fluid 8 so forced flows from the reservoir chamber 10 through the orifice 9a and into the left portion of the cylinder chamber 11 thus a high pressure is realized within the cylinder chamber to the left of the piston ring 14 and owing to the closed loop fluid path a corresponding low pressure is created in the cylinder chamber 11 portion which is right of the piston ring 14 the resultant differential pressure occurring across the piston ring 14 propels the piston right towards the low pressure side the rail 3 being connected to the piston also moves to the right carrying pulleys 15 since the right cable length 17 is attached to the housing structure 1 at 16 and because the right pulley is moving right the portion of the cable length 17 between the right pulley 15 and the door 2 34 shortens 34 in a manner which causes the door 2 to slide right in effect the cable pulls the door thus for every inch of piston 14 rail 4 travel the door travels two inches it is readily apparent that turning the shaft 5 counter clockwise will move the door left also visible in fig4 are threaded holes for reception of the valve pins 6 and 7 turning of the valve pins 6 7 into the threaded holes will close off any of the desired orifices 9a 9b thus the flow of fluid within the closed loop is regulated by adjusting the valve pins 6 7.