How do Hydrostatic Valves Work? How can I know nothing is wrong with mine?

briangreul

Well-known member
Sep 9, 2022
49
Houston, TX
I have some water balance issues that are best solved by a water change.

I'm new to TFP, so if there is a thread that addresses my question feel free to point me to it. I didn't see it when I searched, but I may not be good at searching the forums yet.

I did a little recreational free diving in my pool this afternoon (5# of weight belt, mask, and screwdriver) to remove the cover from my main drain. There was a ton of "crud" in there and what looks like 3 cups of plaster that chipped out. All of which promptly clogged my Hayward cartridge filter... sigh I hate that thing.

Anyhow, I did see a 1.5 or 2 inch plug with the square part sticking up. So that means there is either a hole or a hydrostatic valve. I chipped away enough crud to clearly see the transition from thread to plug. My research suggests it's just a plugged hole, but that could double as a hydrostatic relief port if it's just dirt/sand/muck under it.

I did not build this pool, and I don't believe permits were pulled. In Texas anyone can be a pool builder (which is often the issue) and this pool pre-dates my ownership of the house. I've fixed some other issues that were mind boggling, like flex on the skimmers that was completely bent over and kinked to where there was barely any water flow. So I don't have high hopes for perfection elsewhere in the pool construction. The pool is level within 1/4" so I doubt it has floated, although it's higher than anything else in the yard. That's not uncommon here and was a practice for building pools at one time.

To drain the pool I think I'm supposed to pull that plug, but how do I know if its working properly before I let the water level fall much? I think it would be simpler to drain it, wash the algae off and bid it good bye at the same time, and then refill, balance, and go to slam to dispense the rest of the algae....
 
NO, you do not drain the pool using that plug. It does not have a drain pipe connected to it.

The plug is removed after the pool is drained to relieve water pressure under the pool from popping the pool out of the ground.



 
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NO, you do not drain the pool using that plug. It does not have a drain pipe connected to it.

The plug is removed after the pool is drained to relieve water pressure under the pool from popping the pool out fo the ground.



Thanks, I'm aware that the plug is not connected to anything and won't drain lol. I meant to say when I drain the pool I think I need to pull that plug out. I'm planning to brush the pool hard and rinse the walls off while draining to push the algae out at the same time. So I don't want to have to go in the water once it's pea green. The algae is pretty bad. I also think it will take quite a bit of time to fill the pool, like maybe a day.

Does the plug come out before you drain or after? How critical is it to pull the plug? i.e must be done within 10 minutes of draining the pool.
How fast does a pool float?
How do I know the hole isn't plugged on the other side of that plug?
I have low confidence in the pool being built right. There was a few cups of plaster in the bottom of the drain when I went down there.

I am in Houston, aka the Bayou City. I'm at about 23 feet above sea level and I have a Bayou (ditch) at the end of the street. The water table will not be any lower than the bayou and could be a few feet higher which places it very close to the bottom of the pool. So close I don't want to risk floating it.
The dirt here is a heavy clay and the pool will be sitting in a hole filled with sand. When we did foundation work (underpinning), all the holes filled in with water which is an indicator of a high water table, a pool leak, or both.
 
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A proper hydrostatic valve is supposed to open automatically when the pressure underground becomes larger than the pressure in the pool. As you drain the pool, the water pressure drops on that side of the valve and if the underground pressure is higher water will flow from the ground into the pool.

However, hydrostatic valves can and do fail so it is not fool proof. Also, you need to confirm that you indeed have a hydrostatic valve and not just a plug. The latter would definitely need to be removed before draining the pool. But to be safe, it is best to just remove it before draining in either case.

But can you explain your "balance" issues? There may be other solutions.
 
A proper hydrostatic valve is supposed to open automatically when the pressure underground becomes larger than the pressure in the pool. As you drain the pool, the water pressure drops on that side of the valve and if the underground pressure is higher water will flow from the ground into the pool.

However, hydrostatic valves can and do fail so it is not fool proof. Also, you need to confirm that you indeed have a hydrostatic valve and not just a plug. The latter would definitely need to be removed before draining the pool. But to be safe, it is best to just remove it before draining in either case.

But can you explain your "balance" issues? There may be other solutions.
I have a plug.
Thanks for confirming it should be pulled prior to draining.
Moderately high CYA, high PH and high CA and last time I let Leslie's play with the water it had high Nitrites/Nitrates (organics). I posted the numbers yesterday and today in that section and the consensus from several people is that a water change was the most efficient way to get it under control.
I also have a borderline crisis Algae problem which is exacerbated by the PH/CYA situation.
 
I forgot to mention that there are a couple of alternatives. There are pool services that will remove TDS (CH & CYA) from the water. Also, I and others have used a no drain refill method that works pretty well.

 
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I pulled the plug using two crescent wrenches today... I was going to do a 40% water change to deal with CYA and decided to just do a total drain/fill and flush as much algae in the process as I can. I will refill and balance and go to SLAM until the algae is toast.
 
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