Leak detective work

Noelep

0
Mar 9, 2013
21
Houston, TX
I'm having some fun and games with a new (to us) pool and its plumbing....

Some context: in ground pool, overflow spa. One main drain, two skimmers - diverter at pad.

We had some work done to replace some of the pool deck, and in doing so some of the pipe work got damaged - primarily the spa & pool returns. I needed to drain the pool below the level of the returns in order to replace the damaged pipe.

So - in trying to drain the pool via the main drain only I noticed the pump losing prime very quickly. Skimmer only is fine - but as soon as the main suction was diverted in the pump would lose prime again. The prime loss is dramatic and instant - barely a trickle of water.

This wasn't previously the case - in the fairly recent past I was able to suction just the main.

I hadn't noticed any water loss - so was assuming an air leak above the water line. I have dug up the obvious candidate locations (joints around the previous damage) but nothing obvious.

So, I reversed the flow - pumping water down the suction line from the pad, hoping that the reverse pressure from the pool would be enough to force water out of the air leak...but nothing.

There is one other location (under the deck at the wall by the main drain) that could be it...but given how much water I pumped back down the line I would expect to see some evidence.

All that, coupled with how vigorously the pump loses prime (I.e. As if here was just an open pipe!) I am wondering if something else is going on.

Is it possible these symptoms could be of a blocked main drain line? That it isn't sucking air in - but essentially creating a vacuum?

The drain has a cover of course - but there has certainly been some debris in the pool during the construction work.

Any thoughts!?


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Any chance that MD line tied-in anywhere else underground? Connected to something (sharing a line) that may have been damaged from the decking work? After all, it sounds like all your troubles are related to that project. Blockage? ... perhaps. But if the screen has been in-place, is it likely that something that small could be causing your problems?

Oh, and silly to ask ... any chance your diverter is not properly set or something?
 
I have the line exposed pretty much from the pad through the damaged area and don't see any issues (or it being tied in elsewhere).

I also tried filling all the trenches with water - but no difference. The screen is in place on the drain.

Quite the conundrum - I guess part of the question is could an air leak be so severe to create instant prime loss and no flow...yet be small enough not to allow any noticeable water egress?


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Good question. Others may have personal experience. But I would say from previous suction leaks that air is definitely the toughest to find. And it doesn't take much to drastically effect prime. Normally we'd ask you to rule-out all the suction-side 101 items (pump basket O-ring, drain plug, etc), but your skimmer suction seems to be fine.

When you tried pushing water backwards, were you able to actually seal it off to increase pressure? Did you have a bladder king or something to seal the water from the pad side? I can see where filling the trenches with water would seem to seal anything exposed in those areas. If you get to where you've exhausted everything visible to you, your next option may be a pressure test to see how long that MD line can hold 20-30 psi of water/air.
 
Good question - it was under some pressure...but certainly not sealed. At the various points of the pipe I have exposed I can hear a water trickle every now and then.

I also saw the occasional small air bubble coming out of the main drain in this reverse flow configuration.

A clog buster might be a good next step...


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I agree. Start with the simplest (and cheapest) methods first. :) The one good thing is you should have very good pool circulation with 2 skimmers, so even if you have to keep the MD closed for a while (even indefinitely) it shouldn't effect pool chemistry. Keep us posted. Curious to see how this turns-out.
 
Quick update - I managed to seal the reverse flow...and all it managed to do was start filling the pool via the main drain. At a relatively good rate...with no noticeable leaks.

I found a pump, so am going to drain it a bit...fix the remaining return to keep the chem in line and keep investigating.


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Wow. That's interesting. You wouldn't think one single line could be such a mystery. After you fix the return(s), maybe you'll look back and find something right in front of you that was there the whole time. One can always hope right? :slidehalo: But we can't lose track that a reverse "water" flow may not show immediate signs of a problem (leak) quite as fast or easily as air. So if you are sure about all the MD line connections from the drain itself leading-up to the pump, then a gauged pressure test may still be in order.
 
Latest update. Gave in and called a leak detection company (who were outstanding)

After a good while he located the leak - under the new deck. He said it sounded like a decent size break based on the speed at which the air escaped under the pressure test.

Today we jacked the concrete at his mark and found it. Pipe was completely shattered.

Currently siphoning some water out to get below the pipe, the should be a simple fix.


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