Patent GB-1312372-A (GB)
Title: Pneumatic fastener driving tool
IPC: B25C1/04
Filed: 1970-06-09
Abstract: 1312372 Fastener driving tools FASTENER CORP 9 June 1970 [18 Aug 1969] 27916/70 Heading B4C  A pneumatically actuated fastener driving tool having a fastener driving piston reciprocable within a cylinder between an initial position (illustrated in full lines) and a displaced position (illustrated in broken lines) comprises means whereby, when the tool is not actuated, the piston will be retained in the initial position by compressed air biasing the piston away from the displaced position. The means comprises an enlargement of the cylinder diameter in the region of the initial position, into which sealing means on the piston expands to provide a larger diameter so that pressure air between it and a further sealing means biases the piston to the initial position. In operation of the tool of Fig. 1, actuation of trigger 68 causes movement of main valve 70 and opening of reservoir 14 to passage 20. Compressed air thus acts on the piston 26 to force the piston from its initial position on its working stroke. When the piston reaches its displaced position compressed air above the piston can flow past 0-ring 58 via recesses 62 and into the space defined between sealing rings 58, 60 and from the space into a return reservoir 36 via ports 56. Release of the trigger causes valve 70 to return to its illustrated position thus opening passage 20 to exhaust passage 24 and the air in reservoir 36 will then act via ports 54 on lower surface of the piston to return the piston 16 to its initial position. The piston will be retained in this position by the air within the space. Elastic bumpers 50, 52 are provided. The cylinder bore may be tapered at one end instead of being stepped (Fig. 3, not shown). The groove accommodating the 0-ring 60 may also be provided with recesses (62A) (Fig. 8, not shown) so that 0-ring 60 functions as a one-way valve to permit air flow into the space from below the piston. Alternatively a one-way valve separate from the 0-rings 58, 60 can be provided (Fig. 2, not shown) for permitting supply of air into the space from above the piston. In an alternative form of driving tool (Fig. 4) the space surrounding the upper part of cylinder 104 is connected directly to reservoir 112 and the upper end of the cylinder is normally closed by a resilient diaphragm 124 biased by spring 152 and by compressed air in space 122. Upon actuation of trigger 126 the space 122 is exhausted to atmosphere and air pressure acting on the under surface of the diaphragm 124 causes the diaphragm to be displaced upwardly thus closing communication between the bore 136 and atmosphere and opening communication between the cylinder 104 and the reservoir 112. The piston 102 is thus moved downwardly to drive a fastener. When the piston is in its driven position air will pass via one-way valve 144, 146 and ports 148 into return chamber 150. Release of the trigger will cause return of diaphragm to the position illustrated, and return of piston by air pressure in chamber 150. When the piston attains its illustrated, normal position, air from reservoir 112 passes via port 154 into the space defined between O-rings 140, 142 to thus hold the piston in the normal position. In an alternative embodiment of this latter type, the piston does not include one-way valve 144, 146, and the function of the valve is achieved by one-way valve (162, 164) in the cylinder wall (Fig. 5, not shown). Instead of both 0-rings 140, 142 being carried by the piston the lower 0-ring may be mounted in a groove in the cylinder (Fig. 6, not shown).