Abstract: A gas spring comprises a first bypass with a one-way valve that allows fluid to bypass the piston when the piston moves outward, a second bypass with a spring-biassed valve that allows fluid to bypass the piston when the piston is pushed inward with a force exceeding the combined gas-spring and spring-biased valve forces, and a third bypass having a temperature-responsive valve that allows fluid to bypass the piston when the rod is pushed in but only when the temperature of the gas exceeds a selected level.

Abstract: A support column unit for an adjustable-height chair and the like comprises upper and lower telescoping tubular members, a piston-and-cylinder type pneumatic spring located coaxially within the tubular members and having its cylinder member secured to the lower tubular member, and a gravity dependent locking mechanism for locking the piston rod member of the pneumatic spring to the upper tubular member when the support column is upright and for releasing the piston rod member when the support column is inverted. The locking mechanism comprises a lock body retained within the upper tubular member and having a bore sized and positioned to permit sliding axial movement of the piston rod member therein. The lock body has one or more cavities, each one in communication with the bore and containing a locking member.

Abstract: A support column unit for an adjustable-height chair and the like comprises upper and lower telescoping tubular members, a piston-and-cylinder type pneumatic spring located coaxially within the tubular members and having its cylinder member secured to the lower tubular member, and a gravity dependent locking mechanism for locking the piston rod member of the pneumatic spring to the upper tubular member when the support column is upright and for releasing the piston rod member when the support column is inverted. The locking mechanism comprises a lock body retained within the upper tubular member and having a bore sized and positioned to permit sliding axial movement of the piston rod member therein. The lock body has one or more cavities, each one in communication with the bore and containing a locking member.