The two most common cylinders for propane are the 20 pound and 30 pound cylinders or pressure vessels. The 20 lb. cylinder holds 4.7 gallons of propane but is often referred to as a 5 gallon bottle. The propane is filled to 80% capacity. The extra 20% is used for the expansion of the liquid propane when it boils. Propane boils at -44°F. The boiling process creates the vapor that our RV appliances run on.

There are three ways to tell if the tank is full. The first is with the OPD. On the outside of the cylinder there is a device called the OPD, the overfill prevention device. Inside the tank is this device that acts as a float. It floats to the top when the tank has reached maximum capacity. The second way to be sure you have a full tank is to weigh it. The propane dispenser has a mathematical formula that is used to determine that the tank is full. The third way is to use the fixed liquid level gauge that is on the OPD. This is to be done by a propane dispenser only. The dispenser knows that the tank is full when a white fog is emitted out of a small hole on the OPD.

Since propane is a white liquid that boils at -44°F, if it were to get on you, it will do so in the form of a white cloud and it could cause frost bite. Propane is something to be left alone and the tanks should always be covered and latched with a propane tank cover.