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Pump Size Clarification

Pump Size Clarification

Pump Size Clarification


I have a 500 ft 8" sch 40 black steel pipe connecting to a 400 ft 6" sch 40 black steel pipe and the discharge at the end is 1130 gpm at 160 psi. It is a straight run pipe, no elevations. My client ordered a pump of 3000 gpm at 200 psi to discharge to the pipe run (8" and 6" pipe). can you show/help me clarify the pump is acceptable?

Thank you.

RE: Pump Size Clarification

Make a system curve and use the pump curve. Problem solved.

RE: Pump Size Clarification


Basically pressure drop is proportional to flow squared if you've got no elevation difference.

So your 3000 gpm pump is operating at barely one third rated flow so will probably be quite inefficient and might be below min flow.

Pump is too big.

Your client is an idiot.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Pump Size Clarification

FYI, 1130 gpm in a 6" pipe is 12.8 fps and 3000 gpm (if you could get it) would be 34.0 fps. These are big and BIG numbers for water flow. In water distribution, we try to limit flow velocities to about 5.0 fps except in emergencies (e.g. fire flow, when we may accept a maximum velocity of around 12.0 fps). So, I think the existing pipe is too small for the existing flow and it's definitely too small for his desired flow.

"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

RE: Pump Size Clarification

I rather use the Hazen and William formula with a C=100, meaning that the pipes are 15 years old, for such problems. Therefore, for a flow of 1130 gpm thru your piping arrangement barring any type of fitting, the total pressure drop is estimated at 29.71 psig within the system. As mentioned above by MFJewell, get your pump characteristic curve to determine suitability.

RE: Pump Size Clarification

llaallllaa, please draw your system as I might have been mistaken about the system. Is the 160 psi at the end of the pipe?

Where is the new pump connecting? Start end or middle of this pipe?

Is the flow in addition to what is they now or replacing it?

Judging from the velocities you're already at max flow rate for the pipe size.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Pump Size Clarification

Once again the OP doesn't seem too interested - hasn't bothered with a reply.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

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