Temp/pressure changes in pex

[Burl]

I have about 450 ft. of pex installed, 2 loops, waiting for the concrete. I made up a home-made manifold (black steel pipe), connected everything up to the pipe manifold, plugged the return ends, used stainless crimp fittings. Pumped it up to 50 psi, during that night it lost 5 psi, stayed that for a couple days, went down another 8 psi. Yesterday pumped it back up to 50, soaped all connections, no leaks, it went down to 40 psi last night. The garage has no doors, and the temperature has gone down into the lower 40s-upper 30s every night. Could the temp changes be causing these pressure changes?

 

[72Tunaboat]

Soap it down again around all the fittings and the test gauge. temp should not affect the pressure that much.

 

[ScaldedDog]

Yeah, mine'll fall 5psi from when full, but then it'll stay put. I'm thinking leak...

Mark

 

[thammel]

I can help here. In the past 2-3 weeks I went through the same thing. I put in about 820 feet of 1/2" pex and pumped it up to 30psi. At first it dropped. I had a leaky fitting. Do the soapy solution test and I'll bet you have a slow bubbling spot. I first used teflon tape and it leaked. Then I used non hardening permatex (the black goopy stuff) and it is dead tight. It's held pressure with no change since then. Pressure might change by a few psi due to temp changes. Use the ideal gas law and you'll see that pressure might change by 10% for a 50F change (from 70 to 20F). During the concrete pour, pressure rose by 4-5 psi due to the temp increase during concretization (the exothermic process or concrete hardening) By the way, my pressure test set up consisted of shark-bite fittings to join two ends together at two places, a shark-bite end cap to cap one end and a shark-bite fitting to the pressure gauge. I sweated the pour, but all was ok.

Tom

 

[Red'n'WhiteRebel]

I had my system at 30 psi for a good 12 hours before the pour last week. When the pour was about half done I noticed that the pressure was up 3-4 psi. This was in my shop loop, 4 loops of 250' each.