Operation
1.A chain hoist is operated by hand. An operator will pull down on one of the chain loops on one side of the chain. This will turn a pulley mechanism inside the chain hoist housing. When this pulley turns, it will lift up the end of the other chain which usually has a hook on the end. By pulling down on one chain, the manual hoist is actually able to increase the mechanical work that is being done. This is caused by the gear ratio inside the manual chain hoist.
Design
2.Inside the chain hoist housing are two gears. One is smaller than the other. Most chain hoists use a 20 cm and 25 cm gear. The two gears are attached, so when one moves, the other moves. The chain is looped over the smaller gear, and then hangs down in a loop (the loop you pull on). The chain then continues on over the larger gear and down to a point or another loop, depending on the type of hoist you are using. The operator pulls on the section of chain which is looped over the smaller gear.
Gear Ratios
3.When someone pulls down the chain as explained in Section 1, the smaller gear will turn. However, since it is smaller in size, it turns faster than the larger gear. It makes more rotations than the larger gear in a cycle. Since the larger gear is turning slower, it creates more force, in effect transforming the "pull" on the chain into a larger force. This is a mechanical advantage. An operator can put less force on the smaller gear, but still lift large objects. That is because the larger gear transforms that force into a much larger one.
How Chain Hoists Work
Chain hoists operate via an endless chain looped over a dual pulley system, adding a mechanical advantage in the same way as a pulley. The hoist incorporates a tooth and ratchet system, which prevents the load from slipping. Whilst chain can also break, it does not 'whip' at high velocity as is the case with high tensile steel cable.
For smaller tasks, such as lifting an engine block, manual chain hoists are common, but electric chain hoists are an option for heavy and awkward cargoes. For huge loads, hydraulic hoists and compressed air chain hoists are much more common, and these types are usually incorporated into cranes and jibs. This vertical lifting power of these hoists, coupled with the enhanced safety, makes them the only choice, but the difficulty lies in selecting from the variety of types available.
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