Coffing hoist is the trade name of a well-known group of chain-operated hoists. The name has, however, come to be used by many as a generic description for all similar lifting devices. Coffing hoists may be manually operated or powered by an external power source, and all utilize a system of cogs and ratchets, which lift a hook block suspended on a chain. Manual coffing hoist models are usually operated by a lever or a continuous loop of chain that drives the lifting mechanism via a cog, while powered variants are typically driven by an electric or compressed air motor.
The coffing hoist family of chain-driven hoists is one of the best known in a wide variety of industries. The name has become synonymous in many circles with chain hoists in general, with other brands being generically referred to as coffing hoists. Available in a comprehensive range of load capacities and drive configurations, the coffing hoist is a simple, reliable, and safe hoisting solution that requires little maintenance and operator skill.
Most chain hoists work on the principle of shortening or lengthening a loop of chain on which a hook block is suspended. When the loop is lengthened, the hook block, and any load that it carries, descends. When the loop is shortened, the hook block and load is lifted, achieved by having one end of the loop fixed to a static point within the hoist casing while the other end is attached to a driven take-up spool. The exposed loop of chain below the hoist casing passes around a free spool cog located within the hook block.
When the coffing hoist is activated, the take-up spool will, depending in which direction it is driven, either wind or unwind the chain around its arbor. This has the effect of shortening or lengthening the exposed chain loop. Due to the free spool cog in the hook block, it does not move along the chain in a fixed position, but rather moves straight up or down at the apex of the loop as it lengthens or shortens. This consequently supplies the raising or lowering action of the hoist.
Both manual and powered hoists are available, but work in different ways. Manual coffing hoist models may either utilize a lever to drive the take-up spool or a separate, continuous loop of chain that drives the spool via a cog on its one end. A selector switch is used to set the hoist to lower or lift the load. Powered hoists work in a similar fashion and utilize a reversible electric or compressed air motor to drive the mechanism. The controls for the motor are typically suspended from the hoist casing on a flexible cable allowing the hoist operator to control operations from a safe location.