LP (LIQUID PROPANE) - FUEL SYSTEM Proper service and repair is important to the safe and reliable operation of all gaseous fueled engines. Any servicing or testing of a gaseous fueled engine must only be performed by qualified personnel. Always follow applicable installation and service procedures. An example of these requirements is found in NFPA-58 for liquid propane. These are US Federal standards. Worldwide standards vary. Local, city, and state requirements may also have certain requirements that must be observed.LP (Liquid Propane) is a gaseous fuel and when stored under pressure, becomes a liquid. Although a vapor forms at the top of the tank, this particular system uses a liquid withdrawal method, drawing from the bottom of the tank. This is accomplished with a special valve that is installed on a normal propane cylinder with a tube that is attached to the valve and extends to the bottom of the storage tank. Because of pressure in the tank, liquid propane is forced through the tube when the valve is opened.The LP system starts with a pressure relief valve to prevent excessive pressure from building in the system during shutdown. This is followed by a 12 volt (normally closed) electric solenoid, which prevents the flow of LP when the ignition key is off. Fuel should not flow to the regulator until oil pressure closes the contacts in the oil pressure switch.The LP vaporizer regulator converts liquid propane to a vapor. The vaporizer uses engine or drive system oil to provide heat to aid in the evaporation process. The regulator controls the vapor supply to an amount required by the engine. The engine’s intake vacuum draws Vaporized LP into the carburetor on an on-demand need. When the engine is off, the LP no longer flows from the regulator to the engine