Date: Mon, 19 Apr 2010 20:37:23 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Future propane changes planned. Prepare in advance?
In-Reply-To: <4BCC9395.6020207@mischko.com>
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At 01:32 PM 4/19/2010, Scott Chapman wrote:
>Good plan?
I think so.
>Also, why do they run 2 small lines from tank to fridge & stove rather
>than one line up and T it off inside? I assume you'd need a bigger line
The fewer connections you have inside, the fewer places there are to
leak inside. Also access could be a problem. Just my thoughts, but
they seem (of course) reasonable to me.
Incidentally, this isn't natural gas, which is mostly methane and
lighter than air. LP (stands for liquefied petroleum) gas is a
manufactured gas made up mostly of propane and butane, though it's
commonly called just "propane." It's heavier than air (like gasoline
vapor) and will run down hill. It's usable down to around 0F
IIRC. It's definitely *not* usable for high-pressure applications at
-20F -- I've watched (I was holding it) a propane torch taken from
indoors freeze and go out within a few minutes at that temp.
LP gas is of course extremely flammable in proper concentrations. At
higher concentrations it's an asphyxiant. The liquid is cryogenic
(very very cold) at atmospheric pressure because of its rapid
evaporation. A sudden release of LP will thus pose a severe freezing
danger, then asphyxiate anything within a volume of about 250 times
the liquid volume, then gradually dilute and become explosive. The
three gallons in a Westy tank would evaporate to about 100 cubic
feet, half the total cargo volume of a Vanagon, so for us Vanagoneers
fire/explosion is the primary danger.
If heated in a fire, the tank will vent through its pressure relief
valve. If the rate of heating overwhelms the vent, the tank will
eventually burst in a boiling-liquid expanding vapor explosion, or
BLEVE. There's an excellent non-technical short video about BLEVEs
in home water heaters at http://www.watts.com/mediaCenter/ under the
"Educational" tab. It's called _Explosion Danger Lurks_. In the
video the Watts Regulator Co. stress the importance of using combined
pressure and temperature relief valves, as a BLEVE is not possible if
the temp doesn't exceed boiling point. However in our case normal
room temperature is far above the boiling point of the liquid, so we
have to accept the potential of a BLEVE if the tank ruptures by
mechanical means as well as by excessive heat overpowering the
venting capacity of the relief valve. However our Vanagon tanks are
built very strongly, much stronger than a BBQ tank.
Yours,
David
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