Variable speed pumps: FIXED the air-in-basket-at-low-speed problem!

[MostlyCanuck]

Since pool was built last summer, my Intelliflo was running fine but always 1/4 full of air (down to water intake level). I had read here it meant I had an air leak. Discuss w/PB who dismissed it as normal byproduct of VSPs. I then read loads of posts on this forum stating that it's perfectly normal, with many ppl experiencing that while running their VSPs at low RPMs... so I gave up and let it be.

Wanted to post my experience, hoping it helps someone else, because I do not think it is normal and two seasons later I now fixed it (which itself I suppose proves it isn't normal - meaning you shouldn't have a ton of air in your pump just because you run it slow). It bugged me so much that, after all sorts of soap and shaving cream tests, I took apart every single piece of equipment and plumbing - cleaned, lubed and tightened everything back up. And voila, the Intelliflo now runs with a basket completely full of water at my regular low speed (25GPM). There are a couple tiny bubbles in there, and they do seem to grow in size over time a bit, meaning probably there's still some air leakage somewhere else I still haven't fully addressed, but I went from 25% air to maybe 0.05% air in the basket now.

In my case, properly lubing/tightening all parts might have marginally helped, but I found that the main air gap was at the intake of Intelliflo where the suction-side union is. I had only ever checked/tightened the union and its o-ring (and clearly so did the PB who installed it last year and checked it thereafter). But today I noticed that the smaller threaded section of PVC that screws into the pump was not very tight and had another o-ring on that side too (sealing it to pump). In my case, that was it. Made the difference between pump running 1/4 to 1/3 full of air at all times, to now being just water.

So, no. Don't believe that you should have air in basket just because your VSP runs slow. I think the folks who say that just haven't found the cause yet. (Now maybe the air in basket doesn't materially affect performance/reliability and you can safely ignore it - that I don't know - but it's not a feature of a VSP!)

 

[kimkats]

Thank you for posting this! I like your title name as that should help when people search for this problem.

 

[JoyfulNoise]

I always have a small’ish bubble of air (maybe 1 cup worth) in the wet end at low speed. It goes away at high speed. I consider it normal as the design of the wet end is such that any air sucked into the intake will float to the top of the pump strainer and not move unless the flow is high enough to pull it down. I’m willing to bet that the design of the IntelliFlo wet end exacerbates the problem and that other pumps with different shaped wet ends probably have better results.

I have no unions on my suction or discharge pipes. Unions are fine for pressure applications but the standard SCH40 PVC Union on the suction end is a leak waiting to happen. There is one thin o-ring between the vacuum forces of pump and atmosphere and the union nut thread is very coarse. They really aren’t well suited for that application. My suction side threaded pipe was installed with the gasket and the thread was sealed with Teflon tape and Teflon paste. There is a thick bead of it around the pump intake connection.

But I agree - a small bubble of air is normal, 1/3 the strainer full of air is not normal at all.

 

[MITBeta]

Don't believe that you should have air in basket just because your VSP runs slow.

I have long thought the same. I re-lubed my union gaskets a week or so ago and the air in my pump went away at low speed.

 

[MostlyCanuck]

I always have a small’ish bubble of air (maybe 1 cup worth) in the wet end at low speed. It goes away at high speed. I consider it normal as the design of the wet end is such that any air sucked into the intake will float to the top of the pump strainer and not move unless the flow is high enough to pull it down. I’m willing to bet that the design of the IntelliFlo wet end exacerbates the problem and that other pumps with different shaped wet ends probably have better results.

I have no unions on my suction or discharge pipes. Unions are fine for pressure applications but the standard SCH40 PVC Union on the suction end is a leak waiting to happen. There is one thin o-ring between the vacuum forces of pump and atmosphere and the union nut thread is very coarse. They really aren’t well suited for that application. My suction side threaded pipe was installed with the gasket and the thread was sealed with Teflon tape and Teflon paste. There is a thick bead of it around the pump intake connection.

But I agree - a small bubble of air is normal, 1/3 the strainer full of air is not normal at all.

I haven't added teflon paste/sealant to the threads when putting it back together (don't have any) but will do eventually. Definitely better practice.

 

[JoyfulNoise]

I haven't added teflon paste/sealant to the threads when putting it back together (don't have any) but will do eventually. Definitely better practice.

I learned the trick from a very old plumber. You wrap the threads in 2-3 layers of tape and the you smear a nice layer of Teflon paste on the taped threads (don’t get it on the end of the thread to avoid it getting into the pump). That way, when you tighten it down the tape makes a good seal seal against the pipe and the paste fills in any voids between the threads and the mating surface on the inlet opening. Pipe threads are a tapered conical shape so that when you tighten them down the male threaded end gets compressed by the female opening. This ensures that a tight seal is made. Adding tape and pipe sealant ensures that all internal voids are sealed because the threading is never perfect and there can be mismatches.

I have done this on every water pipe I have ever worked on that was threaded and I have never had a leak.