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?

[wing_zealot]

It's a good thing that knowing the real answer isn't a matter of life and death.

[BB_TX]

BB_TX wrote:

Old-Biscuit wrote:
After a period of non use one does not purge air from propane system.......one establishes flow on a static system and places a demand on LP Regulator.

It's as simple as that.
......

Not that simple. On mine there IS a flow when the burner valve is first opened (as indicated by the match flame being blown about) but ignition does not occur for a minute or more after that flow starts.

D.E.Bishop wrote:
..............
In summary, the liquid propane in the tank becomes a vapor when released, ............... If the flow is stopped for an extended time, the initial vaporization slowly converts back to a liquid or near liquid state .........
........

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.

[BB_TX]

Old-Biscuit wrote:
After a period of non use one does not purge air from propane system.......one establishes flow on a static system and places a demand on LP Regulator.

It's as simple as that.
......

Not that simple. On mine there IS a flow when the burner valve is first opened (as indicated by the match flame being blown about) but ignition does not occur for a minute or more after that flow starts.

[D_E_Bishop]

Well Guys, while I did not receive a definitive answer in plain old English that this electrician/carpenter type guy can wrap his mind around, here is what I have garnered. With all due respect for everyone who replied, I think that Old Biscuit is correct but didn't explain it fully.

Propane unlike "natural gas" is delivered and stored in a liquid state, when the pressurized liquid is released into the atmosphere, it becomes a gas. The liquid propane is not flammable because the air/gas ratio is not such that it can combust. As an example Hydrogen GAS is not flammable until it reaches a ratio of 96% atmosphere and 4% hydrogen GAS(I learned this when performing maintenance on high voltage converters) I am surmising as Old Biscuit indicated that the lack of motion and as Chris Bryant said the changes in temperature modifies the gas and it like liquid propane is not flammable, when the appliance valve is opened, Propane enters the system in a flammable state and when the static propane in the system is expelled by the flammable propane and a spark is introduced, walla, flame.

In summary, the liquid propane in the tank becomes a vapor when released, it then becomes a flammable gas when it is further atomized when passing through the orifice in the nozzle and then oxygen is introduced in the burner tube and passes into the burner as a flammable gas. If the flow is stopped for an extended time, the initial vaporization slowly converts back to a liquid or near liquid state and doesn't atomize into the vapor needed to make a flammable gas when it passes through the orifice nozzle. In short the propane is still there but not in a flammable state.

These are my feelings of what happens which I expanded from what Old Biscuit and Chris Bryant said. At least it makes sense to me and I am no longer inquiring.

[4X4Dodger]

D.E.Bishop wrote:
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?

Ol Biscuit is as usual not entirely correct. cracked and checked hoses, faulty seals in valves, loose connections can all allow air to enter the system. I am also willing to bet that your system is not all hard piping, behind your stove and at your tanks there should be flexible hose.

[JaxDad]

Old-Biscuit wrote:
After a period of non use one does not purge air from propane system.......one establishes flow on a static system and places a demand on LP Regulator.

It's as simple as that.

Well, no, it's not quite that simple. It's pretty common for a seal or seals in various valves in the system to allow a very minute leak. Enough to allow static pressure to bleed off over a period of time, sometimes as little as a week.

[Old-Biscuit]

After a period of non use one does not purge air from propane system.......one establishes flow on a static system and places a demand on LP Regulator.

It's as simple as that.


And the 'bleeder' valve on cylinder or tank is a mechanical means of determining 80% liquid level. Has absolutely nothing to do with downstream propane system

[tll]

Hows this for a thought: Propane is a hydrocarbon fuel in a gas state. Hydrocarbons have the ability to permeate through the flexible rubber gas lines on our trailers. I believe the hydrocarbons in the gas simply pass through the line into the air and what is left is just a gas that no longer has any ignition properties. You can't see it happen, but it does. Engine manufactures have spent lots of time and money addressing this problem with gasoline. Gasoline is just a hydrocarbon in liquid form. Same hydrocarbons, same effect.

[pkunk]

darsben wrote:
If air was not able to enter then the guy filling the tank would not have to open the bleed valve until gas is expelled. A lot of refillers do not but most LP gas companies do. It is always done b the refiller on my motorhome

That's not air but propane vapor that escapes until the tank reaches 80% then liquid comes out indicating full.
So, to answer the question, minute amounts of gas seep past the valves. Not enough at once to smell or pose a danger but over time will drain the line.

[Ex-Tech]

darsben wrote:
If air was not able to enter then the guy filling the tank would not have to open the bleed valve until gas is expelled. A lot of refillers do not but most LP gas companies do. It is always done b the refiller on my motorhome

The bleed valve has nothing to do with venting air. That valve vents propane in a vapor state until liguid propane reaches that valve.
After the initial purging of air from a new propane tank, the 80% bleed valve is used to check for liquid, not vapor.

[newman_fulltime]

In extreme cold or hot days it vents out the vent on the regulator

[Chris_Bryant]

rhagfo wrote:

Chris Bryant wrote:
The solenoid valves are not perfect. Also, LP is extremely temperature sensitive, so after the pressure reaches equilibrium, negative pressure will be created when the temp drops, drawing air back in to the system.

Air should not be drawn into the system through a closed valve. Propane is capable of blowing out a match, and not ignite.

Personally I keep the system pressurized all the time. I believe far better for the valves, I have had several homes with gas never shout off the gas there either.

You should take one of those valves apart. You could then see how they are made to seal in one direction; that direction isn't perfect either.
If you built a valve that drew an amp or so, you could make it better at sealing.

[wa8yxm]

There is a question on the Propane Pump Jockey test which was being reviewed in a room where I was internetting one day.

What happens if you get the ideal mix of air and propane and there is a spark?

Before anyone could say anything I piped up "You land two counties over"

The instructor (once the laughter died down) said "Exactly". (hey I got it right)

To make it burn you need the proper ratio of propane to air.

With the pressure in the lines being far far lower than normal (normally it is 11" of water or roughly 1/2 PSI) you do not get the proper air/gas mix and it does not burn.

But get the right mix and...."She flys through the air with the greatest of screams. Of course she has not a trapeze. Her movements are not graceful and no one is pleased.. For she has been blown away.

[nomad297]

darsben wrote:
If air was not able to enter then the guy filling the tank would not have to open the bleed valve until gas is expelled. A lot of refillers do not but most LP gas companies do. It is always done b the refiller on my motorhome

It is not air being expelled from the tank. It is propane gas. When the bleed begins to expel liquid, that is LP, liquid propane -- not in gas form.

Bruce

[BB_TX]

I am another in the "it goes some where" camp. With all gas appliances off, I can close the propane tank valves and after a few weeks it takes a minute or so before a burner on the range will ignite. Something is blowing on the match during that time, but it will not ignite until propane has time to travel from a tank to the burner. There is never any propane odor anywhere, inside or out.