Sealed belt tensioning device

A belt tensioner comprising:

• a spring case;
• an arm pivotally coupled to the spring case, the arm having an engagement surface and being configured to pivot relative to the spring case about a pivot axis;
• a biasing mechanism operatively coupled to the arm to bias the arm relative to the spring case;
• a bushing positioned between the arm and the spring case;
• a cap enclosing the biasing mechanism within the spring case or a deflected arm plate seated on the arm;
• and
• a seal assembly comprising a primary seal positioned between the spring case and the arm and a secondary seal positioned between the cap or the deflected arm plate and the arm;
• wherein the seal assembly is coaxial with the pivot axis and configured to accommodate relative axial movement between the base and the arm and relative radial movement between the base and the arm while still maintaining a seal at both the primary seal and the secondary seal, thereby blocking contaminants from reaching the bushing;
• wherein the primary seal and the secondary seal operate in tandem such that as one of the primary seal or the secondary seal expands, the other is compressed, the primary seal and the secondary seal both expand or compress in the same manner.