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benjamincall 10-28-2009 12:23 PM

Sizing well pump drop pipe
I'm replacing my submersible 1/2 HP 7 GPM well pump with a 1 HP 12 GPM well pump. I noticed the current black poly drop pipe is 1". Should I use 1-1/2" or 1-1/4" instead? The pump is at a depth of 120'.

Gary Slusser 10-28-2009 01:11 PM

That is a large increase in hp, what gpm is the 1 hp rated at; pumps come in two parts; hp and gpm.

What is your peak demand gpm flow rate?

You size a pump based on the gpm you need and the psi you are running the system at and then find the number of horses needed, not by hp alone. There are negatives in over sizing a pump.

Usually, for a 120' depth and an average peak demand flow rate of like 12 gpm, a 1/2 hp 10-13 gpm pump would be more than enough pump.

The 1" is just fine, and you probably have 1" at the pressure tank, or a 1" tank Tee right, so going larger than 1" is not needed 'cuz ya can't use the additional flow anyway.

Why are you replacing the pump?

benjamincall 10-28-2009 03:06 PM

Thanks for the input, Gary.

12 GPM for this unit. My peak demand is 12+ given the 12 gpm flow rate to my 200 gallon Kohler riverbath (obviously an occasional use). 60/40 psi gives me a maximum of just under 300 feet of head. 50/30 gives 272 feet of head. According to the FE Meyers 12 GPM pump performance chart, the pump can push a little over 11 GPM at 275 feet of head.

I'm replacing the pump because of a ground fault situation. The Goulds pump I pulled out was only 4 years old.

Gary Slusser 10-29-2009 11:39 AM

Then for 12 gpm plus, without looking it up, I believe you need like a 15 or 20 gpm pump but maybe not 1 hp for a 120' pump depth.

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