An idler sprocket is a gadget used to keep up the tension in a chain or chain travel system. Often comprising nothing more than a sprocket installed on a spring tensioned arm, the idler sprocket pulls against the chain in a constant way to keep carefully the chain limited at all times. The size of the sprocket used in an idler sprocket assembly does not have any influence on the efficiency of the chain drive; however; a larger sprocket will often last longer due to the slower rate of the sprocket, which saves use on the sprocket’s bearings. Maintenance for the idler assembly is often no more than an intermittent greasing of the sprocket’s bearings.
When traveling a machine simply by chain, the tension of the chain must be kept at a constant in order to avoid the chain approaching from the travel sprockets. By installing an idler sprocket in the drive program, the chain is kept taut while not being over-tightened. Operating a chain in an over-tight condition can result in premature bearing and chain failing while an idler sprocket positioned in the system is usually a method to greatly lengthen the life span of the chain, sprockets and the bearings on the machine’s sprocket shafts.
The ideal installation of the idler sprocket is on the contrary side of the chain between the travel sprocket and the driven sprocket. The application should place the idler sprocket in a position that has the sprocket pushing or pulling the chain towards itself since it loops the two major sprockets in a shape like the letter B. This style allows the pulleys to draw the chain hard without hindering the idler in any way as the drive chain passes over the sprocket. If a condition presents itself which needs the travel to exert surplus pressure on the drive chain, the idler will flex against the chain, allowing it to expand while staying in touch with the travel sprockets.
While the the greater part of idler sprockets are produced of steel, many materials are accustomed to manufacture an idler sprocket. Many poly or composite sprockets have been used with great success and some wooden sprockets have also been used on some machinery without 
issue. Many machines, so that they can reduce the wear on the drive chain, use an aluminum, cast iron or metal sprocket coated in a nylon material. The metallic hub allows the idler sprocket to stay very strong while the nylon covering is normally soft on the chain links.