Pump gpm problem HELP


Old 06-02-10, 07:36 PM
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Join Date: Jul 2006
Posts: 23
Question Pump gpm problem HELP

I replaced my 3/4 10gpm submersible pump I use in a lake for irrigation with a 1 hp 25 gpm pump. The problem is with the old pump I was actually getting 15gpm after I put the new pump in I am only getting around 10gpm. My setup is 500ft of 1in pipe and 480ft of 12 guage wire at an elevation rise of 50ft. The new pump is a 3 wire pump which I installed the control box and the old pump was a 2 wire. What could be causing this you would think it would be pumping at least 25 gpm if not more. Any help would be much appreciated.
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Old 06-03-10, 12:28 PM
Join Date: Sep 2003
Location: somewhere down in texas
Posts: 506
Sounds like you are running a 220v motor off of 110v power sourse.
Old 06-03-10, 01:58 PM
Join Date: May 2010
Location: South Florida
Posts: 376
Originally Posted by walker45 View Post
What could be causing this you would think it would be pumping at least 25 gpm if not more.
There seems to be at least two separate issues. One issues relates to the comparison of the old pump (“getting 15gpm”) and new pump (“getting around 10gpm”). The second issue is why your not pumping at least 25 gpm regardless of whether it’s the old or new submersible pump.

With respect to old vs. new pump, I’m assuming you put in a new pump having the same specs as the old one. You don’t mention any pressure readings for the submersible or other pump. I’m not familiar with a submersible pump acting in concert with your other pump but wonder if there is any pressure adjustment mechanism on the submersible. Kerry’s point is another possible reason. If you installed the same type pump and everything else was set-up the same way, then I don’t know what is causing the difference in gpm’s.

With respect to your second issue, 500 ft. of 1 inch pipe is a very long run. Another unknown is whether this pipe is sloped down into lake creating additional flow losses caused by the pull of gravity. This link GPM/GPH Flow based on PVC Pipe Size, ie, How much water can flow through Sch 40 Pvc Pipe Size 1/2" 3/4" 1" 1.5" 2" 2.5" 3" 4" 6" may help you understand interplay between pipe sizes, pressure, and flow rates. Also remember the diameter of the suction and discharge sides for each of your pumps may be smaller than 1 inch which also restricts flow. The owner’s manual for your pumps should have a chart showing maximum flow discharge depending upon the pressure they are being run at, and that is the starting point for trying to figure out why you’re not “pumping at least 25 gpm if not more”.

I have three different pumps, each operating different irrigation systems, and capable of drawing water from my lake. None have submersible pumps (not clear to me why you need a submersible pump but may have something to do with distance and depth in lake). Each have filtration systems above ground that can reduce flow if not cleaned. In the lake, I have fine meshed screens over the suction ends which also have to be cleaned about once a yr. to remove algae build-up. If you have any filtration devices, you should check to see they’re clean and operating properly as they can restrict flow.
Old 06-04-10, 01:08 PM
Thread Starter
Join Date: Jul 2006
Posts: 23
Angry Pump GPM

I checked pump out voltage and current are within specs, I am running this pump 25s10-7 Grundfos open no pressure tank when I am checking flow and I am getting just under 10gpm and the pump is rated at 25gpm, another questions the pump has a 1 1/2 inch outlet and I have used reducers to get it down to 1 inch in which I am running 500ft with a elevation rise of 50ft is the reduced pipe size cutting down on output if so can I run a 50ft-60ft of 1 1/2 inch pipe then go down to 1 inch for the remainder will that help or is it not worth trying. The pump I replaced was a 10gpm getting 15gpm with same pipe and all.
Old 06-06-10, 11:28 AM
Thread Starter
Join Date: Jul 2006
Posts: 23

Sorry for the confusion I am running only one pump it is a 25 gpm submersible. The part I don't get it is only putting 10gpm the outlet on the submersible is 1 1/2 in I reduced it down to 1 inch poly and running a total of 500ft with an elevation rise of about 50ft, someone told me because of the reduced pipe 1 1/2 down to 1 inch was causing the loss could this be true. The part I don't understand the pump that I replaced it locked up was a 10 gpm and was putting out 15gpm. I confused you about the pumps but i only have one hooked up and running someone else told me to run the 1 1/2 inch pipe for 75ft or so then reduce it down to the 1 inch will take some of the back pressure off the pump. The pump is a Grundfos 25s10-7 Submersible, any ideas to increase out put would be appreciated or if someone has a good pump or recommendation for me to remove the 25s10-7 and put in something else let me know. If i run the 500ft 1 1/2 inch pipe instead of the 1 inch will this solve my problem.

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