New Member Trying to Chase Down Lost Prime

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SoCalGuy

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Nov 16, 2015
171
San Diego
Hello all, new member here in San Diego looking for some advice and suggestions in tracking down why our filter pump is losing prime.

Pool was built in 2004 and has been a lot of fun for the family over the years. The equipment's been solid and reliable and it's required nothing beyond the usual maintenance. But now that it's almost a dozen years old, we've started to get a loss of prime issue.

Our house is on a hillside and the pool sits behind the house on the downslope. The equipment is located on the side of the house, about 6-8 feet higher than the water level of the pool.

The filter pump began losing a small amount of prime about year ago, but it was always able to prime itself after less than a minute after starting up. I kept an eye on it and figured I'd get to it after summer. Well the time has come. A couple of weeks ago, I found the pump basket drained and the pump will no longer prime itself.

And I have a devil of time getting it primed. I have to pour a couple of gallons of water into the pump, start it, pour a couple gallons more more, start it, gallons more, etc. Once it starts up, a ton of air bubbles come out of the pool. Once primed it works fine. Pressure is ~ 15-18psi.

It loses prime regardless of whether suction is set to "Pool" or "Spa".

I've tested all unions with soapy water and can't see any leaks. I replaced all the filter o-rings, replaced the pump lid o-ring and replaced the o-rings in all the Jandy valves.

The filter pump is a bit noisy, but not unusually so. Once everything is up and running, there are bubbles under the pump lid. Also, it sounds like air is rattling through the pipes.. I can't pinpoint where exactly.. somewhere on the return side of the filter around the heater. This must mean air is entering on the suction side, correct? Bad pump housing or pump shaft seal maybe?

We have in-ground check valves going to the skimmer, spa and the water feature. These are the only things I haven't really tested or checked - because I don't know how. Is there a way to test these? Or should I just pull them, clean them and replace any rings that look suspicious?

Thanks in advance all!

pool.jpg
 
priming a pump 8 feet above the water level is a challenge. That you have been able to do so is a testament to good construction. I would put a check valve on the line(s) that come up to the pump from the pool. That will allow the water to stay in the pump and be ready when you turn it on.
 
Thanks duraleigh, yes it's a well built pool... a lot of thought went into it beforehand and our contractor was a good guy, didn't cut any corners.

As for check valves, as I mentioned, we already have them. They're the "flapper" kind ... sit in the ground between the pump and the pool, like this:
View attachment 43964
4182DrbawkL._SY355_.jpg

I guess I have two questions: Would the "flap" failing cause the pump to lose prime? And would it allow air enter the system?
 
sit in the ground between the pump and the pool, like this:
Click to expand...
Hard to say where that is based on your description. Are they at the level of the pool or the level of the pump?

While the flapper does not cause loss of prime (working or not) somewhere in your system is an air leak that is causing your loss of prime. The check valves are to prevent the water draining away from the pump which it would NOT do if there was no air leak.

There is an article in Pool School on suction leaks which may help. Based on the info you have provided so far, it is possible (but not likely) the leak could be on the pressure side, too.
 
Thanks again, appreciate the input.

The flappers are down by pool. I pulled them yesterday. They look a little ragged around the edges but not terribly worn, and they still open and close.

I'll get new ones, but I think you're right, even if they aren't sealing 100%, the only way water could gurgle back down through them would be if air is getting into the system somewhere. Could air be entering where the lid screws on? There was no o-ring under any of the lids, which seems a little odd, but maybe that's the design?

I read the section about Suction Leaks, and now I'm really scratching my head. It seems to say prime loss can only be caused by air leaks on the suction side.

You mentioned the possibility of a pressure side air leak. Doesn't air have to be getting in somewhere in front of the pump? How could a return side air leak affect prime and where would you start looking? There is no water leaking anywhere around the equipment.

In a set up like ours where the equipment is way above the water level, I can see that gravity is always trying to pull the water back down into the pool. It's like holding water in a straw by putting your finger over the top. The water should stay in the "straw" unless it has a hole in it (yikes!) or air is coming in somewhere on the suction end.

It's a brain teaser.. thanks for the help. Great site you have here!
 
It seems to say prime loss can only be caused by air leaks on the suction side.
Click to expand...
pump running , that is true.

That said, a pressure side leak can allow prime to drop with the pump off.

Let's say you have a pinhole leak on the pressure side and you cannot see water coming from it (pump on). When the pump shuts off, that leak now allows air into the system causing the water to drain back to the pool (like taking your finger off the end of the straw, in a way).

Then, you cannot restore prime because the 8-9 foot lift is simply too much to overcome.
 
Hello SoCalGuy and welcome :wave:

I see you've tested the connections from the pool to the pump.
Have you checked the pump itself ?(i.e. drain plugs at pump and strainer basket. also retaining clamp and gasket around impeller between pump and basket.)

The pump noise could be cavitation from air.
I wonder if there is an air leak at the pump if it would allow water to drain back to pool or should valves keep that from happening ?
 
Ok, so I've got the local pool store lady looking for some replacement flappers. Apparently they're not something they keep in stock.

Meanwhile I'm trying to decide what to check next.

durleigh: I can see how with the pump off, even a pinhole leak air on the pressure side could allow the return lines to drain. What I don't get is how air coming in the pressure side could drain the suction lines. The air leak would have to get past the pump, wouldn't it?

lefty51: Yes, the noise I'm hearing sounds exactly like cavitation. I can also clearly see air bubbles moving thru a couple of the clear valves on the return side. So what does that mean? That the pump is definitely sucking air?

I replaced the pump drain plug o-ring a while back, along with the lid ring. I haven't taken the pump apart yet, but that's where I think I'm going next.

It seems logical that some pump seals could be worn. The pump does get a lot of use. Also, the pump loses prime overnight regardless of where the suction valve is set, so I don't think it's the valve.

Good question whether the Jandy valve would stop an air leak from the pump. I'm sure they're water tight but air tight, I don't know. I put soapy water around all the valves with the pump on and didn't see any bubbles or notice any change in the pump action or sound.
 
So basically a leak at ANY connection - suction side or pressure side - could be the of source of the pump draining overnight. Great.

Other than just pulling things apart and replacing parts at random, is there a logical way to go about pinpointing where the air is likely to be coming in?
 

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Dave is right about pressure side leak. With the distance between flap valve and pump, plus the uphill grade, when pump is shut off enough water will run back down hill to expose pin hole leak even at pump. And just like house plumbing, air behind water would let more water run down hill, even with good flaps. If they are not water tight then all water would return to pool.

But, what I'm wondering, with cavitation in pump and air in lines, I think your definitely drawing in air on suction side. If your pump has a clamp around pump halves, you might check gasket and whether the clamp has worked loose. I tend to think pump impeller is okay, because if it is sealed properly it shouldn't draw air, just pump poorly.

Also my pump is 17 years old and although I've replaced the motor, pump is still working like a champ.

One more thing, my pump has a drain plug at the pump housing AND one on the bottom of the strainer basket. I also had the jandy valve that controls the two bottom drains that allowed air in one spot only and was hard to isolate. That was before this great sight and their tricks like using shaving cream for leak detection :D
 
Hey thanks OPM, appreciate the tip. I'm still waiting on the flapper kits. I try to throw some business to the local mom and pop pool store whenever possible. It's good to have them as an alternative to the big chain. "Cheap" is relative... ~$40 a kit is what I've been quoted. I'll give em another day to get em, then I'll hit the interweb. Should just be a standard Pentair 2" flapper, right?
 
Two valuable tools when looking for a suction side leak are shaving cream (the old fashion foam type) and plastic food wrap. You can smear shave cream on a suspect area and see if its drawn in and appears in the pump basket. You can wrap a suspected area with food wrap, providing a temporary seal which confirms the leak.
 
Quick plumbing question ...

Our vac hose plugs into the side of the pool, so it must share suction with some other inlet, correct?

When the suction valve is set to "Cleaner", and no vac is attached, where would it be pulling water from?

Thanks!
 

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