Where does the propane go?

[D_E_Bishop]

Ol biscuit and I disagreed on whether or not is was possible for there to be air in a propane system basically with the tank valve shut and all the appliances turned off(valves shut). He said impossible but I say there is a gas(inert) in the system that won’t burn but will blow a match out.
As he said, it is a closed system and I agree, however, there is that gas flowing through the pipes that won’t burn. How is this possible? My system is all hard piping, no rubber hoses. I have never had an alarm that I didn’t want, i.e., testing of the alarm. Each appliance has at least three valves between the tank and the igniter and burner.
It makes no never mind, it is just that an inquiring mind wants to know. If I shut off the appliance, turn off the solenoid and shut the valve on the tank, where does the gas go? I’m sure there is a good answer, I just don’t think it is logical.
Any ideas from you experts?

[D_E_Bishop]

I want to thank all of you who were involved with this discussion, for making me think. One of you has a tagline similar to “Sometimes I like a good think”. So do I and resolving this issue was truly a good think, on one hand we had the “the propane leaked out of this closed system and on the other hand we had the group that believed the propane was still in the system. I believe now that both are correct. I am not ignoring anyone, I am just going to use two seemingly experts in the area of RV systems, Chris Bryant and OldBiscuit.

First a little background, I am 75 years and three days old and have tried to listen to the advise that the wonderful guy who raised me gave me. He believed in the Golden Rule, that things are not always as they seem and that you can add apples and oranges, it’s just that it is then fruit salad. I’m not an engineer like my DOD(Dear Old Dad) was, I am severely dyslexic so often I have a extremely difficult time explaining what I think. Sometimes I seem really weird, like saying propane somehow becomes an inert gas, I know that is probably impossible.

OldBiscuit is not really an old curmudgeon like me, he is just mischievous and as he told me, “don’t take anything we say here personally, we’re just having fun”. So if I offended any of you, you deserved it(now I’m having fun).

After THINKING about it for a while, and finally realizing that there were valves in the circuit other than the on/off valve on the tank, the solenoid safety valve that is part of the Propane detector and the on/off on the range, there are the electrically controlled valves on the fridge, water heater and furnace, and as Chris showed us, these are not the positive stop valves like the stop valve on the tank. They do and always have and may always continue to leak propane in minute amounts. On the other hand, Old Biscuit said there was still propane in the lines and could blow a match out without igniting, until flow through the regulator was re-established and the correct fuel to air ratio is reached.

Both guys are, in my beautiful and totally logical mind, correct. And in part validate my inert gas comment. Some or most of the propane leaks out through the individual appliance control valves and the remaining propane does not have the correct ratio of fuel to air to combust but it is still propane. It isn’t truly accurate to say it is inert, but, sometimes my beautiful and logical mind doesn’t have the correct words to express what I envision.

Therefore, in my exalted position as an elder statesman, I have determined that our RVs have closed propane systems which leak and yet, they always have propane in them. “Case closed” and so my fellow RVers, we were all correct but we just explained it differently.

Not to be corny, but, thank you and may who ever made your RV bless you.

[nomad297]

I spoke with an engineer in the gas and fluids regulator industry who provided me with this answer:

Gas Diffusion and Effusion

It sure makes sense to me, but the engineer is going to speak with his Chief Engineer who might be able to provide more answers.

Bruce

[12thgenusa]

Jetstreamer wrote:
Like someone's earlier post, who may have briefly touched upon the idea that maybe it's just a matter of taking time for the regulator to start building up to the proper line pressure. And until that pressure equalizes may be the reason for poor ignition.

Seems like a common problem inherent to many RVers and what are the odds of everybody's propane system leaking?

If it didn't leak down it wouldn't have to build back up again.

[Jetstreamer]

Like someone's earlier post, who may have briefly touched upon the idea that maybe it's just a matter of taking time for the regulator to start building up to the proper line pressure. And until that pressure equalizes may be the reason for poor ignition.

Seems like a common problem inherent to many RVers and what are the odds of everybody's propane system leaking?

[Sport45]

carl2591 wrote:
I service gas logs in my business, chimneykeepers.com and we run into this issue all the time especially in fall when units have not been run in 5-6 months..

Its especially bad on LP systems with long lines from tank to logs.

We will get folks calling they can not get the logs lite, it happens on nat gas as well, we show up looking all official, pull the trim off, remove the glass, check the pilot assembly, open the lower panel and check gas valve to make sure the shut off valve was not turn, push the pilot and stick my long lighter in the pilot and watch it sputter and then PILOT..

We mention on the phone it can take 3-5 mins of keeping the pilot knob pushed in to expel the "stale" gas. Some take the advise and do ok. Others just want us to come and check the logs anyway..

great way to make money.

So why doesn't it go "stale" in the tank when it's not being used???

Our fireplace has a gas burner at the bottom for lighting the firewood. When I crack the valve open on the wall it takes a few seconds for the gas to fill the pipe and burner. Until it gets there the air being pushed out ahead of it will try to blow the lighter out.

Natural gas and propane don't go "stale".

[JimK-NY]

I cannot remember checking my burners days, weeks or months after turning off the tanks to see if they light quickly, but I do have a related concern. When I turn open a tank, I see a mechanical indicator on top of the regulator change from red to green. If I then turn off the tank, the indicator will stay green for a couple hours and even as long as overnight. Then it again turns red. I have found and fixed a couple of very small leaks but without any improvement. I think I still have propane in the lines but the pressure is gone. Where is the system leaking? Solenoids? Regulator? Or somewhere else that I can check?

[BB_TX]

...

[BB_TX]

JaxDad wrote:

BB_TX wrote:
Propane is a liquid under high pressure and changes to a vapor when the pressure is reduced. It does not change back from a vapor state to a liquid state unless repressurized.

While that is true if you're talking about temperatures comfortable to most human beings, it's at the very least misleading.

Propane, at temperatures above -44 F. creates it's own 'pressure', because it's boiling. That is what causes the vapour to form.

At temperatures colder than about -50 F. you could walk around with a bucket full of it and would act pretty much like a pail of water would in warmer weather.

While I agree to some extent, considering the number of RVers who experience temps below -44 degrees I did not consider it relevant.

[westend]

JaxDad wrote:

BB_TX wrote:
Propane is a liquid under high pressure and changes to a vapor when the pressure is reduced. It does not change back from a vapor state to a liquid state unless repressurized.

While that is true if you're talking about temperatures comfortable to most human beings, it's at the very least misleading.

Propane, at temperatures above -44 F. creates it's own 'pressure', because it's boiling. That is what causes the vapour to form.

At temperatures colder than about -50 F. you could walk around with a bucket full of it and would act pretty much like a pail of water would in warmer weather.

Both of you are mostly right but even though I've never tried carrying any propane in a pail, it isn't going to be exactly like carrying a bucket of water. The propane will be interacting with the atmosphere and the container. That segues nicely into my two questions above, which I have done.

The answers: Since the vessel that holds the propane has internal pressure, when the propane is allowed to exit the 1" valve and enter the atmosphere, it is expelled quickly and also "flashes" into it's gaseous state. Since we reduce pressure by opening the valve (say, from 90 PSI to 14.7 PSI) the temperature is also lowered. The instant lowering of temperature causes some propane to remain liquid, some to vaporize, and some to even solidify with water vapor in the air.

Most can now guess the answer to #2--The ten cases of beer will have a glacier of combined propane and ice built around and on top of the stack. It was hard to keep thirsty deckhands away from the "beer cube" with their chipping hammers and sundry steel implements until the ice was allowed to melt and the propane was vaporized. It did work like a charm, ice cold beer in five minutes.

[JaxDad]

BB_TX wrote:
Propane is a liquid under high pressure and changes to a vapor when the pressure is reduced. It does not change back from a vapor state to a liquid state unless repressurized.

While that is true if you're talking about temperatures comfortable to most human beings, it's at the very least misleading.

Propane, at temperatures above -44 F. creates it's own 'pressure', because it's boiling. That is what causes the vapour to form.

At temperatures colder than about -50 F. you could walk around with a bucket full of it and would act pretty much like a pail of water would in warmer weather.

[Old-Biscuit]

Propane is flammable at 2.15% to 9.6% propane to air ratio.

Less and there is not enough propane vapor, more and there is not enough oxygen.

[carl2591]

I service gas logs in my business, chimneykeepers.com and we run into this issue all the time especially in fall when units have not been run in 5-6 months..

Its especially bad on LP systems with long lines from tank to logs.

We will get folks calling they can not get the logs lite, it happens on nat gas as well, we show up looking all official, pull the trim off, remove the glass, check the pilot assembly, open the lower panel and check gas valve to make sure the shut off valve was not turn, push the pilot and stick my long lighter in the pilot and watch it sputter and then PILOT..

We mention on the phone it can take 3-5 mins of keeping the pilot knob pushed in to expel the "stale" gas. Some take the advise and do ok. Others just want us to come and check the logs anyway..

great way to make money.

[westend]

If I have 100,000 barrels of liquid propane and I open a 1" valve to the atmosphere, what will be the result?

For extra credit---If I have ten cases of beer below the 1" valve, will the beer get cold and how long will it take?

[12thgenusa]

K3WE wrote:
There are temperatures where propane becomes a liquid at atmospheric pressure.

Yeah, -43.6 F. Not anywhere I take my camper.