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spencerin
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# Posted: 14 Jul 2021 10:21pm - Edited by: spencerin
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Assuming I'm understanding this all correctly, the jet pumps I'm looking at all rate GPMs based on the depth to water, which is always up to 25 ft. (unless it's convertible). As the depth increases, GPM decreases. But, how exactly is GPM impacted above the pump? I know friction loss impacts PSI, but how exactly does height above the pump impact GPM? Friction loss calculators give me PSI loss, but I'm trying to figure out point-of-use GPMs. Is the GPM at the pump (which depends on the depth to water) at least the starting point? I don't understand all the dynamics at play here.
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darz5150
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# Posted: 15 Jul 2021 12:26am - Edited by: darz5150
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Quoting: spencerin I know friction loss impacts PSI, but how exactly does height above the pump impact GPM?
A simple way to explain would be.
Take a bottle of water and lift it above your head. Then, a gallon, then a case of bottled water, then two.
I don't know about the friction. But the weight the volume, and the distance is what you are dealing with.
More than likely, you won't be able to lift/move two cases of water as high or easily as one small bottle of water.
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Brettny
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# Posted: 15 Jul 2021 05:54am
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What is your head pressure and what's your water level below the pump? What specific jet pump are you looking at?
We use one as a electric transfer pump from a spring to a water tank on a hill. It has 400ft of 1in line and 65ft of head pressure. Its the smallest 1/2hp I could find and 120v. It fills a 275gal ibc tote in 33min.
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spencerin
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# Posted: 15 Jul 2021 09:12pm
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No idea what my head pressure is, nor how to calculate it. If you could point me to a calculator online, maybe I could plug #s in and get it from there. Water level at its lowest is about 4' below the pump. I'm looking at big-box pump-and-tank combos - Simer, Flotec, Burcam, Superior, Little Giant, etc.. I called a couple of places - one (Pentair/Simer/Flotec) said 12GPM but then sent me the model # of an 8.5GPM model, another (Red Lion) said around 10GPM. Both said 1/2 HP. I was giving them pipe size, pipe material, length of pipe, height from bottom to top, and type of fixtures.....but I'm not sure they knew what to do with that info.
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spencerin
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# Posted: 15 Jul 2021 11:10pm
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Pentairaes.com has a calculator that gives me 29.9 total pump head required at 4.7GPM and 60.3 at 8.5GPM. I'm assuming I need to look at pump specs to see if they meet or exceed these #s based on what flow rate I want. Problem is, none of the specs I see talk specifically about total pump head required.
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Brettny
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# Posted: 17 Jul 2021 06:13am
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Pump head pressure is the elevation change between the two surfaces of water or the well level and point of use.
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Fanman
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# Posted: 19 Jul 2021 07:32pm
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The pump manufacturer should provide flow rates at different head pressures. Knowing the total pressure (elevation change + friction loss at your anticipated GPM), pick a pump that can provide that flow rate at that pressure.
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