I am rehabbing my house and just completed the plumbing phase. I'd like to pressure test the copper water pipes without using water (afraid it will freeze) so I've set up to use air pressure by adding a pressure gauge, looped all of the pipes and closed all openings.
My problem is that I don't know what a good test really is. I applied 50lb of air pressure and it lost about 5 or 6 psi in 12 hours. Considering air being thinner than water...is that a good result? Should I use a higher pressure? How long do I monitor?
Thanks in advance for your advice.

when I go out on inspections I look at the presser I like to see 80psi I do my inspection and go back and look if it has droped no more then 10 psi then I call it good if they have a leak it will drop to 0psi in the 20 to 30mins it takes to do the inspection. the code reads 50pis for 15min with no drop so I would call it good if it was me.
good luck
Justin

If the pressure gauge drops, that indicates that you have a leak on the system somewhere. It may be a cap, plug or the testing equipment.

You said you're loosing 5-6 lbs. over 12 hours, you have a slow leak that will need to be located and repaired.

If you test at 100 lbs. for 12 hours, the pressure gauge should remain on 100 lbs.

Good Luck. e-plumber

That would be just great if we wernt in the real world I have been inspecting plumbing system for 5 years and installed for 10years I haved yet to have an inspector including my self worry about 5-6 pounds over 12 hours if you have a leak it will go all the way to zero not just hang out 5-6 pounds less.

mscow, the poster stated their piping work was loosing pressure and was concerned if that was acceptable, the gauge dropped 5-6 lbs. over 12 hours, not that it "hung out".

What if it were over 24 hours, 36, 48?
What if it were gas piping, same leeway?

There aren't supposed to be any leaks, real world or not. Inspectors here will say, the test failed, call when you're ready.

If there are leaks on any type of piping when pressure tested, the gauge or testing equipment doesn't always drop to zero instantly or over a short amount of time.

e-plumber

Your pressure should hold. Period.
It is folly to try and "cheat" on an air test. I find that many "leaks" are the fault of the testing equipment. But I would look until I found it.
Deb
The Pipewench

I would have to say your are sumwhat right but my way is if you fine the leak at it is a test plug or a test cap or even the test equtment way hold up the whole job over smothing like that as for the gas he wasn't asking about gas and here we make the contractor test 15pis for 15 min not drop
Justin

100 pounds. No loss. Look for the leaks and fix them.

A tight system will not lose any pressure. Just because air is lighter/thinner than water does not mean water will not escape from a joint that does not hold air. The standard test is at least 100 psi for 24 hours with no drop in pressure.

If he finds leaks at test caps or plugs, how does that insure that there are not also leaks at the piping joints. Unless he finds and repairs all the leaks, there is no way to insure the integrity of the joint. The inspectors here are not too concerned about the water system because the plumber will have to repair it if it leaks when the water is turned on. They are concerned about gas piping, however, and insist on 10 psi for 15 minutes with no drop, using 1/10 psi gauge graduation.

Many different opinions...

Air test over many hours will have fluctations in PSI reading just from thermal expansion and contraction on piping. You didn't mention how big or how many feet of pipe are involved.
If you pumped it at say 6 in the evening and then checked it the next morning, the pressure will drop because everything has cooled.

May be the reason why short time periods are used for this test.

Just my thoughts....

Thank you that was my point
Justin

If that is the cause of the pressure drop, the the pressure will revert to a higher level when the sun comes out, and it will never drop below a certain point no matter how long it is under pressure.