Pneumatic springs and other telescopic systems

Claim 1

An extreme-position detector device for a telescopic pneumatic spring of the kind comprising a gas filled hermetic cylinder having a sealed bottom closure at one end thereof, and an assembly which is movable with respect to said cylinder and which includes a plunger rod extending gas tightly and slidably through the other end of said cylinder and into the same, and a damper piston fitted at the inner end of said plunger rod and presenting a restricted passage formed therethrough, said piston dividing said cylinder into two pressure chambers which communicate with one another through said restricted passage, wherein the improvement comprises: means for electrically insulating said rod-and-piston assembly and said bottom closure from each other and maintaining the same in electrical out-of-contact relationship when said plunger rod is in its extreme extended position as well as throughout substantially the whole stroke of said piston in said cylinder from said extreme extended position, a source of electric current, means for electrically connecting said rod-and-piston assembly to one terminal of said source, means for electrically connecting said bottom closure to the other terminal of said source, and an electrically actuatable signalling means fitted in series with said source in the electric circuit connecting the same to said rod-and-piston assembly and bottom closure, whereby said signalling means is actuated to indicate upon electric contact engagement between said piston and said bottom closure occurring only when said plunger rod is in its extreme retracted position within said cylinder.