GB846860A - Operating mechanism for reciprocating tools - Google Patents

Abstract

846,860. Valve gear. DENTATUS A.B. May 15, 1959 [May 19, 1958], No. 16757/59. Class 122 (2). [Also in Group XXIX] A valve device for a tool-operating mechanism having a working piston K, Fig. 1, returnable after its working stroke by a counter-acting force S and reciprocable in a cylinder C having an inlet and exhaust port for a pressurized fluid such as air or liquid comprises a valve piston 42, Fig. 2, and a control-piston 46, both pistons having pressure-exposed faces 43, 64, the areas of which are proportioned to each other so as to cause the two pistons automatically to be shifted at the end of the working-stroke and returnstroke of the working piston in response to an increase and decrease, respectively, of the pressure in the said port. The valve piston 42 is formed on the lower end of a tubular rod 44 and slides in a valve cylinder 18 mounted in a casing 12, the upper end of the rod sliding in the control-piston. 42 which is itself slidably mounted in an upper part 14 of the valve casing. The bore in the cylinder 18 is formed with two annular spaces 28, 30, the space 30 being of larger diameter so that the area of the pressureexposed end of the control-valve is larger than the annular area of the valve piston 42, the effect being that when pressurized fluid flows in both spaces, the control-piston 44, together with the valve piston 42, tends to be moved upward and is initially resisted by a spring 82. In operation, with the valve in the position shown in Fig. 2, pressurized fluid is fed through a port 20, groove 24, bores 26, annular passage 27, bores 29, annular spaces 28, 30 and ports 32, 36, 22 into the cylinder C. Towards the end of the stroke of the piston K acting against the resistance of a return-spring S and that of the apparatus to which it is connected, the fluidpressure increases in the annular spaces 28, 30 and overcomes the pressure of the spring 82, thereby lifting the control-piston 46 and valve piston 42 until, at the end of the stroke, the end of the control-valve is lifted clear of the annular space 30 and so allows the pressure-fluid to act on a larger annular area 68 of the control piston, thereby rapidly lifting the latter and the valve 42 to close the ports 29. The pressure fluid is then exhausted through a port 84 and the fluid in the cylinder C is exhausted through the same port via bores 22, 32, annular space 30, a restricted passage 72 in the control-piston, annular space 62 and a port 60 in the tubular rod 44. Due to the reduced pressure in the spaces 28, 30, the valve 42 now descends to its former inlet position at a rate controlled by the fluid passing through the restricted passage 72; by suitably varying the area of this passage a delay may be obtained between the time when the working piston reaches the end of its returnstroke and the time when the valve 42 again opens the ports 29. To ensure that the valve 42 completely uncovers the latter ports, the tubular rod 44 is mounted for limited sliding movement in the control-piston 46 so that when fluid is fed into the spaces 28, 30, the pressure acting on annular area 43 of the piston 42 maintains the latter, against the action of a spring 58, in the position shown in Fig. 2. At the end of the working stroke when the pressure in the space 28 is reduced, the valve is maintained above the ports 29 by the spring 58 (Fig. 3, not shown). In the modification shown in Fig. 4, the piston-valve 42<SP>1</SP> is formed integrally with the control-piston 46<SP>1</SP>, the differential annular areas 43<SP>1</SP>, 64<SP>1</SP> and 681 being formed on the composite piston-valve. The operation is similar to that previously described but the valve is maintained in its open position by a build-up of pressure-fluid acting on the surface 68<SP>1</SP> caused by flow-restricting members 112, 114, positioned in the inlet port 20 and exhaust-port 84<SP>1</SP>, respectively.