Major back pressure problem

Charlie-li · Postby **Charlie-li** » Sun 12 Aug, 2007 09:14

I'm using a standard sand filter & 2HP pump which I've had for a few years. Pressure normally runs at about 10-11lbs.

This year I encountered a problem which the pool store guys can't seem to figiure out. The pool filter goes on & off automatically for 1.5hrs, 4 times a day. Starting this year I noticed that when the filter cycles off there is a rush of water that comes up through the skimmer basket. This problem has been getting much worse over the summer. The skimmer basket literally blows right out of the housing and all the filth from the basket blows into the pool. If I backwash, the problem is eliminated only for one cycle and then returns.

I was originally advised that the sand was "bad" so I replaced it with 100lbs of new sand. That didn't work. Then I was told that the O rings on the control valve may be bad. I replaced them too but that didn't work either. Now none seems to have an explaination as to why this is occuring.

CAN ANYTONE HERE HELP ?

Backglass · Postby **Backglass** » Sun 12 Aug, 2007 10:09

Have you changed the height of any of your components compared to the pool level? Water runs downhill...you could put a check valve on the suction line to prevent backflow. Also the junk shouldn't flow back into the pool if you have a functioning wier flap...it's there to act as a kind of one-way gate, among other things.

If you put your filter on re-circulate, bypassing the filter altogether, do you still get the same rush of water?

harleyd · Postby **harleyd** » Tue 27 May, 2008 16:02

I have the same problem did you ever figure out what was causing it?

morrisss · Postby **morrisss** » Sat 09 Jul, 2011 16:16

I had the same problem. The cause is air in the filter tank which compresses to the normal back pressure of the filter system. When the pump shuts down you have 25 to 30 pounds of compressed air in the filter the blows back through the pump. The more air in the tank, the more blow back. My air in the system came from a loose fitting on the bottom of the skimmer basket, I thought that it was all one piece of cast plastic and could not figure where the air was coming from. Thought I had a bad seal on the pump filter basket but that was not it. I only realized that it was a separate fitting when I went to remove the hose and the fitting turned. Goofy thing is, I never saw any water leak out but it sure could suck air. Added teflon tape and tightened and problem gone.

Postby **czechmate** » Mon 11 Jul, 2011 22:46

You do not really believe this theory of compressed air inside the filter tank, that wil stay there for several hours, do you?
That air wil be forced out to the pool with a great force within 3 minutes and remaider will trickle out thru the fresh water inlets. The cause is an air leak in the system. Backwash valve, pump cover seal, filter ring seal, etc.