Piston-type air motors are generally used where slow-speed, high-torque, heavy-duty, accurate load positioning and control are required and where minimum servicing is desired. Vane-type air motors are generally used for high-speed applications at moderate torque. Vane-type motors are less expensive than piston type and normally require more maintenance.
Pull chain control is least expensive, but pendant control is sometimes selected for combined air hoist and air trolley drive control. Either type can provide precise control.
Air hoists should be connected to an air supply of sufficient capacity and pressure to safely operate the hoist. All air hoses supplying air should be positively connected to prevent their becoming disconnected during use.
Adjustable, automatic, upper- and lower-limit stop valves should be provided to prevent overtravel of the hook in either direction.
If an ordinary hook is used to hang the hoist from its support, it may unhook if an obstruction is contacted when lowering. A clevis, or other device, should be used to prevent the hook from being detached from the hoist support.
Whenever an air hoist is overhauled check that internal parts are properly secured. When a piston-type air hoist has been in operation for a long time, the lock-nut that holds the piston on its rod may become so loose that the rod will pull out of the piston, and let the load drop. The piston can be secured to the rod with a castellated nut and cotter pin. Be sure the piston is well secured to the rod.