Float valve causing pump cavitation?


New member
Mar 12, 2014
United States
Just moved into an older home which has a pool. Noticed the float valve was missing from the skimmer (standard 2 holes: main drain and pump suction), so I ordered one. This is the first pool I've had which has a spa, but the valve arrangement looks pretty simple: supply side can be from the pool or the spa drain, and likewise the output can be adjusted between the pool and the spa jets.

Question: The float valve arrived today, so:
  1. I adjusted the control flap underneath (usually I leave it 50% open so I get some pull from the main drain),
  2. Put it in the skimmer, and
  3. The pump noise level immediately elevated.
It sounds like vibration (cavitation?). I don't understand the problem though, since if for some reason the MD were blocked or clogged, then the flap is only at 50%, hence plenty of suction through the skimmer is available.


Rancho Cost-a-Lotta

Silver Supporter
TFP Guide
Apr 10, 2018
Rancho Cucamonga, CA
Pool Size
Salt Water Generator
SWG Type
CircuPool RJ-45
I've found that if the pump is running at higher speeds, the float can be pulled down and closed, blocking off skimmer suction. Seems to happen most frequently when dropping in the diverter while the pump is running.


In The Industry
Jul 14, 2014
With the pump running and making the noise see if you can remove the float valve. If it is very difficult the float has closed and your pump is attempting to pull off the main drain exclusively. Most older pools have main drains that are slightly or completely blocked. That can be one of the causes for the cavitation issue.


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

I don't see the point of adding the float valve.. Most pools don't ever need a main drain and I have never had good luck them. I have two rent house pools that have no main drains and they work just as well as a pool with a main drain.

I'd just take it out. You will never even know it is missing. :mrgreen:


Jim R.
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