Abstract: A hydraulic fluid tensioner for a toothed belt, having a piston with a piston-carried ball and seat check valve, utilizes a ball pressing spring having a spring force more than 30 times the weight of the ball and less than 60% of force resulting from the hydraulic pressure acting on the ball and urging the check valve open as the piston moves in the projecting direction. The spring force prevents rapid accelerating movement of the piston, or vibrations of the tensioner, from causing irregular piston movements resulting in noise and vibration.

Abstract: In a hydraulic tensioner, shock absorber or lash adjuster having a plunger in a cylinder filled with hydraulic fluid, and having a coiled compression spring acting on the plunger in a pressure chamber on one side of the plunger, air scavenging through the restricted space between the plunger and the cylinder wall is improved by providing radial grooves either on a face of the plunger contacted by the spring, or on the spring-contacting face of a plug which is located between the spring and the plunger. The radial grooves enable air to escape from the interior of the coil spring and move toward the cylinder wall. The grooves increase in depth proceeding from the interior of the spring toward the exterior thereof.

Abstract: In a fluid tensioner for a camshaft drive belt, a piston rod is sealed by a flexible diaphragm having an enlarged inner end clamped in a conforming groove in the piston rod by a spring clamp. This maintains the inner end of the diaphragm at a fixed position on the piston rod, and provides a labyrinthine seal preventing leakage of fluid. A flattened portion of the piston rod fits a D-shaped opening in a cap to prevent rotation of the piston rod and premature failure of the seal. A dust seal located on the cap also has a D-shaped hole, aligned with the D-shaped hole in the cap, and conforming to the flattened part of the piston rod.