Measurement Information for Technicians and Consumers.
Have you ever had your barbeque tank filled? Ever wonder how much propane was put into the tank? Since you can't see the product, it is a bit of a mystery how much propane you may have received. Your tank cannot be completely filled with propane. To do so would be very dangerous as there would be no room for the propane to expand when it warmed up. This would force the safety valve to open and release propane into the surrounding atmosphere.
To fill the tank properly, the dealer must calculate the maximum safe fill from the Water Content (WC) value stamped on the tank. The maximum amount of propane that can be placed in the tank is 42% of the WC value. This ensures adequate room for the propane in the tank to expand safely. The empty (tare) weight of the tank is also stamped on the the collar and allows the dealer to calculate a full or gross tank weight.
Your dealer should weigh your tank before and after the fill to determine how much propane has been pumped into the tank. The calculator will allow you to easily complete the calculations and ensure you get the propane you've paid for.
Many dealers will try and charge a flat rate for filling your tank. This means that you will pay the same amount whether you bring in an empty tank, or a partially filled tank. In some jurisdictions, this is illegal. In others it may not be illegal, but do you want to pay for propane not received? Make the dealer weigh the tank before delivery and again after and you can then calculate exactly how much propane was placed in the tank.
By the way, if your tank has an OPD or Overfill Protection Device, do not let your propane supplier convince you that the tank need not be weighed simply because it is full when the valve closes. This isn't necessarily true! These valves are notoriously unrepeatable and you will have no idea how much propane is actually in the tank. While the tank is full in that no more propane can be placed into it, it doesn't mean that you have received the maximum amount of propane that the tank was designed to hold (i.e. 42% of WC). Make them weigh the tank before AND after the fill.
Of course, some tanks are filled using a meter. This is fairly rare for small barbeque style tanks but is quite common for larger tanks. The tank is usually filled until a "spit valve" starts to discharge liquid propane. The spit valve is set at the correct level in the tank to ensure that the tank is not overfilled. In this case you will be given a statement of quantity in litres or gallons.