sorted is conveyed into the pressure sorter 10 the fiber suspension streams in a helical line through the supply chamber 54 from its first end 54a to its second end 54b whereby a portion of the fiber suspension passes through openings or apertures of the screen 38 and reaches the accepts chamber 58 in this manner the rejected material leaves the supply chamber 54 at its second end 54b and in this manner reaches the rejects chamber 56 from which the rejected material leaves the pressure sorter via the second outlet connecting piece 50 in preferred embodiments of the pressure sorter according to the invention the axis 34 extends at least approximately horizontally fundamentally it would also be conceivable however to assemble the pressure sorter such that its axis 34 extends at least approximately vertically in the following the inventive features of the pressure sorter will be explained as well as the sorting procedure performed thereby due to the relatively fine openings of the screen 38 a pressure difference results between supply chamber 54 and accepts chamber 58 in fact the pressure in the accepts chamber is lower than in the supply chamber in order to determine this pressure difference a measuring device 60 is provided according to the invention which comprises a first pressure transmitting means 62 and a second pressure transmitting means 64 which are arranged in.