| 摘要 |
PROBLEM TO BE SOLVED: To provide a multistage vacuum exhausting apparatus with which the time until the atmospheric pressure is reduced to the degree of an ultimate vacuum can be shortened. SOLUTION: In a multistage vacuum exhausting apparatus which has at least two stage exhausting instruments including at least one stage steam ejector provided at the front stage side and successively operates these exhausting instruments according to lowering of the degree of vacuum, a steam pressure control device 4a which is able to change the driving steam pressure of ejector 2a, provided at the front stage side, of a specified combination of the exhausting instruments, comprising one set having two stages, in the continuously provided combinations of the exhausting instruments, each comprising one set having two stages, which constitute the exhausting apparatus, into at least two values of high pressure and low pressure, a pressure detecting end 7b for measuring the degree of vacuum at the suction side of the exhausting instrument 2b provided at the rear stage side and detecting the degree of vacuum of specific two values of at least the low degree of vacuum and the high degree of vacuum and a control device 12 for changing the steam pressure for driving the ejector provided at the front stage side according to the signal of the degree of vacuum are installed.
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