water shoots out the skimmer when pump is turned off

[campbem]

Hello all,

Background - pool is inground 16 x 32. This will be our 3rd season, so pool is rather new.

After opening my pool this past weekend, I noticed I"m getting air into my pump and filtration system. As I
was trying to diagnose where the air leak was, I turned off the pump and water shot up thru the skimmer cover
plate. It does this each time now. I think I've isolated the source of the leak (couple of tiny pin holes in the return
pipe from the skimmer right up near the 3 way valve. Tonight, I decided to turn the 3 way valve to the "floor drain"
position just to see if the air getting into the filtration would stop (it did), but when I turned the pump off, the skimmer
lid still blew right off.

So, what's the typical cause of water flowing backwards and blowing skimmer lids off? Also, how likely is it that there
are other sources of leaks causing all this air to get into my system? Things like o-rings, gaskets and such? Would it be typical for them to wear out after only 2 seasons?

Thanks
Matt

[Sean OBrien]

I would be inclined to think that what you are seeing is water hammering of some form. There will probably be a bend in the plumbing that has air trapped in it. When the water is being pumped through the system, this compressors the air. When the water is no longer being pumped - the air expands back out to its normal volume, it can be quite energetic and I have seen it burst pipes in residential plumbing applications.

Since it is a new pool, there is a possibility that a pipe that was straight became bent during the winter. The depth of the bend just needs to be greater than the width of the pipe in order to trap air in an otherwise straight pipe. That will be enough in order to form a seal with water before all the air is evacuated from the pipes.

There are a lot of methods of removal - but chances are pretty good that if you let the pump run for a couple of days non-stop it will take care of the problem on its own. Moving water is really good at dissolving air into it.

Regarding the valve switched to floor drain and still getting blow out from the skimmer - as I understand it, the current plumbing runs a secondary pipe from the skimmer to the floor drain in order to prevent a low water level from causing the skimmer to loose suction and burn out your pump. That would allow the hammering to continue if the air pocket was on the main drain line (might check to see if it still hammers when you have the valve set to suck only from the skimmer).

[PoolDoc]

Actually, the most likely cause is accumulated air in your filter.

You can check this by opening the filter air relief valve while after the pump has been running for a couple of hours. Most likely, you'll be able to bleed air ought for quite awhile. If so, you've found your cause.

However, you have not found the problem, which is air getting into the suction line, via a small leak. Large suction leaks cause you to lose prime, so this leak by definition has to be small. Small suction leaks are a pain to find. Two common locations for a first look are the pump basket seal, and the threaded connection between the pump and the suction piping.