Date: Mon, 16 May 2005 10:56:15 -0700
Reply-To: Rocket J Squirrel <j.michael.elliott@ADELPHIA.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Rocket J Squirrel <j.michael.elliott@ADELPHIA.NET>
Subject: Re: measuring propane level in a tank
In-Reply-To: <4288B85F.7070801@colorado.edu>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
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
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