Pump Pressure/GPM

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Bob from Plains

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I live in the country and am on my own well. I recently installed an underground sprinkler system to my yard and don't get the coverage from the sprinkler heads the manufacturer says I should be getting. When first considering putting in the system the manufacturer asked basic questions such as GPM and pressure at an outside faucet. When I took these readings I did it at the hydrant next to the well, 28 GPM at 28 psi with the well running. The well is a 3/4 HP, and is supplied to the house with 1 1/4" inch black polly pipe , when it enters the basement is is changed over to 1 1/4" galvinized up the wall and across the basement to the pressure tank (well x trol wx 252). At the top of the wall over the entry point there is an 1 1/4" T, I came off the T, reduced to 1" and out the wall to my main manifold for the sprinkler system. I also installed a back flow preventor in front of the manifold. When I didn't get the distance from the sprinkler heads I measured the GPM/ press at the hydrant and the 1" exit from the house. With the pump running and one zone on the hydrand was 28psi, 30gpm, house was 18psi, 18 gpm. I removed the back flow to test the pressure and gpm and pressure went up to 20psi and gpm up to 20. Why is there such a difference on psi and gpm from the house and hydrant? the well is only 30 feet from the house. Any ideas would be greatly appreciated. One other thing I have noticed is almost all sprinkler systems in this area are started at the hydrant, they just come off the hydrand with 1" black polly and into the system, when I asked why the only reply was it was esier than coming out of the house.
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Bob :confused:
 

Speedbump

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Without knowing how much water your sprinklers need Bob, it's hard to be of much help.

It sounds like you installed maybe one head too many on the zone and the pump can't do any more than what you are measuring. The solution would be to use smaller nozzles in those heads if they are changable. Or subtract one or two heads to get the required pressure.

bob...
 

Bob NH

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Too much flow demand; pipe too small; not enough pump

Too much flow demand; pipe too small; not enough pump.

You don't say what pump you have, but my catalog show that a 3/4 HP Goulds submersible 18GS07 will deliver 27 psi at 28 GPM with no pressure losses in the pipe. They are usually conservatively rated and it is possible that you would get 30 GPM at 28 psi but that would exceed the rating of the pump.

One inch pipe is way too small for 28 GPM. You will lose about 11 psi for every 50 ft of pipe. The minimum should be 1 1/4 and 1 1/2 would be my choice.

I have checked my Goulds catalog for a pump that would best provide 28 GPM that your irrigation system is designed for, and would pick a 33GS?? with the horsepower depending on depth to water in the well. It is more efficient than the smaller 18GS and 25GS series pumps at those high flows.

The WX-252 is marginal for that pump but it will work. However, it is rated at only 100 psi. If you get a pump that produces more than 100 psi at shutoff, you will need a relief valve that will protect the tank.
 

Bob NH

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First, you should increase the pipe size to 1 1/4" all the way to the manifold, using the shortest path with minimum tees and elbows. Chamfer the inside corner at the inlet of all of the new poly pipe fittings to reduce losses. See how close you come to making the system work.

Then follow Bob's (speedbump) suggestion to reduce the flow. If you get down to about 20 GPM, your pump (if it is a submersible) should produce 40 to 50 psi if it is a fairly shallow well. You should find a good working point somewhere between 20 and 25 GPM.

With the increased pressure, you should be able to get the same range you were expecting before.

You will have to do some experiments with nozzles and flows to avoid having to reconfigure your underground system.
 
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