Sheave

Not to be confused with sheaf, which has the same plural as "sheave".

A sheave (pronounced "shiv" or "shēv") is a wheel or roller with a groove along its edge for holding a belt, rope or cable. When hung between two supports and equipped with a belt, rope or cable, one or more sheaves make up a pulley. The words sheave and pulley are sometimes used interchangeably.

A sheave can also refer to a pulley which has an adjustable operating diameter for use with a belt. This is accomplished by constructing the pulley out of several pieces. The two main "halves" of the pulley can be moved closer together or farther apart, thus altering the operational diameter. The usual construction is some sort of locking collar or set screws to secure the components, one half with a threaded central shaft and one half with a threaded center. By rotating the components one can "screw" the parts closer or farther apart. Thus changing the distance between the two halves and allowing the belt to ride higher or lower in the grove. The adjustments are limited to a specific range of size and is not infinitely adjustable. The sheave is thus purchased for the appropriate application. The adjustability of the sheave allows for the correction of speed of the driven load from a fixed speed driver, or for the adjustment of the load place on the driver. Thus an electric motor can have the load placed on it corrected up or down to match its rated capacity. A typical application would be a Belt Driven Blower Wheel with fixed pulley driven by an electric motor with a sheave. The sheave is adjusted for Max Load Amps of the motor to attain full capacity. Conversely the sheave can be adjusted "down" to lower the amount of air moved or static pressure attained by the blower.

See also

• Block and tackle
• Block (sailing)
• Pulley