that is displaced by the liquid during impregnation also the chamber 16 could be slightly conically shaped and have a lower termination consisting of a bottom with a concentrical outlet to the cooking zone see dotted structure 49 above this bottom a scraper 50 can be placed in order to facilitate the feeding of fiber material to the underlying cooking zone in the digester where higher temperature is maintained as shown in u s pat no 4 028 171 the described apparatus functions as follows steamed fiber material which most often consists of finely comminuted wood or finely comminuted other raw material of e g bamboo bagasse grass reeds or straw in a continuous flow 30 is fed in through line 31 to the high pressure feeder 12 through which two circulations are maintained the one circulation for filling of the high pressure feeder pockets takes place by means of pump 34 and surplus liquid is fed out through line 37 which liquid normally is united with added fresh cooking liquor the other circulation through the high pressure feeder takes place by means of pump 41 and means 13 the digester 11 and the chamber 16 are kept essentially completely liquid filled as is the means 13 and the funnel 43 the digester is kept at a superatmospheric pressure necessary for cooking e g 10 20 atm which is higher than the pressure corresponding to the temperature thereby steam development is prohibited and the sinking tendency of the chips is increased in the digester a heating of the fiber material takes place by a conventional not shown heating device and by use of a circulation system of cooking liquor to the desired temperature e g 170 u00b0 c in the digester counter current washing can take place in.