Impact tool and pneumatic piston return system therefor

Claim 1

IN A FLUID-ACTUATED DEVICE, A CYLINDER HAVING A TAPERED FRUSTO-CONICAL INTERNAL WORKING SURFACE OF SMALL SLANT ANGLE, AN AXIALLY RECIPROCABLE PISTON IN SAID CYLINDER AND MOVABLE BETWEEN A RETRACTED POSITION WHEREIN IT IS DISPOSED ADJACENT THE LARGE END OF THE CYLINDER AND AN ADVANCED POSITION WHEREIN IT IS DISPOSED ADJACENT THE SMALL END OF THE CYLINDER, AN END WALL CLOSING THE LARGE END OF THE CYLINDER, MEANS FOR SELECTIVELY ADMITTING A FLUID UNDER PRESSURE TO THE LARGE END OF THE CYLINDER TO DRIVE THE PISTON FORWARDLY FROM ITS RETRACTED POSITION TO ITS ADVANCED POSITION AND FOR RELIEVING SUCH FLUID PRESSURE TO ALLOW THE PISTON TO RETURN TO ITS RETRACTED POSITION, A PAIR OF AXIALLY SPACED EXPANSIBLE AND CONTRACTIBLE SEALING RINGS CARRIED BY THE PISTON AND IN SLIDING ENGAGEMENT WITH SAID FRUSTO-CONICAL WORKING SURFACE, THE OUTER SIDE SURFACE OF THE PISTON BETWEEN SAID SEALING RINGS OPPOSING SAID FRUSTOCONICAL WORKING SURFACE AND, IN COMBINATION THEREWITH AND WITH SAID SEALING RINGS, ESTABLISHING A VARIABLE- VOLUME FLUID PRESSURE CHAMBER WHICH TRAVELS WITH THE PISTON AND THE VOLUME OF WHICH CONSEQUENTLY IS A FUNCTION OF THE AXIAL DISPLACEMENT OF THE PISTON WITHIN THE CYLINDER, THERE BEING A FLUID PASSAGE IN SAID PISTON ESTABLISHING COMMUNICATION BETWEEN SAID PRESSURE CHAMBER AND THE LARGE END OF THE CYLINDER, AND A CHECK VALVE DISPOSED IN SAID FLUID PASSAGE AND EFFECTIVE TO ADMIT FLUID TO THE PRESSURE CHAMBER WHEN THE PRESSURE OF FLUID IN THE LARGE END OF THE CYLINDER EXCEEDS THE PRESSURE OF FLUID IN THE PRESSURE CHAMBER AND TO PREVENT PASSAGE OF FLUID FROM THE PRESSURE CHAMBER TO THE LARGE END OF THE CYLINDER WHEN THE PRESSURE OF FLUID IN THE PRESSURE CHAMBER EXCEEDS THE PRESSURE OF FLUID IN THE LARGE END OF THE CYLINDER, WHEREBY FLUID UNDER PRESSURE ADMITTED TO THE LARGE END OF THE CYLINDER WHEN THE PISTON IS IN ITS RETRACTED POSITION WILL ENTER SAID PRESSURE CHAMBER THROUGH SAID PASSAGE, THE FLUID THUS ADMITTED TO THE PRESSURE CHAMBER WILL BECOME PROGRESSIVELY COMPRESSED DURING MOVEMENT OF THE PISTON TOWARD ITS ADVANCED POSITION DUE TO THE PROGRESSIVE DECREASE IN THE VOLUME OF THE PRESSURE CHAMBER, AND THE EXPANSIVE FORCE OF THE THUS COMPRESSED FLUID WITHIN THE PRESSURE CHAMBER WILL BE EFFECTIVE TO RETURN THE PISTON TO ITS RETRACTED POSITION WHEN THE PRESSURE OF FLUID IN THE LARGE END OF THE CYLINDER IS RELIEVED.