Major blowback every time I shut off the pump.

[TreeFiter]

There is a pool I service weekly, where there has been a problem with the system blowing back when it is shut off. Its a very unique pool. It appears to be a home made inground, where they built the walls out of cinder block and troweled a sand bottom. Then they put a vinyl liner in it. Instead of a skimmer in the wall, there is a small skimmer that is inside the pool and connects to an 1 1/2 port in the wall. There is one return. Hayward Super Pump with a Hayward Sand filter.

Every time the system is shut down, there is so much blowback the skimmer basket gets blown out into the pool. It seems to be air blowing back. When I turn it off and rotate the multiport to backwash, I get a blast of air out the waste line. So why is this pressure building up? I'm pretty sure the sand was changed in the filter within the last two years. The filter itself doesn't look more than a few years old. Pump was just replaced about a week ago. System seems to run fine until it is shut down.

Any ideas?

 

[JohnT]

Air leak on the suction side of the pump. Air accumulates in the filter and is compressed by the pump. When the pump shuts off, the air expands and pushes water out of the filter through any open line.

 

[TreeFiter]

Air leak on the suction side of the pump. Air accumulates in the filter and is compressed by the pump. When the pump shuts off, the air expands and pushes water out of the filter through any open line.

Why doesn't the air find its way out the return? I would think this problem would be more common if it was that simple. I mean if I let a pump take a gulp of air, the pump loses prime, but picks back up in a few minutes, and the air works its way through the system and out the return.

I think what you are saying makes sense, but I'm just not understanding what causes it to build pressure instead of being pushed out of the system.

 

[JohnT]

It is fairly common. Some filters just don't move the air through the system, especially with a constant source of air.

 

[TreeFiter]

I'm going to have to start looking for air leaks. It would certainly be nice to get rid of this problem. Having to fish the skimmer basket out of the deep end every week gets kind of old after a while.

Thanks for the input.