Mike the Poolman

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Pool pump struggling to prime? It might be Air Lock…

September 21, 2013

Is your swimming pool pump struggling to prime? It might be “Air Lock”. Air lock exists when the pool and spa plumbing rises above the horizontal inlet of the pool (or spa) pump.

Pool pump air lock illustration

In almost every air lock situations there is a three-way valve involved -yes I know, the illustration above doesn’t show one but its the only one I could find 🙂  .
I doubt the original plumber created your raised three-way valve manifold out of malice, but rather, because he wanted the valve to be more accessible and plumbed it high so you, the homeowner, wouldn’t have to bend those old knees over to reach a valve plumbed closer to the ground (I’m trying to stay on the bright side and hoping he did it out of ignorance, not negligence…)

In any case, the deed is done and the pump will struggle until its replumbed correctly (and the higher the plumbing, the more the pump will struggle to prime). My experience is when air lock is in action and the pump is struggling to prime, a surging action will occur that is visible- and audible- within the pump pot (if you can still see through the clear plastic lid).

Typically the pump eventually will prime, but not without heat being generated on the pump and fittings. Over time this heat creates vacuum leaks on the threaded inlet and the pump acquires another obstacle to overcome :(.

The inlet plumbing to a swimming pool pump shouldn’t ever rise above the level of the pump inlet height.
These photos illustrate poor plumbing and air lock in action, and, the same system corrected with proper plumbing:

Swimming pool plumbing, air lock - 1

Swimming pool plumbing, air lock – 1

Swimming pool plumbing, air lock - 2

Swimming pool plumbing, air lock – 2

Swimming pool plumbing, air lock - 3

Swimming pool plumbing, air lock – 3

Swimming pool plumbing, air lock - 4

Swimming pool plumbing, air lock – 4

Swimming pool plumbing, air lock - 5

Swimming pool plumbing, air lock – 5

Swimming pool plumbing, NO AIR LOCK - 1

Swimming pool plumbing, NO AIR LOCK – 1

Swimming pool plumbing, NO AIR LOCK - 2

Swimming pool plumbing, NO AIR LOCK – 2

Swimming pool plumbing, NO AIR LOCK - 3

Swimming pool plumbing, NO AIR LOCK – 3

By the way, air lock only exists on the suction (vacuum) side plumbing (before the pump). It is perfectly fine to plumb the return side (after the pump) three-way valves higher for easy access (knee height is ideal). Pumps are designed to push water more than they’re designed to pull (think of a dirty filter or a solar system on the roof) so plumbing the return side higher than the suction/ inlet side is acceptable.

I hope I have been of help.

Sincerely,
Mike the Poolman
Pool Service & Repair in Folsom, CA since 1995

P.S.
Thanks to Fred Hare, Sue Robach and everyone involved at the old Sta-Rite water hydraulics lab in Delavan, WI.
You are missed!

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