New pump, can't maintain pressure

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Roger Striffler

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I've recently replaced my sprinkler system pump with a 1 HP shallow well pump from Harbor Freight. The pump turns on, runs and seems so far to maintain a prime. The problem is, it does not build any pressure; the pressure gauge stays at zero and only one sprinkler head runs.

I also have an output to a spigot, and the water comes out, but with super low pressure. If I turn off all of the outlets, it will eventually build pressure and cut off at the specified max pressure. When I open the system, pressure immediately drops back to zero.

My guess is that it is not drawing water fast enough to build any pressure, which means one of the following:
  1. The water level in the well is low. I don't believe this is the case as we've had a very wet spring.
  2. There is a leak in the inlet line from the well, and the pump is sucking air. Everything is sealed PVC, with the exception of a union I installed so that the pump could be easily disconnected in the even of failure/repair. The union is properly installed so I don't *think* that's the problem.
  3. Water flow between the well pipe and the inlet is restricted. It may be important to note that the old pump was fed by 1 1/4" pipe, but the new pump has a 1" inlet, so I had to adapt the pipe from the well from 1 1/4" down to 1" pipe. Is it possible that this could restrict the flow enough to cause the issue?
Any ideas, or things I might be missing?

Thanks!
 

WorthFlorida

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Is it an irrigation pump? You want an irrigation pump and if you bought their green unit with a tank, NG. It will not work for irrigation but good for domestic water use. A 1" inlet is small for irrigation. Most of underground irrigation will use 1" or 3/4" pipe and then branch with a 1/2" pipe to the sprinkler head. For irrigation only, a pressure tank is not wanted. The pump without a tank and is cast iron will give problems because of the pressure switch. As long as the water is not closed with a valve, it should work.

Definitely, the suction side from the well cannot have any leaks at all, not even a pin hole for you'll never pull full prime. There also should be a check valve between the well head and the pump.


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Roger Striffler

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Is it an irrigation pump? You want an irrigation pump and if you bought their green unit with a tank, NG. It will not work for irrigation but good for domestic water use. A 1" inlet is small for irrigation. Most of underground irrigation will use 1" or 3/4" pipe and then branch with a 1/2" pipe to the sprinkler head. For irrigation only, a pressure tank is not wanted. The pump without a tank and is cast iron will give problems because of the pressure switch. As long as the water is not closed with a valve, it should work.

Definitely, the suction side from the well cannot have any leaks at all, not even a pin hole for you'll never pull full prime. There also should be a check valve between the well head and the pump.


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Thanks for the reply! I went with the pump + tank setup, because the original system that died had both a pump and a tank. I thought the tank was required to maintain pressure.
I'm surprised, since the reviews of that pump have several people very happily using it for their sprinkler systems (which is why I bought it).
It supposedly delivers 950 GPH, which I guess is too low for a sprinkler system?

Thanks!
 

valveman

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That pump will work for sprinklers, as long as you don't use more than about 10 GPM. If your sprinklers put out more than 10 GPM the pressure just falls to zero. You need the pump with the tank and switch if you have any hydrants or faucets on the system.
 

Roger Striffler

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There is faucet on the system (though I don't really use it) - so that explains the presence of the tank in the old system.

There is a check valve on the inlet pipe, I did prime the pump before starting it initially, and the pump seems to hold a prime, so I think we're good there.

I suspect the sprinkler system is putting out more than 10GPM...not 100% sure because I inherited it when we bought the house, but that would explain the symptoms. I also am pretty unimpressed with the amount of water/pressure that comes out of the faucet if I turn the sprinklers off and the faucet on, which makes me wonder if the union I installed on the inlet line is allowing air into the system...
 

Reach4

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I also am pretty unimpressed with the amount of water/pressure that comes out of the faucet if I turn the sprinklers off and the faucet on, which makes me wonder if the union I installed on the inlet line is allowing air into the system...
Slather any suspect joints with
index.php
. If there is a vacuum leak, it will suck in.
 

fitter30

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Just looked at the shut off pressure which is 50 lbs. What that means if you would close a discharge valve and have a gauge on it 50 lbs is max pressure zero flow. Need a true pump curve to see where they come up to 950 gph = 15.8 gpm. It can't be 26' suction.
 

Reach4

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Just looked at the shut off pressure which is 50 lbs. What that means if you would close a discharge valve and have a gauge on it 50 lbs is max pressure zero flow. Need a true pump curve to see where they come up to 950 gph = 15.8 gpm. It can't be 26' suction.
Specs say
  • 5 gal. hardened steel alloy tank
  • Maximum flow: 950 GPH (gallons per hour)
  • Pressure switch operation: 30 PSI On / 50 PSI Off
  • Maximum suction lift: 26 ft.
  • Stainless steel pump housing
  • Maximum water pressure: 50 PSI
  • Thermal protection with automatic reset
  • Intake and discharge ports: 1 in.
So that may mean 50 psi @ 0 gpm or 950gph @ 0 psi.
 
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