Cylinder structure

Claim 1

Piston and cylinder structure comprising a hollow cylinder having open ends, an annular piston positioned within the cylinder for reciprocation axially thereof, a hollowed out piston rod attached to the piston at one end thereof and having a closed end extending out of the one end of the cylinder, means for sealing against admission of external atmosphere between the piston rod and the one end of the cylinder, the inner surface of the cylinder being slightly greater in diameter than the outer surface of the piston rod whereby the outer surface of the piston rod is in spaced relation to but closely adjacent the inner surface of the cylinder, said piston rod being hollowed out over most of the length thereof, and the hollowed out portion of the piston rod having a substantially greater radial extent than the non-hollowed out remaining portion of the piston rod, means for securing the other end of the cylinder to a source of gaseous actuating medium under pressure to provide the gaseous actuating medium directly to the inside of the piston rod, rigid positive stop means for limiting piston travel under said pressure, means for evacuating the space defined between the cylinder, piston, piston rod and sealing means through the piston rod without contaminating the surfaces defining said space or restricting movement of the piston and piston rod, comprising radial openings in the piston rod extending between the space and the interior of the piston rod, a manifold for gaseous actuating medium connected to the other end of the cylinder, and a control panel connected between the manifold and the source of actuating medium under pressure for providing an indication of the actuating medium as charged.