Patent GB-547930-A (GB)
Title: Improvements in and relating to fluid pressure operated servo motors for operating electrical switches
IPC: H01H33/34
Filed: 1941-05-27
Abstract: 547,930. Pneumatic single stroke motors. FLURSCHEIM, O. H., and METROPOLITANVICKERS ELECTRICAL CO., Ltd. May 27, 1941, No. 6803. [Class 8 (ii)] [Also in Groups XXXVII and XXIX] The control valve of a fluid-pressure servomotor is provided with control means comprising a piston or the equivalent adapted, when subjected to pressure, to hold the valve in operated position. The cylinder or working space of the piston is connected with a passage through which pressure is applied to the space under control of the valve when the latter is operated to apply fluid to the motor. Means responsive to motor-movement cause reclosure of the control valve when the motor has executed all or part of the movement initiated by the valve. The invention is applicable to electric switches, railway-coach doors, traversing mechanisms, in machine tools such as broaching machines and planers, and the operation of ventilators. In Fig. 1, the valve 1 is adapted to be lowered to connect a source 4 of fluidpressure to the servomotor via conduit 7. The valve is opened by a solenoid 17 acting on a bellcrank lever 12 which transmits the force to a second bellcrank 22 over a set toggle 18, 19, the pivot 24 of which slides across a pillar 26. When valve 1 opens, the pressure is admitted also through pipe 32 to a piston 29 which holds the valve open notwithstanding de-energization of solenoid 17. At a given point in the stroke of the servomotor, a part is uncovered, as 91, 93 in Fig. 3, and pressure is admitted beneath the piston 27 which rises and breaks toggle 18, 19, so allowing valve 1 to reclose. The toggle may alternatively be tripped mechanically by movement of the servomotor. In Fig. 2 (not shown), the solenoid core 16 is modified so as to serve as the holding piston 29. Fig. 3 shows a double-acting servomotor employing as two control units modified arrangements of that of Fig. 1. The motor comprises a pair of pistons 45, 46 connected by a rack 47, operating a pinion 49 and shaft 50. The control units 40, 41 are similar. A master control valve 79 when operated by solenoid 84 connects passage 56 with those 86, 87 whereby air is admitted beneath a servo piston 62 which opens the valve 54 by the linkage of Fig. 1, and air passes in addition to the motor through ball valve 89 to the piston 62 to hold it displaced. When the port 91 is uncovered by the movement of piston 45, air passes beneath piston 63, and brakes the toggle 70 thus allowing valve 54 to reclose. The air beneath 62 exhausts through the escape port 81, assuming the solenoid 84 has been de-energized, whereupon a spring 77 remakes the toggle. The cylindrical top 57 of valve 54 lifts and brings the part 60 having three flats above the valve body 52, so exhausting the valve casing. The master-control valve may be remotely located and control the airflow from a separate reservoir over a pipe connected to the passage 87. In the case of an electric switch wherein contact-movement is assisted by a spring, it is not necessary for the servo motor to complete its movement before port 91 is uncovered, an arrangement which minimizes the cushioning necessary. Further, where a switch is to be made to complete a closing movement before it can be opened, the pipe 59<SP>1</SP> may be connected through a pipe 94 to the upper side of piston 62 to prevent its being moved when unit 41 is in operation. Alternatively the provision of a pipe 95 between the passage 87 and pipe 92 ensures that the switch will be opened before completion of a closing movement, so providing a trip free feature ; alternatively, toggle 70<SP>1</SP> of unit 41 may. be broken by a connection with the lever 69. The toggle may alternatively be collapsed by external means to provide a locking feature, such as in dependence on the position of an isolating switch or of draw-out switchgear. Types of switch to which the servomotor is applicable are gas blast switches directly actuated by the motor and those in which gas blast contacts are opened by the gas pressure whereas the motor operates series-connected isolating contacts.