We have two electric motor driven centrifugal fire pumps installed in a high rise office building. Both pumps are side by side and feed into the same header and at the same elevation, each pump delivers 500 USGPM at 125 PSI.
I know that the flow will be doubled, but will the pressure also double to 250 PSI at the header??
You will maintain the same pressure with one or two pumps on.
Thanks for your response, so even if I run two pumps in unison, I will still only acheive 125 PSI?
Was your system designed to have both pumps operating at the same time? If so, then you should get twice the flow at the rated pressure of the pumps. If not, then the flow and pressure will depend upon the pump curve. Chances are you will get less than twice the rated flow at a pressure above the rated pressure — but the flow will not double and the pressure most certainly will not double.
In general terms parallel operation of two identical pumps will double the flow at the same pressure. However centrifigal pump output is controled by the system they feed.Besides elevation, friction loss of pipe, elbows Ts valves,etc. add resistance to flow. For example if the sytem was designed for two pump operation(1000gpm at 125psi) then the first statement will be true. However if the system was designed for 500gpm then running two pumps will result in something less than 1000 gpm and a higher pressure than 125, dependent on the pump performance curve.
short answer:when opperating pumps in parallel your flow will double and pressure will remain the same. When operating the pump in series (one pump feeds directly into the second pump) the flows will remain the same and the pressure will double. This is assuming a unrealist condition because you must account for additonal losses when flow rates are elevated. But for round numbers double your flow and the pressure is the same. I agree with David on the previous post. Good luck.
Many thanks to David Goodsell, Micheal L and Lisa W.
This now confirms my fears and I can now confront the fire system installer with this information
pumping into a common main, depends what type of pumps you working with .
pressure will increase when pumping into a common main,IF the second pump can provide more pressure than the first pump. A check valve should be installed on both pumps discharge as one pump can overcome the pressure of the other pump, where by the pressure will over come and migrate into the lesser pressure pump system. If both pumps are identical with identical impellers and impeller trims including syncronous speeds,about the only way one pump would negitivly pressurize another pump is if the suction pressure effects the Total Dynamic Head and then the less pressure pumping susytem would be compermized. There are others, but this is the most expected.