A tensioner pulley is a device that can be used to tighten the belt in any system of belts and pulleys. These systems typically consist of a number of wheels known as pulleys and a belt that is wound around them. In order for the belt to fit around the pulleys, some part of the system typically needs to be adjustable. One way to allow for this type of adjustment is a tensioner pulley, which can be either manual or automatic. Manual tensioners usually are pried into place or adjusted by turning a bolt, and automatic tensioners typically are spring-loaded.
In belt-and-pulley systems, pulleys are essentially wheels that either drive the system, power a device or simply freewheel, which means that they turn but do not use or provide power. Some of these systems consist of only the power and accessory types of pulleys, in which case one of the accessory pulleys usually is adjustable. This adjustment is often made by sliding or tilting the entire device until the belt is taught, after which it can be bolted into place. In some cases, the accessory device might also be slid or tilted into place by turning an adjustment screw. The other way to tighten a belt is to make use of a tensioner pulley.
The two main types of tensioner pulleys are manual or automatic. Sometimes a manual tensioner pulley needs to be pried into place until the belt is tight, at which point the pulley can be bolted down. Other varieties include an adjustment screw, which is a device that can allow the tensioner pulley to move in or out depending on which way it is turned. After the belt has been installed, this screw can be turned until the correct belt deflection is obtained. These pulleys usually have a bolt that needs to be tightened as well, because the adjustment screw might loosen from vibration otherwise.
Automatic tensioner pulleys usually are spring-loaded so that they are able to keep the correct tension on a belt at any given time. This type of tensioner pulley usually is pried back to release tension if the belt needs to be replaced. The pulley can be released after the new belt has been installed, at which point it will swing back into place and automatically provide the correct amount of tension. This type of pulley typically needs to be replaced somewhat regularly, because the spring tension can weaken over time. If an automatic tensioner pulley becomes weak, the belt can loosen, and the system might stop working properly.