Elusive suction side air leak

[Kevin Gobeil]

I have been struggling to find an air leak that is allowing air into the system. I've checked all the usual culprits and have not located the leak, so I'm looking for any other advice that the forum may offer. The symptoms are seeing air in the pump strainer basket during operation with air continuing to enter the system and losing the pump's prime after the system has been shut down for a little while. I also have a small water leak at the mechanical seal (Pentair whisper-flo) but I believe this is just collateral damage from the pump starting each morning without being primed. I'm hoping to address the air leak first and then address the mechanical seal so I don't just burn up another one.

First, I'm confident it's a suction side leak because it is pulling in air during operation (see air in pump strainer and every few minutes you can bleed air off built-up air from vent on top of filter). So far I've:
- smoke tested to see where smoke may be pulled in during operation, no findings.
- I've run the hose on all the suction side fittings to see if the leak stops, no findings.
- I've proactively replaced the shaft seal O-rings and body O-rings on the 3 Pentair diverter valves on the suction side
- I've replaced the pump strainer basket o-ring, inspected the cover for cracks, heavily lubricated it and carefully tightened, several times.
- I've replaced the O-rings on both pump plugs (strainer basket and main pump body plugs)
- I've removed and replaced a bead of silicone that I have where the male adapter threads into the pump inlet (previous known leak point, annually I strip and replace with fresh silicone). Just in case, I also put a bead of silicone at each fitting interface on the suction side.
- I've cycled the valves on the suction side to prove that it's not in the underground piping either, unless 3 different underground lines all have leaks (impossible)
- The suction piping coming off the pump splits with a 3-way diverter valve, with one side going to the spa and one side going to the floor drain and vacuum line (separated by a diverter valve). No matter which way I position the downstream diverter valve (spa on or floor drain/vacuum on), the air in-leakage persists, this tells me it's not an underground line that is the issue (unless all 3 are leaking which is not probable) and that the issue is isolated to the area between the closest valve to the pump, the 1 foot or so piping between that valve and the pump inlet, and the negative pressure portion of the pump itself.

Only other things I can remotely think of:
- The main drain and spa both have vacuum breakers, but with the valve configuration I can isolate one at a time with no change in the air leakage rate, so unless they're both leaking air at the same rate they can be excluded (very unlikely).
- Is it possible my mechanical seal leak is somehow letting air in? (even though it is dripping water out since it's on the positive pressure side of the pump)
- Crack in the pump housing on the negative pressure side - I've looked visually and can't see anything, doesn't leak water when pump shutdown either.

Any help would be greatly appreciated as I am losing my patience with this thing.

 

[mknauss]

You have done some testing! Can you fill out a signature so we have a better understanding of your pool equipment?
See Pool School - Getting Started

What about the drain plug on the pump? Would be odd but seems about the last thing ----

Take care.

 

[JohnT]

The basket drain plug is a common culprit like Marty said. Another trick is to cover seals on the suction side with shaving cream. The air leak will create a small void in the foam.

Any water spits or drips when the pump shuts off?

 

[Kevin Gobeil]

Thanks MK and John, I’ll try to fill out a signature tomorrow. I think my pool is ~12k gallons, gunnite, Pentair whisperflo pump, with spa, Pentair 48 cu. ft. DE filter.

As for the drain plugs, I put a new o-ring on the basket plug and on the pump plug. I also don’t see any water spitting or leaking at shutdown. I like the shaving cream idea, I see the wife went crazy on 2 for 1 whipped cream so I may douse the inlet fittings with that tomorrow, good idea.

Here’s something else I didn’t mention because I believe it’s either unrelated or collateral issue caused by the suction side leak and loss of prime after shutdown, but here it is: 2 months ago I noticed that in the mornings prior to the system starting up the water level in the spa had dropped several inches overnight (I keep the supply valve to the spa about 1/4 open with the drain valve closed, letting it overflow into pool). I noticed the finish on the top step starting to chip from getting dry then wet each day. As a test I closed the supply valve to the spa prior to the pump shutting down the next day. The next morning the spa level had not dropped so this told me the check valve in the supply line to the spa was leaking, so I replaced it. The new check valve worked for 2 months but now I find the spa level dropping overnight again. I’m not too excited about this yet since the system can act strange until I get the suction leak fixed, but figured i’d Put this out there in case somebody sees a connection i’m missing.

 

[Kevin Gobeil]

Tried shaving cream on all joints and valves above ground on suction, nothing. Thinking it must be something with the pump strainer lid, removed it again and cleaned, inspected very closely for cracks, lubed o-ring again, and ground off corner of stop on lid retainer so I could crank it down a bit further, reinstalled clocking it a bit further/tighter than before. No change, still pulling air into basket from somewhere. I’m beyond frustrated at this point. I guess I may just replace the lid, can’t think of anything else to do...

 

[Texas Splash]

Personally, I found the shaving cream to be a it messy, and if the leak is very (very) small, it might be tough to notice a difference in the cream pulling/sucking in. Just me though. The smoke can also be tough unless it's a pronounced suction leak as the smoke might just blow away. Have you tried plastic wrap? It's not perfect either, but you can wrap some parts and then easily remove it once finished. Once I went so far as to wrap my entire basket lid to rule-out that area when nothing else (even water from a hose) seemed to work. At this point I figure you could try any options. Even though you've worked the 3-way valve, maybe plastic wrap can show a difference. As a very last resort, if you have nothing else to go on, you could always grab some spare pieces of PVC and a union, then run it directly from the pump intake, above ground, and straight into the water. This way you rule-out absolutely everything else - even underground. I understand your thoughts about all 3 pipes not leaking simultaneously, so that's why I mention it as a last resort. When all else fails, you can try this ......

 

[JamesW]

Try pushing water into the pump from a skimmer. That way the suction is under pressure and a leak will be obvious.

Rig up a garden hose into the skimmer hole with adaptors and push water through the system.

Make sure that the water can flow through the system because city water pressure can be too much for the equipment if the water is blocked

Or, just pressurize the system to about 10 psi to see if the leak becomes obvious.