Abstract:
A mechanism for controlling the opening and closing of a closure object, comprising an outer cylinder whose inner chamber, contains hydraulic fluid, a distal end of the outer cylinder being attachable to either a closure object or an object to be closed. A circumferential single groove is located in an inner wall of the outer cylinder and a piston shaft telescopically received within the outer cylinder extends proximally therefrom, being attachable to either a closure object or an object to be closed, and distally into the inner chamber. A piston head is mounted distally on the piston shaft. The piston head contains a bore therethrough, a peripherally located circumferential retaining groove, and an inclined outer surface which increases in cross section in the distal direction. A seal prevents hydraulic fluid from passing around the piston head between the distal chamber and the proximal chamber. A snap ring, partially housed within the single groove, engages the inclined outer surface of the piston head.