On 5/16/2005 8:12 AM Richard A Jones wrote:

> Determining the level of propane in a tank is harder than
> you might think.  Propane boils at -44 degrees F; only the
> pressure in the tank keeps it liquid, the same as your
> sealed radiator system keeps the water liquid at temps
> above 212 degrees F.
>
> The amount of liquid propane in the tank has no connection
> to the vapor pressure of the gas in the space above it--
> only temperature does.  At -45, the vapor pressure is zero.
> At -20 it is 11 PSIG, rising to 257 at 130 degrees.  This
> is why you cannot measure the remaining liquid propane by
> any kind of pressure gauge.  The pressure remains constant
> (at a fixed temp) until the last molecule of liquid propane
> boils.
>
> What you can do is attempt to find the level on the tank
> where the liquid/gaseous line is.  When you are using
> propane, some of the liquid is turning to gas.  The
> molecules becoming gas take the heat, leaving the liquid
> colder.  Ergo, just find that temperature gradient point.
> Again, compare to water.  A pan of boiling water stays at
> 212 degrees (at sea level--the pressure factor again) until
> all gone.  All the heat you apply to the pan goes out in
> those hot water vapor molecules.  You can't get the liquid
> water hotter than its boiling point.
>
> Campingworld (for example) has two "gauges" that do that:
> http://www.campingworld.com/browse/products/index.cfm?prodID=4800&src=SRQB
>
> or http://tinyurl.com/dv8qq
> http://www.campingworld.com/browse/skus/index.cfm?skunum=4317&tab=desc
> or http://tinyurl.com/drkeu
> How well these would work on our skinny horizontal tanks, I don't
> know.  How well they really work on larger DOT tanks, I don't
> know either.  ;-)
>
> Next time I'm near CW, I'll get them and experiment.  Of course
> it may mean that I also have to get the one-piece RVer jumpsuit,
> some 12V patio lights with American flag motif, the giant outdoor
> carpet and the gizmos to dispense paper plates one-at-a-time....

We want to see pictures.

--

Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
83.5 Westfalia: Mellow Yellow ("The Electrical Banana")
KG6RCR