Flow Rate question on water transfer line
Flow Rate question on water transfer line
(OP)
In a ZLD combined cycle water plant, a problem is occuring in achieving flow rate for a gravity filter backwash sump being piped back to a clarifier for water processing. There are two pumps rated at 250 GPM hooked in parallel driving the backwash water. The run is approximately 300 feet and has 12 90 degree bends. The backwash water line is 4 inch carbon steel with no corrosion on the pipe. The pipe flow meter reads 180 GPM, while 250 is needed to empty the sump fast enough for filter backwashing. Another restriction on the pipe is that the pipe narrows into a 2 inch control valve. Thinking the valve restricted the flow it was bypassed with a 3 inch carbon steel line. This increased the flow 15 GPM but still not enough to empty the sump. Also, the backwash pipe dumps into a clarifier feed water pipe flowing at 3600 GPM. Curious if anybody knew if the 300 feet and 12 90's is enough to lower the flow rate or perhaps something else is causing this drop. I am a new graduate and can not seem to figure it out.





RE: Flow Rate question on water transfer line
What head does the pump curve give at 180 GPM?
What is the actual delivery pressure on the pumps?
What is the change in static head?
What type of control valve?
What is the pressure where the 4" line dumps into the 3600 GPM line?
Was 250 GPM ever achieved, or is this a "day one" problem?
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RE: Flow Rate question on water transfer line
I'm just a civil engineer, but you have to plot your system curve (the total static plus friction head at a range of flows) on top of your pump curve.
Theoretically, the pump will discharge the flow noted at the intersection of the pump curve and the system curve.
When you have two pumps in parallel, the combined pump curve will have twice the flow at the same head as one pump.
Then plot your system curve and the pump curve, you can see whether the pump is theoretically sufficient to discharge the design flow.
If it is theoretically sufficient, there may be something wrong with the pump.
If it is not theoretically sufficient, you will have to change your system or get new pumps.
Hopefully some of the real pump engineers will have more information.
I just spec pumps for pumping sewage.