referring now to the figures of the drawings in detail and first , particularly , to fig1 thereof , there is seen a processing machine for sheets , for example a printing press 1 having a feeder 2 , at least one respective printing unit 3 and 4 and a delivery 6 . sheets 7 are removed from a sheet pile 8 and fed singly or in a shingle - shaped manner over a feed table 9 to the printing units 3 and 4 . the printing units 3 and 4 each include a respective plate cylinder 11 , 12 in a conventional manner . the plate cylinders 11 and 12 each have a respective device 13 , 14 for securing flexible printing plates thereon . furthermore , a device 16 , 17 is assigned to each plate cylinder 11 , 12 for semi - automatic or fully automatic printing plate exchange . the sheet pile 8 lies on a controlled liftable pile or stack plate 10 . the removal of the sheets 7 takes place from the upper side of the sheet pile 8 by a so - called suction head 18 which , among others , has a number of lifting and pull suckers 19 , 21 for the singling or separation of the sheets 7 . moreover , blowing or blast devices 22 are provided for aerating or loosening up the upper sheet installation , and test elements 23 for pile or stack resetting . a number of lateral and rear stops 24 are provided for adjusting or aligning the sheet pile 8 , especially the upper sheet 7 of the sheet pile 8 . the feed table 9 is formed as a so - called suction - belt table having first , second and third suction chamber regions or consumers or loads 27 , 28 , 29 disposed behind one another , as is shown more particularly in fig2 . the first suction chamber region 27 is disposed downstream of the sheet pile 8 as seen in the sheet transport direction . a first suction source 31 acts upon the first suction chamber region 27 through a supply line 32 . as is further shown in fig3 , the supply line 32 is provided with a controllable by - pass flap 33 for surrounding or ambient air . a second suction source 34 acts upon the second suction chamber region 28 through a supply line 36 . the supply line 36 has an adjustable throttle flap 37 for controlling throughput quantities of the suction air , and a switchable bypass flap 38 for surrounding air . the second suction chamber region 28 is longer in the sheet transport direction than the respective first and third suction chamber regions 27 and 29 . the second suction chamber region 28 is therefore further subdivided into several smaller suction chambers for reducing leakage losses , all of which can be acted upon in common by the second suction source 34 . a third suction air source 39 acts upon the third suction chamber region 29 with suction air through a supply line 41 . the supply line 41 has a switchable bypass flap 42 to the surrounding air and a rotary valve 43 for making ready pressure levels of varying height within a work cycle of the sheet processing machine 1 . the three suction sources 31 , 34 and 39 may also be replaced by a single suction source having an output of corresponding size . the rotary valve 43 has a housing 44 , which accommodates therein a rotatably mounted rotor 46 driven in the work cycle of the printing press 1 . moreover , a mixing chamber 47 is provided , which is connected through an axial passage 48 with a control slot or groove 52 of the rotor 46 , through a connector 49 to the supply line 41 and through a passage opening 51 to the third suction chamber region 29 . the control slot 52 of the rotor 46 of the rotary valve 43 connects the axial passage 48 with a radial inlet 53 to the surrounding air . the radial inlet 53 is provided with an exchangeable filter 54 for cleaning the intake air from the surroundings . a removable cover 56 closes an opening at an end side of the housing 44 . access to the mixing chamber 47 is made available by removing the cover 56 . due to this feature , a cylindrical filter tube or filter element 57 may be removed from the mixing chamber 47 and cleaned or exchanged . the filter tube 57 is formed with at least one first opening 58 , which faces towards the passage opening 51 , and at least one second opening 59 , which faces towards the connection 49 . control of the suction air and the negative pressure level in the suction regions 27 , 28 is respectively effected by the suction sources 31 , 34 , preferably through the bypass flaps 33 , 38 respectively assigned to the suction regions 27 , 28 . the negative pressure supply in the suction region 29 is controlled by the suction source 39 with which , additionally , the assigned bypass flap 42 may be employed . air from the surroundings is added through the control groove 52 of the rotor 46 of the rotary valve 43 to the mixing chamber 47 for cycling the negative pressure level in the suction region 29 . since the main suction flow at the rotor 46 of the rotary valve 43 is conducted past , or in parallel over , the mixing chamber 47 , the rotary valve 43 remains substantially free of fouling or dirtying such as by dust or powder . this application claims the priority , under 35 u . s . c . § 119 , of german patent application 10 2005 004 562 . 6 , filed feb . 1 , 2005 ; the entire disclosure of the prior application is herewith incorporated by reference .