facing to the left in the figure a flexible membrane 58 is arranged thus an annular enclosure 57 is arranged between the disks 42 44 and delimited by the flexible membranes 52 58 and the flange 50 and with air communication passages through the openings 54 in the flange in a manner that will be described below the outer surface of the flange is further arranged with distance pieces 60 that are in contact with the inner wall of the trigger housing disk chamber there is thus a space 59 formed between the trigger housing disk chamber and the disks this space is in flow communication with the interior of the mouth piece via channel 61 further a longitudinal groove 62 is arranged in the piston rod 34 which is in air flow communication with a space formed between two sets of disks via the cut outs 48 in the hub the sets of disks are u201c stacked u201d one set after the other where the flanges are abutting each other the last fixed disk the leftmost in the figures is arranged with an annular protrusion 63 fig6 which when the mechanism is inserted into the trigger housing disk chamber snap fits into an annular groove 65 fig1 in the inner wall of the chamber in an air tight manner holding all the fixed disks in place inside the chamber return means 64 fig2 attached to the outer surface of the trigger housing disk chamber in the form of.