Hydrostatic Relief Valve - question

[D.Gillum]

Hi all,
We have been scratching our heads trying to find the cause of water loss in our pool, which seems to have started after we received over 40 inches of rain from Hurricane Harvey. We've had 2 pressure tests conducted by a third party and both have come back clean; no pressure leaks. My question is, if the problem is with the hydrostatic valve, would that have been picked up in the pressure test? My initial thinking would be that it would NOT be picked up as my understanding is that the hydrostatic valve is not incorporated into the plumbing system, but rather in addition to it to relieve pressure from the ground water table. Thoughts? Thanks for the help!!

 

[JoyfulNoise]

It is as you say, not connected to the plumbing. Someone will have to swim down to the MD, remove the cover and look to see if the hydrostat valve is closed. It could have popped open from groundwater and then got clogged with sand such that it could not close properly.

But here’s the test - if you let the water leak, how far down does the water level fall?

 

[PoolGate]

My hydrostatic valves (4 of them) are all closed off with a screw cap. They were even plastered over when the plaster was installed (the recesses in the cap where you would remove them). My PB never explained how they worked but I assumed they would only need to be removed if the pool was ever drained. Is that the case?

 

[D.Gillum]

That's what we are currently testing. We had originally thought that the leak(s) were occurring along the back side of our pool where decorative rocks from the waterfall meet the pebble tec. That was where we had thought the water level had stabilized (just below the decorative rocks, which is also below the skimmer level and above the returns) but I'm now thinking that perhaps we jumped the gun on making that assessment. My brain logically said, oh, it stabilized under the rocks, that must be it.....but I probably didn't wait long enough to see if it ACTUALLY stabilized there. After using hydraulic cement to re-seal all the mortar joints on the seams where the rocks meet the pebble tec we re-filled the pool. Alas overnight last night we still lost over 1/2 inch of water, which is roughly the same rate as before re-sealing the mortar joints. So my new strategy is wait and see.....yet again. We're running the pump off the main drain only and will see if it does truly stabilize below the rocks, or, if as I suspect, that it continues to drop even lower.

Question -- if there IS a problem with the hydrostatic relief valve - would the rate of loss be GREATER when the system is OFF? I'm not that familiar with hydrostatic relief valves, but being located right next to the main drain I would tend to think that water loss would be less when the system is ON as the water is being sucked right past the valve and into the drain. However when the system is OFF there isn't any offsetting current and thus the water would be allowed to seep out through the valve if it is faulty. Am I off base?

Thanks all!

 

[Swampwoman]

Hi D. I'm not sure about your question, but it would make sense to me that in a flood condition a relief valve could get stuck open by merely a small pebble or some such as the groundwater swelled up.

In case you haven't run across it, here's a YouTube video about the valve and how it works:
$20 part that can save your pool from permanently breaking - YouTube

 

[Mayorb]

The hydrostatic is designed to pop when the differential pressure is greater under the pool than inside the pool. Unless the pool was largely empty your pool water should keep the valve closed. Unfortunately some people drained their pools right after the flood when our water table was high and our "gumbo" soil fully saturated. In that instance the hydrostatics could have opened. In some cases the pools actually floated, raised up out of the ground.

If any doubt, you can cement them shut. In the event of needing a new surface applied, most companies will drain at an appropriate time and punch several holes in the vessel anyway.

 

[wjr75]

I have had issues with a leaky hydrostatic valve in the past. Once in the main pool and another time in the spa. Took a diver to locate the one in the pool in which I think he used dye to locate. I also had a small leak around my skimmer which they also fixed at that time..