With Bleed Valve and Pump
Most balloonists use this method of refueling. You go to the local propane dealer
and utilize their pump the same way you would fill your vehicle with gasoline. The bleed
valve on top of your propane tank is connected to a dip tube which extends into the
tank. The end of the tube is at the 85% capacity level for the tank. When the liquid fuel
reaches the end of the tube it spills out the bleed valve telling you that the tank has
reached the recommended capacity.
Like the prior example you would go to your local propane dealer (or they could come to you with a truck). This time instead of opening the bleed valve and waiting for the liquid to spurt out you fill the tank to a specific weight. As described below the procedure is somewhat more complicated. Since all balloon propane tanks have bleed valves why worry about this method? At least one state, Florida, in the late 80's considered a rule that would require all tanks to be filled by weight. Florida had experienced some problems (not balloon related) where the dip tube, which is screwed in, has come out and fallen to the bottom of the tank. Without this measure the tank will become completely filled before liquid propane comes out of the bleed valve. Read Overfilling Fires... beginning on page 18. Likewise should you suspect that this has happened you can check the accuracy of the bleed valve by using this method to refuel.
To calculate the weight of the tank filled, multiply the water capacity by the specific gravity of propane (about .5 at 70 F). Then multiply by .85, since the tank should only be filled to that capacity. This will give you the amount, in pounds, of propane that the tank can safely hold. Add to this the tare weight and you have the total weight when the tank is full (For "10 gallon" vertical aluminum tanks; Full weight = (103.6 x .5 x .85) + 26.5 = 70.5 lbs.).
Bleed Valve And No Pump
This method is sometimes mistakenly called gravity feed. What is
actually taking place is an equalization of pressure between two vessels. In this case
our propane tank and the main fuel source. The method is used whenever a pump is
not available such as a remote sight or transferring propane from one cylinder to
another.
This method can be accomplished using either the bleed valve or by weight. Filling a tank by this method will be slow. It works best if the receiving tank's internal pressure can be reduced well below that of the source.
Whenever you are refueling always wear gloves.