LP Vapor Withdrawal - With a vapor withdrawal system, the LP fuel is vaporized in the fuel tank by heat input from the ambient. The pressure is reduced to about 11" water column (0.4 psi) at the tank outlet with a regulator. The vaporized fuel is then brought to the engine and the demand regulator on the generator which reduces the pressure even further before it enters the carburetor.
LP Vapor Withdrawal is a simpler system for the generator set. Same low pressure vapor system as other appliances.
LP Liquid Withdrawal - With a liquid withdrawal system, the LP fuel is removed from the tank in liquid form and is brought to the generator set at tank pressure. The generator set supplies the heat to vaporize the fuel. The Marquis and Emerald LP liquid withdrawal systems include a coil that wraps around the exhaust manifold to add heat. In addition, the 2-stage regulator supplies additional heat as well as reduces the pressure to supply directly to the carburetor.
LP Liquid Withdrawal provides better operation in colder temperatures. If a complete vaporization pressure regulation system is on the generator from the factory, it will allow for a smaller capacity fuel tank.