A chain hoist is a mechanical device used for lifting heavy loads of objects and equipment. It is made with a pulley, which is held together by a closed chain. The closed chain forms a loop, which makes it easy to be pulled by hand.
There are several large and small pulleys located throughout a chain hoist. There is one large and one small pulley are situated on the same axle, as well as a also a mobile pulley that holds the load in place.
For the load to be raised with the chain hoist, the closed chain has to be pulled. When it is pulled, the large pulley draws in more chain than what is released by the smaller side. From here, the lifting process begins.
Although the history of pulleys is unclear, it is known that primitive methods were employed to move heavy objects around. One of the early attempts at a pulley system was the single fixed pulley, which failed because friction prevented the wheel from being turned. Rope pulleys, which were commonly used for pulling water out of wells and are still in use today, are thought to have been invented next.
Archimedes, a Greek inventor of the early 3rd century BCE, has been credited for inventing a pulley designed to haul ships out of the sea. This was accomplished with a special block and tackle system which is still used today. Such early pulley inventions led to the development of the chain hoist.
There are three types of chain hoists: air, manual, and electric. The manual one and the air one are designed with reduction gears, hook pivots, and swivels. Suspended by a top hook, or by a push or geared trolley, these devices move objects slowly and carefully while making height adjustments. The attached load is well secured so it can be left fixed without requiring a great deal of supervision.
The electric chain hoist, on the other hand, is generally used for lifting heavy-duty industrial loads. It allows the user to pull from the side as well as vertically.
