cooling air opening or port 82 entering laterally through the body of the end cap 16 the bore 30 of the rod portion 23 at its lower end is widened to accommodate an annular bearing 86 and an annular seal 90 which are fixed to the rod portion 23 to slide against the outer sidewall surface of the second tubular member 44 within the second tubular member 44 beginning at the upper end of the liner 46 an annular bearing 92 and an upwardly successive annular seal 94 are fixed to the inside surface of the tubular member 44 to slide against the sidewall outer surface of the tubular member 38 the internal groove 58 in the upper end of tube 44 fig5 accommodates a snap ring to retain the bearing 92 and seal 94 in position against the outer end of the liner 46 in the function of the mechanism 10 shown in fig1 and 7 pressurized air to drive the piston 20 is delivered to the chamber 14 through an air inlet port 98 and into an annular piston recess 100 to move the piston 20 from the maximum down position shown in fig1 to the maximum up position shown in fig7 by other means not shown the piston 20 is held in the intermediate blank loading position during operation of the mechanism incoming cooling air flow moves from the port 82 through the transition 80 and upwardly through the lower coaxial tube arrangement 44 and 46 the air flow then moves through the upper tube 38 through the rod bore segment 34 and into the central air passage of the plunger the means of exhausting the air flow from the plunger would not differ from that which is currently practiced in the art and accordingly.