Pressure testing criteria


LifeTime Supporter
May 31, 2007
Rocklin, Ca
Can anyone tell me what is an acceptable amount of leakage while pressure testing pool plumbing? I went from 41psi on Saturday morning to 34psi Sunday night.

Sorry to skirt the rules a bit. I posted this same question within my pool build thread. It may not get noticed as much as being on it's own and I need some feedback fairly soon.



LifeTime Supporter
Apr 9, 2008
SC Midlands
I have always heard you only need around 20 PSI for an adequate pressure test. However, any drop in pressure is indicative of a leak. Determine where the the leak is correct and retest.


Well-known member
Mar 28, 2007
Morris, IL
I feel that it depends on what you are using to pressure test. Air, or water? Air is always less than water when you test, I think it is because they compress differently. If it took 36 hours to lose 7psi, I would not worry about it. Any significant leak is going to let the pressure go down to nothing. We used to air test sewer mains at 5psi for 5 minutes, and water mains at 150psi, or 250psi if it was a fire loop for 2 hours. Never as long as 36 hours. I would be more inclined to think that your valves are leaking a bit somehow rather than an actual leak.


LifeTime Supporter
May 31, 2007
Rocklin, Ca

Thanks for the additional input. I feel a bit better about losing a few PSI now.

They assembled all the pipe and then hooked up the water hose to the system. So nopw the system has both air and water in it. It seams to me that if the system was almost full of water, which is nearly incompressible, that a leak would result in a larger change of pressure on the gauge. On the other hand, if the system is only full of air a leak would take longer to show up on the gauge but the air would leak out much easier since it's a smaller molecule.

Back in a previous life, I used to work at a company that designed vacuum chambers. We would use helium to test for leaks because it's the smallest 'safe' molecule. If a system can prevent leaking helium, air is easy.


Well-known member
Sep 7, 2007
Lafayette, Louisiana
I work offshore oil and pressure test steel pipelines on a regular basis. Granted...these are welded steel pipelines, but the same principles apply.

When we test, we flush all air from the system and flood with water, pressure up to some specified pressure and hold for 8 hours AFTER the pressure stabilizes. The system cannot lose ANY pressure for the final two hours of the test. These tests are usually in the 1500 to 3500 psi range.

If you leave air in the system, your pressure is very likely NOT to stabilize for quite a while, and can fluctuate. It can actually go UP if the ambient air temperture rises and causes the gas (air) to expand. Also, if you have a leak, it will be very very slow to show itself.

At 45 psi, one volume of air compresses down to about 1/4 volume. Meaning 4 cubic feet of air becomes 1 cubic foot. So if you have a leak with air in the system, it takes alot of air volume lost to show a psi loss on the gauge. Since water is non-compressible, if you purge all or most of the air, a leak will show itself very quickly. It is best to fill a piping system from the bottom up, and bleed the air from the top. Also, even though the air molecules are smaller than water, there may be water sitting against the leak now, so don't count on those smaller molecules to prove your test. That compressed volume of air may be trying to force those large water molucules through the hole...very slowly.

The act of compressing the system, will also cause a temperature rise, starts the pressure high and when cooling occurs, the pressure will drop off over a period of time and then stabilize...and then fluctuate a little with ambient temperture. This is amplified the more air you have in your system.

All that being said, this is pool plumbing and not steel pipeline, and you probably cannot get all of the air out of the system because of all the Tees and turns.

Your real question...Is your pressure still dropping or has it stabilized at 34 psi? If you are still losing pressure below 34 psi, you have a leak. If not, I'd say it was just the air in your system cooling and then stabilizing.

I did have a small leak in my system when I pressured up to 50 psi, but was able to locate it visually at the PVC threads for the testing plug inside the skimmer bucket. PVC threads just don't seal well sometimes and this is a fitting that gets removed anyways. If you end up deciding you have a leak and can't find it visually, I'd be careful about blowing it off. You may have to isolate the return side of your plumbing from your suction side and test separately to narrow down the search.

Hope this helps a little...