A dump hoist is a mechanism mounted to some types of trucks that allow the bed of that truck to be lifted; this in turn allows the contents of the bed to be unloaded rapidly, or "dumped." The mechanism is usually controlled by hydraulic arms mounted in such a way that the solid metal arms of the dump hoist can scissor upward, thereby pushing one end of the truck bed skyward. Hydraulic arms feature two parts: stanchions and pistons. The stanchions are loaded with hydraulic fluid, usually some type of oil, and the pistons are mounted inside the stanchions. As the stanchions are pressurized, the pistons press outward, expanding the hoist.
Dump trucks most commonly use a dump hoist system. These trucks feature large capacity beds with hinged gates that allow material to fall out freely when the dump hoist is activated. The top of the dump bed is usually open, allowing other heavy machinery to load materials into the bed for transport. Many dump trucks feature some sort of covering system that prevents material from flying out of the bed during transport. The dump hoist is housed beneath the bed, and it is generally hidden from view when the bed is in its normal transport position.
The driver of the dump truck can usually operate the dump hoist by using controls mounted in the cab of the truck, or on the side of the truck. Controls mounted on the side of the truck tend to be more convenient because the operator will be able to see where material is being dumped, whereas operating the unit from the cab of the truck can obscure the operator's view. Many trucks feature controls in both locations to make dumping possible from various positions.
Sometimes a dump hoist is designed for use with a standard pickup truck rather than a specifically designed dump truck. These units mount underneath the factory bed, which will have to be removed for proper installation of the hoist. These hoists tend to be smaller and lower capacity than dump truck hoists, but they are perfect for full-size pickup trucks or even mid-size trucks in some cases. The arms of the hoist are made of steel, just like the larger models, and the hydraulic arms will do the lifting and supporting of the load. Some smaller hoists may only feature one hydraulic arm, however, while most larger models feature two or more.