A. If the pressure within the vehicle tank exceeds that of the economizer’s setting, the economizer valve will open and allow the excess pressure to be introduced to the liquid withdrawal stream.

B. The process of pulling the vapor from the top of the tank will reduce the pressure within the tank very rapidly. When the pressure within the tank drops to the set point of the economizer, the economizer will close, allowing only liquid to be withdrawn.

C. The tank is protected against over pressurization by two relief valves. If the vehicle has not been operated for some time, the liquid will take on heat and expand, causing the pressure within the tank to rise.

D. The primary relief valve will open and relieve the excess pressure by exhausting the vapor into the atmosphere. For safety, the primary relief valve is plumbed to vent away from the vehicle.

E. If the primary relief valve or its plumbing should become obstructed or malfunction, the pressure within the tank would reach the setting of the secondary relief valve. The secondary relief valve would open, relieving the excess pressure.