Pressure testing copper supply lines?

I recently installed a lot of copper piping and "tested" everything by just turning the water on. I had two leaks, one of which was due to a bad sweating job. With the pipes now wet, I had to cut out the bad joint, and actually quite a few joints around it to redo the section.

I have heard that the supply system can be pressure tested with an air compressor, but can't find anything online about how to do this.

I could just turn the water on again, but testing with air would enable me to find and repair any leaks without cutting them out completely, right? The leak should still be dry enough to solder I'd think.

I'm not sure what the device is called, or if it's something I can buy. I have heard they aren't too hard to build, but I don't know what's involved. Maybe it's more trouble than it's worth?

You've already put water in the lines.

At this point, going back and testing with air wouldn't help. Water has a way of washing out the flux.

Testing with air involves would involve a test fitting with an air valve that a pump can use.
Plumbing supplies have these on the shelves.
You can use a compressor or a hand pump.

Finding leaks with air is easy.
If you can't hear it, you can try soapy water in a spray bottle and spray it on the joints.
Leaking air will bubble up.

Pressure testing water lines might work in your situation where you know nothing leaks except possibly a couple of joints in a small area. Though, if you plumb a whole house and then rely on air, it might be tough to track down a leak. As far as building the valve, I suppose you could put one together using some threaded fittings. A plumbing supply house would have the valve and could build the adapter for you.

You could solder a tee into the supply line with a short nipple out of that. Then adapt to your air hose. All standard fittings. Charge the line with air and soap test each joint to check for leaks. After you are finished, cut the adapter from the nipple at the tee and cap. Actually, I don't think it's really necessary to air test the line, you've already tested it and found the leaks. Usually you can get enough play in a line to cut a bad joint out and replace it without disassembling too much, but in some instances, you might have to cut some out.

couldnt he use a set up thats used for gas. low pressure guage with a zerk fitting. this way he could watch if there is a pressure drop. if there is then look for leaks.

I'll have to do the same tests soon myself, and I was under the impression that you charge the system to 50lbs (around normal water pressure) and then watch for the pressure to drop over several hours. It should not drop.

Local Code officer tells me I need to have the test on when they arrive for inspection, and it must be an air test. I need to make an adapter also....

In my system, I have two dielectric unions at the end of all my new copper piping, one for the hot pipe, one for cold, where the new pipe transitions to old galvanized. I thought that would be a good place to do the pressure test.

For just over $8 I put together a little conversion kit to hook an air compressor up to the 3/4" union. Once pressurized, this should allow me to test all the new pipe first on the cold side, then on the hot.

I made the connection, and turned on the compressor, but after a half-hour the pressure gauge hadn't moved above zero. I don't have experience with compressors, so maybe it takes much longer than I expected. I'm going to talk to the guy I borrowed it from about that.

I'm too impatient to monitor the pressure over time, so I'm just planning to go around with the spray bottle immediately after I get the pipes pressurized and hit all the joints with soapy water and watch for bubbles.

I'm assuming a few bits of bread and a very small amount of water being in the pipes aren't going to screw anything up?

A compressor builds pressure rather quickly, and since the gauge is still on zero after a considerable time, I'd suspect the gauge unless you have a faucet open or a massive leak. Also, if the compressor is building pressure, it should shut off once maximum PSI is reached, probably 100-125 PSI, and hold that pressure for a long time.

Your inspector requires an air test for water lines? Is there water available at your site? I guess every place does it their own way.

welll

the city of chicago requires air tests at 120 lbs for 24hrs...and yes i do mean in residential work

air testing is done in freezing climates

pressure is 125 psi in new construction with no heat the pipes would freeze
with water test.

i use to live in mass. with tough winters ,it,s air test there