Abstract:
A rotary valve is interposed between an intake pump and an exhaust pump for supplying an air, and at least one suction head or one nozzle that performs a predetermined operation upon reception of the air supplied from the intake and exhaust pumps, to supply/stop supplying the air. This rotary valve includes a valve body, a main body, a notch, and a hollow portion. The valve body is rotatably driven in a cylinder. The main body rotatably supports the valve body. The notch is formed in a circumferential surface of the valve body and is connected to the intake pump. The hollow portion is formed in the valve body in an axial direction and is connected to the exhaust pump.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a rotary valve disposed between intake and exhaust air sources and suction and discharge units, to supply or stop supplying air. 
     In the sheet feeding unit of a sheet-fed offset printing press, a suction unit connected to an intake air source and a discharge unit connected to an exhaust air source are used to feed stacked sheets to the feeder board one by one. More specifically, in order to draw the highest sheet by suction with the suction unit, the air of the suction unit is taken by an intake pump serving as the intake air source. In order to blow air to the stacked sheets or to separate the top sheet drawing by the suction unit from the second top sheet underneath, or in order to discharge reverse air that facilitates separation of the sheet conveyed from the suction unit to the feeder board, exhaust air is supplied by an exhaust pump serving as the exhaust air source. 
     The ON/OFF timings of each of the intake air and exhaust air correspond to the rotation angle of the printing press main body. This series of timings are controlled by a rotary valve. 
     FIG. 9 shows a conventional rotary valve. 
     Referring to FIG. 9, in a rotary valve indicated by reference numeral  30 , a main body  2  formed into a substantially rectangular parallelepiped shape is fixed to a frame  5  of a sheet feeding unit through a bracket  5   a . The first and second suckers, a leveling foot, and an air blower (not shown) are provided to the sheet feeding unit. As shown in FIGS. 10A and 10B, the lower portion of the main body  2  in one end side in the direction of an arrow Z swells in an arcuated manner to constitute a swelling portion  2   a.    
     A through hole  3  extending in the direction of an arrow X is formed in the swelling portion  2   a , and a cylindrical sleeve  4  is fixed to the inner circumferential surface of the through hole  3 . A valve body  6  is engaged in the sleeve  4 . End shafts  6   a  and  6   b  on the two ends of the valve body  6  are rotatably supported by the sleeve  4  through bearings  7   a  and  7   b . The valve body  6  rotates in an interlocked manner with rotation of the printing press through one end shaft  6   a.    
     Four air passages  9   a ,  9   b ,  9   c , and  9   d , each having an open upper end and a lower end communicating with the through hole  3 , are formed in the upper portion side of the main body  2  corresponding to the swelling portion  2   a , to extend in the vertical direction (the direction of an arrow Z). Of the air passages  9   a  to  9   d , the air passages  9   a  and  9   b , on their upper end side, are connected to an intake pump (to be described later) through hoses  17   a  and  17   b . The air passages  9   a  and  9   b  constitute an intake air passage. The air passages  9   c  and  9   d , on their upper end side, are connected to an exhaust pump (to be described later) through hoses  17   c  and  17   d . The air passages  9   c  and  9   d  constitute an exhaust air passage. 
     Air passages  10   a ,  10   b ,  10   c , and  10   d  are formed in the main body  2  to extend in the direction of the arrow Y perpendicularly to the intake air passages  9   a  and  9   b  and the exhaust air passages  9   c  and  9   d , respectively. One end of each of the air passages  10   a  to  10   d  opens to the outside of the main body  2  while the other end thereof communicates with the through hole  3 . 
     Of the air passages  10   a  to  10   d , the air passages  10   a  and  10   b  are connected to suction heads (to be described later), serving as the first and second suckers, through hoses  18   a  and  18   b . The air passages  10   a  and  10   b  constitute a suction air passage. The air passages  10   c  and  10   d  are connected to nozzles (to be described later), respectively serving as a leveling foot and an air blower, through hoses  18   c  and  18   d . The air passages  10   c  and  10   d  constitute a discharge air passage. 
     Reference numeral  31  denotes a reverse air passage for the suction heads. The reverse air passage  31  is formed between the suction air passages  10   a  and  10   b  to extend from the upper end of the main body  2  to the circumferential surface of the valve body  6  through the sleeve  4 . The exhaust pump (described above) is connected to the upper opening end side of the reverse air passage  31  through a hose (not shown). At a certain machine angle of rotation of the valve body  6 , the lower end of the reverse air passage  31  communicates with the suction air passages  10   a  and  10   b  through a notch (to be described later) formed in the valve body  6 . 
     Vent holes  11   a ,  11   b ,  11   c , and  11   d  are formed in the sleeve  4  to respectively correspond to the intake air passages  9   a  and  9   b  and the exhaust air passages  9   c  and  9   d . Vent holes  12   a ,  12   b ,  12   c , and  12   d  are also formed in the sleeve  4  to respectively correspond to the suction air passages  10   a  and  10   b  and the discharge air passages  10   c  and  10   d.    
     As shown in FIG. 10A, a notch  13   a  through which the vent holes  11   a  and  12   a  communicate with each other is formed in the circumferential surface of the valve body  6  corresponding to the intake air passage  9   a  and the suction air passage  10   a . Similarly, a notch  13   b  through which the vent holes  11   b  and  12   b  communicate with each other is formed in the circumferential surface of the valve body  6  corresponding to the intake air passage  9   b  and the suction air passage  10   b , at a position displaced from the notch  13   a  in the axial direction and to be phase-shifted from the notch  13   a  in the rotating direction of the valve body  6 . 
     As shown in FIG. 10B, a notch  13   c  through which the vent holes  11   c  and  12   c  communicate with each other is formed in the circumferential surface of the valve body  6  corresponding to the intake air passage  9   c  and the suction air passage  10   c . Similarly, a notch  13   d  through which the vent holes  11   d  and  12   d  communicate with each other is formed in the circumferential surface of the valve body  6  corresponding to the intake air passage  9   d  and the suction air passage  10   d , at a position displaced from the notch  13   c  in the axial direction and to be phase-shifted from the notch  13   c  in the rotating direction of the valve body  6 . 
     In this arrangement, when the valve body  6  is rotated in an interlocked manner with rotation of the printing press main body, the notch  13   d  of the valve body  6  is in communication with the vent holes  11   d  and  12   d  of the sleeve  4 , and the exhaust air passage  9   d  and the discharge air passage  10   d  communicate with each other through the notch  13   d . Thus, air exhausted from the exhaust pump flows through the air passages  9   d  and  10   d  that communicate with each other through the notch  13   d , and is discharged from the nozzles to blow air to the sheets. 
     When the valve body  6  is continuously rotated, the notch  13   a  is in communication with the vent holes  11   a  and  12   a , and the intake air passage  9   a  and the suction air passage  10   a  communicate with each other through the notch  13   a . Thus, as shown in FIG. 10A, intake air A taken by the intake pump flows through the air passages  9   a  and  10   a  that communicate with each other through the notch  13   a , to draw the top sheet by suction with the first sucker. 
     When the valve body  6  is continuously rotated, the notch  13   c  is in communication with the vent holes  11   c  and  12   c  of the sleeve  4 , and the exhaust air passage  9   c  and the discharge air passage  10   c  communicate with each other through the notch  13   c . Thus, as shown in FIG. 10B, exhaust air B exhausted from the exhaust pump flows through the air passages  9   c  and  10   c  that communicate with each other through the notch  13   c , and is discharged from the nozzle serving as the leveling foot. At this time, the discharged air is blown to a portion between the top sheet drawn by the suction heads and the second top sheet underneath, to separate them from each other. 
     When the valve body  6  is further rotated, the notch  13   b  opposes the vent holes  11   b  and  12   b , and the intake air passage  9   b  and the suction air passage  10   b  communicate with each other through the notch  13   b . Thus, the intake air taken by the intake pump flows through the air passages  9   b  and  10   b  that communicate with each other through the notch  13   b , to draw a sheet by suction with the second sucker. 
     Simultaneously, the notch  13   a  is displaced from the vent hole  12   a , and the intake air passage  9   a  and the suction air passage  10   a  are disconnected from each other. Thus, suction air supply is stopped, and the sheet suction operation with the first sucker is stopped. 
     Since a notch  32   a  of the valve body  6  is in communication with the reverse air passage  31 , the reverse air passage  31  and the suction air passage  10   a  communicate with each other through the notch  32   a . The exhaust air exhausted from the exhaust pump flows through the air passages  31  and  10   a  and is blown out of the first sucker, and the sheet is quickly released from the first sucker that has ended the suction operation. As a result, a sheet which is conveyed over the feeder board while being drawn by the second sucker will not be cut or bent. 
     When the second sucker during sheet conveyance is located above the feeder board, the notch  13   b  is displaced from the vent hole  12   b  in accordance with rotation of the valve body  6 , and the intake air passage  9   b  and the suction air passage  10   b  are disconnected from each other. Thus, intake air supply is stopped, and the sheet suction operation with the second sucker is stopped. At this time, a notch  32   b  is in communication with the reverse air passage  31 , and the reverse air passage  31  and the suction air passage  10   b  communicate with each other through the notch  32   b . The exhaust air exhausted from the exhaust pump flows through the air passages  31  and  10   b  and is blown out of the second sucker. The sheet is quickly released from the second sucker that has ended the suction operation, and is supplied onto the feeder board. 
     In the discharge operation of the nozzles, if the air discharge time of the nozzles is shorter than the suction time of the suction heads, the notch  13   c  constituting the air passage from the exhaust pump is formed smaller along with the rotation of the valve body  6  than the notch  13   a  constituting the air passage from the intake pump, as shown in FIGS. 10A and 10B. Inversely, in the suction operation of the suction heads, if the suction time of the suction heads is shorter than the air discharge time of the nozzles, the notch  13   a  is formed smaller than the notch  13   c , as shown in FIGS. 12A and 12B. 
     As shown in FIG. 10B, if the notch  13   c  is made small to shorten the air discharge time from the nozzles, along with rotation of the valve body  6 , as the opening of the vent hole  11   c  is enlarged, the opening of the vent hole  12   c  is narrowed. For this reason, a predetermined air pressure cannot be obtained on the nozzle side. 
     Accordingly, the amount of air from the nozzles becomes short and air blowing to the stacked sheets is not performed sufficiently, and two or more sheets are undesirably drawn by the suction heads. In this case, operation of the printing press must be stopped, or the printing press may cause a trouble to decrease the productivity. Since the supply amount of reverse air from the suction heads becomes short to delay sheet release from the suction heads, the sheet may be cut or bent to degrade the printing quality. 
     When the operation speed of the printing press increases, the time of forming the air passage in the rotary valve is shortened. Then, a predetermined discharge air pressure from the nozzles cannot be obtained, in the same manner as described above. 
     Meanwhile, as shown in FIG. 12A, if the notch  13   a  is made small to shorten the suction time of the suction heads, along with rotation of the valve body  6 , as the opening of the vent hole  11   a  is enlarged, the opening of the vent hole  12   a  is narrowed. As a result, a predetermined air pressure cannot be obtained with the suction heads, and defective sheet supply may occur. 
     FIG. 11 shows the relationship in pressure of the input/output air of the rotary valve of FIG. 10B during the discharge operation. Referring to FIG. 11, reference numeral b 1  denotes the pressure of the exhaust air input to the rotary valve  30 . The pressure b 1  is the pressure of the exhaust air from the exhaust pump. Reference numeral b 2  denotes the pressure of the discharge air output from the rotary valve. The pressure b 2  is the pressure of the discharge air from the nozzles. 
     When the machine angle of rotation of the printing press becomes β 1 , the notch  13   c  of the valve body  6  is in communication with the vent holes  11   c  and  12   c  of the sleeve  4 , and discharge air is supplied from an exhaust pump  36  to the nozzles through the exhaust air passage  9   c , the notch  13   c , and the discharge air passage  10   c . The pressure of air supplied to the nozzles at this time is expressed as a pressure P. Subsequently, when the machine angle of rotation becomes β 2 , the notch  13   c  is displaced from the vent hole  12   c , the vent hole  12   c  is closed with the circumferential surface of the valve body  6 , and supply of the discharge air to the discharge air passage  10   c  is stopped. 
     At this time, in the conventional rotary valve  30 , a pressure b 3  of the discharge air between the machine angles β 1  and β 2  of rotation becomes lower than a necessary pressure b 4  by a pressure difference ΔP. This is due to the following reason. Since the notch  13   c  is small, along with rotation of the valve body  6 , as the opening of the vent hole  11   c  is enlarged, the opening of the vent hole  12   c  is narrowed, so the air exhausted from the exhaust pump  36  is not sufficiently supplied to the nozzles. 
     FIG. 13 shows the relationship of the input/output air of the rotary valve shown in FIG. 12A during the suction operation. As shown in FIG. 13, even during the suction operation, a pressure loss in air of the rotary valve occurs. Reference numeral a 1  denotes the pressure of the intake air input to the rotary valve  30 . The pressure a 1  is the pressure of intake air from the intake pump. Reference numeral a 2  denotes the pressure of the suction air output from the rotary valve  30 . The pressure a 2  is the pressure of the suction air of the suction heads. As shown in FIG. 13, a pressure a 3  of the suction air between the machine angles β 1  and β 2  of rotation becomes higher than a necessary pressure a 4  by a pressure difference ΔP. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a rotary valve which can obtain a predetermined air pressure even when the actuation time by the air is short. 
     It is another object of the present invention to provide a rotary valve in which a pressure loss in air in its interior is decreased. 
     In order to achieve the above objects, according to the present invention, there is provided a rotary valve, which is interposed between first and second air sources for supplying an air, and at least one air unit that performs a predetermined operation upon reception of the air supplied from the first and second air sources, to supply/stop supplying the air, the rotary valve comprising a valve body rotatably driven in a cylinder, a main body for rotatably supporting the valve body, a notch formed in a circumferential surface of the valve body, to be connected to the first air source, and a first hollow portion formed in the valve body in an axial direction to be connected to the second air source. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a rotary valve according to the first embodiment of the present invention; 
     FIG. 2A is a sectional view taken along the line I—I of FIG. 1, and FIG. 2B is a sectional view taken along the line II—II of FIG. 1; 
     FIG. 3 is a diagram showing the schematic arrangement of the sheet feeding unit of a printing press to which the first embodiment is applied; 
     FIG. 4 is a plan view of a rotary valve according to the second embodiment of the present invention; 
     FIG. 5A is a sectional view taken along the line III—III of FIG. 4, and FIG. 5B is a sectional view taken along the line IV—IV of FIG. 4; 
     FIG. 6 is a diagram showing the schematic arrangement of a sheet feeding unit to which the second embodiment is applied; 
     FIG. 7 is a plan view of a rotary valve according to the third embodiment of the present invention; 
     FIG. 8 is a sectional view taken along the line V—V of FIG. 7; 
     FIG. 9 is a plan view of a conventional rotary valve; 
     FIG. 10A is a sectional view taken along the line VI—VI of FIG. 9, and FIG. 10B is a sectional view taken along the line VII—VII of FIG. 9; 
     FIG. 11 is a graph showing the relationship in pressure of the input/output air of the rotary valve of FIG. 10B during discharge operation; 
     FIG. 12A is a sectional view showing the main part of another example of the rotary valve that corresponds to FIG. 10A, and FIG. 12B is a sectional view showing the main part of still another example of the rotary valve that corresponds to FIG. 10B; and 
     FIG. 13 is a graph showing the relationship in pressure of the input/output air of the rotary valve of FIG. 12A during suction operation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described in detail with reference to the accompanying drawings. 
     FIG. 3 shows the schematic arrangement of a sheet feeding unit for a printing press to which the present invention is applied. Referring to FIG. 3, the air source side of a rotary valve  101  is connected to an intake pump  134  serving as an intake air source, and an exhaust pump  136  serving as an exhaust air source, through hoses  117   a  and  117   b , and a hose  119 , respectively. The suction/discharging side of the rotary valve  101  is connected to suction heads  135   a  and  135   b  serving as the suction units, and nozzles  137   a  and  137   b  serving as the discharge unit, through hoses  118   a  and  118   b , and hoses  118   c  and  118   d , respectively. The suction heads  135   a  and  135   b  serve as the first and second suckers of the sheet feeding unit, and the nozzles  137   a  and  137   b  serve as a leveling foot and an air blower. 
     FIG. 1 shows the rotary valve shown in FIG. 3, which is the first embodiment of the present invention. Referring to FIG. 1, a main body  102  formed into a substantially rectangular parallelepiped shape is fixed to a frame  105  of the sheet feeding unit through a bracket  105   a . As shown in FIGS. 2A and 2B, the lower portion of the main body  102  in one end side in the direction of an arrow Z swells in an arcuated manner to constitute a swelling portion  102   a.    
     A through hole  103  extending in the direction of an arrow X is formed in the swelling portion  102   a , and a cylindrical sleeve  104  is fixed to the inner surface of the through hole  103 . A valve body  106  is engaged in the sleeve  104 . End shafts  106   a  and  106   b  on the two ends of the valve body  106  are rotatably supported by the sleeve  104  through bearings  107   a  and  107   b . The valve body  106  rotates in an interlocked manner with rotation of the printing press through one end shaft  106   a.    
     Two air passages  109   a  and  109   b , each having an open upper end and a lower end communicating with the through hole  103 , are formed in the upper portion side of the main body  102  corresponding to the swelling portion  102   a , to extend in the vertical direction (the direction of an arrow Z). As described above, the air passages  109   a  and  109   b , on their upper end side, are connected to the intake pump  134  through the hoses  117   a  and  117   b , and the air passages  109   a  and  109   b  constitute an intake air passage (air passage for the intake air source). 
     Air passages  110   a  and  110   b  are formed in the main body  102  to extend in the direction of the arrow Y perpendicularly to the intake air passages  109   a  and  109   b . Also, air passages  110   c  and  110   c  are formed in parallel to the air passages  110   a  and  110   b . One end of each of the air passages  110   a  to  110   d  opens to the outside of the main body  102  while the other end thereof is connected to the through hole  103 . 
     Of the air passages  110   a  to  110   d , the air passages  110   a  and  110   b  are connected to the suction heads  135   a  and  135   b  through the hoses  118   a  and  118   b , as described above. The air passages  110   a  and  110   b  constitute a suction air passage (air passage for the suction unit). As described above, the air passages  110   c  and  110   d  are connected to the nozzles  137   a  and  137   b  through the hoses  118   c  and  118   d , and the air passages  110   c  and  110   d  constitute a discharge air passage (air passage for the discharge unit). 
     Vent holes  111   a  and  111   b  are formed in the sleeve  104  to respectively correspond to the intake air passages  109   a  and  109   b . Vent holes  112   a ,  112   b ,  112   c , and  112   d  are also formed in the sleeve  104  to respectively correspond to the suction air passages  110   a  and  110   b  and the discharge air passages  110   c  and  10   d.    
     As shown in FIGS. 2A and 2B, a blind hole-like hollow portion  114  is formed in the valve body  106  to have an opening in the end face of the valve body  106  on one end shaft  106   b  side and to extend in the direction of an arrow X to a position corresponding to the intake air passage  109   a . As described above, the exhaust pump  136  is connected to the opening side of the hollow portion  114  through the hose  119 . Accordingly, the hollow portion  114  constitutes an exhaust air passage (air passage for the exhaust air source). 
     A communication hole  115   a  (FIG. 2A) is formed in the valve body  106 . The communication hole  115   a  allows the hollow portion  114  to communicate with the suction air passage  110   a  through the vent hole  112   a . Similarly, a communication hole  115   b  is formed in the valve body  106  at a position displaced from the communication hole  115   a  in the axial direction and to be phase-shifted from the communication hole  115   a  in the rotating direction. The communication hole  115   b  allows the hollow portion  114  to communicate with the suction air passage  110   b  through the vent hole  112   b.    
     A communication hole  115 c (FIG. 2B) is formed in the valve body  106 . The communication hole  115   c  allows the hollow portion  114  to communicate with the discharge air passage  110   c  through the vent hole  112   c . Similarly, a communication hole  115   d  is formed in the valve body  106  at a position displaced from the communication hole  115   c  in the axial direction and to be phase-shifted from the communication hole  115   c  in the rotating direction. The communication hole  115   d  allows the hollow portion  114  to communicate with the discharge air passage  110   d  through the vent hole  112   d.    
     As shown in FIG. 2A, a notch  113   a  through which the vent holes  111   a  and  112   a  communicate with each other is formed in the circumferential surface of the valve body  106  corresponding to the intake air passage  109   a  and the suction air passage  110   a . Similarly, a notch  113   b  through which the vent holes  111   b  and  112   b  communicate with each other is formed in the circumferential surface of the valve body  106  corresponding to the intake air passage  109   b  and the suction air passage  110   b , at a position displaced from the notch  113   a  in the axial direction and to be phase-shifted from the notch  113   a  in the rotating direction of the valve body  106 . 
     Therefore, the characteristic feature of this embodiment resides in that the blind hole-like hollow portion  114  having a circular section is formed in the valve body  106  to extend in the axial direction and that this hollow portion  114  serves as the exhaust air passage. The conventional exhaust air passages  9   c  and  9   d  and reverse air passage  31  shown in FIG.  9  and FIGS. 10A and 10B are replaced with the hollow portion  114 , so that the reverse air passage  31  and the notches  32   a  and  32   b  formed in the valve body  6  become unnecessary. 
     The switching operation between intake and exhaustion done by the rotary valve having this arrangement will be described with reference to FIG.  3 . 
     When the valve body  106  is rotated in an interlocked manner with rotation of the printing press, the communication hole  115   d  of the valve body  106  is in communication with the vent hole  112   d  of the sleeve  104 , and the hollow portion  114  serving as the exhaust air passage and the discharge air passage  110   d  communicate with each other through the communication hole  115   d  and the vent hole  112   d . Therefore, exhaust air from the exhaust pump  136  flows through the hollow portion  114  and the air passage  110   d , and is discharged from the nozzle  137   b  to blow the air to stacked sheets (step S 11 ). 
     When the valve body  106  is continuously rotated, the notch  113   a  is in communication with the vent holes  112   a  and  111   a , and the intake air passage  109   a  and the suction air passage  110   a  communicate with each other through the notch  113   a . Thus, as shown in FIG. 2A, intake air A from the intake pump  134  flows through the air passages  109   a  and  110   a  that communicate with each other, and is supplied to the suction head  135   a  serving as the first sucker, to draw the top sheet by suction (step S 12 ). 
     When the valve body  106  is continuously rotated, the communication hole  115   c  is in communication with the vent hole  112   c  of the sleeve  104 , and the hollow portion  114  serving as the exhaust air passage and the discharge air passage  110   c  communicate with each other through the communication hole  115   c  and a vent hole  111   c , as shown in FIG.  2 B. Exhaust air B from the exhaust pump  134  is supplied to the nozzle  137   a , serving as the leveling foot, through the hollow portion  114  and the air passage  110   c . The air is blown to a portion between the top sheet and the second sheet underneath, to separate them from each other (step S 13 ). 
     When the valve body  106  is continuously rotated, the notch  113   b  is in communication with the vent holes  112   b  and  111   b , and the intake air passage  109   b  and the suction air passage  110   b  communicate with each other through the notch  113   b . Therefore, intake air from the intake pump  134  is supplied to the suction head  135   b , serving as the second sucker, through the air passages  109   b  and  110   b , to draw a sheet by suction (step S 14 ). 
     Simultaneously, the communication hole  115   a  of the valve body  106  is in communication with the vent hole  112   a , and the hollow portion  114  and the suction air passage  110   a  communicate with each other through the communication hole  115   a  and the vent hole  112   a . The exhaust air from the exhaust pump  136  is supplied to the suction head  135   a , serving as the first sucker, through the hollow portion  114  and the air passage  110   a . The sheet is quickly released from the suction head  135   a  that has ended the suction operation (step S 15 ). As a result, a sheet which is conveyed over the feeder board while being drawn by the suction head  135   b , serving as the second sucker will not be torn or bent. 
     When the suction head  135   b  during sheet conveyance has been located above the feeder board, as the valve body  106  is rotated, the communication hole  115   b  is in communication with the vent hole  112   b , and the hollow portion  114  and the suction air passage  110   b  communicate with each other through the communication hole  115   b  and vent hole  112   b . The exhaust air from the exhaust pump  136  is supplied to the suction head  135   b  through the hollow portion  114  and the air passage  110   b . The sheet is quickly released from the suction head  135   b , and is supplied onto the feeder board (step S 16 ). 
     According to this embodiment, during the air discharge operation, the air is supplied from the exhaust pump  136  to the nozzles  137   a  and  137   b  through the hollow portion  114  and the communication holes  115   c  and  115   d . Therefore, the air blowing and leveling foot operation can be reliably performed within a short period of time with the sufficiency high-pressure air. 
     During the air discharge operation, the hollow portion  114 , the communication holes  115   c  and  115   d , the vent holes  111   c  and  111   d , and the discharge air passages  110   c  and  110   d  are located on a substantially straight line, so that the air loss during the leveling foot operation and air blowing is decreased. Therefore, an exhaust pump having a comparatively small power can be used. 
     Since the exhaust air is supplied through the hollow portion  114  of the valve body  106  which has a large sectional area, the pressure loss of the air at the valve portion is decreased. Also, the exhaust air passages  9   c  and  9   d  conventionally formed in the main body  2  or the vent holes  11   c  and  11   d  conventionally formed in the sleeve  4  become unnecessary, and only the hollow portion  114  and the communication holes  115   a  to  115   d  need be formed in the valve body  106 . Therefore, the structure is simplified and machining becomes easy. 
     Since the notches  32   a  and  32   b  of the valve body  6  and the reverse air passage  31 , which are conventionally necessary, becomes unnecessary, the structure is simplified. Since the hollow portion  114 , the communication holes  115   a  and  115   b , the vent holes  111   a  and  111   b , and the suction air passages  110   a  and  110   b  are located on a substantially straight line, the air pressure loss during reverse blowing is decreased. 
     FIG. 4 shows a rotary valve according to the second embodiment of the present invention. FIG. 5A shows a section taken along the line III—III of FIG. 4, and FIG. 5B shows section taken along the line IV—IV of FIG.  4 . In FIG.  4  and FIGS. 5A and 5B, portions that are identical to those of FIG.  1  and FIGS. 2A and 2B are denoted by the same reference numerals as in FIG.  1  and FIGS. 2A and 2B, and a detailed description thereof will be omitted. 
     The second embodiment is different from the first embodiment in that, as shown in FIG. 4, a partition wall  114   c  is formed at the center of a hollow portion  114  to divide the hollow portion  114  into a first hollow portion  114   a  and a second hollow portion  114   b.    
     As shown in FIG. 6, the first hollow portion  114   a  is connected to an intake pump  134  through a hose  119   a  to constitute an intake air passage. The second hollow portion  114   b  is connected to an exhaust pump  136  through a hose  119   b , in the same manner as in the first embodiment. Air passages  116   a  and  116   b  formed in the upper end side of a main body  102  are connected to the exhaust pump  136  through hoses  117   a  and  117   b  to constitute an exhaust air passage. 
     A communication hole  215   a  (FIG.  5 A), where the hollow portion  114  extends to communicate with a suction air passage  110   a  through a vent hole  112   a , is formed in the valve body  106 . Similarly, a communication hole  215   b , where the hollow portion  114  extends to communicate with the suction air passage  110   b  through a vent hole  112   b , is formed in the valve body  106 , at a position displaced from the communication hole  215   a  in the axial direction and to be phase-shifted from the communication hole  215   a  in the rotating direction. A communication hole  215   c  (FIG.  5 B), where the hollow portion  114  extends to communicate with a discharge air passage  110   c  through a vent hole  112   c , is also formed in the valve body  106 . Similarly, a communication hole  215   d , where the hollow portion  114  extends to communicate with a suction air passage  110   d  through a vent hole  112   d , is formed in the valve body  106 , at a position displaced from the communication hole  215   c  in the axial direction and to be phase-shifted from the communication hole  215   c  in the rotating direction. 
     The switching operation between intake and exhaustion done by the rotary valve having this arrangement will be described with reference to FIG.  6 . 
     When the valve body  106  is rotated in an interlocked manner with rotation of the printing press, the communication hole  215   d  of the valve body  106  is in communication with the vent hole  112   d  of the sleeve  104 , and the second hollow portion  114   b  serving as the exhaust air passage and the discharge air passage  110   d  communicate with each other through a communication hole  115   d  and the vent hole  112   d . Exhaust air from the exhaust pump  136  is supplied to a nozzle  137   b  through the second hollow portion  114   b  and the air passage  110   d , to blow air to stacked sheets (step S 21 ). 
     When the valve body  106  is continuously rotated, its communication hole  215   a  is in communication with the vent hole  112   a , and the first hollow portion  114   a  serving as the intake air passage and the suction air passage  110   a  communicate with each other through the communication hole  215   a  and the vent hole  112   a . Intake air from the intake pump  134  is supplied to a suction head  135   a , serving as the first sucker, through the suction air passage  110   a  and the first hollow portion  114   a , to draw the top sheet by suction (step S 22 ). 
     When the valve body  106  is continuously rotated, the communication hole  215   c  opposes the vent hole  112   c  of a sleeve  104 , and the second hollow portion  114   b  serving as the exhaust air passage and the discharge air passage  110   c  communicate with each other through the communication hole  215   c  and the vent hole  112   c , as shown in FIG.  5 B. Exhaust air B from the exhaust pump  136  is supplied to a nozzle  137   a , serving as the leveling foot, through the second hollow portion  114   b  and the suction air passage  110   c . The air is blown to a portion between the top sheet and the second sheet underneath, to separate them from each other (step S 23 ). 
     When the valve body  106  is continuously rotated, the communication hole  215   b  of the valve body  106  is in communication with the vent hole  112   b , and the first hollow portion  114   a  and the suction air passage  110   a  communicate with each other through the communication hole  215   b  and the vent hole  112   b . Intake air from the intake pump  134  is supplied to a suction head  135   b , serving as the second sucker, through the first hollow portion  114   a  and the suction air passage  110   a , to draw the top sheet by suction (step S 24 ). 
     Simultaneously, a notch  113   a  is in communication with the vent hole  112   a  and a vent hole  111   a , and an exhaust air passage  116   a  and the discharge air passage  111   a  communicate with each other through the notch  113   a , as shown in FIG.  5 A. Thus, the exhaust air B from the exhaust pump  136  is supplied to the suction head  135   a , serving as the first sucker, through the air passages  116   a  and  110   a . The sheet is quickly released from the suction head  135   a  that has ended the suction operation (step S 25 ). As a result , a sheet which is conveyed over the feeder board while being drawn by the suction head  135   b , serving as the second sucker, will not be torn or b ent. 
     When the second suction head  135   b  during sheet conveyance has been located above the feeder board, as the valve body  106  is rotated, a notch  113   b  is in communication with the vent hole  112   b  and a vent hole  111   b , and an exhaust air passage  116   b  and the discharge air passage  110   b  communicate with each other through the notch  113   b . The exhaust air from the exhaust pump  136  is supplied to the suction head  135   b  through the air passages  116   b  and  110   b . The sheet is quickly released from the suction head  135   b , and is supplied onto the feeder board (step S 26 ). 
     According to this embodiment, during the suction operation, the air is supplied from the intake pump  134  to the suction heads  135   a  and  135   b  through the first hollow portion  114   a  and the communication holes  215   a  and  215   b . Therefore, the suction operation can be reliably performed within a short period of time with the sufficiency high-pressure air. 
     During the suction operation, the first hollow portion  114   a , the communication holes  215   a  and  215   b , and the vent holes  112   a  and  112   b  are located on a substantially straight line, so that the pressure loss of the suction air is decreased. Since the first hollow portion  114   a  of the valve body  106 , which has a large sectional area, serves as the intake air passage, the pressure loss of the air at the valve portion is small. 
     FIG. 7 shows a rotary valve according to the third embodiment of the present invention, and FIG. 8 shows a section taken along the line V—V of FIG.  7 . 
     A rotary valve  120  of the third embodiment controls to supply/stop supplying of the air of the first sucker of the sheet feeding unit. More specifically, a through hole  122  is formed in a main body  121  of the rotary valve  120 . A valve body  123  which rotates in an interlocked manner with the printing press is rotatably engaged with the inner surface of the through hole  122 . An intake air passage  124  and a suction air passage  125  are formed in the upper portion of the main body  121 . The air passage  124  has an open upper end and a lower end that communicates with the through hole  122 . The suction air passage  125  has an L-shaped section. 
     The upper end open side of the intake air passage  124  is connected to an intake pump through a hose  127 . The upper end open side of the suction air passage  125  is connected to a suction head, serving as the first sucker, through a hose  128 . A notch  126   a  is formed in part of the circumferential surface of the valve body  123 . A blind hole-like hollow portion  126   b  is formed in the valve body  123  to extend in the axial direction. A communication hole  126   c , through which the hollow portion  126   b  and the suction air passage  125  communicate with each other, is also formed in the valve body  123 . The open end side of the hollow portion  126   b  is connected to an exhaust pump through a hose  129 . The hollow portion  126   b  constitutes an exhaust air passage. 
     In this arrangement, when the valve body  123  is rotated in an interlocked manner with the printing press, the notch  126   a  is in communication with the intake air passage  124  and the suction air passage  125 , and the two air passages  124  and  125  communicate with each other through the notch  126   a . Intake air A is supplied to a suction head, serving as the first sucker, through the air passages  124  and  125 , to draw a sheet by suction. 
     When the valve body  123  is continuously rotated, air intake is controlled by another rotary valve (not shown), and the sheet is drawn by suction with a suction head serving as the second sucker. 
     Simultaneously, the communication hole  126   c  of the valve body  123  is in communication with the suction air passage  125 , and the hollow portion  126   b  and the suction air passage  125  communicate with each other. Exhaust air B from the exhaust pump is supplied to the first suction head, serving as the first sucker, through the suction air passage  125 , and the sheet is quickly released from the suction head that has ended the suction operation. As a result, the sheet which is drawn by the suction head, serving as the second sucker, and is conveyed over the feeder board will not be torn or bent. 
     According to this embodiment, during the reverse operation, a sufficient amount of air can be supplied to the suction heads through the hollow portion  126   b  and the communication hole  126   c  within a short period of time. Since the hollow portion  126   b , the communication hole  126   c , and the suction air passage  125  are located on a substantially straight line and the distance between the hollow portion  126   b  and the suction air passage  125  becomes minimum, the air pressure loss in the air passage is decreased. 
     In the third embodiment, when the intake air operation time is short, an exhaust pump  137  may be connected through the hose  127  so that the air passage  124  serves as the exhaust air passage, and an intake pump  134  may be connected to the open end side of the hollow portion  126   b  through the hose  129  so that the hollow portion  126   b  serves as the intake air passage. 
     In the first and second embodiments, the sleeve  104  formed with the vent holes  111   a  and  111   b  is provided. However, the valve body  123  may be directly engaged in the through hole  122  of the main body  121 , as in the third embodiment. With this structure, the vent holes  111   a  to  111   d  become unnecessary. In fine, it suffices if the valve body is rotatably held in a cylinder including a sleeve formed in the main body. 
     In the above embodiments, the rotary valve is applied to the sheet feeding unit. However, the present invention is not limited to this, but can similarly be applied to, e.g., the convertible cylinder unit or a sheet discharge unit of a printing press main body. Although the hollow portion is formed to have a circular section, it can have various other sections, e.g., an elliptic section, a square section, or a triangular section. Although only one rotary valve is used in the above embodiments, a series of a plurality of rotary valves may be used. 
     As has been described above, according to the present invention, the valve body of the rotary valve has a hollow portion and a notched portion respectively connected to different air sources, and the hollow portions and notched portions are combined with air passages that require predetermined characteristics. If the hollow portion is used as an air passage having a short air operation time and the notched portion is used as an air passage having a long air operation time, predetermined air pressures required for the respective air passages can be obtained. 
     Since the hollow portion and the notched portion are formed in the valve body, the entire rotary valve can be made compact. The reverse air passage from the suction unit can also be constituted by a hollow portion or a notch formed in the valve body, thus decreasing the manufacturing cost.