How to diagnose where a leak is [air suction]?

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Lucky13F

Lucky13F

Well-known member
Jun 9, 2020
60
Basking Ridge, New Jersey
Pool Size
21000
Surface
Vinyl
For all who read my previous odyssey -- that much is finally behind me.

To my dismay -- I am only able to get my pump going on Recirculate -- and only after soaking it with a hose all over the Strainer Cover.
Once it starts rolling - the outflow is nothing short of powerful.

However - every few seconds -- while standing at the Strainer -- it slows down for a second or 2 before getting back up to full force. This is a continuous repetitive pattern that happens the entire time.
I was able to get it to Waste -- also after soaking the Strainer Cover.

When I try to set it on Filter -- it starts to work -- but fades to a trickle after a minute and does not pick back up to a stronger flow.

I replaced the O-ring with a brand new one and lubed it up.
I sure hope it's not the pump itself -- but the rest of the PVC that enters in to the pump is almost completely new as of a couple days ago.

So what can I do to diagnose where the air is sucking in from?
If I can determine it is just the lid that needs to be replaced perhaps -- no problem. I can do that.
But what if it is not?
What kind of tricks can I use to find the exact spot and take whatever action is needed?

As always - thanks in advance.
 
It is the strainer cover seal.

Take the cover off. Take the o-ring out. Wipe it down again, lube with a silicone LUBRICANT like magic lube II. Don't use a PTFE/Teflon based lube. Clean the cover where the o-ring goes very throughly with denatured or rubbing Alcohol. Do the same on the volute where the o-ring seats. You need to make sure there are no scratches or any material on the seat. I got some 3000 grit sandpaper on a block and smoothed mine. All leaks disappeared.
 
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Don't know. Can't find it either...never know what Leslie's puts out.

Go ahead and use it for now to get you up and going. You can wipe it off and replace in the future.
 
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Did it all - might have to try again -- but it didn't work.
Same problem.
Still am able to get suction with Waste and / or Recirculate after pouring water from the hose onto the Strainer Lid -- but not when set to Filter.
I even put on a brand new clear lid.
It felt so snug.

I'm so sad.
 

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Lucky13F said:
Yes.
Click to expand...
Ok, but it primes while not on filter. Odd.
Lucky13F said:
Maybe I need to re-lube the DE Filter Belt O-Ring?
Click to expand...
No, that will not cause it to prime, it will leak on the pressure side. You have some sort of blockage on the pressure side.

Did you rebuild the MPV lately?
What is the condition of the filter? Has it been cleaned? Was it assembled correctly? Post pictures of the entire pad area. Current pictures don't show the pressure side real well.
 
So -- we might be getting somewhere...

The pressure side:
I have a return at my pool steps which is like a geyser while in recirculation mode.
I have a second return across on the other side of my shallow end - and sometime last year, it stopped pushing water out down to a trickle. [in any mode]
However - the filter ran just fine for the season and the pool was clean and the filter was on in normal operating fashion.

I have come to believe that it might have a crack somewhere in there -- because I tried to blow it out and even used an underwater "spy" camera to look up it about 18 inches -- and saw nothing.
I cannot afford to have a company come rip up all of it -- if it does indeed need to be repaired. And I do not possess the skills to do it on my own.
I was actually thinking about if I should cut the PVC and just stop it up -- taking that return out of the equation -- if indeed it is inevitable that I will need to rip the ground up etc.
But that seems like a bad idea net net.
I have idea how to test for something like this -- to detect a crack in the line or rule it out.

As for the condition of the filter...
Just last week I opened it - and washed it out and cleaned the screens. Squeaky clean. I did this because I had been repetitively filtering and backwashing all the algae out when I took the cover off. And I figured it was probably all caked up in there.
I did forget to relube that giant O-Ring. Which is what made me thing of it in my post above.

One more thing - my feeling about not being able to get the prime while in filter mode is that the circuit becomes so much longer than it is in recirculate. And thus it can't hold the prime / pressure once it gets going. Just a guess. FWIW -- it was working 2 weeks ago -- and it's not as if a giant boulder fell on it since then.
 
Did it stop working at the same time you cleaned the filter? I'm thinking something is not right in the filter. The MPV is working because it works in recirc and waste. I'd break down the filter and confirm it is constructed correcty.
 
PoolStored said:
Did it stop working at the same time you cleaned the filter? I'm thinking something is not right in the filter. The MPV is working because it works in recirc and waste. I'd break down the filter and confirm it is constructed correcty.
Click to expand...

It started pouring and I did not have a chance yet -- but for context -- air in my strainer has been an issue for years -- as far as I can tell it was that way when I moved in.
So I am skeptical this will help -- BUT as soon as I can - I will dismantle and reconnect everything tomorrow.
By the way -- looking at my skimmer from where I am sitting in my kitchen - I don't even see a Weir Door.

And still I'm confounded -- no matter what I do above - I don't understand why any of it will matter when pouring water on the strainer cover seems to have such a correlating effect on getting the pump running.
So I will also clean that up again and take another look.
 
when pouring water on the strainer cover seems to have such a correlating effect on getting the pump running.
Click to expand...
That means you are sucking air into the pump through the lid. When you run the hose over it, that suction leak is blocked and the pump then primes You must find the air leak somewhere along the lid
 
duraleigh said:
That means you are sucking air into the pump through the lid. When you run the hose over it, that suction leak is blocked and the pump then primes You must find the air leak somewhere along the lid
Click to expand...
Yea - I agree.
But how?
I need a magic bullet to figure it out -- as you can see above... I have tried a few different things.
Gonna try and refit the lid on again today.
 
duraleigh said:
Don't overtighten the lid. hand tight is enough. Look for damage on the o-ring or grit in the o-ring

Have you read the article on suction side air leaks in Pool School?
Click to expand...
I have not read it in a long time -- I'll go find it and re-read.

I do not think I am overtightening it -- I don't think I'm that strong! :)
I just replaced the o-ring -- it's brand new. I just replaced the clear part of the lid -- also brand new -- as in 24-48 hours old.
I did all the steps PoolStored mentioned above as well.

I was going to try it all again today at some point -- since it's sunny and dry and yesterday I was doing it in between rain showers.
 

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