Method and apparatus for emptying the contents of a tank carried by an engine-powered vehicle

A method of emptying a petroleum product contained within a tank, said tank having a selectively operable control valve to permit egress of the petroleum product, said tank further being carried by an engine-powered vehicle when the vehicle is equipped with an air pump, adapted to be operated by the engine of the vehicle, a first surge tank coupled with said air pump for accumulating air under pressure, and air brakes that are operated by the pressurized air accumulated within said first surge tank, said method comprising the steps of:

• accumulating within said first surge tank air from said air pump to provide a first source of air under pressure said first source of air under pressure being used to operate said air brakes;
• accumulating within a second surge tank air from said air pump whenever the pressure of the air within said first surge tank is above a preset value to thereby provide a second source of air under pressure, said preset value being above the minimum pressure needed to operate said air brakes;
• directing air from said second source of air under pressure to a point within said tank above the level of said petroleum product to thereby force said petroleum product from the tank when said control valve is open;
• and
• turning off the engine of the vehicle whenever air from said second source of air under pressure is being directed to said tank.