Variable Speed Belts & Sheaves are a specialty mechanical drive system that allows the varying of the driven speed either manually or automatically. In the manual method of speed changing some systems require that they be shut down for the adjustment to be made, while others can be made while the system is in use. The typical systems in this category are V-Belt Systems, V-Flat Systems, and Variable Speed Systems.

V-Belt Systems - These systems are used in many restaurant exhaust fans over grills and fryers. The sheave can be multiple grooves for higher horsepower applications and are usually manually adjusted by screwing the sheave sides in or out, on a threaded shaft, to change the effective pitch diameter of the sheave. In the same application, however, it is possible to add a "screw" adjustable motor base to the project and us a "spring loaded" sheave. In this manner, when the motor base is moved with the adjusting screw, the tension on the belt increases, thereby pushing out on the sheave sides and "automatically" adjusting the pitch diameter of the spring loaded sheave. An inexpensive, yet practical way to change speeds. In still another variation of this latter method of speed change, we can add a "motor" to the adjusting screw and automate the speed changing mechanism. By simply energizing the motor in either the forward or reverse direction, we can press a button at a remote location and vary the speed of the exhaust fan. 

V-Flat System - This is a hybrid of a more standard V-Belt variable speed drive system. In this case, one of the sheaves (usually the driven) is a "Flat Belt" and the belt being used is a "wide" variable speed belt that looks very similar to a synchronous belt with drive teeth. This system will transmit less power than a V-V system. Keep in mind that, as with all V-Belt drives, power is transmitted by the friction on the SIDES of the belt, not by the teeth on the inner circumference.

Variable Speed Systems - This category of system is dedicated to the higher power variable speed systems. Where the V-Belt system is normally a "Fractional Horse Power" system, this type of variable speed combination will go from small integral horsepower (5HP or 7.5HP), upward to the 125HP range. In these systems we are talking about a "fixed pitch diameter" sheave (normally on the driven equipment) and a spring loaded variable speed sheave on the driver (usually an electric motor). The smaller of the belts will be 7/8" wide and the larger of the belts will be 3" wide. The fixed pitch diameter sheave in these systems is referred to as the "companion" sheave and is typically a wide faced sheave (flat face is wide enough to accept the belt being used) with side flanges. These flanges are extensions of the face edges and are approximately the height of the belt thickness. There are times when a standard "flat pulley" is used as the companion sheave and of course, this pulley is without the flanges.

The various sheaves come in "Bore to fit" types as well as those that use a "Tapered Bore Bushing" for those times when you're not sure of the shaft size or simply wish to have the convenience of being able to use the sheave in some other application at a different time by simply buying a different tapered bushing. Keep in mind, also, if you need to have a "special" size bore that is NON-STOCK, the A.R.& E. machine shop can bore that sheave to the proper size in a lot less time than it'll take us to get it special ordered from the factory.