Lawn sprinkler system keeps losing prime

[billdz]

Hi,

My lawn sprinkler pump 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 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

 

[Reach4]

If you have a single pipe from your above ground pump to the lake, it will be a suction pipe. So there will be no water leaking out even though air is leaking in. The leak would be above ground and probably near the pump. It is hard to find such a leak.

A submersible pump has no problems with priming.

 

[Sponsor]

 

[billdz]

Thanks for the reply. Yes, it is a single pipe from and above ground pump (in the garage) to the lake (in back of house). Sounds like a new pump would not fix the problem. Any ideas on how to find the leak?

 

[Magneto]

Do a pressure test and check that you pump is actually the source of the problem. It should be fairly easy to distinguish a leak.

 

[Reach4]

I am not a pro, and have not done it. Since your system takes a long time to lose prime, the leak will be small.

I would first try to tighten fittings near the pump. If that does not do the job, for galvanized pipe I think I might run the pump so that a vacuum develops, make sure the joints are dry, and then put liquid 5-minute epoxy on each joint interface while the pump is running. Mix the stuff in small batches, because you probably only have a minute to apply while the glue is liquid enough to flow into the crack. Then run the pump for another half hour after the last application.
There might be a better choice than 5 minute epoxy. I am not a pro, and because I think I would do something does not make it a good thing to do. This presumes metal joints. For ABS joints, I would be using ABS cement. For PVC, I am not sure. Maybe a cement that does not need a primer. But in any case, the deal is that you have a tiny leak. You want something thin enough to get sucked into the leak.

I am confident that a submersible pump would take all of the drama out. Yes, you have to run power to the pump. But it will be more efficient, and it will be much much quieter. If you had a 1 HP jet pump, I would be looking at a 1/2 HP submersible. You want to not only get the HP right, you want the right number of stages. That will depend on things including how much pressure you want and how much rise in elevation you have. Your elevation needs must be fairly low because your jet pump works most of the time.

 

[billdz]

OK, thanks. It's the fittings on the intake side we are worried about, right? On the intake side, the pump connects to the pipe that runs to the lake. On the discharge side, the pump connects to a Finco 4 zone hydro indexing valve that was replaced 8 months ago. What if the new valve was not installed properly?

Your submersible pump idea sounds appealing, I could do without the noise, will check into that.

 

[Reach4]

Intake side, yes. I don't know that a problem on the output side could cause your problem.

 

[billdz]

I read in another forum that a way to find an air leak is to coat the connections 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?

 

[Reach4]

Yes.

 

[DonL]

A lot of check valves need pressure to keep them closed.

Trash from the lake in the valve does not help either.


Good Luck.

 

[billdz]

When the pump is off, is there supposed to be water in the intake pipe all the way to the pump? The check valve is supposed to stop any water from flowing out, right? So where is the water going, if the check valve is OK (it is brand new, but maybe they installed it wrong). There does not appear to be any water leaking out anywhere near the pump.

 

[billdz]

Anyone have an answer or thought, is there supposed to be water in the intake pipe all the way to the pump and, if yes, where is the water going if the problem is a hole that allows air in but does drip any water?

Today the pump again worked properly without priming, so if the problem is an air leak it seems the remnants of two-day old shaving ream were enough to keep it sealed.

Thanks much for the help,
b

 

[DonL]

What happens sometimes is Air can leak where water don't.

The pipe should stay full of water, all the way to the pump. If the foot valve is holding, and you have no pipe leaks.

The pipe will drain from the pump to the leak point. Because air will go thru the pump, unless it has a valve on the outlet, or a tank.

Water does not disappear unless you boil it.

Do you turn the water off by killing power to the pump ?

Good Luck.

 

[billdz]

Thanks for the reply. Maybe I'm not communicating my question clearly, let me try again.
* We know the intake pipe is filled with water all the way up into the pump when the pump is running.
* According to DonL, when the pump is turned off, the water is supposed to remain up in the pump
* The water apparently does remain up at least for a few hours after the pump is turned off, because no priming is needed if I restart the pump even 3 0r 4 hours later
* At some point (e.g., overnight), the water apparently goes down
* Once the water goes down, the pump will not start without priming
* As Reach4 suggested yesterday, it appears that there is a gap in the pipe above ground and near the pump, at least the shaving cream patch suggests this to be the case, because the cream is stopping air from getting sucked in
* So where did the water go? If it was escaping through the check valve (brand new, but possibly defective or installed incorrectly), then the shaving cream patch should not have cured the problem. On the other hand, if the water was leaking through the gap in the pipe, I should have seen water on the ground, and my garage floor has not seen even a drop of water. How does the water get down to the point past the gap where air is being sucked in?

Yes, the water is turned off by killing power to the pump.

 

[Reach4]

So where did the water go? If it was escaping through the check valve (brand new, but possibly defective or installed incorrectly), then the shaving cream patch should not have cured the problem. On the other hand, if the water was leaking through the gap in the pipe, I should have seen water on the ground, and my garage floor has not seen even a drop of water. How does the water get down to the point past the gap where air is being sucked in?

Good question. I don't know.

I am still confident you could avoid the problem with a submersible pump. You could also presumably avoid that problem with a 2-pipe jet pump system, but the submersible would be preferable if running electricity is not a problem.

 

[DonL]

Yes, the water is turned off by killing power to the pump.

You should put a ballvalve at the pump outlet and close it after you kill power.

That should keep the pump full even if you have a leak or "Lake suck back". (New Gov term)

 

[Ken E]

Just a thought... What about putting a second check valve close to the pump ?seems like that would help to keep water in the pipe close to the pump and might help it to stay "nearly" primed... Just a thought