When will Parallel Pumps Fight?
When will Parallel Pumps Fight?
(OP)
Hello, This was inspired by the recent thread on series vs parallel pumps.
I would like to understand in general terms when to worry about 2 pumps discharging into a common header fighting with each other?
If the two pumps and associated piping are identical, then they back up to the same point on their individual pump curves at the intersection of the system curve, and pump flows are equal at equal heads. No issues with this mode of operation.
On the other hand, if one pump generates double the head at the same flow rate as the other pump, the higher head pump will win and the actual total flow will be at the intersection of the system curve and combined pump curve. The higher head pump will be pumping more flow than the smaller pump. To get the actual flow rate of each pump, you would go to the individual pump curves, locate the observed system head, and read the flow for each pump at this value for head.
Is the main concern with having dissimilar pumps in parallel service the potential to dead head the smaller pump? What are other items to worry about besides inefficient operation?
Thanks,
I would like to understand in general terms when to worry about 2 pumps discharging into a common header fighting with each other?
If the two pumps and associated piping are identical, then they back up to the same point on their individual pump curves at the intersection of the system curve, and pump flows are equal at equal heads. No issues with this mode of operation.
On the other hand, if one pump generates double the head at the same flow rate as the other pump, the higher head pump will win and the actual total flow will be at the intersection of the system curve and combined pump curve. The higher head pump will be pumping more flow than the smaller pump. To get the actual flow rate of each pump, you would go to the individual pump curves, locate the observed system head, and read the flow for each pump at this value for head.
Is the main concern with having dissimilar pumps in parallel service the potential to dead head the smaller pump? What are other items to worry about besides inefficient operation?
Thanks,





RE: When will Parallel Pumps Fight?
RE: When will Parallel Pumps Fight?
Johnny Pellin
RE: When will Parallel Pumps Fight?
"No issues with this mode of operation."
Even two "identical" pumps have issues if you're operating in a flat area of the pump curve or you have high static head and many threads show large variance in flow between two so called "identical" pumps.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: When will Parallel Pumps Fight?
To minimize the concerns with having dissimilar pumps in parallel service it's required, at least, they have similar shut off pressure and steep curves...
RE: When will Parallel Pumps Fight?
1. Correctly sized and placed check-valves, preferably soft-closing will help against gulping actions, along with correctly sized piping for all production variations will help to avoid problems.
2. In addition to visible problems ono pump (of two or more in parallell) might supply less than others against higher pressure and give more wear. Solution: check or measure flow from each pump.
3. Pumping up and then downwards piping to open tank may give suction with uneven results for the pumps.
4. Construction details as larger piping size or vessels (manifolds) for evening out feeding and reception pressure could help.
5. Air pockets in the system could give (for all pumping solutions) give problems if not correctly vented.
RE: When will Parallel Pumps Fight?
Johnny Pellin
RE: When will Parallel Pumps Fight?
Johnny Pellin
RE: When will Parallel Pumps Fight?
RE: When will Parallel Pumps Fight?
Currently I am working on some project to run two dissimilar pumps inn parallel,
I have seen your recommendations about the pump shut off head and I fully agree with that.
in my case the two pumps are not sharing a common suction. each pump has its own suction vessel however the operating pressure for the two vessels is the same; off course the two pumps share a common discharge header.
my concern here is the friction losses in both suction and discharge sides. what if there is a pressure drop at some side which is different at the same side of the other pump??