Measuring Pump Header Flow Rates
Measuring Pump Header Flow Rates
(OP)
Greetings
For centrifugal circulator pumps operating in parallel, isn't important to be able to verify the flow for each pump individually?
I know that given the pressure gauge readings and the pump curves the flow can be determined but I'm asking about verification of flow of each pump while operating in parallel.
Is it enough to measure the differential pressures and the RPM or is it possible for a pump to produce an unexpected flow due to damage to the impeller?
This is an inquiry regarding general practice as I have never come across a design showing pump headers that have flow meters for each pump.
Maybe I am answering my own question but if had to verify flow I would use the flow meter on the main return pipe an take the reading when only one pump is operating.
Much obliged for sharing your expert opinions.
For centrifugal circulator pumps operating in parallel, isn't important to be able to verify the flow for each pump individually?
I know that given the pressure gauge readings and the pump curves the flow can be determined but I'm asking about verification of flow of each pump while operating in parallel.
Is it enough to measure the differential pressures and the RPM or is it possible for a pump to produce an unexpected flow due to damage to the impeller?
This is an inquiry regarding general practice as I have never come across a design showing pump headers that have flow meters for each pump.
Maybe I am answering my own question but if had to verify flow I would use the flow meter on the main return pipe an take the reading when only one pump is operating.
Much obliged for sharing your expert opinions.





RE: Measuring Pump Header Flow Rates
If your pump curve is fairly steep at the flow rate where the pumps work then it shouldn't be too bad - maybe 5 to 10% difference, but if you end up working at a point on the curve where it is much flatter it could be 50% or worse.
Usually the easiest method is to be able to compare running current to see which pump is talking the lions share of the work.
what each pump dies when it is working on its own is no indication of what happens when a second or third or fourth unit is operated in parallel. Of course all these pumps should have a common inlet and common discharge otherwise all bets are off.....
Remember - More details = better answers
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RE: Measuring Pump Header Flow Rates
Not sure how common it is to measure individual flows in circ systems but it is very common in many industrial applications.
RE: Measuring Pump Header Flow Rates
RE: Measuring Pump Header Flow Rates
Alternative methods are balancing valves (caution, when measuring you are reducing the flow since you need a large pressure drop to measure) or some flow meter. If you have enough straight pipe you could use one of those ultrasonic strap-on meters - they are very accurate.
RE: Measuring Pump Header Flow Rates
RE: Measuring Pump Header Flow Rates
unless you want to show the pumps don't work as advertised, why do you want to measure the flow? I've never seen a situation of too little flow where the pump was to blame.
RE: Measuring Pump Header Flow Rates
After reading the replies in this post I think measuring the current input, the shaft RPM and taking the readings from the pressure gauges at suction and discharge should be enough to verify that the pumps are operating at equal capacities- at least for HVAC chilled water applications.
A single DP sensor across the parallel pumps installation is more accurate than the pressure gauges but this reading will include the losses from common header to pumps (pipes + valves).
RE: Measuring Pump Header Flow Rates
I would program into the maintenance schedule a check on each unit running alone every 6 months or so to see if any unit is significantly less than any other and also to plot any changes over time.
Ditto a check on the running amps on a regular basis, once a month?
I would say a normal range of operating current in parallel mode is 10%. Anything more should be investigated
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Measuring Pump Header Flow Rates
Again, not sure what you want to accomplish. If a pump fails it stops... there is no slow degredation unless you believe the stainless steel impeller wears out. And unless the manufacturer installed the wrong impeller, the pump will perform as advertised (unless you buy a chinese knockoff, like those Glundfos or Cinosset pumps
If you have a lack of flow it is a design error, or contractor installed too small pipes etc. It isn't the pump.