Self-blocking gas spring released by external force

A gas spring arrangement comprising:

• (a) a cylinder having an axis and bounding a sealed cavity with first and second ends therein, an end region being provided at the first end of said cavity;
• (b) a piston rod member extending from the second end of said cavity and being axially movable inward and outward of said cavity;
• (c) a piston member mounted in said cavity on said piston rod member for movement therewith and axially separating said cavity into a first, inward compartment and a second, outward compartment, said piston member having a diameter smaller than the diameter of the cavity outside the end region;
• (d) a body of fluid under a pressure higher than atmospheric pressure sealed in said cavity for acting on said piston member to bias said piston rod member axially outward of said cavity, the diameter of the piston member being small enough to create an annular space between it and the cylinder outside said end region sufficient to allow the passage of said fluid;
• (e) valve means operatively interposed between said compartments for connecting the same in response to outward movement of said piston rod member from said cavity, said valve means including an annular disc mounted to the piston member and a piston ring mounted between the disc and piston member for limited axial movement such that movement of the piston rod into the cavity causes the piston ring to block and seal the annular space between the piston member and the cylinder, while movement out of the cavity causes the piston ring to unseal the annular space;
• (f) blocking means for blocking movement of said piston rod member inward of said cavity and responding to a predetermined axial force applied to said piston rod member in a direction inward of said cavity for releasing said piston rod member for said movement inward of said cavity, said blocking means including (1) means defining an axial passage in said piston rod member extending from the end of the rod in the first compartment to just beyond the piston member in the second compartment and remaining continuously open to said first compartment, (2) a radial passage extending from the axial passage to the second compartment so as to provide the only connection between said first and second compartments during inward movement of said piston rod and (3) pressure-relief valve means for closing said radial passage in the absence of a fluid pressure differential between said compartments generated by said predetermined force and for opening said passage in the presence of said fluid pressure differential, said pressure-relief valve being in the form of a resilient sleeve surrounding said piston rod at the location of said radial passage and yieldably closing said radial passage.