The fixed liquid level gauge, also called the bleeder valve is the one and only gauging device that accurately depicts the level of propane in the tank when it is being filled. The face gauge is not to be used during the refueling process. This section will explain why the bleeder valve is open during the refueling process. Many people believe that using the fixed liquid level gauge during gas delivery results in a large amount of lost propane. Even if two cubic feet of propane gas is lost through the bleeder valve, this is only .05 gallons of gas. At $2.00 per gallon, this would be equal to ten cents worth of propane expelled through the bleeder valve.
The bleeder valve is designed so that during the filling process, when the propane going into the tank reaches 80%, liquid will come out of the opened valve. This lets the delivery driver know that the tank has reached its maximum filling capacity. The valve is connected to what is called a dip tube that goes into the container. The dip tube is fixed and set at length equal to 80% liquid level tank capacity. In other words, the tip of the dip tube is at the level equal to the container being 80% full. The dip tube itself should always be located in the vapor space and never submerged in liquid propane.
In simple terms, the fixed liquid level gauge tells the person delivering the propane that the tank is at the maximum safe capacity. The picture to the left is of a service valve with the dip tube protruding from the bottom. When installed by the tank manufacturer, the dip tube is pre-set to indicate when the tank is legally full during the filling process.
Think of it this way: When drinking a soda through a straw, you will not be able to get soda through the straw if the tip of the straw is above the level of the soda. When the tip of the straw is in the soda, you are able to drink the soda. A dip tube works along the same principal as a straw.