, then the pump only needs to be large enough to supply the process requirement.

 

[pumpking]

As a rule of thumb in a single stage centrifugal pump, use 10% of BEP to identify Minimum continuous flow. This is the figure at which is the minimum point to let the pump operate at. As mentioned above, if there is a recirc line to be used, then control it with an orifice plate, and add to required flow rate.

Similarly the best way to protect the pump is by means of a digital load monitor to trip the pump when minimum flow is reached (a power curve of such units is crudely speaking a straight line curve )

For further information on such devices see

http://www.cdrpumps.co.uk

- we recomend them for ALL pump insallations asminimum flow is a common problem in pump installations.


Ash Fenn

http://www.cdrpumps.co.uk

 

[BigInch]

I think overheating is a high probability at 10% with most systems and use a minimum of 20% BEP, but only for start-ups. API minimum recommended continuous operation is much much higher at 60%.

http://virtualpipeline.spaces.msn.com

 

[TenPenny]

I think 10% of BEP for a minimum flow seems way too low for a standard centrifugal pump - if you want to be safe, use 25%, or ask the manufacturer.

In the absence of other data, look at the lowest flow at which the family curves published show an efficiency line.

 

[BigInch]

The operation method needs some rethinking, if not a tank.

http://virtualpipeline.spaces.msn.com