Pressure testing new system - slow pressure loss

[Zimm0who0net]

I've got a fairly small plumbing system that I just put in a guest house we're building. 2 bathrooms, a bar sink and a laundry. It's generally PEX-A with some copper stub-outs. To test, I turned the system on, then turned off the main ball valve and I've been watching for pressure loss. It started 3 days ago at 58 psi and it's now at 54 psi.

So my guess is that I've got a small leak somewhere, but I've been to every fitting trying to feel for water and can't find anything. This is a brand new system and there's a ton of air in the line (especially at the dead end stub outs). I tried purging where possible, but it's not possible everywhere. I'm wondering if maybe the air in the line is dissolving into the water causing a very very slow pressure drop?

I don't think it's temperature related because as I watch throughout the day it doesn't seem to ever go up...

My little test setup has an industrial pressure gauge along with an air fitting, so theoretically I could put compressed air into the line as well, but I've been a bit nervous to go over the 58psi that my city water is at for fear of blowing out shower or wall-mounted faucet valves.

 

[Terry]

You lost 4 pounds in three days?
I would call that good. You might have lost that in the gauge itself. If you had any kind of leak, after three days you would have had next to nothing.

 

[Sponsor]

 

[Zimm0who0net]

Thanks! that makes my weekend..

 

[Reach4]

My little test setup has an industrial pressure gauge along with an air fitting, so theoretically I could put compressed air into the line as well,

I thought loss-of-pressure tests were only done with air or other gas.

When testing with water, don't you look for drop in the water column or a leak?

 

[Jeff H Young]

when water and air are in a system the test wont be that good it will drop .... also pex expands when pressurized might be a problem . just turn water on leave it on and monitor it. if your scared leave it on for few hours at first but it sounds good

 

[Sylvan]

Water is the safest way to check a system especially plastic (except for gas)

The easiest way to show why most plumbers use water when possible is this example

Take two balloons one filled with air and the other filled with water

Pop each balloon and the one with water plops open, the one filed with air acts violently

When doing a 5 year test a a large boiler steam for example we close the King valve fill the boiler with water gag the safety valves and test same with a sprinkler and stand pipe for fire suppression

 

[Kathleen O'Brien]

I'm trying to air-test test a new system--also not very involved--using a Pasco gauge with a bicycle valve. I THINK I have everything capped, but exactly zero pressure builds. None at all, acts as if it's a wide-open system. Of course, something--or everything--major is not actually closed off. Anyone have ideas about what the "usual suspects" could be? I'm using pex-A and rings.

 

[Reach4]

I'm trying to air-test test a new system--also not very involved--using a Pasco gauge with a bicycle valve. I THINK I have everything capped, but exactly zero pressure builds. None at all, acts as if it's a wide-open system. Of course, something--or everything--major is not actually closed off. Anyone have ideas about what the "usual suspects" could be? I'm using pex-A and rings.

Slow pump combined with an insensitive gauge?

Close all valves, such as the one in line with the water heater, and see if you can build pressure. An empty water heater can take a lot of air with not a lot of pressure rise. If you build pressure, start opening some valves that are in line with pipes.

For a more sensitive gauge for early testing, try plunging a clear plastic tube into a bucket. Connect the other end to a pipe being pressurized. Have the opening about a foot down. If you blow bubbles, you know you can build 0.4 psi. You can probably figure out a way to connect the clear plastic tube to the plumbing being tested.

If the problem is that your pump is building pressure too slowly, see if you can borrow a compressor with a cfm or scfm rating.

 

[Kathleen O'Brien]

This is very helpful. I had also overlooked the fact that, though I have two main lines run, they intersect at the shower mixer valve (rookie move made by a total rookie). So instead of testing two lines, I really need to test just one as a system. Unfortunately, I am currently ONE PLUG short. But I'll grab one tomorrow and try again. If it's a no-go, I'm going to start in on your suggestions.

 

[Sylvan]

Air tests can be very inaccurate

Pressure temperature ratio. . As the ambient temperature increases so does the pressure, when it cools down the pressure decreases.

 

[Reach4]

When air testing pex, especially pex a, the tubing will relax. I don't find the procedure now, but it involves bringing the pex to a higher pressure for a while to let the expansion happen, and then reducing the pressure for the test.

I do find this: https://www.uponor-usa.com/en/customer-support/faq

For residential applications: Use a mixture of water and air (or air when allowed by local code), and pressurize to 25 psi (1.7 bar) above working pressure, or 100 psi (6.9 bar).

For large commercial applications: Fill the system with potable water, air or a combination of both. Then, condition the pipe to 1.5 times the test pressure or 120 psi (8.2 bar) for 30 minutes. After 30 minutes, release excess pressure until you reach desired test pressure [80 psi (5.5 bar) recommended].
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The document I don't find had a graph of pressure vs time.... Ahh, here we go: See page 51 of https://www.gwkent.com/media/pdf/product/4245/AQUAPEX_Install.pdf