| 摘要 |
PURPOSE:To improve the vacuum degree by opening the atmosphere opened valves installed in the low and high stage gas passages only in the case when the low stage discharge temperature is lower than a set temperature and the high stage discharge temperature is higher than a set temperature. CONSTITUTION:Oil-free screw pumps 1 and 2 are arranged in series, and an opening/closing valve 6 is installed into the branched flow passage 5 between the both pumps 1 and 2. The discharge temperature on the low stage side is detected by a thermocouple 7, and the discharge temperature on the high stage side is detected by a thermocouple 8. When the discharge temperature of the thermocouple 7 is lower than a set temperature which is lower than the max. allowable temperature and the detection temperature of the thermocouple 8 is higher than the max. allowable temperature, the opening/closing valve 6 is opened. Therefore, the both pump stages can be operated in the nearly equal discharge temperature state.
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