Patent GB-1310758-A (GB)
Title: Impact air driven tool
IPC: B25D9/14
Filed: 1970-05-20
Abstract: 1310758 Pneumatic actuated percussive tool NIPPON PNEUMATIC MFG CO Ltd 20 May 1970 [19 Feb 1970(2)] 24503/70 Heading B4C [Also in Division F2] A pneumatic actuated percussive tool comprising a hammer piston reciprocable within a cylinder to impact one end of a chisel slidably received in the tool housing, includes a first spool valve which in one end position connects one side of the piston to a compressed air source and in the other end position connects the other side to the compressed air source and a throttle valve for controlling axial sliding movement of the first valve between its end positions, the adjustment of the throttle valve determining the dwell between the end of an impact stroke and the start of the return stroke. In the tool illustrated in Figs. 1 and 2 compressed air introduced into the cylinder via the first valve 17 and passage 39 will cause the piston to move on an impact stroke, air below the piston being exhausted via a valve (56) (Fig. 4, not shown) in housing 54. When the piston moves past passage 46 a second spool valve 25, which was previously in its non- illustrated end position, will be moved to the illustrated position so that compressed air can pass through port 48 both to groove 36 and, via the throttle valve 32, to chamber 24. When the air pressure in chamber 24 reaches a predetermined value the valve 17 will commence moving to the left at a slow rate until the groove 36 is opened to the chamber 24. Air supplied directly to groove 36, and by-passing the throttle valve, will then effect a rapid movement of the valve 17 to the left. The passage 44 will then communicate with the inlet 18 and air will be supplied via the passage 44, the valve in the housing 54, and passage 68 to the cylinder below the piston so that the latter will move on a return stroke. The cylinder space above the piston will now be open to atmosphere via passages 46 and 43. When the piston closes passage 46 air compressed by the piston will pass via passages 39 and 50 to act on the right hand end of the second valve 25 to move it to the left, thus connecting chamber 24 and annular passage 29 to atmosphere via ports 48, 52. Air acting on the differential areas of the valve 17 will now move the latter to the right. When the groove 36 is no longer open to the chamber 24 air in that chamber will be exhausted via passage 31, check valve 27, passage 29 and ports 48, 52. The cycle will now be repeated. In an alternative embodiment (Figs. 5-9, not shown) the movement of the second valve is controlled by a system including the throttle valve and the check valve, and movement of the second valve from one end position to the other end position commences after the piston moving on its impact stroke releases a spring biased valve and air pressure in a chamber at one end of the second valve, to which it is supplied via the throttle valve, has reached a predetermined value. When the second valve is in its other end position the first valve moves from one end position to its other end position to cause a return movement of the piston. Engagement of the spring biased valve (116, 118) by the piston on its return stroke opens the chamber to atmosphere to enable the second valve to return to its one end position. During the latter part of the second valve return movement the air in the chamber will be exhausted to atmosphere via the check valve. The first valve will now return to its one end position, and the cycle will be repeated.