| 摘要 |
A secondary, smaller vacuum pump is connected to the system's dust collecting tank to maintain a predetermined, minimum vacuum in the tank when the primary vacuum pump is not in use. When one of the covers sealing the system's several outlets is removed to insert a cleaning attachment, the sudden rush of atmospheric pressure into the tank momentarily closes a first pressure switch, which actuates the primary pump. The primary pump motor is kept energized through a holding circuit including a normally-closed pressure switch, which finally opens and deenergizes the motor for the primary pump, when the system pressure has been lowered to a predetermined minimum value. The secondary pump, nevertheless, continues to run.
|
