area of rod 14 to be approximately the same as the piston assembly 16 surface area associated with rod side chamber 60 allows for approximately the same force being applied to rod 14 in opposite directions when valves 50 and 52 are sequenced as discussed herein advantageously this reduces the physical size of the cylinder that is required in order to produce the desired extending force in rod 14 rod 14 is connected to a mass 76 which can be a movable member 76 such as a door the overall assembly of mass 76 with articulator assembly 10 can be referred to as a movable assembly as mass 76 is extended away from articulator assembly 10 it may encounter an obstacle 78 in the prior art pressure may build in head end chamber 62 and when obstacle 78 is removed or yields the built up pressure in head end chamber 62 unchecked by pressure in rod end chamber 60 would cause mass 76 to be rapidly moved causing possible damage to the prior art cylinder assembly or to something that mass 76 may contact in the present invention this is prevented or moderated by communicating pressurized air to both sides of the piston as rod 14 is extended a pathway is provided to maintain balanced air pressure on both sides of the piston when an outside force acts to overcome air pressure and cause the piston rod to retract the term u201c moderate.