May 22, 2019

Having an issue on the pressure side with air getting into the system when the pump gets turned off and I cannot seem to locate the leak. Started noticing about 8 months ago with a little air being forced through returns whenever the pump would turn on. Gradually got worse so I decided to try to change out multiport gasket and o-ring when I cleaned DE filter this fall. After performing that work, the leak got worse to the point where I would lose prime in the pump basket. It always started on the pressure side where I could hear air seeming to enter the multi-port, then eventually the pump would lose prime. When on, the system works just fine - no visible leaks anywhere, and no air entering pump basket. pool doesn't appear to be losing any water.

Called in a pool repair company that I had used when I first moved in to help me open. He insisted it had to be on suction side, couldn't find anything and recommended check valve after my pump. Put in the check valve and would still lose prime after turning off. Started playing with the multi-port handle after I turned the pump off, and I can hear the leak stop when the handle is pressed down just the right amount. Changed the multiport gasket and o-ring again, with same result.

I'm at a loss for where to look and how to fix. The multi-port gasket handle has been "loose" when locked into position since i've changed the gasket. I don't remember it being super tight previously, but it does now appear to have more play into it. I read a link earlier that multiport gaskets may be a little thicker now, causing the handle play that i'm seeing, but not sure if it would cause the air leak

~13K gallon gunnite
1 HP Pentair Challenger pump
Quad DE 60 filter
2" hiflo multiport (261050)
Mastertemp 250
IC40 salt cell
Booster pump


Silver Supporter
In The Industry
Aug 15, 2017
Spring Valley, NY
I think you have 2 issues. For one, the check valve should hold the water in the pump basket when shut off so I assume the check valve is faulty because you stated when turning pump on again it primes so it couldn't be a leak on the suction side. Obviously air is getting introduced where you mentioned at the valve. You'll need to revisit your work a see what's in there that doesn't hold possibly a crack somewhere. Check the filter air bleed valve maybe your problem is there.


Mod Squad
TFP Expert
Apr 4, 2007
SW Indiana
Pool Size
Liquid Chlorine
When there is a leak anywhere above the water line it allows water to drain from the pipes when the pump is off. Obviously an exterior leak on the pressure side would show itself unless it seals under pressure.

A check valve after the pump will likely only help when there is water under at least a little pressure (gravity could create enough pressure) on the filter side. If that water siphons into the pool through the filter and the returns, the suction that holds the water in the pump basket will be released and allow the pump basket to drain through the skimmer. Unless your check valve is spring loaded, which is not the norm for pools.

Do you get any water drips anywhere on the suction side when the pump shuts off?

How do things behave if you set the multiport to closed right after turning the pump off?


May 22, 2019
Thanks all and apologies for the delay in my response - waited to take apart again until there would be no risk of nigh-time freeze.

To answer some questions:
1. No water drips on the suction side that are visible when pump is off or on
2. when set to "closed" on the MPV, no water loss on the pressure side.
3. I also replaced the spring thinking that could be the issue with the same results.

I did some additional diagnostics, and found that I did have a suction side leak at my 3-way valve. Was actually able to turn this valve completely off just before the pump basket, isolating the pump basket and pressure side. Turned off pump, closed the valve completely, and still lost water on the pressure side back to the pool. With the valve off, I did not lose prime on the pump. The issue on my 3-way valve appears to be the o-rings as I saw water under the handle after turning it. That seems like an easy fix.

After still hearing the pressure side leak with the suction side mostly isolated, I took the MPV apart again. I think I have pinpointed the issue to a small hairline crack in the MPV. I definitely have a crack in the top of the MPV near one of the screw holes that extends into the small ridge that meets the gasket. I believe I also have a crack on the underside of the MPV right underneath the "closed" port. Not sure if either of these cracks could be enough to let air into the system, so that it leaks back to the pool but not allow any water to leak from them.

BTW - the leak back to the pool takes at least 30 minutes until I stop hearing air enter the pressure side of the system.

Based on cost, I'm thinking I replace the entire MPV rather than just the top portion.


Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
Bedford, TX

How often do you backwash, or do you even have to backwash? The reason I ask is that I have two rent house pools that have DE filters. Over time both of them had bad MPVs. Since I just open and clean them twice a year, and never backwash, I just took the MPV completely out of the system. In its place I added a 2 way valve just so I could shut the filter off when I wanted to open the pump lid.

Doing that dropped by filter pressure from 10 or 12 down below 5 PSI.. But, I have VS pumps running at 1200 RPM most of the time..


Jim R.


May 22, 2019
I typically will backwash once, maybe twice between DE grid cleanings twice a year, but could probably get away without backwashing. When I first moved into the house I was doing it more frequently based on recommendations from the inspection, but I realized after cleaning the grids that I should do that more often, which eliminated many of the backwashes.

I typically run about 20psi with my challenger pump (single speed 3450RPM), so probably have room to come down. Anyone else work with this type of setup?
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