The tech training tip for the month is going to be the basic anatomy and operation of the forklift propane fuel cylinder. Propane cylinders are constructed of either steel or aluminum. They are built to the specifications of the dept. of Transportation (DOT). They are rugged, but should never be mishandled or abused. The bottom footing is designed to keep the cylinder steady when the cylinder is in the upright position. The top collar is designed to protect the fittings and provide positioning holes for properly mounting the cylinder on a forklift. A propane cylinder is designed to contain propane in its liquid form. Propane is stored in the cylinder under pressure to keep the propane in a liquid state. Liquid propane reacts in much the same way to temperature and pressure as water, except propane’s boiling point is much lower on the thermometer. Propane’s boiling point is around –44 deg. F. and with any temperature above this point it would look and act just like water boiling in a pot on a stove, the propane would boil and vaporize. When water or propane vaporizes it causes pressure and that pressure is contained inside the propane cylinder ranging from 30 to 200 psig. The ambient temperature outside the container governs the vapor pressure in the tank, not by the amount of liquid propane inside (see Fig. 1).
When the pressure reaches 128psig it acts against the liquid propane and the boiling point has been raised to slightly more than 80 deg. F. So if the propane container temperature is 80 deg. F or less the propane will remain in a liquid form. If the temperature of the cylinder were to exceed roughly 130 deg. The tank contains a safety relief valve (located in the vapor section) that would release any pressure in an excess of 300psig. Propane is then drawn out through the liquid service valve supplying propane to your forklift. The liquid service valve is connected to the liquid withdrawal tube (see Fig. 2 Item 8) which is a tube that extends down below the surface level of liquid propane.
It is very important that the end of this tube is submersed in the liquid propane. The locator pin (see Fig. 2 item 10) on the truck is there to assist in placing the liquid withdrawal lube into the liquid propane. If the tank were to become rotated so that the tube was out of the liquid (see Fig 3), the truck would run out of fuel simulating an empty tank. So in-order to utilize all the fuel in the propane cylinder, make sure all your trucks have the locator pin in place and your forklift operators locate there tanks on that pin.