Swimming Pool Mystery - PVC pipe deforming

[MotoSook]

I have an in-ground and indoor pool. I have a bit of a mystery that my preliminary Google search hasn't turned up any potential cause or solution.

Last year I had a problem with the sand filter multi-port valve leaking. To fix it I had to cut the old PVC pipe off and re-plumb with new PVC.

But before I go further let me add some history. The pool liner was replaced before we bought the house. That was about 3 yrs ago, so the liner is probably no older than 4 years old. After the first winter, I noticed the liner was bunching up in certain areas. The liner was not coming off the wall, and it was not bubbling. Just wrinkling. I thought that was odd and figured the liner was just too loose on initial install since it isn't pulling away from the perimeter of the pool.

We have well water that is considerably hard with H2S which we treat to eliminate the H2S and that smell. Because of the hard water, the alkalinity in the pool water is always high, but I keep the PH and Chloride level in the safe range according to the test strips.

After I fixed the leak last year everything worked fine until the PVC pipe started to deform. The span of the PVC isn't long, and I used plenty of fittings to make the connections, so I can't blame span for the drooping that the pipe developed. The pipe eventually droop/deformed enough to twist the multi-port valve off the sand filter housing. Even the fittings were deforming. It was toward the end of the season last year, so I just said screw it. I though maybe the Chinese made PVC I got from Menard was to blame. This is regular PVC, schedule 40.

So about about 10 days ago, I installed a new sand filter, new sand and new PVC plumbing. I bought PVC from Home Depot this time, Eagle, IIRC, made in the US.

Everything seemed to be fine, and I ran the pool 24/7 for almost a week after shocking. The pool temperature was about 60F, but I ran the heater during those 5 days. Eventually the water got to 80-84 degrees F and the water cleared up.

The last few days we've run the pump to cycle the water and during swimming.

3 days ago, I went swimming with the kids and turned the pump on. Didn't notice any drooping of the PVC. 2 days ago, the pool didn't run at all.

Last night I was on my way home from work and called ahead to have the kids turn on the pump. I didn't go check on it when I got home, but after dinner one of the kids came down to my shop to tell me there is a puddle of water in the pool room. I go to find that the pipes drooped and pulled a couple connections loose and water was spraying everywhere.

The water temperature isn't high enough to soften the PVC, and other than high alkalinity and high Chlorine from the shocking, I cannot figure out what is causing the PVC to soften.

Has any pool owner experienced this?

Any chemist or Chem E have ideas? PCV should not react with the level of chlorine in the pool water. What else could be causing a chemical reaction?

The pump, filter and heater are in a small "closet" within the pool room, but the temperature in there isn't so hot that I expect to see PVC soften. The old PVC seems fine, but all the new fittings and pipe are affected.

Solve my mystery! Please.

[Rot 911]

What diameter is the PVC?

[cstreit]

The simplest explanation is the best.... Heat. Nothing else other than a solvent will soften a PVC pipe. I think Chlorine tends to make it more brittle over time no?

Is the heater before of after this pipe? I'm betting before and that the water coming out is hotter than you think?

[Cajundaddy]

Heat from an older gas heater. When your system shuts down with the heater running, water in the heat exchanger is boiling and migrating back through the plumbing and thermo-forming the pipe. Add a fireman's switch to your timer that will shut the heater off 30 minutes before system shutdown. Always shut down your heater first and allow a 20 minute cool-down period before system shut down.

Modern pool heaters don't retain heat in the exchanger to the same degree so when you upgrade you will no longer have this problem.

[MotoSook]

Kurt, it is 1-1/2" PVC.

Chris, the PVC before and after the heater is drooping.

It's 82-86F before the heater. Flow goes from the three valves in the foreground through pump, then through filter, then to heater.



This is just after I re-plumbed. I'll take a picture tonight of the current condition.

[MotoSook]

This is the most plausible! I should have thought of it! Anyone want a slightly used engineering degree? I don't deserve to hold on to it


THANKS!

Originally Posted by Cajundaddy

Heat from an older gas heater. When your system shuts down with the heater running, water in the heat exchanger is boiling and migrating back through the plumbing and thermo-forming the pipe. Add a fireman's switch to your timer that will shut the heater off 30 minutes before system shutdown. Always shut down your heater first and allow a 20 minute cool-down period before system shut down.

Modern pool heaters don't retain heat in the exchanger to the same degree so when you upgrade you will no longer have this problem.

[Cajundaddy]

That is an old Laars Series One heater that is famous for melting pvc on shutdown. Installation instructions called for 5' of copper in and out of the heater as a heat sink.

[porsche4life]

A new heater would be cheaper than 10' of copper that big wouldn't it?

[MotoSook]

As long as you're paying attention, perhaps you can help with another potential headache.

See the pipe going into the sand after the heater? I'm getting water around it and suspect a fitting is leaking. I'm hopeful the leak is not under the concrete and I can repair it.

If I have a leak under the concrete, is there a method to replace the pipe under the concrete that doesn't involve a concrete saw and a lot of dust (e.g. lining it)?

[JeremyD]

Use schedule 80 PVC - schedule 40 - or even plain jane PVC is cheaply made and has very little temperature tolerance. (especially the crap that they sell in bulk at HD and Lowes)

[nota]

Originally Posted by MotoSook

As long as you're paying attention, perhaps you can help with another potential headache.

See the pipe going into the sand after the heater? I'm getting water around it and suspect a fitting is leaking. I'm hopeful the leak is not under the concrete and I can repair it.

If I have a leak under the concrete, is there a method to replace the pipe under the concrete that doesn't involve a concrete saw and a lot of dust (e.g. lining it)?

little smaller dia pipe inside the old pipe if not flow volume critical
1 1/2 fits inside 2''
and up the pressure [better pump or bigger upstream pipes] if flow volume is needed
and relooking that is the heater in water so very volume CRITICAL

there maybe guided drilling rigs that small but I have not seen them
is there more room on the other end for a drill rig?
btw it will not be cheap!!!!!!!!!!

[Cajundaddy]

Originally Posted by MotoSook

As long as you're paying attention, perhaps you can help with another potential headache.

See the pipe going into the sand after the heater? I'm getting water around it and suspect a fitting is leaking. I'm hopeful the leak is not under the concrete and I can repair it.

If I have a leak under the concrete, is there a method to replace the pipe under the concrete that doesn't involve a concrete saw and a lot of dust (e.g. lining it)?

There are leak repair specialists that add liners but I probably would not. If the equipment is below the water level in the pool and you are only seeing dampness I would ignore it. You are not losing much water at that leak. If you see spraying/puddling it needs to be fixed because it will begin to hollow out around the plumbing. Residual heat from your Series One heater probably deformed that fitting as well.

If it were mine I would just bust the concrete around the pipe and replumb. It will go faster than you think and you will get good exercise in the process. A concrete chisel and a 3lb sledge would make short work of that replumb job.

[eastbay]

Originally Posted by Cajundaddy

That is an old Laars Series One heater that is famous for melting pvc on shutdown. Installation instructions called for 5' of copper in and out of the heater as a heat sink.

This is spot on... you can put in copper or steel or do the usual swimming pool thing and use 12" or more of CPVC at the inlet/outlet of the heater. Ask for it at your pool store.

[NY65912]

Best to use CPVC stubs out of the heater. Be careful though, you need a cement good for both PVC and CPVC. I had the same heater and it required CPVC nipples at the heater. I would not use metallic piping due to the introduction of metals into the water over time.

[MotoSook]

I really appreciate the input guys.

I just placed an order for $190 worth of Sch 80 CPVC pipe and fittings from McMasterCarr.

Will be headed to "Will Call" after lunch. Hope to have it done today.

Yes...I will be using proper CPVC/PCC compatible cement.