Air pressure testing water lines

[dcourtney]

I've got my waterlines for a full bath all set up all the way except to connect into the water sources and capped all ends. I placed my air pressure gauge on the hot water line where it will eventually connect to the hot water pipe. My cold water line has a male threaded adapter at the end to test that line. It is not currently capped. When I fill the hot water line with air pressure Air escapes through the male threaded adapter on the cold water line. 1st is this normal? I'm assuming that the air is escaping through the shower valve since that's the only place where the hot water and cold water lines intersect, but that doesn't seem normal, is it?
Thanks
Dave

 

[FullySprinklered]

Don't know it all but I know a little bit. Some Delta valves come with a stopper that would allow a crossflow in the system prior to installing the cartridge.
Customer had me doing plumbing in one part of the house while another dude was doing a bathroom in another part. He was more of a tile setter/handyman guy.
Drove me nuts. Customer called me back a couple of times because her kitchen sink faucet was dispensing water that varied greatly in temperature.
I finally went into the bathroom where he was working and quickly figured out what was going on. Thanks, a lot.
Some ex-military dude trying to get started in civilian life, bless his heart.

An air test on copper can be up to 50 PSI
No air testing for plastic pipes.