Pump installation

eaaaazizo

in college days it is known that if you want double pressure install the pumps in series if you need double flow install the pumps parallel. but in actual field i have two pumps installed in parallel in Sewer Pump Station one as on duty and the second one is assist. but while both pumps running, i never get flow rate equal to two pumps flow rate for example i have two pumps with each pump capacity 100 l/s but if both if them runing i have only 120 l/s

i cant understand this ? and how to control raising main diameter to get maximam flow while both pumps are running ? it is really difficult ?

russ_watters

In a fixed piping system, you can neither double the pressure without affecting flow nor double the flow without more pressure. The rule of thumb ignores the piping system.

eaaaazizo

Thanks for your kind replay but now in design stage how could I reach douple flow while both pump runing by increasing pipes dia ??

russ_watters

With two pumps in parallel and twice the piping cross sectional area.

eaaaazizo

but if i increased the cross sectional area to be twice. while one pump runing the area will be very wide which will reduce the head and increase the flow and increaing the power consumed

chaos_zzy

The pipe system flow resistance normally is binomial equation to flowrate. So when two pumps working together, the system flow resistance will also increase, finally you will not get double flowrate.

One way to increase the flowrate for two pumps working, you'd try best to seperate the connecting pipe of the two pumps. Like as: the pipe for each pump only gather with short length; each pump outlet need valve to control "open" or "close".