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Old 06-21-2020, 06:12 PM   #1
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1972 29' Ambassador
San Antonio , Texas
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Question fully replacing gas lines, advice for ensuring it is leak proof

We picked up a 72 ambassador and have spent the last year fully gutting and modernizing. I'm currently running new copper for the gas lines and I'm struggling to leak-proof the system.

The entire system is 3/8" soft copper pipe (using 1/2" pex as a sheath on the underbelly) using flared fittings. I've hooked up a quick connect and a wc inch gauge to one end of my circuit so that I can charge the system using my air compressor (with the pressure dialed waaaay down).

I've been testing by charging up my system with 15 wc inch of pressure and then shutting the valve leading to the air compressor. Over the course of 15 minutes I'm losing about 1/4 to 1/2 of a wc inch. I've been bubble testing all of my fittings but haven't been able to pinpoint where the leak is. It's about 90 degrees outside, but the temperature isn't varying that much in 15 minutes -- is there a chance that could contribute to the drop that I'm seeing?

I'd imagine that any gas leak is a problem -- is my approach of charging using an air compressor providing a valid test? We don't have all of our appliances yet, so I don't have any way to do a proper load test. I haven't hooked up an actual propane tank to the system yet either.

Thank you in advance
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Old 06-21-2020, 06:40 PM   #2
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the copper and rubber tubing, but not connected devices are good to 50 psi or more so first off don't mess with inches of water, go to 25-30 psi. Air is compressible so you'll need to let it stabilize for 30 min. Record the pressure as you go, if the changes are declining exponentially to a stable pressure, you have no leak, of the pressure just continues to decline you do have a leak. At 30 psi the soap test should easily find the leak. Good luck.
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Old 06-21-2020, 06:56 PM   #3
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Sounds like a lot of fun. When we installed the copper in both trailers, we used L and, as you, using water hose or PEX on the belly pan for protection. We placed valves underneath at the final run to all items requiring LP. Also, I found it easier to use double flares versus single. Some think thatís an overkill, but didnít have any leaks. I think with the double flare you have a thicker roll of copper to conform to the flared fitting when tightened. Good luck
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Old 06-21-2020, 07:12 PM   #4
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In addition to double flares (DOT requirement) it's also great to use forged flare nuts.
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Old 06-22-2020, 10:44 AM   #5
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Valves could be leaking by? It's very possible. We always test to 50 with the appliances isolated by valves.
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Old 06-22-2020, 10:44 AM   #6
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To check your complete system wait until you have all of you appliances installed and you can do a leak down test with one of those gauges that hook up in series with you propane tank. That will tell the smallest of leaks. Just turn on the gas and bleed the system, the turn off the gas and see if the gauge goes down. It is not unusual for slight variations in the gauge because of temperature change.
I don’t know if 30 or 40 pounds of pressure would damage the regulators in each individual appliance.
I have used the method for years and do it at least once a year on my unit.
Good luck.
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Old 06-22-2020, 01:58 PM   #7
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Do no apply more than 7 inches of water column (or 0.5 psi) pressure to gas generator regulators. You will blow them. That is why they are downstream of you low pressure regulator.
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Old 06-22-2020, 07:23 PM   #8
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I did the initial test with air during the rebuild, but want a long term approach to being able to test. Since this isn't stationary like a house and subject to stress, I wanted to be able to test whenever it seemed appropriate. I got a leak detector for propane.

https://www.amprobe.com/product/gsd600/

The probe makes it easy to pinpoint the leak and is fairly small so we just carry it with us. Peace of mind

Can always use it at home. We're in the country and have propane.
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Old 06-22-2020, 08:02 PM   #9
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Most RV appliances are tuned for/sized for 11 inches of water column on the low pressure supply side but have a fair cushion for overrating, still if appliances are attached, its best not go much higher than 11 inches and certainly not much over 1 psi. Isolated, the copper and rubber tubing is good for well over 50 psi.

To each their own, but in the petroleum industry, they add odorant for a reason. Your nose is your friend and the smell of the mercaptan is more than an adequate test for leaks.
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Old 06-22-2020, 08:22 PM   #10
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Quote:
Originally Posted by BayouBiker View Post
the copper and rubber tubing, but not connected devices are good to 50 psi or more so first off don't mess with inches of water, go to 25-30 psi. Air is compressible so you'll need to let it stabilize for 30 min. Record the pressure as you go, if the changes are declining exponentially to a stable pressure, you have no leak, of the pressure just continues to decline you do have a leak. At 30 psi the soap test should easily find the leak. Good luck.

This worked for me - thank you very much. Bumping the pressure up to 30 PSI gave me enough to work with to find the leaks that I had. After another day scooting around under the trailer I got it into a state where it's been holding at 32 PSI.
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Old 06-23-2020, 09:04 AM   #11
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Very nice, Now as you add appliances you won't have to worry that any leak you encounter is in the supply lines. Let us know how the renovations are going. Should be a fantastic looking trailer when you're done!
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