Gallons per Minute

Old 06-06-02, 06:16 PM
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Question Gallons per Minute

Is there a way to get the gpm if you know your psi?
Old 06-06-02, 08:27 PM
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Yes, with qualifications.

There are 2 types of pressure. Static and "operating" (I forgot the real term). The static pressure is when everything is at rest and no water is moving, this will be your max pressure. Once water starts to move, pressure drops to a steady level, (for the most part) and this would be the operating pressure. You will need to know this pressure and the size of pipe you are measuring.
Years ago I measured fire flows at fire hydrants using pressure drop and how far it took for the water stream from a hose connection to fall 12". Forgot the formula, (getting old), but should be fairly easy to find on internet with an engineering site.

Have fun on the web doing a quick search.

Found this site in just a few seconds, you might give it a look...
Old 06-07-02, 09:51 AM
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I'm not sure what you are ultimately trying to do but Static pressure is really not a very useful number if you talk about GPM in the same sentence. What you are looking for can be calculated but the easier way is to get a garden hose, a five gallon bucket, and a watch. Time how long it takes to fill the bucket and calculate GPM from there. While the water is running, note the pressure.
Old 06-07-02, 01:35 PM
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Originally posted by notuboo

There are 2 types of pressure. Static and "operating" (I forgot the real term).
Residual pressure is the term you was thinking of.
Old 06-08-02, 07:31 PM
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Thumbs up Thank You

Thanks to all for the responces, I was going to try the bucket but then notuboo put the link for Irrigation Tutorials great site.
Thanks again.
Old 06-08-02, 09:03 PM
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Yep. Jess Stryker's site is excellent, and also please check Ron (Pumpman) Peeks' site at
They are absolutely the best tutorials that I have seen on the subject.
Good luck!

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