Sorry about the length but I hope with enough details someone can explain what is a mystery to me. After 5 years or so my propane pigtails had hardened. Since the regulator was the original from 2004, I decided I should replace it also. What motivated both was what seem to be very slow leak. I left one of my half empty propane tanks with the valve open but without using any propane for several months. When I finally checked the tank was empty. I put in a new tank, charged the propane lines, ran both the stove and the furnace. I shut off the tank and noticed the regulator showed red after a couple hours. I switched the regulator to the other tank, opened and then closed the valve and again the regulator showed red in a couple of hours.After changing the regulator and pigtails. I did a careful leak test. No soap bubbles and absolutely no propane odor. This time, I used the stove and furnace and then shut the valves. I expected to see a green indicator on the regulator for many hours. Instead it changed to red in well under 2 hours. I switched over and had the same results with the other tank. I did several checks and the pattern repeated with about 1 1/2 hours until the regulator changed from green to red. I checked for odors and leaks everywhere with no problems.It has now been several days since I replaced the regulator and pigtails. Last night I did another test and the regulator was still green after 4 hours when I went to bed. Today I did another check and it took 8 hours for the regulator to show red. Any ideas that can explain this or point to additional testing?

Maybe I'm missing something, but is this about the regulator not showing red quickly enough, or another leak?

A leak that big should smell. Are you sure you can smell it? I know I temporarily lost my sense of smell from Covid. I didn't even realize it until I tried to clean something with bleach and there was no smell. I couldn't even smell gasoline in my jerry can for a couple of weeks.Is there a BBQ port under the RV that might be leaking?You're going to have to take your soapy water and hit every propane joint until you find it.

2oldman wrote:Maybe I'm missing something, but is this about the regulator not showing red quickly enough, or another leak?Sorry, I should have made it clear that I am using a dual tank regulator with automatic switch over. When the pressure is not maintained the regulator will show red, instead of the normal green for a pressurized system.

opnspaces wrote:A leak that big should smell. Are you sure you can smell it? I know I temporarily lost my sense of smell from Covid. I didn't even realize it until I tried to clean something with bleach and there was no smell. I couldn't even smell gasoline in my jerry can for a couple of weeks.Is there a BBQ port under the RV that might be leaking?You're going to have to take your soapy water and hit every propane joint until you find it.I have not had Covid and have a very sensitive sense of smell especially for the mercaptans in propane. My tanks and regulator are contained in a small cabinet. There is absolutely no odor of propane. I also soap tested every connection from tanks to the outlet. I checked my appliances. No odors and no bubbles with soap testing. There may be a hidden connector somewhere, but again, I cannot smell propane anywhere in or outside of the RV. My interior propane detector is fairly new and has not gone off.I read somewhere that an RV propane system should maintain pressure for several hours. One or two hours seems quite short. Maybe the current 8 hour period is normal. I have no idea and certainly no idea where the propane is going.

JimK-NY wrote:Sorry about the length but I hope with enough details someone can explain what is a mystery to me. After 5 years or so my propane pigtails had hardened. Since the regulator was the original from 2004, I decided I should replace it also. What motivated both was what seem to be very slow leak. I left one of my half empty propane tanks with the valve open but without using any propane for several months. When I finally checked the tank was empty. I put in a new tank, charged the propane lines, ran both the stove and the furnace. I shut off the tank and noticed the regulator showed red after a couple hours. I switched the regulator to the other tank, opened and then closed the valve and again the regulator showed red in a couple of hours.After changing the regulator and pigtails. I did a careful leak test. No soap bubbles and absolutely no propane odor. This time, I used the stove and furnace and then shut the valves. I expected to see a green indicator on the regulator for many hours. Instead it changed to red in well under 2 hours. I switched over and had the same results with the other tank. I did several checks and the pattern repeated with about 1 1/2 hours until the regulator changed from green to red. I checked for odors and leaks everywhere with no problems.It has now been several days since I replaced the regulator and pigtails. Last night I did another test and the regulator was still green after 4 hours when I went to bed. Today I did another check and it took 8 hours for the regulator to show red. Any ideas that can explain this or point to additional testing?check to see if the relief in the regulator is letting anything out. I have seen a bunch of brand new regulators fail in the last 5 years.

Mysterious Propane "Leak" | Good Sam Community

3_tons
Explorer III
Oct 21, 2022
For the uninitiated, here’s the (above referenced…) ideal gas law, but then again this seems to be delving more into abject nuance than application…Bottom line with gasses remains when temperature goes up pressure goes up (this was my only point…), though I have no idea if this is the true cause of the OP’s particular issue:

https://sciencetrends.com/in-pvnrt-what-is-the-r-constant/

3 tons
JimK-NY
Explorer II
Oct 21, 2022
PV=nRT applies to all gases including propane. I showed the calculations above for the variation in temperature that occurred for my last leak test. Temperature for the universal gas law is expressed in degrees Kelvin. A drop of 10 degrees F was only about a drop of a bit over 1% in Kelvin degrees so the pressure would have dropped by that same small amount.

The tables cited by 3tons are for vapor pressure over liquid and would not apply for a leak test with no liquid in the system and the tank valve closed. The tables are quite useful for other purposes. As we can easily experience vapor pressure of gaseous propane over liquid propane changes greatly with temperature. This reflects a decrease in the rate at which gas can be produced from liquid propane. The tables show a substantial drop in the ability of various sized propane tanks to provide gas for heating or other purposes. The drop is so bad I long ago stopped trying to use a propane BBQ in the winter months.
Bobbo
Explorer II
Oct 21, 2022
JimK-NY wrote:
Thanks, that is an interesting web site. Those temp/pressure tables really do not apply to this topic. They are about vapor pressures over liquid propane, not about temperature changes in pressure for propane in a gas state.

Ummmm, "vapor pressures over liquid propane" IS "propane in a gas state." The material BELOW the "propane in a gas state" is liquid propane.
wolfe10
Explorer
Oct 20, 2022
JimK-NY wrote:
Thanks, that is an interesting web site. Those temp/pressure tables really do not apply to this topic. They are about vapor pressures over liquid propane, not about temperature changes in pressure for propane in a gas state.

????

PV=nRT.
JimK-NY
Explorer II
Oct 20, 2022
Thanks, that is an interesting web site. Those temp/pressure tables really do not apply to this topic. They are about vapor pressures over liquid propane, not about temperature changes in pressure for propane in a gas state.
3_tons
Explorer III
Oct 20, 2022
JimK-NY wrote:
A drop in temperature would decrease the propane pressure. The drop is insignificant. During my testing, the temperature dropped from about 60 F to about 50F. Pressure of a gas is directly related to absolute temperature in degrees Kelvin. 60 degrees F is about 493 degrees Kelvin. 50 degrees F is about 487 degrees Kelvin. So the drop in temperature and the drop in pressure were insufficient at only a bit over 1%.

Not to get tooooo far into the weeds, but here’s a temp vs pressure chart:

https://www.propanewarehouse.com/helpful-information/lp-gas-properties/

3 tons
JimK-NY
Explorer II
Oct 20, 2022
A drop in temperature would decrease the propane pressure. The drop is insignificant. During my testing, the temperature dropped from about 60 F to about 50F. Pressure of a gas is directly related to absolute temperature in degrees Kelvin. 60 degrees F is about 493 degrees Kelvin. 50 degrees F is about 487 degrees Kelvin. So the drop in temperature and the drop in pressure were insufficient at only a bit over 1%.
3_tons
Explorer III
Oct 20, 2022
Oh, so I had misinterpreted your ‘made it faster’ for made the leak faster…

3 tons
StirCrazy
Moderator
Oct 20, 2022
3 tons wrote:
StirCrazy wrote:
3 tons wrote:
“So how does the leak test go from under 2 hours to 6 hours and now to over 14 hours without any changes?”

However, note that the temperature is what changed…

3 tons

getting colder should have made it faster not longer.

How so?? From my perspective, getting colder would decrease pressure, thereby increasing the leak down time.

3 tons

increasing.... faster..., same thing isnt it ? ;) point being that the colder temps should have made the propane shrink, a miniscule amount, but I would have expected the red flag to come on faster , not longer.
3_tons
Explorer III
Oct 19, 2022
wolfe10 wrote:
3 tons wrote:

How so?? From my perspective, getting colder would decrease pressure, thereby increasing the leak down time.

3 tons

True, but it would also "shrink" the metal, perhaps allowing for more clearance in the component that is leaking.

Well, considering the principle of Occam’s Razor it would seem that a mere change in ambient temperature might have a much greater effect on a liquified petroleum gas (resulting in a decrease or increase in internal tank pressure) than the shrinking of metal components…This is exactly why tanks are fitted with Overfill Prevention Devices which provide sufficient unused volume for expansion (due to changes in ambient temps) to prevent over pressure…

3 tons

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