air in return lines


Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
Sebring, Florida

Poolsean's thought of the drain plug on the pump strainer basket makes a lot of sense. It is possible it would be loose enough to allow air to suck in. I doubt you would see any bubbles in the strainer lid because they are immediately pulled into the pump. That said, I'd think the bubbles would show in the basket lid once the pump was turned off....maybe not. Anyway, it's really easy to ensure that it's tight.

Poolsean, like you, I am very interested in tphaggerty's problem. I remember it very well and am completely baffled that that can happen in an IG pool.

Pool in Carolina Blue

LifeTime Supporter
May 28, 2007
Poolsean said:
Check the grease fitting on the Jandy valve. Sometimes these get broken off and allow air to draw in. Did you check the bottom drain plug on your pump trap?

I did previously check the drain plug and it is tight and secure. I have never taken the jandy valve apart so I will check that out. Thanks for the tip.


LifeTime Supporter
Jun 27, 2007
Poughquag, NY
Poolsean said:

I understand what you're describing.


I'm very interested in hearing where the leak finally is found. Please keep us (me) posted!
Based on the sound of the air escaping when we pressure tested, it appears that there is a bad join at the elbow right at the return. In my pool, the return is flex PVC and comes up to a 90 elbow that goes directly to the return. When we pressurize the line when it has water in it, we can hear a bubbling/burping/hissing sound under the concrete right at that point.

I don't think I was completely clear on how I blocked the return. It is blocked in 2 places, at the pool with a cap on the return and right after the T split where the return line is split. In fact, when I originally blocked the line at the T, I thought the leak wasn't in the return because the water kept dropping. When I opened the T again, the cap I used to block the line internally has turned sideways and was still allowing water into the return line. I had to seal the cap in place with some removable caulk to get it to stay. Sometime soon I am going to cut the concrete and fix it, I'll let you know what I find.

Pool in Carolina Blue

LifeTime Supporter
May 28, 2007
Pool in Carolina Blue said:
duraleigh said:
Dave, are you saying I have a blockage?
No, not at all.

I was commenting on the pressure reading you got when you hooked up the Ray Vac. That indicated virtually no flow on the pressure side of the pump because pool pumps are incapable of producing much more than that. I would take from that test that your pump IS producing the energy you would expect.
Thanks for the insight. The terminology was a little over my head. I am very appreciate of the time you have spent helping me with this issue.
Dave (or anyone else who understands pool hydraulics!!):

I noticed something odd when I direct all flow back through the Jandy ray-vac cleaner line to the pool. The pressure gauge on the cleaner line goes up to 35 psi (my installer goofed up and did reinstall the jandy valve that allows you to reduce the flow to the cleaner line) and the pump stops "pulling" water from the skimmer lines. Water is still being moved through the system so it must be pulling from the main drain. Any reason why the system would do this?



May 29, 2008
Newburgh, IN
I have a Hayward NorthStar and had the same issue. Fought it for two seasons. Finally applied a very small amount of dielectric grease on the threads of the pump skimmer basket drain plug and no more bubbles. It was always tight but I guess that the threads had just enough misalignment to draw in air. It was never very much but always enough for me to wonder what the heck was going on. Now I coat all my o-rings and threads with with a very, very small amount of silicone grease at the start of the season and have had no issues for 4 years running now. This also make threading and unthreading fittings and connections a breeze.


Well-known member
Feb 8, 2008
Milford, CT
I had the same issue with my Northstar pump....the drain plug (on the suction side) was leaking ever so slightly. easiest way to see it was have someone cycle the pump on and off while you were looking around. A small amount of water would squirt out after the pump shut down, and if you turned it on quick enough it would get sucked back in.

I have to ask about another theory Ive had......if the pipe from pump to multiport, or the multiport inlet port iself is cracked, would this not cause a venturi effect to pull outside air into the flowing water and eventually eject the bubbles out the returns......masquerading as a suction side leak, but actually (technically) NOT being on the suction side? If its true, perhaps trying to seal the inlet from the filter with thread sealant (for some reason I thought I heard NOT to use teflon tape). I used red RTV and its holding up nicely.