Propane Test Question

[MCilenti]

Ahoy Team,

Looking for a quick gut check. We just completely replaced our entire propane system and conducted the standard pressure test.

The system pressure drops ~4-5 PSI over the first 4-5 minutes, but then it stays rock solid (we continued to monitor for over 20 minutes with absolutely no change in the pressure gauge). Of course we also soap tested every connection and didn't find anything at all.

Everything I read says that ANY drop at all means you have a leak, but I'm at a loss to understand how that's possible since the pressure stabilizes after a few minutes. Of course I'm equally at a loss to understand why the pressure would initially drop a few PSI. As you can imagine, we've completed the test several times with the same result.

Has anyone had a similar experience or have any explanation?
Thanks for the help.
Cheers,
Mike

[MikeHoncho]

Does it do it after every time you use the gas? How big is your tank? Are you saying it has say a psi of 100 and your stop using the gas and it drops gradually 4 or 5 psi over 5 minutes or are you saying it drops that pressure while using the gas for 5 minutes?

[RaymondR]

Assuming you are pressuring with a propane cylinder and then shutting the valve off and monitoring the pressure.

The propane could be condensing in the piping if it's cooler than the cylinder, cylinder in sun and piping in the shade perhaps.

[MCilenti]

Mike,
We've only just completed the install, so we don't have a large enough sample size to say it does it every time.

As Raymond said, the pressure drop is NOT while using it, but conducting the standard leak test - we open the tank and solenoid and then close the tank valve and monitor the pressure. During that test the pressure drops ~4-5 PSI over about 5 minutes. Then the drop stops and it maintains that pressure.
For example:
Time Pressure
00 130 PSI
01 129 PSI
02 128 PSI
03 127 PSI
04 126 PSI
05 125 PSI
06 125 PSI
10 125 PSI
15 125 PSI
20 125 PSI

Maybe that's clearer? It's an 11 lb steel tank.
Cheers,
Mike

[tkeithlu]

Hmmmm. It does not act like a leak. I'm hesitant to champion RaymondR's hypothesis because the condensation would be exothermic and the event erratic. My suspicion runs to the regulator. It's a pressure regulating device in your system that is losing pressure, and all the rest is tubing or hose. You might try taking the regulator off your BBQ grill, or picking up one at Megamart, substitute it in, and see if that solves the problem.

I suppose it is possible that you have a leak only above 125 PSI, but the odds would be really low.

[tkeithlu]

Hummm again. The time course of the pressure drop sounds like a regulator reaching equilibrium between the high and the low pressure sides. I've got an oxygen regulator on my torch setup that takes its merry time doing that. There I suspect elasticity in the "Siamese" hose to the torch itself. Have you got a particularly long run or old hose between the regulator and the stove?

Consider disconnecting the hose and plugging the low pressure outlet on the regulator. If that stops it, the problem, whatever it is, is down stream from there.

[cal40john]

I've noticed when I have air in the lines after it has been off for a long time I get an initial pressure drop when testing. I open the burners one at a time until they all light so I know I have displaced all the air, then I have no pressure drop in my test.

I have no idea why this is.

[Bill O]

IMO the pressure test is fine and passes, especially w/the added info of no detectable leaks (soap test) at any connectors.

Agree it has to be an equilibrium/stabilization of the system when observing the 4-5 psi drop over the first 5 minutes, then rock solid at 125 psi for the next 15 minutes.

If the system psi started at a much lower (15-30 psi) then saw 4-5 psi drop then may have more concern with the relatively high percentage of pressure loss in the system. Luckily not the case here.

Mike, since you just replaced the whole system would do checks (pressure checks and soap leak tests on the connectors) until you've sailed the boat a bit to eliminate any possibility of loosening of the connectors by vibration. After that random pressure checks are helpful to know you don't have any leaks.

[MCilenti]

Thank you guys for all of the thoughts, I really appreciate the outside perspective.

We have soap tested all of the connections with absolutely no observable leaks. As Bill wisely suggested, we'll keep conducting the pressure test frequently and I like John's point about making sure the line to the burners is full before conducting the test.

Cheers,
Mike

[steve77]

Our analog pressure gauge that we have installed for propane pressure would never see a 1 psig drop. I'm interested, what pressure gauge do you have installed with a 1 psig resolution?

Thanks!

Steve

[RaymondR]

This sort of test is complicated by the fact of the regulator having high pressure on the tank side and low pressure on the appliance side. The slight drop in pressure is most probably just the regulator settling and consequently not indicative of any leakage.

[MCilenti]

Steve- I didn't like the very cheap looking gauge that came with the regulator from Trident (come to think of it, I thought the regulator was pretty cheap too) so I installed a different (more accurate gauge). Nothing fancy, but thought it was something better given the importance of the tests:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Ray: That was my theory as well. If the connections are leaking it can only be the regulator or the gauge.

Cheers,
Mike

[MikeHoncho]

I’m trying to figure out how a regulator would “settle” and allow 4-5psi to go from its low pressure side back to its high pressure side? I need some help there......
I’ve been actually thinking about this a lot today, the psi loss, and the physics behind it. Rule out the condensation theory, not possible with lpg in the gas state without adding energy or cooling. The vapor would be cold when introduced into the line them warm and expand. Any air and moisture trapped would do the same. As it expands it would generate pressure not lower pressure and not in any noticeable amounts.
I’m stumped . I’d like to hear more on the regulator. But I keep going back to air/moisture trapped in the line but don’t know why.

[MCilenti]

Mike,
The pressure gauge is upstream of the regulator...in other words, it's measuring high pressure, so the 'settling' is going from high pressure down, not the other way.
Cheers,
Mike

[RaymondR]

Good points folks so let's go to the appliance end and look for mechanisms at that end which might need to settle, including the flex hose.