| 摘要 |
PROBLEM TO BE SOLVED: To quickly increase an exhaust amount up to a required amount when an increase of the exhaust amount is required.SOLUTION: When reducing the exhaust amount of air in the state of setting three vacuum pumps 2a-2c in operation to exhaust air of which the exhaust amount is smaller than the exhaust amount of air at the time when setting two vacuum pumps 2a, 2b in operation at 100% rotating speeds, if the rotating speeds of the vacuum pumps 2a-2c are each higher than a 55% rotating speed, an exhaust system reduces the rotating speeds of the vacuum pumps 2a-2c without stopping them, and if the rotating speeds of the vacuum pump 2a-2c are each the 55% rotating speed, the exhaust system stops the vacuum pump 2c out of the vacuum pumps 2a-2c, increases the rotating speeds of the vacuum pumps 2a, 2b continuously set in operation, and then reduces the rotating speeds of the vacuum pumps 2a, 2b depending on the required exhaust amount. |
