Swivel chair height adjusting mechanism

Abstract From the Canadian patent

A chair seat support apparatus includes a base column internally housing means automatically operable only when the chair seat is unoccupied to allow vertical altering of the height of the seat upon rotation thereof. A screw post is journalled within the base column by means of vertically displaceable upper and lower bearings between which is disposed a notched adjustment nut carried by the screw post. Spring means responsive to an unoccupied chair seat urges the lower bearing, upwardly which in turn vertically displaces the adjustment nut and its captive screw post. Stop means carried by the base column limits the vertical displacement of the adjustment nut when elevated such that …