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An air hoist is a device used to raise vehicles to allow them to be worked on from below. An air compressor feeds air through an air line that is connected to an air bladder within the hoist's main cylinder. By using a switch located in the air line, an operator can add air pressure to raise the hoist or release air pressure to lower the hoist. While in the raised position, the air hoist has a manual locking pin which ensures that the air hoist cannot drop unexpectedly. The operator simply pulls the pin out of the locked position when the air hoist is ready to be lowered.
Many of the vehicles manufactured around the world today require service and maintenance from underneath. This necessitates that service stations be able to raise the vehicles to access critical areas. Hydraulic hoist designs are much slower than the air hoist and require a dedicated hydraulic system solely for the purpose of operating the hoist. The air hoist is able to utilize the air from a compressor, which is typically already in use for several other functions within the garage area.
The hazard with an air hoist is that the locking pin safety feature often goes unused by the hoist operator. This can allow the hoist to drop unexpectedly and without notice. Serious injury and death can result from this action. Loss of air pressure, a undetected leak in the air bladder or a number of other occurrences can be the cause of the air hoist dropping suddenly.
Due to the drop characteristics of the air-operated hoist, most new garage construction incorporates the mechanical screw hoist into the design. This type of hoist uses a threaded rod and an electrical-driven motor to raise and lower the hoist. This eliminates the potential of the sudden drop. The electric hoist is slower than the air-powered version; however, it is thought by many to be safer.
Taking precautions, such as always engaging the safety lock and performing regular maintenance on the hoist, allows the air hoist operator to feel safe when working with the hoist. While there are several versions of the hoist in use around the world, the most common and widely used model is the single-cylinder type. This hoist uses a single ram positioned at the center of the vehicle, with arms that extend outward and contact the vehicle's chassis at the proper lifting points.