METHOD FOR EVACUATING DEAERATOR

PURPOSE:To intermittently exhaust the air oozing out into a reduced-pressure vessel with a small-sized and inexpensive vacuum pump having low output by providing a highly airtight two-position and three-port solenoid valve in a pipeline between the reducedpressure vessel and vacuum pump of a deaerator. CONSTITUTION:The change in the vacuum in the reduced-pressure vessel 1 is detected by a pressure sensor 7. The vacuum pump 5 and solenoid valve 11 are operated so that the vacuum is controlled within the upper-limit and lower-limit values set by a pressure control circuit 8, and repeatedly and intermittently operated. In this case, the pipelines of the always closed port 13 and always opened port 14 are switched by the time-lag operation of the vacuum two-position and three-port solenoid 11 to allow the always closed port 13 to communicate with a selector port 15, hence the exhaust port 16 of the reduced- pressure vessel 1 communicates with the suction port 17 of the vacuum pump 6, and the air oozing out into the vessel 1 is discharged to the outside. As a result, the exhaustion by the intermittent operation can be performed even with an inexpensive commercially available pump.