shown the rotary valve 18 can swivel around its axis 19 in such a manner that it establishes a connection between the negative pressure channel 15 and one or several of the negative pressure lines 11 12 13 or 14 the rotary valve 18 can furthermore be brought into a position in which the negative pressure channel 15 is closed so that none of the negative pressure lines 11 12 13 or 14 is supplied with negative pressure in the present example of an embodiment as shown in fig2 the rotary valve 18 of the distributor 3 is driven and adjusted via a motor 20 and gearing 21 motor 20 and gearing 21 are secured on a platform 22 on the cover 16 the drive shaft 23 of gearing 21 is connected to the rotary valve 18 in the axis 19 of said rotary valve 18 the rotary valve 18 can be rotated into any desired position by actuating the motor 20 a positioning disk 26 is connected by means of screws 25 permanently to the rotary valve 18 or to the shaft 23 the positioning disk 26 interacts with a limit switch 27 the motor 20 is controlled via the limit switch 27 the needed position of the rotary valve 18 is set on the positioning disk 26 when the rotor and gearing 21 rotates the shaft 19 the rotary valve 18 and the positioning disk 26 the rotary valve 18 is rotated until the limit switch 27 detects.