Patent GB-1353261-A (GB)
Title: Pneumatic percussive power tool
IPC: B25D9/08
Filed: 1972-08-01
Abstract: 1353261 Percussive tools INSTITUT GORNOGO DELA SIBIRKOGO OTDELENIA AKADEMII NAUK SSSR 1 Aug 1972 35938/72 Heading B4C A pneumatically actuated percussive hand tool comprises a housing 1 receiving at one end a tool bit 13 and defining a cylinder space in which a hammer 2 and a differential valving piston 3 (3a, 3c) are reciprocable in a manner which reduces vibrations transmitted to a handle (not shown). Compressed air is supplied to the tool continuously via port 9 (9a, 9c), and the spaces 11, 17 (17a, 17c) are in constant communication via conduit 19 (19a, 19c). Ports in the housing enable venting of the spaces 11 and 4 (4a, 4c) when the hammer 2 and the piston are appropriately positioned. In operation of the tool of Fig. 1, air passing through port 9 into space 15 forces the piston forwardly to bring port 8 in the piston into communication with the port 9 so as to allow air to be supplied to space 4. Compressed air when delivered to the space 4 forces the hammer 2 forwardly against the tool bit and causes rearward movement of the piston, so as to vent the space 4 via ports 8 and 10. The air pressure in space 11 and the recoil of the hammer due to impact with the tool bit will force the hammer on its return stroke, during which vent port 14 is opened to exhaust chambers 11 and 17. Also while the hammer is moving in its return stroke the rearward movement of the piston will stop and a further forward stroke of the piston will occur so as to again open space 4 to compressed air port 9. Thus the hammer will again be moved on a working stroke and the piston will be moved rearwardly. If the tool is oriented so that, when at rest the hammer and piston 3 assume their forwardmost positions (Fig. 2) air supplied to port 9 will move the piston rearwardly and compress air in space 17 (and also raise pressure in space 11). Upon the space 4 being vented via port 10 the compressed air in space 11 will move the hammer rearwardly and the tool will cycle as described above. In the embodiment of Fig. 3 air is supplied continuously to space 15a, and is supplied to space 4a to move the hammer 2 forwardly and the piston 3a rearwardly upon the rear end of the piston opening communication between the spaces 15a and 22a. The operation of this tool is similar to that of Fig. 1. In a modified embodiment (Fig. 4, not shown) communication between spaces 4a and 22a is via a passage 23b in the housing instead of via bore 7 in the piston. In the embodiment of Fig. 5 air is supplied continuously via port 9c, and, with the piston in the illustrated position, is supplied to space 22c. Upon the piston moving forwardly communication between spaces 15c and 22c is closed and the space 22c is open to space 4c via port 8 and bore 7 in the piston to allow the air in space 22c to flow into space 4c to effect the working stroke of the hammer and the rearward stroke of the piston. In a modification (Fig. 6, not shown) a compression spring is provided between the piston and the hammer, and at the instant of recoil the hammer space (15d) defined in part by the rear surface of the piston head is open to the passage (19d) communicating with the cylinder space forwardly of the hammer via a passage in the piston and a groove in the cylinder wall communicating with the passage (19d).