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...http://www.google.com/patents/US5073149?utm_source=gb-gplus-sharePatent US5073149 - Diaphragm seal type tensioner
