TheSamba.com :: View topic - Propane Tank Main Valve Closed: how long to burn residual fuel?

Wed Aug 22, 2018 2:49 pm

Hi folks.

Thought this might be worthy of a new thread.

If you close your propane tank main valve, how long does it take one stove burner, full flame, to burn off the fuel in the lines? 5 minutes? More? Less?

This thread:

https://www.thesamba.com/vw/forum/viewtopic.php?t=...tor++valve

suggests it takes 5-6 minutes to burn off fuel in the propane lines once the tank shut off valve is closed.

Thanks

Neil.

Wed Aug 22, 2018 3:10 pm

5 minutes ? :shock:

I did this procedure a few times, when I was working on the copper lines to install a new line for the heater. Every time I emptied the gas by lighting one stove, it stayed on for something between 10 and 20 seconds.

Wed Aug 22, 2018 3:17 pm

The RV shop comment quoted in the linked thread might be based upon the RV techs' experience with systems involving longer lines? But, the Vanagon Westy owner in that thread found the same 5-6 minute result.

I thought maybe the shut off valve on my 10 year old tank had failed. Shut off valve closed, flame burned long enough to boil water. BUT.... when I lit the other burner, both flames got a lot smaller though they kept going. I'll keep burning off propane and see what happens.

Of note, this van has a TruckFridge (DC only fridge). The OE line to the Dometic fridge is still in place but is capped off. I assume it would contain fuel even though its not being used.

Neil.

Wed Aug 22, 2018 3:28 pm

I'm with VicVan on this one, 10 seconds of burner tops.... maybe extend that a few seconds with some flickering but no real pressure.

Wed Aug 22, 2018 4:40 pm

Ya there must be a small amount of fuel passing by the "closed" valve. Tank and valve are "only" 10 years old. Not sure why the valve would fail so "soon". Excess moisture in tank might cause that?

I doubt the unused capped fridge supply line is what's keeping the burners lit.

After removing a bunch of stuff to get at the stove on my '88 Westy, with newer LP tank, I opened the tank valve, lit the stove, closed the tank valve. Flame went out pretty quick.

Thanks SyncroButter, VickVan.

Neil.

Wed Aug 22, 2018 4:42 pm

Interesting that just a couple days ago I was running my stock fridge on gas and when I was ready to shut it down, I decided to see how long the it would take for the small red lamp to come back on and start flickering once I shut off the tank's main valve. I'm guessing it took about 20 seconds.

Wed Aug 22, 2018 4:54 pm

I'm left wondering why one would want to measure this? Even as a no-real-point-to-it experiment.

Wed Aug 22, 2018 5:03 pm

cmayna wrote: Interesting that just a couple days ago I was running my stock fridge on gas and when I was ready to shut it down, I decided to see how long the it would take for the small red lamp to come back on and start flickering once I shut off the tank's main valve. I'm guessing it took about 20 seconds.

That is interesting. The orifice in the Dometic fridge burner jet is very small, as I'm sure you know. But then after the tank valve is closed, once residual pressure in the supply lines falls far enough, maybe there isn't enough to move the gas through the burner jet?

Neil.

Wed Aug 22, 2018 5:09 pm

fxr wrote: I'm left wondering why one would want to measure this? Even as a no-real-point-to-it experiment.

I suspect that my propane tank shut off valve is not closing completely. Didn't initially post that detail as I was hoping that wasn't the case, so I wanted to rule out whether or not residual fuel took a long time to burn off. And, if in the process it did take some time to burn off that fuel, thought it might help others observing a similar thing. (as per the thread I linked to). But it sure seems thats not the case.

Neil.

Wed Aug 22, 2018 5:30 pm

i've had the not-closed-all-the-way happen too. in one case, i came off the ferry and went to light the stove, but it was still lit! doh.

i can get it turned off all the way; opening it and closing it again tends to work eventually.

Wed Aug 22, 2018 7:19 pm

So, light the burner and then turn off the tank valve. After the flame dies out turn off the burner knobs. Come back later and try to light a burner again without turning the tank back on. If it lights then you know the valve isn't shutting off completely. Try waiting overnight. Of course if it is enough of a "leak" to cause the burner to stay lit extra long after you close the tank valve then you shouldn't have to wait long to try lighting again.

Mark

Wed Aug 22, 2018 7:36 pm

atomatom wrote: i've had the not-closed-all-the-way happen too. in one case, i came off the ferry and went to light the stove, but it was still lit! doh.

i can get it turned off all the way; opening it and closing it again tends to work eventually.

heh heh. "doh" indeed! ;)

Thanks for that.

I tried the valve in different positions, then turned in CW closed then opened several times. It's possible it made the seal in closed position worse. ... maybe. My concern is that further use might make the seal worse.

IF the valve is failing at the seat, I have to wonder if thats a warning that the seal between valve and body will fail soon enough. If that seal fails, I assume it's allow a leak to atmosphere. I really don't want a propane leak to happen where I live.

I've been searching for an exploded diagram of the valve parts to no avail so I speak from a fair point of ignorance.

Wed Aug 22, 2018 8:11 pm

crazyvwvanman wrote: So, light the burner and then turn off the tank valve. After the flame dies out turn off the burner knobs. Come back later and try to light a burner again without turning the tank back on. If it lights then you know the valve isn't shutting off completely. Try waiting overnight. Of course if it is enough of a "leak" to cause the burner to stay lit extra long after you close the tank valve then you shouldn't have to wait long to try lighting again.

Mark

Thanks Mark.

With tank valve closed, flame lights but only rises to a medium size. With both burners on, each flame gets smaller but remains lit. If they're on for more than 5 minutes, the flame size gets smaller yet. Gas is likely getting past the "closed" valve. Maybe I'm expecting too much of such a crucial part but if it's "leaking" gas, I'm not impressed with the longevity of that valve.

This then new tank, reg etc. was installed by a pro so I assume they purged it. IIRC, purging is intended, in part, to remove excess moisture. Regardless, if the tank has excessive moisture in it, I'm curious if that hastened the valve seals' life span. Some years ago, I adjusted the regulator WC but my guess is that shouldn't have had any affect on the main valve life span or cause the issue I'm seeing.

Fuel in the tank is quite low now but I assume that would not affect the shut off valve.

Neil.

Thu Aug 23, 2018 9:52 am

If it were me, I'd get a new valve !

Thu Aug 23, 2018 1:08 pm

Vanagon Nut wrote:

I thought maybe the shut off valve on my 10 year old tank had failed. ......

Maybe I'm expecting too much of such a crucial part but if it's "leaking" gas, I'm not impressed with the longevity of that valve. ......

IF the valve is failing at the seat, I have to wonder if thats a warning that the seal between valve and body will fail soon enough. ....

I've been searching for an exploded diagram of the valve parts ...

So this small file size pdf showing a cutaway view diagram of a similar shut off (service) valve sheds some light

http://www.regoproducts.com/lpgproductpdfs/9106c0.pdf

Ironically, it shows a "10 year" guarantee on the part. ;)

If the valve stem on my Manchester valve is brass i can totally see that part wearing out or at least malforming enough, over time and use, to allow a small amount of fuel past it when "closed".

This thread suggests checking and tightening the valve stem nut

https://www.thesamba.com/vw/forum/viewtopic.php?t=613188

I'll see if mine is loose and it carefully tightening it helps the valve stem seat and seal.

Neil.

Thu Aug 23, 2018 4:22 pm

crazyvwvanman wrote: So, light the burner and then turn off the tank valve. After the flame dies out turn off the burner knobs. Come back later and try to light a burner again without turning the tank back on. If it lights then you know the valve isn't shutting off completely. Try waiting overnight. .....

So the stem nut was tight, the valve stem has a little play only at midpoint. After cleaning off the dirt, I applied a little chain lube to valve stem threads then turned valve hard shut. Even after 40 minutes, no flame when attempting to light the stove. I'm calling it good for now.

I never turn valves hard closed or open so that may have been part of the issue. Seeing how the valve is likely constructed helped; I knew I could turn it closed a little harder and not damage a seal. But regardless, the valve should be replaced.

Neil.

Thu Sep 06, 2018 10:23 am

Vanagon Nut wrote:

... then turned valve hard shut. Even after 40 minutes, no flame when attempting to light the stove. I'm calling it good for now.

I never turn valves hard closed or open so that may have been part of the issue. ... But regardless, the valve should be replaced.

Neil.

So I spoke on the phone with a service tech at what I believe to be a reputable RV repair shop. If I understood him correctly, he said that when they pressure test a propane system, if it holds even pressure for 15 minutes, they call it good. (it's not leaking). In other words, when I told him that with the shut off valve closed, a very small amount of fuel gets into the line "overnight" resulting in a very short split second small puff of flame at burner when lit, he said that's ok. Especially if there's no excessive play between valve stem and body (and obviously no leak at that point)

Tech also said that the valve should be turned all the way out (open) or in but not halfway and that it's ok to turn it fairly hard closed.

Just my .02 and of course YMMV.

Neil.