Chain tensioners are a type of mechanical device that helps maintain the correct tension in a chain. Slackness in a chain or belt can cause vibration and noise and prevent the chain from engaging properly with the sprocket and operating effectively. Chain tensioners are used to take up this slackness and ensure continuous and effective operation. They also help extend the life of the chain.Automatic TensionersThese tensioners are designed to provide constant, automatic belt or chain tension by using built-in compression springs. Frequent manual adjustment is not required. These tensioners can be used for drives operating in any direction. The tensioner is mounted on the unloaded strand of the chain with the springs in the compressed condition to take up the slack in the chain. As the chain encounters more wear the tensioning spring extends and takes up the extra slackness. Two versions of these are the rotary tensioner and the linear tensioner.Rotary Tensioner – These automatic tensioners provide a full 90° of useable tensioning action. The body of the tensioner contains compression springs that provide an automatic take up action.Linear Tensioner – These automatic tensioners provide straight line take up for a range of drive mechanisms. Two spring loaded shafts are attached to a triangular mounting block or plastic chain guide.Fixed Chain TensionersThese tensioners require manual adjustment and consist of a metal slotted frame with a plastic chain guide. The tension is adjusted using a single bolt. These are suitable for use where automatic tensioning is not needed and in drives where torque reversals and speed changes are frequent.Universal Tensioning ElementThese tensioners are used on belts and chains where access to the rear of the tensioner mounting surface is not possible. The tensioner is fitted using a rear mounted bold and is held in place by friction. Alignment is carried out using a spigot. These universal tensioners are available in a ‘Chain Rider’ style which has a flexible head that can be used on both sides.