Pneumatic piston return system for impact tools

Claim 1

IN A PNEUMATICALLY OPERABLE DEVICE, A CYLINDER HAVING A SIDE WALL AND END WALLS DEFINING THEREBETWEEN AN INTERNAL CHAMBER, A PISTON SLIDABLE IN SAID CYLINDER BETWEEN A RETRACTED POSITION ADJACENT ONE END OF THE CYLINDER AND AN ADVANCED POSITION ADJACENT THE OTHER END THEREOF, A PLUNGER MOVABLE WITH THE PISTON AND PROJECTING THROUGH ONE OF SAID END WALLS, SAID PISTON, IN ANY POSITION THEREOF, DEFINING, IN COMBINATION WITH SAID SIDE AND END WALLS, A PRESSURE CHAMBER ON ONE SIDE OF THE PISTON AND AN EXPANSION CHAMBER ON THE OTHER SIDE THEREOF, FIRST VALVE MEANS SELECTIVELY OPERABLE TO ADMIT AIR UNDER WORKING PRESSURE TO SAID PRESSURE CHAMBER TO DRIVE THE PISTON FORWARDLY TOWARD ITS ADVANCED POSITION AND TO RELIEVE SUCH WORKING PRESSURE TO ALLOW THE PISTON TO MOVE REARWARDLY AND RETURN TO ITS RETRACTED POSITION, BY-PASS MEANS EFFECTIVE WHEN SAID PISTON SUBSTANTIALLY IN ITS FULLY ADVANCED POSITION ESTABLISHING DIRECT COMMUNICATION BETWEEN SAID PRESSURE CHAMBER AND THE EXPANSION CHAMBER TO ADMIT AIR UNDER WORKING PRESSURE FROM THE FORMER TO THE LATTER, AND SECOND VALVE MEANS MOVABLE BODILY WITH THE PISTON AND EFFECTIVE DURING FORWARD MOVEMENT OF THE PISTON FROM ITS RETRACTED POSITION TO ITS ADVANCED POSITION FOR BLEEDING SAID EXPANSION CHAMBER TO THE ATMOSPHERE TO THUS EXHAUST THE SAME, AND ALSO EFFECTIVE DURING REARWARD MOVEMENT OF THE PISTON FROM ITS ADVANCED POSITION TO ITS RETRACTED POSITION TO DISABLE SAID VALVE MEANS AND THUS SEAL THE EXPANSION CHAMBER, WHEREBY THE EXPANSION OF AIR ADMITTED TO THE EXPANSION CHAMBER BY SAID BY-PASS MEANS AND ENTRAPPED THEREIN WILL RETURN THE PISTON TO ITS RETRACTED POSITION, SAID SECOND VALVE MEANS COMPRISING AN EXHAUST PASSAGE EXTENDING THROUGH THE PISTON AND PLUNGER AND DEFINING AN EXHAUST PORT, AND A VALVE ELEMENT MOVABLY CARRIED BY THE PISTON AND SLIDINGLY ENGAGEABLE WITH THE CYLINDER SIDE WALL, SAID VALVE ELEMENT MOVABLE INTO AND OUT OF SEALING ENGAGEMENT WITH SAID PORT DURING MOVEMENT OF THE PISTON IN OPPOSITE DIRECTIONS RESPECTIVELY UNDER THE INFLUENCE OF ITS SLIDING CONTACT WITH SAID CYLINDER SIDE WALL, SAID VALVE ELEMENT BEING EFFECTIVE DURING MOVEMENT OF THE PISTON TOWARD ITS ADVANCED POSITION TO OPEN SAID PORT AND DURING MOVEMENT OF THE PISTON TOWARD ITS RETRACTED POSITION TO CLOSE SAID PORT.