Stand-by Pump auto-change over pressure set point

[FluidME]

Can you suggest me how do i decide the set point for a pressure switch for auto changeover of stand-by pump?

The system consists of two condensate pumps, one working and one stand-by, for a condenser, with a pressure switch at the discharge for auto-changeover.


Below is the flow-head characteristics for the pump

Measuring points	-	1	2	3	4	5	6
Level at the weir	mm	-	34	43	47	51	55
Flow	m3/min	0	0.643	0.909	1.037	1.171	1.311
Head	m	32.816	31.905	29.994	29.048	28.112	27.254

 

[LittleInch]

What's your duty point?

a PFD or P&ID might be useful, but you need to describe the process or changeover logic a bit better.

My guess is that you want the second to start if the first one stops or trips or somehow isnt working?

Not sure what the weir has to do with anything?

 

[georgeverghese]

Pressure switch may not be a reliable indication of "OFF" for the running pump for many reasons; why not get a signal from the MCC from the starter cubicle for this pump ?

 

[shvet]

two condensate pumps, one working and one stand-by
stand-by for what? to double capacity in case of the condenser upset or to maintain capacity in case of a working pump failure?

if the second option then what is a pump failure mode and what the weir has to do with pump failure?

 

[FluidME]

Yes, the intention is to start the stand-by pump in-case of failure of running pump
The weir is at the hotwell of the Condenser

 

[LittleInch]

Still can't understand your system, but in general you set the auto changeover on pressure - if you want to use pressure - at a pressure lower than the pressure the first pump can supply when working.

As this is a change over, you will then only have one pump working at any one time?

Your data supplied is for pump differential head, so the pressure setpoint needs to take note of pump ilet pressure.