Pressure test Satisfactory ?

[TroyM]

Hello, we trenched 120 feet and installed a 2” Sch 80 pvc line to site of new duplex. We used primer and medium body, gray PVC cement . The line has sand bedding 6 inches below and 4 inches above the pipe and we compacted/backfilled with sheeps foot compaction equipment.
We pressurized to 75 psi using a neighbor’s garden hose.
The Next day it was down to 70 after two days. It was to 61
At the end of three full days, it’s down to 55 psi.
I’ve got a guy from a leak detection company coming in tomorrow. He wants to pressurize it with helium and use a sniffer to determine where the leak is.
My question is, it’s obviously very minor after 24 hours.
Is it considered a leak or not.
Thanks

 

[Sylvan]

• Pressurizing PVC pipes with compressed gas (air or helium) can be extremely dangerous. If the pipe fails, it can explode and splinter into dangerous shards.
• Manufacturer Warnings:
  Many manufacturers warn against pressurizing plastic pipes with gas due to this severe risk.

 

[Sponsor]

 

[Slomoola]

If the pressure starts at 75, and in the morning you have 74psi, you, have, a, leak. No way of getting around it. Leak is a leak.

I would of used PEX A pipe. All those fittings trying to run PVC every 10 feet. Nothing but a time bomb. Main failure points are at the fittings.

 

[Reach4]

If the pressure starts at 75, and in the morning you have 74psi, you, have, a, leak. No way of getting around it. Leak is a leak.

You are mistaken.

 

[Slomoola]

You are mistaken.

Even I, can deduce 74 from 75 and get a loss of 1. My edu' ma' cashion is pretty pooooor.

 

[Reach4]

Even I, can deduce 74 from 75 and get a loss of 1. My edu' ma' cashion is pretty pooooor.

If you were not so certain, and open to an experiment, I would propose a test.

Make sure that any thermal expansion tank precharge are at least as high as your water pressure. Place a pressure gauge on a hose spigot or the drain for the water heater. Turn your WH off or to vacation. Turn off the water after your pressure tank or from the city. Open a faucet to let the pressure drop to near zero. Close the faucet to minimize dripping and air coming in.

Let the pressure stay low for at least an hour. Turn the water to the house back on, and 2 to 5 minutes later, turn that water back off. Note the pressure.

My expectation is that the pressure will drop as your PEX pipe volume slowly increases due to creep.

(PVC creeps less than PEX, but it does slowly and minutely expand with pressure and time.)

If the water were truly incompressible, the pressure drop would be faster. I expect there is some air mixed in, so the presence of air will reduce the rate of fall. But it will fall, despite you not having a leak.

Pressure can also fall if the water cools.

When a pressure leak test is done with PEX, the pressure is made higher so the pipe expands with time, then the pressure is reduced for the test. The PEX having been pre-expanded will not cause the pressure to fall.

But this was hypothetical I expect. But maybe somebody else thinks it would be worth an experiment.

So I am saying if the pressure starts at 75, and in the morning you have 74psi, that does not lead to a firm conclusion. But we can disagree on this point-- that's fine.

Edit: I did find an Uponor article on water pressure test for PEX. https://brandportal.uponor.com/m/68...l/TI-MLC-tap-water-and-heating-EN-1119966.pdf page 47 describes a procedure. It also has a graph showing how water pressure will go down, and you only do the remainder of the test after the pipe has been held at an overpressure for a period.

 

[Slomoola]

NOW you are making sense, for me LOL. Didn't take pipe expansion into the mix. Good catch Reach4.