Date: Wed, 20 Dec 95 10:03:50 mdt
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: jonesl@tcplink.nrel.gov
Subject: Propane Tank Gauge
Merry Xmas Everybody!!
Just so that everyone understands - - propane is a hydrocarbon
compound with a vapor pressure somewhat greater than atmospheric
pressure. This means that it will stay liquid in its thin metal tank,
yet vaporize when the pressure drops to the regulator downstream
pressure (6 or 7 inches water column) to burn in stoves, furnaces,
water heaters, etc.
I have seen many large propane tanks that had either mechanical float
operated gauges or sight glass guages. Most of these tanks were at
least as large as your VW bus. Obviously not a practical application
for small tanks!
There are several ways to tell propane tank level on a small tank.
These are based on the fact that propane liquid, like water, requires
heat to vaporize into a gas.
- if it is humid out, turn on your stove or furnace and watch the
tank. The distribution tubing, the regulator and the top of the
tank will be colder than ambient temperature due to evaporation of
the propane being used. So frost will start to form on the tank
down to the level of the propane liquid.
- If it is not humid out, turn on an appliance for a few minutes,
then throw a cup of water on the tank. Approximately same result
as above will occur.
- If you have a few bucks, stop by your propane or RV dealer and buy
a stick-on propane tank guage. You may have to cut one of these to
fit on a VW camper propane tank. These things are made of a
thermally sensitive material that changes color at different
temperatures. If the temperature has recently changed (like when
sun comes up in the morning), the temperature of the liquid section
of the tank will lag behind the temperature of the vapor section
due to the diffence in heat capacity and density of the two
sections (Engineering students, please see Thermo 101). At any
rate, the tank level will be at the point where the color of the
gauge material changes. If the tank has been setting at an even
temperature for several hours and the liquid and the vapor are at
thermal equilibrium, you may have to turn on an appliance or vent a
little propane to generate enough temperature difference for it to
show on the gauge.
please e-mail me if you have any questions