Very Small Propane Leak

[ssanto]

Hooked up a spa heater to my LP line outside the house. I've got a T off of the high pressure (10 PSI) line and about a foot of 3/4 pipe running to a regulator for the heater. And then maybe 6 feet of 3/4 pipe at 13 inches of water column going to the heater.

I put a pressure gauge on the high side of the regulator. It read 10 PSI. Then I shut off the incoming pressure. The gauge held steady at 10 PSI for a few hours. Overnight, the pressure in the gauge dropped to about 3 PSI. So I think I have a very small leak somewhere.

From what I read, the standard inspection tests for houses wouldn't catch this. I hear they just check the pressure after 15 minutes. So maybe it isn't a real concern.

I calculated the following:

The high pressure line (from the valve to the regulator) is about 1 foot. I calculated the volume of the high pressure gas is about 0.04 cubic feet
So say I lost 75% of that volume overnight... so that's only 0.03 cubic feet of gas lost
36 cubic feet of gaseous propane = 1 gallon of liquid propane
0.03 / 36 = 0.0008 gallons of liquid propane
That comes to about $0.005 dollars a day or $1.75 a year in lost propane.

It's outside so the leaking propane shouldn't bother anybody.

So I figure I'm fine but wanted a second opinion...

 

[Twowaxhack]

Get a soap and water solution mixed up in a spray bottle and spray everything down and watch for bubbles forming like grapes.

 

[ssanto]

Did that... no bubbles form anywhere on the joints. I think the leak is too small for that to show.

 

[Twowaxhack]

Leak might be in the gauge. Id use a manometer for the test, it’s much more sensitive.

Record the outside temp when you start the test. Temp variations will affect the gauge if left on the piping long enough.

You may not even have a leak.

 

[JG plumbing]

Did you get a thermometer for your calculations? Lol google Charles law.

 

[JG plumbing]

You can calculate the difference pressure if you know the temp difference. Soap bubbles are a better indicator of whether or not you have a leak. A 15 min test with a 0-15 psi gauge is all you really need. Or you'll drive yourself crazy.

 

[Twowaxhack]

I use a testo unit, it calculates the pressure change in relation to temp for you. I use this for high pressure tests.
https://www.testo.com/en-US/testo-550/p/0563-1550
I use a manometer to check for leaks typically, it much more sensitive than a psi gauge. You’ll know if you have a tiny leak almost instantly.
https://www.fieldpiece.com/product/...XazfZqy9uxMlE8dChpzlODrUMkcmI66BoC2kIQAvD_BwE

 

[Twowaxhack]

Pulling a vacuum is also a good way to test the tightness of a system. I pulled my mini split piping down to 500 microns for 6 hrs. But that was for evacuating the system before releasing the freon charge. Still, if the system leaks you’ll never get it to near 500 microns vacuum.

Flare joints too, that’s after a nitrogen test at 250 psi for 4hrs.