An idler sprocket is a device used to keep up the tension in a chain or chain drive system. Often comprising only a sprocket installed on a spring tensioned arm, the idler sprocket pulls against the chain in a constant manner to keep the chain tight all the time. How big is the sprocket used in an idler sprocket assembly has no influence on the functionality of the chain drive; however; a larger sprocket will often last longer because of the slower rate of the sprocket, which saves use on the sprocket’s bearings. Maintenance for the idler assembly is often only an occasional greasing of the sprocket’s bearings.
When traveling a machine by chain, the tension of the chain must be kept at a constant to avoid the chain coming from the get sprockets. By installing an idler sprocket in the travel program, the chain is definitely kept taut without being over-tightened. Operating a chain within an over-tight condition can result in premature bearing and chain failure while an idler sprocket placed in the machine is often a way to greatly expand the life of the chain, sprockets and the bearings on the machine’s sprocket shafts.
The ideal installing the idler sprocket is on the contrary side of the chain between your get sprocket and the driven sprocket. The application should place the idler sprocket in a position that has the sprocket pressing or pulling the chain towards itself since it loops both main sprockets in a form similar to the letter B. This style will allow the pulleys to draw the chain hard without hindering the idler at all as the drive chain passes over the sprocket. If a condition presents itself which needs the travel to exert extra pressure on the drive chain, the idler will flex against the chain, allowing it to expand 
while remaining in contact with the drive sprockets.
While the vast majority 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 plus some wooden sprockets have also been applied to some machinery without concern. Many machines, so that they can reduce the wear on the drive chain, use an light weight aluminum, cast iron or steel sprocket coated in a nylon materials. The metallic hub enables the idler sprocket to remain very strong while the nylon covering is usually soft on the chain links.
