| 摘要 |
A gas spring having a main gas chamber, a secondary gas chamber and sealing surfaces which, during a portion of the stroke of the piston rod, define a gas tight seal between them to provide two separate gas chambers each providing a force acting on the piston rod in opposed directions to each other to reduce the n et force on the piston rod. When the piston rod is near its fully extended position the sealing surfaces provide the gas tight seal and the net force on the piston rod is minimal and in the direction to move the piston rod to its fully extended position. Thus, until the cooperating surfaces are displaced to terminate the gas tight seal, only a slight force is required to initially move the piston rod from its fully extended position. This greatly reduces the impulse or impact force imparted to a press ram upon initial actuation of the fully extended piston rod. A second seal assembly may also be provided which controls the rate at which the piston rod assembly returns to its fully extended position. After the gas tight seal is terminated, the gas spring functions generally a s a conventional gas spring with a single gas pressure acting on the piston rod and biasing the piston rod towards its extended position against the force of the ram displacing it.
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