Violent backflush when pump goes off

Pool pumps, pool filters and the plumbing of
swimming pools. Sand filters, cartridge filters,
fabric filters and alternative filter media.

Violent backflush when pump goes off

Postby jaxpool » Thu 13 Sep, 2012 11:25

I have to physically prime my pump each time, and when the pump/filter ends it's cycle, get a violent backflush back through the skimmer and maindrain at the bottom of the pool.

Note: if pool is set to "RECIRCULATE", pump holds it's prime and no backflush.



Swimming Pool Pro
Swimming Pool Pro
Posts: 168
Joined: Sat 28 Apr, 2012 17:52
Location: Orlando FL

Violent backflush when pump goes off

Postby CGPoolman » Fri 14 Sep, 2012 11:36


Sounds like you have a lot of pressure building up in your system. When you set the valve to "recirculate" you are bypassing the filter. You're not having the pressure problem when you bypass the filter, so start there. If it is an older DE filter, you should open it up and remove the filter element so you can give it a real good cleaning. You should clean it all out with a hose and then soak it over night in a mixture of muriatic acid and water (approx 5 parts water to 1 part acid). You'll need a large plastic container to do this, you may need to dis-assemble the unit to soak the grids. Soak them for 24 hours, rinse it out real good, and re-install the grids. If that doesn't solve the pressure problem, you may need to replace the filter grids. There are youtube videos that can walk you through this as well.

Also - you may want to get a new tank o-ring for your filter before you open it up. If the o ring is old, it may not fit back properly and leak when you turn everything back on.

User avatar
Swimming Pool Pro
Swimming Pool Pro
Posts: 199
Joined: Tue 08 Sep, 2009 10:40
Location: Pleasanton, CA, USA

Violent backflush when pump goes off

Postby mas985 » Fri 14 Sep, 2012 13:42

Usually, when you get a burst of pressure back through the suction when the pump is turned off, it is because of a suction side air leak. Air is compressible while water is not so when air builds up in the filter and the pump is shut off, it releases that pressure back through the suction side of the pump in a burst of energy. You won't see it in recirculate because the air bypasses the filter and cannot build up.

Try lubing the pump lid gasket and pump drain plugs with silicone plumbers grease. Also, check the skimmer weir door and make sure it isn't stuck so the skimmer sucks air.
Hydraulics 101 ; Pump and Pool Spreadsheets ; Pump Ed 101
18'x36' 20k gallon plaster/gunite pool, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sq-ft Cartridge Filter, Solar Panels, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

Return to “Pool Pumps, Filters, Plumbing & Piping”

Who is online at the Pool Help Forum

Users browsing this forum: No registered users and 0 guests