Abstract: A gas spring with a piston rod assembly received for movement between retracted and extended positions in a casing defining a main gas chamber. The piston rod assembly when in its extended position cooperates with a portion of its retainer and the casing to at least in part provide a secondary gas chamber separate from the main gas chamber and having gas trapped therein at a higher pressure than that of gas in the main gas chamber to reduce the force required to initially move the piston rod assembly from its fully extended position toward its retracted position.

Abstract: A gas spring with a piston rod assembly received for movement between retracted and extended positions in a casing defining a main gas chamber. The piston rod assembly when in its extended position cooperates with a portion of its retainer and the casing to at least in part provide a secondary gas chamber separate from the main gas chamber and having gas trapped therein at a higher pressure than that of gas in the main gas chamber to reduce the force required to initially move the piston rod assembly from its fully extended position toward its retracted position.

Abstract: A 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 net 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.

Abstract: For a hydraulically actuated device a hydraulic power cylinder with an actuator slidably received for reciprocation within the cylinder and a piston slidably received for reciprocation within a sleeve of the actuator and defining a gas chamber on one side of the piston and a hydraulic fluid chamber on the other side of the piston so that the maximum pressure in the hydraulic fluid chamber is limited as a function of the force of compressed gas in the gas chamber acting on the piston. In this way, the maximum system pressure is a function of and substantially corresponds to the pressure of the compressed gas within the gas chamber and acting on the piston. Desirably, the pressure of the compressed gas in the gas chamber can be readily changed to change the maximum hydraulic fluid pressure.

Abstract: A hydraulic actuator for a hydraulically driven device has a hydraulic cylinder, a first piston slidably received for reciprocation within the cylinder and defining a hydraulic fluid chamber with the cylinder, a second piston slidably received for reciprocation within a cavity in an actuator rod connected to the first piston and defining a gas chamber on one side of the second piston and an accumulator chamber on the other side of the second piston. A passage formed in the first piston communicates the hydraulic chamber with the accumulator chamber and a pressure relief valve selectively permits hydraulic fluid flow through the passage from the hydraulic chamber to the accumulator chamber to limit the maximum pressure of the hydraulic fluid within the hydraulic chamber and the hydraulically driven device. Preferably, during normal operation of the actuator and the hydraulically driven device the pressure of the hydraulic fluid is less than that required to open the pressure relief valve.

Abstract: A gas spring that momentarily dwells in its retracted position after the retraction force is removed. The gas spring has a casing, a first piston received within the casing, a piston rod protruding from the casing and connected to the first piston, and a second piston received within the casing. A compressible gas is received within the casing between the second piston and the other end of the casing. A hydraulic fluid is received within the casing between the first and second pistons and between the first piston and the one end of the casing. A delay valve and a check valve carried by the first piston controllably transfer hydraulic fluid between the two fluid chambers, the delay valve causing the first piston and rod to dwell in the retracted position by delaying the free transfer of fluid between chambers.