Pressure testing new outflow PVC .. can't find leak to save our lives

[kbkbkb]

We have soaped multiple times, caught all the big leaks, but still can't find the apparently still existent small one(s). We even tried just adding a layer of glue to every joint and that didn't work, either. We're running out of ideas. Interested in hearing your suggestions and stories. When you couldn't find the leak anywhere, how did you end up finding it in the end?

 

[Gary Swart]

OK, I'll bite. If you had lots of leaks in a PVC drain, you must have really not had a clue about using PVC. Even one leak is hard to believe, but several? Starting from scratch. Understand "PVC glue" is not really glue. It is a solvent that melts the outer surfaces of the pipe end and interior of the fitting. You actually will be making a welded connection. First step is to prime the pipe and fitting. Then apply the solvent to the pipe end and fitting and immediately insert the pipe into the fitting. A slight twist as you insert is a good idea, but not totally necessary. Hold the pipe in the fitting for a few seconds until the solvent has begun to set. Otherwise, the pipe will push itself part way out of the fitting. Do not try to dry fit the pipe. PVC uses what is termed an interference fit and will not seat in a dry fitting. So, it's a cut, fit, glue each joint as you go. You can not just add more solvent to a bad joint. Going by what you have described, I think your best course of action is to cut every fitting off and start over. You will have to add pieces of pipe to make up for the loss from cutting the fitting. By the way, drains are not pressurize, but when assembled properly, they will not leak. I have PVC irrigation lines that have been in use since 1984 and not leaks yet. These lines are under reasonably high pressure when in use.

 

[Sponsor]

 

[Kreemoweet]

Pressure testing? Does that mean using compressed air? That is not a recommended method, and will often
have you chasing your tail until you finally tire of it all and revert to water testing or just declare it all
"good enough". Air pressure inside a pipe system varies with temperature. Filling with air from a compressor
(which is "hot") will immediately begin cooling off and dropping pressure. If using "foam core" DWV pipe,
air will travel thru the foam core from the pressurized area past any plugs, etc., and result in pressure drop.
Use water only for testing. Fill your system up to the roof vent, or a 10' temporary stand pipe above the section
to be tested. If it does not have observable leaking after a reasonable period, then you are good to go.

 

[hj]

Read the instructions. They say "Do NOT use compressed air to test PVC drain piping", for the very reason you are asking us about leaks.

 

[Jadnashua]

If a pressure test is required or wanted, often, you add a plug and fill it up with water. In a drainage system, there should never be any more pressure than being full of water, and that would only occur if there was a clog somewhere.

 

[Cacher_Chick]

Where I live it is common to do air pressure testing, even on PVC, which the manufacturers recommend against because of the shrapnel danger of bursting a damaged pipe or fitting. Most of the time it is done in new construction because the water is not yet on, but it is also used for additions and remodels when the new work will be tied into old work.
5 PSI is the max test pressure, and it is vital to seal the ends of exposed piping, such as where a closet flange or transition to c.i. is to be installed, as the air will pass through the core of the piping, so a test ball or cap is fruitless anywhere there is an exposed pipe end which is not sealed.

 

[Jadnashua]

5psi would be the equivalent of a little less than 12' of standing water.

 

[Cacher_Chick]

5psi would be the equivalent of a little less than 12' of standing water.

Yes, it is basically the same test as 10' head of water, but rounded off to a common pressure gauge spec.

 

[Gary Swart]

Not exactly to the question, but there seems to be an opinion that PVC can not withstand pressure. Not talking about compressed air at all here, but there must be literally hundreds of miles of PVC irrigation lines that operate under water pressure without leaks. My own sprinkler system was installed 33 years ago and still shows no leaks. Granted it's underground and is only pressurized for a few minutes per day, so perhaps a very minor leak might not show, but there is a portion of the system between the backflow and the valve control box that is under full pressurization for the entire season and it has never leaked. I must maintain as I stated in my original reply that a properly assembled PVC line should never leak.

 

[Gary Swart]

Not exactly to the question, but there seems to be an opinion that PVC can not withstand pressure. Not talking about compressed air at all here, but there must be literally hundreds of miles of PVC irrigation lines that operate under water pressure without leaks. My own sprinkler system was installed 33 years ago and still shows no leaks. Granted it's underground and is only pressurized for a few minutes per day, so perhaps a very minor leak might not show, but there is a portion of the system between the backflow and the valve control box that is under full pressurization for the entire season and it has never leaked. I must maintain as I stated in my original reply that a properly assembled PVC line should never leak.

 

[Jadnashua]

You can buy PVC pipe rated for pressure, it's just that most of it is designed for drainage, and unless it is specified for pressure, it will not survive when pressurized at typical supply line pressures. none of the stuff really likes UV exposure, but pressure-rated stuff underground should be fine.

 

[Gary Swart]

No question about PVC that is exposed to the UV, that's not part of issue. Not even concerned about this OP use of PVC as a drain. He/she seems to have a problem with their joints leaking when pressure testing. Now, as long as we are not talking about ultra high pressure, a properly installed PVC pipe, regular grade, will not leak. Yes, drains don't get pressurized, I know that, and drains are not normally tested under air pressure, but the wording of the original question was they could not find the leaks. That lead me to think they were using air pressure because water leaks in a drain line should be pretty obvious. I'll stand by my original suggestion that they made some errors in assembly and they need to cut out the joints and re do everything correctly. BTW, my irrigation systems use old very thin PVC and after 33 years still has not leaked. The old PVC is prone to break easily if digging around it because even a slight poke with a shovel will shatter it. I have had a few repairs of that nature. New pipe is far stronger.

 

[Jadnashua]

When looking, I found one PVC pipe that was rated for 480psi...drainage pipe made in PVC is often less than 10psi...they are made differently, but of the same family of material. I agree, if you cleaned and put on a proper, continuous coat of cement, did the recommended twist while inserting, and didn't wait too long before inserting the pipe into the fitting, it should not leak. Now, one thing that might be an issue is the use of 'old' cement. If not stored properly, you can lose much of the solvent content, and all that's left is mostly gelled pvc that was dissolved in it. On some of them, you can buy just the solvent, then mix it into your remaining cement, but for most people, if it gets old, just buy a fresh can of the stuff...it does not last forever!

It could be crappy fittings made overseas.