A mechanical or electrical pump for drawing fuel from a storage tank and forcing it to an engine or furnace. The type of pump chosen for a given fuel depends to a great extent on the volatility of the liquid to be pumped. In a gasoline engine the fuel is highly volatile at ambient temperature. Therefore, the fuel line is completely sealed from the tank to the carburetor or fuel-injection system to prevent escape of fuel and to enable the pump to purge the line of vapor in the event of vapor lock—a condition in which the fuel vaporizes owing to abnormally high ambient temperature.