Pump losing prime during pool drain

[bigmoguls]

I was trying to drain some water out of my pool to lower the CYA. I was using the main pump with the waste port on the filter plumbed for waste.

When the level dropped by 7", the pump started to cavitate. Why would this be the case?

 

[4knights]

Do you have the ability to switch where you draw water from? Main drain or skimmer? Sounds like you have dropped the water level below the skimmer and are getting air. If you can shut ff the skimmer and just draw from main drain you should be good.

 

[bigmoguls]

Do you have the ability to switch where you draw water from? Main drain or skimmer? Sounds like you have dropped the water level below the skimmer and are getting air. If you can shut ff the skimmer and just draw from main drain you should be good.

Sorry, I should have included that detail. I did have the skimmer valved off when draining. The water level drops below the skimmer intake after about 3-4 inches have been drained, I was able to go 3-4 inches beyond that before the pump started sucking air. It has to be something else.

 

[BigIslandPoolService]

Aloha bigmoguls!

I bet your pump is up above the pool water level, and as the water level drops, your pump has to work harder to pull the water up, and it eventually develops a suction leak somewhere, or just can't handle the pressure.

If this is the case, you can go to a local HD (the orange leviathan) store, or a "service rentals" establishment, and rent a gas-powered trash pump. Most of the rental units I use will pump out about 10,000 gallons in an hour, so you can get the job done quickly and cheaply!

Aloha!

 

[bigmoguls]

Aloha bigmoguls!

I bet your pump is up above the pool water level, and as the water level drops, your pump has to work harder to pull the water up, and it eventually develops a suction leak somewhere, or just can't handle the pressure.

If this is the case, you can go to a local HD (the orange leviathan) store, or a "service rentals" establishment, and rent a gas-powered trash pump. Most of the rental units I use will pump out about 10,000 gallons in an hour, so you can get the job done quickly and cheaply!

Aloha!

Yes, the pump is above the pool water level, it's hard to judge because of the distance and you can't see one from the other. Yesterday, I went to Harbor Freight and bought a 1/3 hp submersible pump for $65. It drains about 5"/hour. I was able to drain about 15" out yesterday. Now my CYA is a manageable 65, it had been over 200!

Thanks for the likely explanation.