Violent back pressure when turning off pump - Best way to find leak???

Nov 20, 2017
22
Newcastle, Oklahoma
When I turn off my pool pump, I get violent back pressure through the suction side pipes out through the skimmer. From searching posts, I found multiple comments from duraleigh saying it's probably due to a leak in the suction side plumbing.

I know I have a leak because I'm losing water and I see a puddle near the skimmer/pump, so that makes sense.

My questions are...

Is there something I can do before turning off the pump to reduce the risk of damage until I get the leak fixed? Is taking off the skimmer lid and just letting it blow out probably the best I can do for now?

Any tips/tricks on finding the leak in the suction side pipes? The pipe from the skimmer to the pump is probably only 6-8 feet in length. It's flexible hose.

This is my first year in this house and with a pool, so I wasn't planning on redoing all the plumbing to PVC until the end of the season, just in case something didn't go as planned and it took a few days to get right, but maybe now is the time.
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
20,833
Bedford, TX
cc,

I don't have an immediate answer, but do have a couple of questions...

I just want to confirm that you have an Above Ground pool??? Is your equipment pad below the water level in the pool or is the equipment pad above the water level in the pool?

A picture of your set up would help...

Thanks,

Jim R.
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
20,833
Bedford, TX
cc,

Thanks for the pics...

So, when you shut off the pump the water blows the lid off the skimmer??? I'm puzzled as the would require water to flow back up hill... :confused:

Just so that we are both the same page... A skimmer is mounted in the side wall of a pool. A pipe leaves the bottom of the skimmer and goes to the pump input. After the pump input, the water passes through the pump basket and then into the pump.. Out of the pump into your filter and then back to the pool returns (eyeballs)..

Is that what you have or do I misunderstand your set up???

Thanks,

Jim R.
 

JamesW

TFP Expert
Mar 2, 2011
23,219
This happens when air gets compressed in the filter and decompresses when the pump turns off.

A check valve between the pump and filter would stop the backflow but it's not addressing the problem of where the air is coming from.

Also, the pump is oversized for the pool and filter.

What is the filter pressure?
 
Nov 20, 2017
22
Newcastle, Oklahoma
cc,

Thanks for the pics...

So, when you shut off the pump the water blows the lid off the skimmer??? I'm puzzled as the would require water to flow back up hill... :confused:

Just so that we are both the same page... A skimmer is mounted in the side wall of a pool. A pipe leaves the bottom of the skimmer and goes to the pump input. After the pump input, the water passes through the pump basket and then into the pump.. Out of the pump into your filter and then back to the pool returns (eyeballs)..

Is that what you have or do I misunderstand your set up???

Thanks,

Jim R.

Yes. When I shut the pump off it violently shoots water out of the skimmer. If the lid was just sitting on the skimmer and not tight, it would blow it a few inches off the skimmer.

Yep. That's the setup. Skimmer on side of pool...to pipe to pump basket....to pump....to filter...back in to pool via two returns. It definitely goes back uphill.

- - - Updated - - -

This happens when air gets compressed in the filter and decompresses when the pump turns off.

A check valve between the pump and filter would stop the backflow but it's not addressing the problem of where the air is coming from.

Also, the pump is oversized for the pool and filter.

What is the filter pressure?

It's a 33 ft pool with 2 returns. Do you think the pump is over-sized? I believe it's a 1.5HP motor from the numbers I can still read on it.

Filter pressure is around 18 PSI.
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
20,833
Bedford, TX
It's definitely oversized. You could operate easily on a 1/2 hp pump.

James,

Would it be a problem if he was not getting air into his system?... or is the air getting in because the pump is overpowered???

Jim R.
 

JamesW

TFP Expert
Mar 2, 2011
23,219
The air is from a suction side leak or maybe the skimmer is getting too much suction and pulling in some air.

Having an oversized pump will use too much power, will push water through the sand at an excessive velocity and can cause sand loss when backwashing.

If no air was getting in, there wouldn't be a huge blowback when the pump went off. There can be some backflow due to filter pressure but it shouldn't be dramatic.

With air getting compressed by the pump, there's going to be some blowback. The bigger pump creates more compression and a more dramatic blowback.

If there are about 2 cubic feet of air trapped in the filter under pressure, the air volume will increase by about 2 x when the pump is off. That's going to mean that about 15 gallons of water will be pushed as the air expands.
 
Nov 20, 2017
22
Newcastle, Oklahoma
James,

Would it be a problem if he was not getting air into his system?... or is the air getting in because the pump is overpowered???

Jim R.

This is a new problem that just started a few days ago, so the pump shouldn't be the cause of this issue if there wasn't an air leak. Before this, there was very little, if any, back pressure when turning off the pump.
 

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JamesW

TFP Expert
Mar 2, 2011
23,219
Look in the skimmer to see if there is air getting pulled in.

Maybe a vortex due to too much suction. Maybe the weir is getting stuck. Maybe the water is too low.
 
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