1. Field of the Invention
The invention relates to a longitudinally adjustable gas spring for adjustable-height chairs and tables, comprising an exterior cylinder with a central longitudinal axis, an interior cylinder arranged concentrically to the central longitudinal axis in the exterior cylinder, a piston arranged displaceably in the direction of the central longitudinal axis in the interior cylinder, a piston rod arranged concentrically to the central longitudinal axis and mounted on the piston and guided out of the one end of the exterior cylinder and a valve on the other end of the exterior cylinder. The valve has a valve body with an annular groove open towards the inside wall of the exterior cylinder which contains an annular seal. A sealing arrangement is formed between the piston rod and the inside wall of the exterior cylinder on the one end of the exterior cylinder, which arrangement has a sealing body with an annular groove open towards the inside wall of the exterior cylinder which accomodates an annular seal. A deformation provided on the edge of the exterior cylinder retains the valve body, and a deformation provided on the edge of the exterior cylinder and retains the sealing body. The invention further relates a longitudinally adjustable column for adjustable-height chairs, tables or the like, having such a longitudinally adjustable gas spring and having an upright tube with a first end a second end, and comprising a guide bush arranged on said first end of the upright tube and guiding the exterior cylinder of the gas spring, a bottom plate arranged on said second end of the upright tube and having an opening passed through with some radial clearance by a pin of the piston rod, a pivot bearing bearing against the bottom plate on the one hand and against the piston rod on the other hand, a safeguard element between the piston rod and the bottom plate, and a damping member arranged on the piston rod between the pivot bearing and the sealing body.
2. Background Art
Longitudinally adjustable gas springs of the generic kind known from U.S. Pat. No. 4,844,392 have a valve body having, among other things, an annular groove on its outside, in which an annular seal is located bearing sealingly against the inside wall of the exterior cylinder. Conventionally, the sealing body is of two-piece design, an annular groove open to the outside being formed in an external closing disc and being completed on one side by a sleeve. This sleeve houses a seal bearing against the piston rod. A seal bearing against the inside wall of the exterior cylinder is arranged in the annular groove. The pre-assembled unit consisting of a valve, a piston with a piston rod and a sealing body with seals and-the interior cylinder is inserted with one side, regularly with the valve ahead, into the exterior cylinder. Then the edges of the exterior cylinder are beaded around the valve body and the closing plate, respectively. Since with this kind of insertion, the seal located in the annular groove of the valve body is pushed through the full length of the exterior cylinder, the latter's surface must have excellent surface qualities and little roughness for the annular seal not to be damaged. For this reason, seamless drawn steel tubes or at least welded steel tubes subjected to follow-up drawing are used. Seamless drawn tubes or follow-up drawn welded tubes are very expensive. The valve body on the one hand, and the sealing body on the other are arrested in the direction of the central longitudinal axis by beads of the adjacent edges of the exterior cylinder. When gas springs of this type are used in longitudinally adjustable columns for chairs, tables or the like, the end of the housing assigned to the sealing body and located on the side of the piston rod exit contacts the elastic damping member conventionally consisting of an annular cylindrical rubber body and located on a pivot bearing, when the housing is inserted as far as possible into the upright tube of the column. When the gas spring is extracted as far as possible from the upright tube, the housing of the gas spring is no longer arranged full length in a guide bush in which it is guided in relation to the upright tube. This increases the risk of tilting.