Propane Tanks
Here's what I (mostly) remember from my hot air balloon pilot exam - the pressure guage indicates the vapor pressure of propane, which varies with temperature. The pressure will not vary with liquid volume, until the tanks are empty. Pressure is useful in knowing the burner efficiency - which is critical in ballooning, and slightly less so when making rice-a-roni. While were on the subject, here's one thing balloon pilots are very careful about that is useful on boats: Let's say the temperature is 30 degrees out, and you've just finished using the stove for the last time and you turn off the tank. Now fast forward to spring time, and the temperature is 80. If you have propane in the line between the tank and stove, the pressure will build, risking a rupture in the line. I always empty the line after closing the tank. Possibly excessive, but safe. The propane tanks that balloon pilots use have a guage that reads volume, but is notoriously inaccurate. So the only way to really know the amount in the tanks is to weigh it: I seem to remember that propane weights 4.34 pounds per gallon. (I could be wrong - my propane manual has turned up missing) The empty weight (tare weight) of the tank should be etched into the tank. The only way I know to avoid the inevitable half-cooked meal is to either weigh the tanks regularly, or carry a spare tank. My personal contingency plan involves a local restaurant - I'm too lazy to take the tank out and weigh it.
