Support devices for swivel chairs

Claim 1

A device for supporting a chair at a selected height, comprising a hydraulic cylinder arranged to support the chair, the cylinder being contractable to lower the chair under the weight of the chair occupant, a spring member acting to extend the cylinder to raise the chair when unoccupied, means defining two fluid-filled chambers in the cylinder, valve means separating the chambers, and manually-operated control means for selectively opening and closing the valve means, said fluid flowing between said chambers via the open valve means during adjusting expansion and contraction of the cylinder, and said valve means when closed blocking the fluid flow whereby to hydraulically lock the cylinder against expansion and contraction, each chamber including a portion immediately adjacent the valve means, said portions being axially spaced such that there is a substantially direct axial flow between the chambers substantially without reversal of the flow direction, one of said chamber being of smaller cross-sectional area than the other of said chambers, a plunger reciprocable within the cylinder and defining a boundary of said other chamber, said spring member acting between the plunger and the cylinder to bias the plunger in a sense to reduce the volume of the said other chamber, and the fluid flowing from said one chamber to said other chamber during contraction of the cylinder and causing the plunger to be displaced against the bias of said deformable spring member.

Claim 2

A device for supporting a chair at a selected height, comprising a hydraulic cylinder arranged to support the chair, the cylinder being contractable to lower the chair under the weight of the chair occupant, a spring member acting to extend the cylinder to raise the chair when unoccupied, means defining two fluid-filled chambers in the cylinder, valve means separating the chambers, and manually-operated control means for selectively opening and closing the valve means, said fluid flowing between said chambers via the open valve means during adjusting expansion and contraction of the cylinder, and said valve means when closed blocking the fluid flow whereby to hydraulically lock the cylinder against expansion and contraction, each chamber including a portion immediately adjacent the valve means, said portions being axially spaced such that there is a substantially direct axial flow between the chambers substantially without reversal of the flow direction, one of said chamber being of smaller cross-sectional area than the other of said chambers, a plunger reciprocable within the cylinder and defining a boundary of said other chamber, said spring member acting between the plunger and the cylinder to bias the plunger in a sense to reduce the volume of the said other chamber, and the fluid flowing from said one chamber to said other chamber during contraction of the cylinder and causing the plunger to be displaced against the bias of said deformable spring member.

Claim 3

A device for supporting a chair at an adjustable height, said device comprising a hydraulic cylinder arranged, in use, with its axis vertical and including a body member and a piston member reciprocable within the body member, means defining two fluid-filled chambers within the body member, valve means within the body member, said valve means separating the two chambers, manually-operable control means for selectively opening and closing the valve means to control fluid flow between the chambers, a plunger reciprocable within the body member, a deformable spring member biasing said plunger, one of said chambers being defined between the body member, the piston member, and the valve means, and the other of said chambers being defined between the body member, the valve means and the plunger, one of said members being arranged to support the chair from the other of said members via the hydraulic fluid contained in said one chamber when the valve means is closed, and the said piston member when the device is loaded with the weight of the chair when occupied effecting displacement of fluid from said one chamber to said other chamber, via the valve means, when the valve means is opened whereby to lower the chair, said fluid flow into said other chamber displacing the plunger against its spring bias, said spring bias acting to displace the plunger to return fluid to the said one chamber when the valve means is opened and when the chair is unoccupied to thereby to raise the chair, the valve means being mounted in the interior of the body member directly between the two chambers, and each chamber including a portion immediately adjacent the valve means, said portions being axially spaced, and said valve means including means defining a fluid passage extending substantially axially between the said portions of the two chambers, said one chamber having a cross-sectional area less than that of the said other chamber whereby the displacement of the plunger during lowering of the chair is less than the distance by which the chair is lowered.

Claim 4

A device for supporting a chair at an adjustable height, said device comprising a hydraulic cylinder arranged, in use, with its axis vertical and including a body member and a piston member reciprocable within the body member, means defining two fluid-filled chambers within the body member, valve means within the body member, said valve means separating the two chambers, manually-operable control means for selectively opening and closing the valve means to control fluid flow between the chambers, a plunger reciprocable within the body member, a deformable spring member biasing said plunger, one of said chambers being defined between the body member, the piston member, and the valve means, and the other of said chambers being defined between the body member, the valve means and the plunger, one of said members being arranged to support the chair from the other of said members via the hydraulic fluid contained in said one chamber when the valve means is closed, and the said piston member when the device is loaded with the weight of the chair when occupied effecting displacement of fluid from said one chamber to said other chamber, via the valve means, when the valve means is opened whereby to lower the chair, said fluid flow into said other chamber displacing the plunger against its spring bias, said spring bias acting to displace the plunger to return fluid to the said one chamber when the valve means is opened and when the chair is unoccupied to thereby to raise the chair, the valve means being mounted in the interior of the body member directly between the two chambers, and each chamber including a portion immediately adjacent the valve means, said portions being axially spaced, and said valve means including means defining a fluid passage extending substantially axially between the said portions of the two chambers, said one chamber having a cross-sectional area less than that of the said other chamber whereby the displacement of the plunger during lowering of the chair is less than the distance by which the chair is lowered.