Only leaks when the pump is on?

[Colonel Travis]

New guy here, been reading and learning a lot about pool leaks but I can't figure out what's going on with mine. Water level is fine with the pump off. It drops when it's on, so I changed all the gaskets and o-rings of the backwash valve, which haven't been changed in who knows how long. We ran the pump afterward for 24 hours straight and the water didn't drop anymore, I thought that was that. But a couple days after running the pump on the regular timer, it's dropping again. What the heck is going on? There aren't water drips around the pump equipment. The pool plumbing is connected directly to the sewer line, we don't have a backwash line that I could see if water is dripping out.

Pool:
18,000 gallons
DE
gunite
Pentair WhisperFlo pump

 

[Bama Rambler]

Do you have a multiport or slide backwash valve?

If it only leaks with the pump on it's either the backwash valve (common) or the return plumbing underground (rare).

I would disconnect the waste line even if I had to cut it and add a union and see if it's leaking there. That's a common place for it to leak.

 

[ps0303]

Pool only, no spa? Have you used a die kit to test for leaks around the skimmer or inlets?

 

[Colonel Travis]

Photos makes things a little easier, sorry. It's an older slide valve.
No spa, just the pool. Yeah, we've done the dye test, repaired some tiles we thought the water might have been leaking behind.

 

[duraleigh]

How much is it leaking? If it is still only leaking when you run the pump, the leak is after the pump....not before it.

 

[Bama Rambler]

Did you lube that valve good when you reassembled it?

Are there any scratches or gouges in the barrel of it?

 

[Colonel Travis]

I lubed around the gaskets a little bit. Not afraid to admit I don't know what the proper amount should be - got plenty of it left. I don't see any scratches in the pipe. The pump was running this morning for about three hours and the water level dropped about 1 inch then I turned it off.

 

[Colonel Travis]

Lube is DAP Auto/Marine Sealant 100% RTV silicone.

 

[Bama Rambler]

You shouldn't use sealant. It should be marine or pool lube. It should not harden.

Oh, and use plenty of it on all o-rings and seals.

 

[Colonel Travis]

Good grief - thanks for mentioning that and the overall help here. I got that stuff at Home Depot, do they sell marine/pool lube or is this something found typically at pool stores or online? There's a great pool store not far but HD is closer. Just a laziness question.

 

[Colonel Travis]

Sorry, didn't ask above - is there any way for that kind of backwash valve to fail and allow a leak, aside from the o-rings and gaskets?

 

[Bama Rambler]

If one of the disks are cracked, but that is rare and easy to spot.

 

[Colonel Travis]

Bama and others, thanks very much for your help here. I've added proper lube to the backwash valve and the pump has been running for a few hours with no water loss. We'll see what happens....