Cylinder with an elastic device for returning a working piston unit to a neutral position

A cylinder with an elastic device for returning a working piston unit to a neutral position, this working piston unit being fixed onto a working rod and mounted so as to slide, in at least one working chamber, between a rest position and a working position, said neutral position being between the above two positions, the elastic device for returning said working piston to a neutral or intermediate position is of the pneumatic type and operates an auxiliary piston unit with a relatively small section, slidably mounted in an auxiliary chamber which is pneumatically supplied independently of that which operates said working piston unit, said elastic device has at least one auxiliary piston unit connected to said working piston unit and slidably mounted in an auxiliary chamber, this auxiliary piston unit being designed to be displaced inside said auxiliary chamber in one direction or the other by said working piston unit when the latter is displaced between its rest position and its working position, or vice versa, and to elastically compress a gas inside said auxiliary chamber so as to be able to return said working piston unit elastically to said neutral position, namely said rest position or said intermediate position, said working piston unit has two working pistons fixed onto a common working rod and in that it has, between the two working pistons, an auxiliary piston unit slidably mounted on the one hand on said working rod and on the other in an auxiliary chamber of a central part of a power cylinder, this auxiliary chamber being permanently subjected to a pneumatic pressure.