A sheave is a wheel with a groove in the middle and raised edges. It is also known as a sheave pulley and is part of a system used to raise or lower heavy loads. Some types include rope sheaves, wire sheaves, wire rope sheaves, belt sheaves and a cable sheaves.
Rope sheaves were the first type invented and work by pulling the rope to lift the load. A length of rope is guided on the groove and between the raised edges of the sheave. The rope can then either be tied on one end to the item that needs to be lifted or can be guided through another sheave to create a compound pulley.
Compound pulleys are often used because the item needs to move over a longer distance or is too heavy to lift with just one sheave. Some common uses for rope sheaves are on boats or ships for lifting cargo or traps and are called blocks or block and tackle. Rope pulleys have also traditionally been used to pull water buckets from wells.
Wire sheave pulley systems are constructed of several wire ropes. Many thin lengths of wire are coiled around one larger wire to add strength. They are also known as wire rope sheaves and typically are banded with approximately six other coiled wire lengths to create one large, strong wire rope.
This type of pulley system is often used in industrial machinery, such as cranes. It is used in cranes because of the significant amount of force being applied to the rope. Some cranes are required to lift objects weighing several tons, so to ensure the pulley can handle the weight, coiled wire sheaves are used.
Belt sheaves are part of a belt and pulley system. They are made of two or more sheaves working together and use a belt instead of ropes or wires. The sheaves are usually different diameters in order to move the belt faster with less effort. Belt sheaves are constructed like a chain drive but are smooth instead of having cogs.
Cable sheaves are similar to belt sheaves but typically used for much heavier objects. Cable sheaves also usually have spokes in the center instead of smooth grooves. The most common use for cable sheaves are for cable cars. The sheaves are attached at each end of the cable car route and the cable is strung through the middle. As the cable car travels down the cable, the sheave feeds the cable and propels the car forward.