PURPOSE: To remove condensed water easily and positively from a compressed air system with atmospheric pressure applied thereto in a resting state by evacuating the compressed air system immediately after energizing positive pressure at least at a time interval, and impeding the mechanical action of at least one load.

CONSTITUTION: A control circuit 3 of a dual pump 2 receives starting pulse through a push button switch 6 to put the pump 2 in positive pressure generating operation. After the pump 2 is stopped by a pressure switch 7 in a compressed air system 1, the control circuit 3 puts the pump 2 in negative pressure generating operation over specified time width or until the switch 7 generates a suitable changeover signal. The slight adjusting motion of an adjusting element 5 generated in this case is not a problem, but the compressed air system 1 is evacuated to temporarily generate negative pressure therein, and this negative pressure re-evaporates condensed water. The pump 2 makes vapor flow through in the resting state, and after the pump 2 is finally stopped, the atmosphere enters the evacuated system 1, and the system 1 has atmospheric pressure.