GB790770A - Improvements relating to valve mechanism for controlling pneumatically operated apparatus - Google Patents

Abstract

790,770. Pneumatic single-stroke apparatus. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd., and LEECH, K. H. Oct. 12, 1955 [Oct. 12, 1954], No. 29345/54. Class 8(2). [Also in Group XXIX] In apparatus having a ram piston movable in a cylinder 18, Fig. 1, by air under pressure supplied to one side of the ram piston, there is provided a pressure sensitive valve 13, which opens in response to increasing pressure acting on the ram piston to cause air from a reservoir 16 to also act on the piston. Operation of the manual valve 8 causes air from the source 9 to be supplied through a choke 7 to a valve chamber 4 and the cylinder 18 so that the ram piston moves slowly into engagement with an obstruction, such as the axle of a colliery tub. A piston 3 in the chamber 4 moves rightwardly until its thrust rod 11 abuts the stem of the poppet valve 13 ; when the valve piston engages the obstruction the pressure builds up in the chamber 4 until it unseats the valve 13 against its spring 20 whereupon the reservoir 16, charged vja a choke 17 from the source 9, supplies air to the cylinder 18 through the valve seat 22 and a chamber 15, the valve 13 then opening rapidly to its full extent. The feed through the chokes 7, 17 ensures that the ram piston completes its stroke even if the resistance to its movement is too great to enable this to be effected by the expansion of air alone. A check valve 23 in parallel with the choke 7 allows the cylinder 18 and chamber 4 to be vented when the valve 8 is operated to cause the return of the ram piston to its original position, the valve 13 then seating under the action of its spring 20. In a modification, Fig. 2 (not shown), the valve piston is spring-loaded and the reservoir is charged via a valve instead of a choke, which valve is open when the poppet valve is closed and vice versa ; the charging valve is axially aligned with and mechanically closed by opening of the poppet valve whilst its opening is effected by air pressure. This arrangement is applicable to any of the subsequent embodiments. In another modification, which provides for a reduction in the amount of air used for each operation, the admission of pressure to the chamber 4, Fig. 3, causes rightward movement of the interconnected pistons 3a, 3b against a spring 26 until the rod 11 abuts the poppet valve 13 whereupon further movement of the pistons is prevented by the combined effect of springs 26, 20. When the ram piston meets the tub axle the resulting increased pressure in the chamber 4 unseats the valve 13 so that air discharges from the reservoir 16 to the cylinder 18 by way of ports 27, 28. The valve 13 abuts a sliding stop 30 loaded by a spring 29 until continued pressure increase in the chamber 4 causes the valve 13 to move to its fully open position against springs 20, 29 ; during this period, when the pressures in the reservoir 16 and cylinder 18 are almost equalized, the piston 3a moves a shuttle 25 to sever communication between ports 27, 28. In another modification, Fig. 4 (not shown), another port is provided adjacent the port 27, Fig. 3, which is connected via a choke to the downstream side of the manual valve so that an additional air supply is available to enable the ram piston to overcome any small or first resistance encountered before the axle is engaged. In either of the two foregoing embodiments a second poppet valve may be fixed to the valve 13, which valve would co-operate with a seat in the stop connected with the pressure source ; this arrangement replaces the choke 17. In a further modification, the initial pressure in chamber 4, Fig. 5, causes movement of the piston 3a which is transmitted through a buffer 36a, a cam lever 35 and a second buffer 36b to the second piston 3b thus opening the port 28. A first resistance to ram piston movement increases the pressure in chamber 4 so that further travel of the piston 3a moves the cam lever 35 against the resistance of a spring 26 until a first cam 37a opens a first poppet valve to permit a first reservoir, (not shown) to discharge into the cylinder .18, whereupon the ram piston overcomes the resistance. Immediately before the pressures in the first reservoir and cylinder become equalized the shuttle 25 is moved to close ports 27a so disconnecting the first reservoir from the cylinder. Upon the ram engaging the object to be moved the resulting further pressure rise in chamber 4 again moves the piston 3a and hence via lever 35 opens the second poppet valve 13b to enable the second reservoir 16b to discharge into the ram cylinder, in consequence the shuttle 25 is moved to close the ports 27b just before the pressure in the reservoir 16b and cylinder 18 are equalized. In any of the foregoing embodiments the poppet valves may be replaced by piston valves whilst diaphragms may be used instead of the valves actuating pistons in these instances where the pistons do not act as closure members. Specification 761,578 is referred to.