| 摘要 |
PURPOSE:To suitably use throttle valves in accordance with the degree of vacuum to make the variation rate of conductance thereof appropriate to control the degree of vacuum over a wide range with a high degree of accuracy, by disposing at least two throttle valves having areas different from each other in one valve casing. CONSTITUTION:At least two throttle valves 20, 30 are disposed fitted respectively on rotary shafts 21, 31 in one valve casing 10. Further, the above-mentioned valves 20, 30 are formed such that one end thereof is overlapped with each other when they are fully closed. Meanwhile the rotary shafts 21, 31 is rotated by means of motors through worm wheels 25, 35 and worm gears 24, 34. In this arrangement the original points of the above-mentioned valves 20, 30 are set between detecing plates 40a, 40b and photosensors 41a, 41b, are pulse motors are used as the above-mentioned motors. With this arrangement, the above-mentioned valve may be suitably used in accordance with the degree of vacuum to attain a desired purpose. |
