Pump sucks air every 15 seconds

[johntate]

Hi, I live in malaysia where there are no Pool Supply Stores and advice is extremely limited, so hope someone can provide some help.
I have an inground concrete, tiled, free form pool approx 28,000 US gallons.
The pool perimeter has about 90% of its length with an overflow edge (approx 150 feet) and is raised 9 inches above ground level. There is a concrete gutter drain to the balancing tank.
The balancing tank is approx 4 feet deep and holds over 700 gallons. It is around 50 feet away from the pump room and the suction pipe is 4 inch diameter up to the pump room where it reduces to 2 inch.
The filtration pump is a 2 HP Pentair Whisperflow pumping to a S900 Waterco sand filter. There are 2 vacuum points, one main drain point and the balancing tank connected to this pump. Normally I operate the pool with the main drain valve set about 70% open and the balance tank 100% as it seems to give good circulation and keep the overflow edge nicely wet and the pool clean.
The problem is that every 15 seconds there is a puff of air coming into the pump leaf basket, then a little turbulent water then totally calm (no air) for another 15 seconds. When I fully open all of the valves there is no sign of any air.
The pool is about 1 year old and has done this from the beginning but is now annoying me that I am unable to find any leak or solve the problem.
One further point is that I do get some air rattling from the filter return to the pool but not when its on recirculate. When I release the pressure guage only water comes out - no air.


Any, ideas, help, etc. would be appreciated.

John

 

[Bama Rambler]

Welcome to TFP.

It has to be a suction side leak. It may not be leaking water but when under suction it's leaking air. How far is the surge tank level above the pump suction? Does the pump suction ever create a vortex in the surge tank?

 

[johntate]

Dave,
Thanks for reply.
The water auto leveller keeps the surge tank filled to a level about 30 inches below the pump suction intake.
However when we get a tropical storm (regular) it fills very quickly right up to the overflow which is just below ground level and therefore about 6 to 9 inches below the pump suction intake.
I still get air sucking into the pump even when the surge tank is full to the top, thus eliminating the non-return valve connections in the surge tank as a source of leak. I have never seen any signs of vortexing in the surge tank even when level is low (when I have lowered the level to clean it).
That leaves only 3 off, 4 inch 90 degree bends and one straight connector to the pump room.
Fortunately they are under the garden (lawn) and I dug them up to check for leaks.
At first I suspected one connection as the ground was wet around it but left exposed for a few days there were no further signs of leaks.
I have checked all the 2 inch connections in the pump room.

If you rule out anything to do with the surge Tank and vortexing then it has to be a suction leak.
Why then is there 15 secs of calm water followed by a puff of small bubbles followed by turbulance then back to calm water again.
Its a constant cycle.

Actually I feel better about it already just being able to discuss it with someone.

It is not affecting the performance of the pool nor the pump but I like things to work correctly.

John

 

[Bama Rambler]

The water auto leveller keeps the surge tank filled to a level about 30 inches below the pump suction intake.
However when we get a tropical storm (regular) it fills very quickly right up to the overflow which is just below ground level and therefore about 6 to 9 inches below the pump suction intake.

I hope you mean that the water level stays above the pump suction at all times.

Why then is there 15 secs of calm water followed by a puff of small bubbles followed by turbulance then back to calm water again.

It actually makes sense that it runs in cycles.

Here's the scenario.

1. The pump is pumping water so the suction head is strong thereby causing the "leak" to open and suck air into the piping.[/*:m:3vjltdtr]
2. The air reaches the pump causing it to partially lose prime, reducing the suction head, causing the "leak" to stop sucking air.[/*:m:3vjltdtr]
3. The air is discharged from the pump filling it with water again, which raises the suction head.[/*:m:3vjltdtr]
4. The increased suction head opens the "leak" and it sucks in air again.[/*:m:3vjltdtr]
5. The viscious cycle repeats.[/*:m:3vjltdtr]

Does that make sense?? That's why I asked about the vortex. That's also why when you open both valves 100% it doesn't suck in air. By opening both valves 100% you're reducing the suction head.

I'd give the place in the plumbing where you found the dampness a good going over again. Air is a lot easier to suck in than water is to leak out. It's very possible to have a suction air leak without any water leaking out.

Just as a matter of due diligence; You are sure that the air isn't coming in the pump strainer basket lid? You have removed it and cleaned and lubed it with silicon pool lube, right?

 

[4JawChuck]

What kind of valves do you have?

If there are gate style valves in the system the packing gland may need a tightening, a gate style valve has a rotating knob that raises and lowers the gate requiring multiple turns of the wheel to close. Balls valve usually don't have this issue unless they are very worn but can cause a suction side intermittent air leak as you describe.

You can easily test for air leaks at the valve by tightening the gland follower nut on gate style valves or by spraying a soapy water solution on a ball valve and look for foam in the pump basket or a reduction in air infiltration. If its a ball valve leaking you need to replace it, there are no adjustments available on this valve type.

 

[johntate]

Dave,
Sorry for the confusion. It is the pump itself that is 30 inches above the surge tank water level. The suction pipe normal intake level is around 24 inches below the water (more when it rains).

Thanks for the scenario on the air cycles - it makes perfect sense.

I have 3 Pentair pumps (waterfall & Fountains, Spa, and Filtration) and have changed around the basket lids so i am sure it is not the cause.

Looks like I need to dig up the lawn again and upset my wife.
Also I dont fancy messing around with the 4 inch pipe connections.
The plumbers seemed to have a difficult time with it.
Maybe I can find someone to run a plastic weld around all of the 4 inch fittings.

Once again , many thanks.

 

[johntate]

The valves are Ball valves.
I decided to replace them last week but the result was exactly the same.
That was what led me to this Forum.

 

[johntate]

I exposed all of the 4 inch pipework fittings and no sign of any leaks.
Out of curiosity I blanked off the surge tank overflow and let it fill to the very top.
The suction intake was then 48 inches below water level.
Fantastic - No Air whatsoever - just a very calm leaf basket.

The suction pipe is vertical with a non-return valve at the bottom and a 90 degree bend at the top.
Thinking I might have a leak on the bend I lowered the water level to normal and covered the 90 degree bend connections with expoxy putty.

After it cured I started the pump again and air was present once again.

I now think it has to be something to do with the head of water above the suction intake in the surge tank. It must be vortexing although nothing is visible.

Any comments on this?

 

[PoolGuyNJ]

Do you have a negative edge or gutter pool?

"If you rule out anything to do with the surge Tank and vortexing then it has to be a suction leak.
Why then is there 15 secs of calm water followed by a puff of small bubbles followed by turbulance then back to calm water again.
Its a constant cycle."

What is the filter pressure during the "calm water" period?

 

[johntate]

Its actually both (or neither).
The pool perimiter is almost a complete (over 90%) overflow edge and is 9 inches above ground level. The pool overflows the 9 inch wall into a gutter drain which runs around the periphery of the pool and returns water into the surge (balancing) tank.

The filter pressure is steady all of the time. There are some air rattling sounds from the filter return line.

 

[gordiec]

Any chance the non-return valve is causing the problem?

 

[Bama Rambler]

Here's what I thought of. You have a suction side piping leak and when you fill the surge tank completely full, the positive head created by the water is enough to keep the suction from sucking air into the leak. Did I make any sense with that explanation?

 

[PoolGuyNJ]

Do the gutters feed directly to the surge tank or the 4" drain line?

Scott

 

[johntate]

'Here's what I thought of. You have a suction side piping leak and when you fill the surge tank completely full, the positive head created by the water is enough to keep the suction from sucking air into the leak. Did I make any sense with that explanation?'

Absolutely correct. I found the leak and your above suggestion is exactly what was happening.
Leak now temporarily fixed and I cannot stop watching the leaf basket which of course shows no movement whatsoever.

Thanks for keeping me on the right path. I thought I had uncovered all of the connections but my wife remembered one more and sure enough there was a small leak.