Self-contained tensioning device for a belt or similar structure

Claim 1

A self-contained tensioning device for a belt or similar structure which contacts a movable idler pulley, comprising: a body member having a shoulder portion; a plunger slidably mounted in said body member; a free piston slidably mounted in said plunger and having a head portion extended from said shoulder portion of said body member and contacted with said idler pulley so as to apply a tensioning force to said belt; a projection provided on said shoulder portion of said body member and projecting axially so as to minimize a distance between a portion of said idler pulley contacting said head portion and said shoulder wherein said plunger is slidably mounted in said body member so as to form a large diameter fluid chamber within said body member and said free piston is slidably mounted in said plunger so as to form a small diameter fluid chamber in said plunger; a spring for biasing said plunger in the direction of said large diameter fluid chamber; and a one-way check valve for permitting fluid flow only from said large diameter fluid chamber to said small diameter fluid chamber and wherein said projection comprises stopper means for limiting movement of said movable idler pulley.