There are numerous kinds of forklifts that are operated by propane gas. Forklifts that use propane are easy to refill. The gas is stored in a pressurized tank on the truck's back. The propane is pushed into the engine, where it is converted into vapor and the vapor mixes with air. The forklift throttle is used to control the vapor flow. A spark plug ignites the air and vapor mixture producing pressure which moves the pistons. The pistons turn the wheels and power the hydraulic pump.
Forklifts that use propane are suggested for use inside warehouses and other buildings since they are clean burning with low emissions.
The forklift's hydraulic system is what allows it to raise and move very heavy things from location to location. Cylinders, a pump and tubes make up the hydraulic system. The pump forces dense fluid in the tubing and into the cylinders. The pressure build up pushes a piston, which raises the forks. When the operator lowers the forks, the hydraulic fluid flows out of the cylinders and back into the pump.
Propane forklifts work well where maneuverability is needed. Not like an automobile, a forklift uses its rear wheels to turn, that enables the forklift to rapidly turn on a tight radius.