Abstract: A double-acting cylinder and piston mechanism comprising a cylinder (1) substantially closed at both ends by front (5) and rear (7) end walls, a piston (8) axially displaceable within the cylinder (1), a first region (6) defined between the piston (8) and the rear end wall (7) of the cylinder (1) and a second region (4) defined between the piston (8) and the front end wall (5) of the cylinder (1), a piston rod (2) extending from the piston (8) through the front end wall (5) of the cylinder (1), an air inlet port (19) for communication with said first region (6) of the cylinder (1) and at least one exhaust vent (14) which is exposed during axial displacement of the piston (8) for release of air delivered to the cylinder (1) through the air inlet port (19).