Flow to be considered for ARC valve sizing

[nirlt]

We are engineering a BFW multistage pump (8 stages) being supplied from reputed pump manufacturer alongwith ARC valve (to be supplied by Pump Manufacturer). They have indicated Pump min. Thermal continuous flow of 52.5 m3/hr and Pump min. Stable continuous flow of 63 m3/hr in the Pump datasheet. Allowable operating flow values given by Pump manufacturer is from 63 m3/hr to 252 m3/hr.
Also, they have considered 52.5 m3/hr flow value for sizing of ARC valve, which is lower than stable continuous flow value?

What should be the flow value to be considered for ARC valve sizing, keeping pump safety aspect into consideration?

 

[BigInch]

Minimum continuous stable flow is defined by API-610 as the lowest flow at which a pump can operate without exceeding acceptable vibration limits. Ask the manufacturer if his definition of the min stable flow is the same as API-610 and for them to review and clarify their data sheet values accordingly.

I would not operate below 63 m3/h at all.
I would plan on running between minimum flow and 60% BEP with ARC open, only during start-up of the pump.
I would not plan to operate continuously below 151 m3/h to comply with API recommended minimum continuous (60% BEP) flowrates.

Therefore note that the ARC valve must be designed for the range of possible flow conditions described by:

1.) MINIMUM FLOW of 63 m3/h with a pressure differential across it equal to the pump differential head at a pump flow of 63 m3/h... minus the pressure drop of the recycle pipe system.

2.) MAXIMUM FLOW can be calculated using the boiler's pressure as the recycle pipe system's inlet pressure and the pump's suction pressure as the recycle pipe system's outlet pressure, because the ARC valve can always be closed whenever the recycle pipe system's inlet pressure is equal to the boiler's inlet pressure.

If there is a minimum boiler operating pressure and a maximum boiler operating pressure, you may need to check both of those as the recycle pipe system's inlet pressure to determine the ARC valve's Maximum Required Flowrate.

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