PURPOSE: To simplify a high frequency reduced pressure drying device by a method wherein the device is comprised of a vacuum pump for absorbing evaporation moisture, a rough drawing vacuum pump, a cooling water flow meter for the vacuum pump, a cooling water supplying device for a mixing and discharging vacuum pump, a gas-water separation tank and a discharged water flow meter.
CONSTITUTION: Water is supplied to water supplying devices 29 and 31. A vacuum pump 14 and a rough drawing vacuum pump 20 are driven. As cooling water is accumulated in a gas-water separation tank 27 and reaches a specified amount, resulting in that the cooling water is discharged by a water discharging pump 34. As an interior of a drying tank 1 shows a vacuum state, a fibrous material 2 between electrodes 1a and 1b is heated by a high frequency oscillator 3 and then moisture content is evaporated at a relative low boiling point. At this time, a water supplying valve 28c of a water supplying device 28 for cooling discharged gas is opened. A drain amount is displayed with a difference amount between that of water supplying flow meter 30 and discharging water flow meter 30'. Air discharging valves 15 and 15' are alternatively opened or closed and suck a part of the drain from a bottom part of a drying tank 1 and air containing evaporation moisture from above. The rough drawing vacuum pump 20 is operated to perform at an initial time of drying and at a finishing drying time. Discharged gases from both vacuum pumps are merged and communicated with the gas-water separation tank 27, the evaporated moisture content is condensed and the remaining air is released from a discharging port 37.