Lawn sprinkler system keeps losing prime

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  #1  
Old 08-17-15, 11:20 AM
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Lawn sprinkler system keeps losing prime

Hi,

My lawn sprinkler pump (in the garage) attaches to a pipe that runs into a lake. The end of the pipe is held by a plastic floating duck. If I turn on the pump twice a day, everything is OK. However, if left off for 1 day or longer, the pump loses its prime. I called for service and they replaced the check valve (foot valve?) at the end of the pipe in the water. They explained that, if this valve is loose, water will slowly leak out and prime will be lost.

Unfortunately, replacing this valve did not solve the problem. Now they are saying I should replace the pump. I'm skeptical, as the pump sounds fine, just as it did when everything was working properly. I assume there is a leak somewhere, but I do not see any leakage around the pump or anywhere else where the pipes are above ground.

Any thoughts on what might be wrong?

Thanks much,
b
 
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  #2  
Old 08-17-15, 11:28 AM
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It is possible that the new foot valve also has a leak. It would still be my prime (ye, I'm punny) suspect. Have you inspected the pump and suction piping between the lake and pump for leaks?

Have you considered replacing the foot valve yourself? If it's floating in the lake it should be easy to access and I'd trust your labor more than a stranger that doesn't care so much.

As a last resort I would try a different float. The duck might not be doing it's job. Maybe a floating frog or alligator would do better. I'd never suggest a boring round ball or buoy as they're too boring though I have a spray painted milk jug holding the intake for my pump.
 
  #3  
Old 08-17-15, 11:51 AM
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Thanks for the reply. Is there a difference between a foot valve and a check valve? The serviceman called it a check valve but you and others have called it a foot valve.

I have not dug up the pipe but have inspected everything above ground on land and don't see any leaks. Someone suggested it may be air leaking in rather than water leaking out.

You're joking about the float, right?
 
  #4  
Old 08-17-15, 03:28 PM
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Foot and check valves do the same thing. Foot valves have a intake or screen on one side where check valves are usually connected to piping on both sides, but they're basically the same.

I still suspect your foot valve is leaking and allowing the water to drain down. If you don't want to replace the foot valve you can put a check valve in the line somewhere convenient.

Yes, and the float was a joke though I did use a plastic alligator for my float for several years.
 
  #5  
Old 08-19-15, 08:04 AM
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I read elsewhere that an air leak can cause my problem. They said the way to find an air leak is to coat the connections on the intake pipe with shaving cream, run the pump unprimed, and then look for suction holes in the shaving cream. I tried this yesterday but did not see any suction holes. However, when I turned on the pump today it worked perfectly without priming. Is it possible that the cream somehow is temporarily blocking the leak?
 
  #6  
Old 08-19-15, 09:33 AM
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An air leak can cause the pump to loose prime but if the foot valve is sealing properly it can only leak down as far as the leak. The pipe and the part of the pump below the leak will still hold water.

If there is a leak and your foot valve is sealing you should see water leaking out. After all if it's leaking it has to go somewhere. But if the foot valve is leaking then the weight of the water causes the leak to suck air in as the water drains downhill. So, if you're not finding a puddle of water somewhere you may still have a leaking foot valve.
 
  #7  
Old 08-19-15, 10:22 AM
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That makes sense, when the pump is off, is there supposed to be water in the intake pipe all the way to the pump? As you say, the check valve is supposed to stop any water from flowing out, so if the valve is OK the water must be going somewhere. So where is the water going, if the check valve is OK (it is brand new, but as you say maybe they installed it wrong or maybe the new one is bad). There does not appear to be any water leaking out anywhere near the pump.
 
  #8  
Old 08-19-15, 10:38 AM
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Yes, that's the job of the foot valve. When the pump is not running the weight of the water above should hold the valve closed so the intake pipe and pump stay filled with water. That way the pump does not need to prime each time it turns on.

In a lake there could be a bit of sediment or trash caught that prevents the foot valve from making a perfect seal. I used to live on a lake and irrigate with lake water. At least once a season the pump would not hold prime and I'd have to go swimming and remove the algae, twig or leaf that was preventing it from sealing.
 
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