Abstract:
According the present invention, an oxygen enriched gas is generated by adsorbing and removing nitrogen gas from air with an oxygen concentrating apparatus which conducts the steps of (1) pressurizing one of the adsorption cylinders by directing the compressed air; (2) removing the oxygen enriched gas from said one of the adsorption cylinders to the output conduit; (3) reducing the pressure in said one of the adsorption cylinders by directing the oxygen enriched gas into one of the other adsorption cylinders to increase the pressure in the one of the other adsorption cylinders; (4) evacuating the internal gas out of said one of the adsorption cylinders; and (5) increasing the pressure in said one of the adsorption cylinders by directing the oxygen enriched gas into said one of the adsorption cylinders from one of the other adsorption cylinders in which the pressure is decreased in step (3).

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an oxygen concentrating apparatus and a rotary valve.  
         [0003]     2. Description of the Related Art  
         [0004]      FIG. 29  is a schematic illustration of a pressure swing type gas oxygen concentrating apparatus  300  which includes two adsorption cylinders  302   a  and  302   b ,an air compressor  304  for supplying compressed air to the adsorption cylinders  302   a  and  302   b  through conduit  308 , four-way directional control valve  306 , conduits  310   a  and  310   b , an O 2  tank  320  to which the oxygen enriched gas is supplied from the adsorption cylinders  302   a  and  302   b  through output conduits  312   a  and  312   b  and shut off valves  318 . The oxygen enriched gas is supplied from the O 2  tank to a user through a conduit  322  and a flow control valve  324 . Provided between the output conduits  312   a  and  312   b  are a orifice  314  and a pressure equalizing valve  316 .  
         [0005]     According to the oxygen concentrating apparatus  300 , it is difficult to control each of the steps of the oxygen concentrating process, which are disclosed in, for example U.S. Pat. No. 2,944,627, U.S. Pat. No. 3,237,377 and Japanese Unexamined Patent Publication (Kokai) No. 10-151315, and to increase the efficiency of the apparatus because four-way directional control valve  306  is used.  
         [0006]     JPP &#39;315 also describes an oxygen concentrating apparatus including a rotary valve, instead of the four-way directional valve, for switching the flow direction and controlling the steps of the oxygen concentrating process. However, the conventional rotary valve has a problem that there is unbalance in the pressure applied to the interface between the rotor and the stator of the rotary valve.  
       SUMMARY OF THE INVENTION  
       [0007]     The invention is directed to solve the above mentioned prior art problems, an the objective of the invention is to provide an oxygen concentrating apparatus which solves the above-described problems of the prior art.  
         [0008]     According to the present invention, there is provided with an oxygen concentrating apparatus, for generating an oxygen enriched gas by adsorbing and removing nitrogen gas from air, comprising: a plurality of adsorption cylinders which is filled with holding an adsorbent which selectively adsorbs nitrogen gas more than oxygen gas, the adsorption cylinders having first and second orifices; a output conduit for directing the oxygen enriched gas to a user through the first orifice; means for supplying compressed air to the adsorption cylinders through the second orifice; means for evacuating nitrogen gas from the adsorption cylinders through the second orifice; and valve means for allowing the oxygen concentrating apparatus sequentially in each of the adsorption cylinders:  
         [0009]     (1) to pressurize one of the adsorption cylinders by directing the compressed air through the second orifice thereof;  
         [0010]     (2) to remove the oxygen enriched gas from said one of the adsorption cylinders to the output conduit through the first orifice thereof,  
         [0011]     (3) to direct the oxygen enriched gas as a purge gas from said one of the adsorption cylinders through the first orifice thereof into one of the other adsorption cylinders through the first orifice thereof, from which one of the other adsorption cylinders the internal gas is evacuated; and  
         [0012]     (4) to evacuate the internal gas out of said one of the adsorption cylinders through the second thereof.  
         [0013]     Further, according to another feature of the present invention, there is provided an oxygen concentrating apparatus, for generating an oxygen enriched gas by adsorbing and removing nitrogen gas from air, comprising: a plurality of adsorption cylinders for holding an adsorbent which selectively adsorbs nitrogen gas more than oxygen gas, the adsorption cylinders having first and second orifices; a output conduit for directing the oxygen enriched gas to a user through the first orifice; means for supplying compressed air to the adsorption cylinders through the second orifice; means for evacuating nitrogen gas from the adsorption cylinders through the second orifice; and valve means for allowing the oxygen concentrating apparatus, sequentially in each of the adsorption cylinders:  
         [0014]     (1) to pressurize one of the adsorption cylinders by directing the compressed air through the second orifice thereof;  
         [0015]     (2) to remove the oxygen enriched gas from said one of the adsorption cylinders to the output conduit through the first orifice thereof,  
         [0016]     (3) to reduce the pressure in said one of the adsorption cylinders by directing the oxygen enriched gas through the first orifice into one of the other adsorption cylinders through the first orifice thereof to increase the pressure in the one of the other adsorption cylinders; and  
         [0017]     (4) to evacuate the internal gas out of said one of the adsorption cylinders through the second thereof.  
         [0018]     Further, according to another feature of the present invention, there is provided a method of generating an oxygen enriched gas by adsorbing and removing nitrogen gas from air with an oxygen concentrating apparatus having a plurality of adsorption cylinders for holding an adsorbent which selectively adsorbs nitrogen gas more than oxygen gas, a output conduit for directing the oxygen enriched gas to a user, means for supplying compressed air to the adsorption cylinders, and means for evacuating nitrogen gas from the adsorption cylinders, the method comprising the steps of:  
         [0019]     (1) pressurizing one of the adsorption cylinders by directing the compressed air;  
         [0020]     (2) removing the oxygen enriched gas from said one of the adsorption cylinders to the output conduit;  
         [0021]     (3) reducing the pressure in said one of the adsorption cylinders by directing the oxygen enriched gas into one of the other adsorption cylinders to increase the pressure in the one of the other adsorption cylinders;  
         [0022]     (4) evacuating the internal gas out of said one of the adsorption cylinders; and  
         [0023]     (5) increasing the pressure in said one of the adsorption cylinders by directing the oxygen enriched gas into said one of the adsorption cylinders from one of the other adsorption cylinders in which the pressure is decreased in step (3).  
         [0024]     Further, according to another feature of the present invention, there is provided a rotary valve, adapted to use in a flow system including a plurality of common flow passages and a selective flow passage group composed of a plurality of subgroups, each of the subgroups including the same number M of flow passages, for switching the fluid communications between at least one of the plurality of common flow passages and at least one of the flow passages of the selective flow passage group and/or between the flow passages of the subgroups, the rotary valve comprising: a stator comprising a plate member including opposing front and rear sides, a plurality of ports which extend between the front and rear sides through the plate member and fluidly communicate with the common flow passages and the flow passages of the plurality of subgroups of the selective flow passage group; a rotor rotatable about an axis relative to the stator, the rotor comprising a plate member including a front side contacting with the front side of the stator and an opposite rear side, the plate member of the rotor defining in its front side a plurality of openings each of which can fluidly communicate with each of the ports of the rotor, the plurality of openings of the stator being disposed symmetrically about the axis so that the configuration of the front side coincides with the configuration of the front side of the rotor when the rotor rotates by 1/n rotations (n: integer); the ports of the stator, which fluidly communicate with the flow passages of the different subgroups of the selective flow passage group, being disposed along circles of different diameter about the axis; each of the ports, fluidly communicating with the flow passages of one of the subgroups, is disposed at any one of (i)th point, (m+i)th point, (2m+i)th point, (3m+i)th point, . . . , ((n−1)m+i)th point (i: integer=1 to m) along the circle; and the points which equally divide the circle into a plurality of (nm) segments. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0025]     These and other objects and advantages and further description will now be discussed in connection with the drawings in which:  
         [0026]      FIG. 1  is a schematic illustration of an oxygen concentrating apparatus according to a first embodiment of the present invention;  
         [0027]      FIG. 2  is partial section of a concentrator according to the first embodiment of the present invention;  
         [0028]      FIG. 3  an exploded perspective view of a rotary valve with a lower header of the concentrator of  FIG. 2 ;  
         [0029]      FIG. 4  is a plan view of the lower header;  
         [0030]      FIG. 5  is plan view of a stator of the rotary valve attached to the lower header;  
         [0031]      FIG. 6  is a plan view similar to  FIG. 4  with the lower header shown by broken lines;  
         [0032]      FIG. 7  is a plan view of a front side of a stator of the rotary valve;  
         [0033]      FIG. 8  is a plan view of a rear side of a stator of the rotary valve;  
         [0034]      FIG. 9  is a plan view similar to  FIG. 7  with the stator shown by broken lines;  
         [0035]      FIG. 10 a  section of the assembly of the stator and rotor along line X-X in  FIG. 9 ;  
         [0036]      FIG. 11 a  section of the assembly of the stator and rotor along line XI-XI in  FIG. 9 ;  
         [0037]      FIG. 12  is a plan view of the front side of the rotor with the stator shown by solid lines for explaining the operation of the oxygen concentrator according to the first embodiment;  
         [0038]      FIG. 13  is a plan view similar to  FIG. 12  showing the front side of the rotor which rotates 15 degrees, relative to the stator, from the position shown in  FIG. 12  in the rotational direction R;  
         [0039]      FIG. 14  is a chart showing the cycle of the process conducted by the oxygen concentrator according to the first embodiment;  
         [0040]      FIG. 15  is a chart showing the cycle of the process conducted by the oxygen concentrator according to the first embodiment;  
         [0041]      FIG. 16  is a partial section of a concentrator according to a second embodiment of the present invention;  
         [0042]      FIG. 17  is a plan view of a rotary valve with a lower header of the concentrator of  FIG. 16 ;  
         [0043]      FIG. 18  is a plan view of a stator of the rotary valve;  
         [0044]      FIG. 19  is a plan view the lower header;  
         [0045]      FIG. 20  is a plan view similar to  FIG. 19  with adsorption cylinders shown by broken lines;  
         [0046]      FIG. 21  is a plan view of a rear side of a rotor of the rotary valve;  
         [0047]      FIG. 22  is a plan view of a front side of a rotor of the rotary valve;  
         [0048]      FIG. 23  is a section of the rotor along line A-A in  FIG. 22 ;  
         [0049]      FIG. 24  is a section of the assembly of the lower header, the stator and the rotor along line IIXIV-IIXIV in  FIG. 17 ;  
         [0050]      FIG. 25  is a section of the assembly of the lower header, the stator and the rotor along line IIXV-IIXV in  FIG. 17 ;  
         [0051]      FIG. 26  is a chart showing the cycle of the process conducted by the oxygen concentrator according to the second embodiment;  
         [0052]      FIG. 27  is a plan view of the front side of the rotor with the stator shown by solid lines for explaining the operation of the oxygen concentrator according to the second embodiment;  
         [0053]      FIG. 28  is a plan view similar to  FIG. 12  showing the front side of the rotor which rotates 15 degrees, relative to the stator, from the position shown in  FIG. 12  in the rotational direction R; and  
         [0054]      FIG. 29  is a schematic illustration of an oxygen concentrating apparatus of a prior art. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0055]     With reference to the drawings, preferred embodiments of the present will be described below.  
         [0056]     In  FIG. 1 , an oxygen concentrating apparatus according to a first embodiment of the present invention is shown. The oxygen concentrating apparatus  10  has an oxygen concentrator  100  which generates an oxygen enriched gas by adsorbing and separating nitrogen gas from the air, an air supplying means, comprising a compressor  12  and a filter  14 , for supplying compressed air to the oxygen concentrator  100  through an air supply conduit  16 , an exhausting means, comprising a vacuum pump  18  and a muffler  20 , for drawing nitrogen gas through exhaust conduit  22 , a reservoir or an O 2  tank  26 , a pressure regulating valve  28 , a flow control valve  30  which are disposed along an oxygen supply conduit  24  for directing the oxygen enriched gas to a user.  
         [0057]     With reference to  FIG. 2 , the oxygen concentrator  100  includes a plurality of adsorption cylinders  102  which are arranged parallel to each other and filled with an adsorbent, for example, zeolite for selectively adsorbing nitrogen gas more than oxygen gas, upper and lower headers  104  and  106  holding the plurality of adsorption cylinders  102  therebetween, a rotary valve  120  and drive mechanism, comprising a motor  108  and a gear box  110 , for rotating the rotary valve  120  about an axis parallel to the adsorption cylinders  102 , a spring  112  for biasing a cover of the rotary valve  120 , as described below, and a bearing  114  which allows the rotary valve to rotate  120 .  
         [0058]     The oxygen concentrator  100  according to the first embodiment has four adsorption cylinders  102  each of which includes a top or first orifice (not shown) and a bottom or second orifice (not shown). The upper header  104  includes six passages  104   a  which are fluidly connected to the upper orifices of the adsorption cylinders  102 . The lower header  106  includes a supply passage  106   a  which is fluidly connected to the compressor  12  through the air supply conduit  16 , an exhaust passage  106   b  which is fluidly connected to the vacuum pump  18  through the exhaust conduit  22 , first passages  106   c  which are fluidly connected to the bottom orifices of the adsorption cylinders  102  and second passages  106   d  which are fluidly connected to the passages  104   a  of the upper header  104  through connection conduits  116 .  
         [0059]     With reference to  FIGS. 3 and 4 , the lower header  106  further includes a C-shaped output groove  106   g  extending around the centrally disposed supply passage  106   a , a output passage  106   e  which opens to the output groove  106   g  and is fluidly connected to the oxygen supply conduit  24  and an exhaust groove  106   f  around the output groove  106   g  which fluidly communicates with the exhaust passage  106   b.    
         [0060]     In  FIG. 3 , the rotary valve  120  includes a stator  130  comprising a circular plate member, stationarily attached to the lower header  106 , and a rotor  140  comprising a circular plate member which is rotated by the motor  108  relative to the stator  130 . With reference to  FIGS. 5 and 6 , the stator  130  includes a centrally disposed supply port  130   a , four output ports  130   b , four first ports  130   c , four exhaust ports  130   d , four second ports  130   e  and a sealing port  130   f  which extend through the plate member of the stator  130 . The supply port  130   a  fluidly communicates with the supply passage  106   a  of the header  106 . The output ports  130   b  fluidly communicate with the output passage  106   e  through the output groove  106   g . The first ports  130   c  fluidly communicate with the second passages  106   d  of the lower header  106 . The exhaust ports  130   d  fluidly communicate with the exhaust passage  106   b  through the exhaust groove  106   f . The second ports  130   e  fluidly communicate with the first passages  106   c  of the lower header  106 . The sealing port  130   f  fluidly communicates with the exhaust passage  106   b  through the exhaust groove  106   f.    
         [0061]     With reference to  FIGS. 7-11 , the rotor  140  has a front face  141   a  contacting the stator  130  and an opposite rear face  141   b . On the front face  141   a , the rotor  140  defines three first recesses  140   c , three second recesses  140   e  which are fluidly connected to each other by a circular groove  140   f , three third recesses  140   g  and a circular sealing recess  140   i . The circular groove  140   f  is disposed to fluidly communicate with the exhaust ports  130   d  of the stator  130 . On the rear face  141   b , the rotor  140  defines a receptacle  140   m  for receiving a cover  144 , an inner groove  140   j  and a outer groove  140   k . A flow passage  143  is defined between the cover  144  disposed in the receptacle  140   m  and the rotor  140 . The rotor  140  further includes a centrally disposed supply opening  140   a , three first openings  140   b , six second openings  140   d  and three third openings  140   h  which axially extend through the rotor  140 . The third openings  140   h  fluidly connect the third recesses  140   g  to the inner groove  140   j.    
         [0062]     With reference to  FIGS. 12-15 , the operation of the oxygen concentrator  100  according the first embodiment will be described below. In the first embodiment, the oxygen concentrator  100  includes four adsorption cylinders  102  the positions of which are indicated by reference numbers  1 - 4 , in  FIGS. 12 and 13 . In the following description, the operation of the oxygen concentrator  100  will be described in relation to one of the adsorption cylinders, cylinder  1  which is disposed at position  1 .  
         [0063]     Step I (Pressurization Step)  
         [0064]     The rotor  140  is at the home position shown in  FIG. 12  where one of the first openings  140   b  aligns with one of the second ports  130   e  of the stator  130  so that the air is supplied to cylinder  1  from the compressor  12  through the air supply conduit  16 , the supply passage  106   a  of the lower header  106 , the supply port  130   a  of the stator  130   a , the supply opening  140   a  of the rotor  140 , the passage  143  defined between the stator  140  and the cover  144 , the first opening  140   b  of the rotor  140 , the second port  130   e  of the stator  130  and the lower orifice of cylinder  1 .  
         [0065]     Step II (Pressurization-Generation Step)  
         [0066]     The rotator  140  rotates in the direction R to a rotational position at 15 degrees from the home position where the first opening  140   b  is still aligned with the second port  130   e  and the compressed air is supplied to cylinder  1 , as described above. At the same time, the first recess  140   c  of the rotor  140  aligns with the output port  130   b  and the first port  130   c  of the stator  130 . This rotational position of the rotor  140  allows the oxygen enriched gas to flow from cylinder  1  to the user through the upper orifice of cylinder  1 , the passage  104   a  of the upper header  104 , the connection conduit  116 , second passage  106   d  of the lower header  106 , the first ports  130   c  of the stator  130 , the first recess  140   c  of the rotor  140 , the output port  130   b  of the stator  130 , the output groove  106   g , the output passage  106   e  of the lower header  106  and the output conduit  24 .  
         [0067]     Step III (Generation Step)  
         [0068]     The rotator  140  rotates to a rotational position at 30 degrees from the home position where the first opening  140   b  of the rotor  140  is not aligned with the second port  130   e  of the stator  130 , and therefore, the supply of the compressed to cylinder  1  is terminated. However, the first recess  140   c  is still aligned with both the output port  130   b  and the first ports  130   c  of the stator  130 . Therefore, the oxygen enriched gas is still supplied to the user from cylinder  1  as described above.  
         [0069]     Step IV (Depressurization-Equalization Step)  
         [0070]     The rotor  140  rotates to a rotational position at 45 degrees from the home position where two of the six second openings  140   d  align with the first ports  130   c  communicating with cylinders  1  and  3 . This rotational position of the rotor  140  allows the oxygen enriched gas to flow from cylinder  1  to cylinder  3  through the upper orifice of cylinder  1 , the passage  104   a  of the upper header  104 , the connection conduit  116 , the second passage  106   d  of the lower header  106 , the first port  130   c  of the stator  130 , the second opening  140   d , the outer groove  140   k , the second opening  140   d  of the rotor  140 , the first port  130   c  of the stator  130 , the second passage  106   d  of the lower header  106 , the connection conduit  116 , the passage  104   a  of the upper header  104  and the upper orifice of cylinder  4 . Thus, the pressure in cylinder  1  is reduced and the pressure in cylinder  3  is increased to equalize the pressure in cylinders  1  and  3 .  
         [0071]     Step V (Cocurrent Depressurization Step)  
         [0072]     The rotor  140  rotates to a rotational position at 60 degrees from the home position where two of the three third recesses  140   g  of the stator  140  align with the first ports  130   c  communicating with cylinders  1  and  4 . This rotational position of the rotor  140  allows the oxygen enriched gas to flow from cylinder  1  to cylinder  4 , as a purge gas through the upper orifice of cylinder  1 , the passage  104   a  of the upper header  104 , the connection conduit  116 , the second passages  106   d  of the lower header  106 , the first port  130   c  of the stator  130 , the third recess  140   g , the third opening  140   h , the inner groove  140   j , the third opening  140   h , the third recess  140   g  of the stator  140 , the first port  130   c  of the stator  130 , the second passages  106   d  of the lower header  106   d , the connection conduit  116 , the passage  104   a  of the upper header  104  and the upper orifice of cylinder  4 . At the same time, a purge step, which will be described below, is conducted in cylinder  4 .  
         [0073]     Step VI (Evacuation Step)  
         [0074]     The rotor  140  rotates to a rotational position at 75 degrees from the home position where the second recess  140   e  of the rotor  140  aligns with the second port  130   e  of the stator  130 . This rotational position of the rotor  140  allows the gas in cylinder  1  to be evacuated by the vacuum pump  22  through the lower orifice of cylinder  1 , the first passage  106   c  of the lower header  106 , the second port  130   e  of the stator  130 , the second recess  140   e , the circular groove  140   f  of the rotor  140 , the exhaust port  130   d  of the stator  130 , the exhaust groove  106   f , the exhaust passage  106   b  of the lower header  106  and the exhaust conduit  22 .  
         [0075]     Step VII (Purge Step)  
         [0076]     The rotor  140  rotates to a rotational position at 90 degrees from the home position where the second port  130   e  of the stator  130  still aligns with the second recess  140   e  and two of the three third recesses  140   g  of the stator  140  align with the first ports  130   c  communicating with cylinders  1  and  2 . Therefore, the oxygen enriched gas is supplied, as a purge gas, to cylinder  1  from cylinder  2  as described in relation to Step V while the gas in cylinder  1  is still evacuated as described above.  
         [0077]     Step VIII (Pressurization-Equalization Step)  
         [0078]     The rotor  140  rotates to a rotational position at 105 degrees from the home position where two of the six second openings  140   d  align with the first ports  130   c  communicating with cylinders  1  and  3 . This rotational position of the rotor  140  allows the oxygen enriched gas to flow from cylinder  3  to cylinder  1  as described above in relation to Step IV.  
         [0079]     As shown in the drawings, in the first embodiment, the four output ports  130   b , the four first ports  130   c , the four exhaust ports  130   d , and the four second ports  130   e  are disposed along different circles about the rotational axis of the rotor  140 . Further, each of the ports fluidly communicating with each of the adsorption cylinders  102  are disposed at any one of (i)th point, (m+i)th point, (2m+i)th point, (3m+i)th point, . . . , ((n−1)m+i)th point (i: integer=1 to m) along the circle. Here, i is integer i=1 to m, m is number of the adsorption cylinders and n is the number of cycle of the above described process during one rotation of the rotor, that is 3 in the first embodiment. This arrangement prevents the concentrator  100  from executing the same steps of the above described process at a rotational position of the rotor  140 .  
         [0080]     Further, according to the first embodiment of the present invention, the supply passage  106   a , the exhaust passage  106   b  and the output passage  106   e  provide a common flow passages. The upper or first orifices of the adsorption cylinders  102  provide flow passages of a first subgroup of a selective flow passage group and the lower or second orifices  102   a  of the adsorptions cylinders  102  provide flow passages of a second subgroup of the selective flow passage group.  
         [0081]     With reference to  FIGS. 16-28 , a second embodiment of the present invention will be described below.  
         [0082]     The oxygen concentrator  200  according to the second embodiment includes a plurality of adsorption cylinders  202  which are arranged parallel to each other and filled with an adsorbent, for example, zeolite which selectively adsorbs nitrogen gas more than oxygen gas, upper and lower headers  204  and  206  holding the adsorption cylinders  202  therebetween, a rotary valve  220  and drive mechanism, comprising a motor  208  and gear box  210 , for rotating the rotary valve  220 , a spring  212  for biasing a cover of the rotary valve  220  and a bearing  214 , between the spring  212  and the rotary valve  220 , which allows the rotary valve  220  to rotate.  
         [0083]     The oxygen concentrator  200  has six adsorption cylinders  202  each of which includes a top or first orifice (not shown) and a bottom or second orifice (not shown). The upper header  204  includes six passages  204   a  which are fluidly connected to the upper orifices of the adsorption cylinders  202 . The lower header  206  includes a supply passage  206   a  which is fluidly connected to the compressor  12  ( FIG. 1 ), an exhaust passage  206   b  which is fluidly connected to the vacuum pump  18  ( FIG. 1 ) through the exhaust conduit  22  ( FIG. 1 ), first passages  206   c  which are connected to the bottom orifices of the adsorption cylinders  202  and second passages  206   d  which are fluidly connected to the passages  204   a  of the upper header  204  through connection conduits  116 . With reference to  FIGS. 19 and 20 , the lower header  206  further includes a C-shaped output groove  206   g  extending around the centrally disposed supply passage  206   a , a output passage  206   e  which opens to the output groove  206   g  and is fluidly connected to the oxygen supply conduit  24  ( FIG. 1 ) and an exhaust groove  206   f , around the output groove  206   g  which fluidly communicates with the exhaust passage  206   b.    
         [0084]     The rotary valve  220  includes a stator  230  comprising a circular plate member, stationarily attached to the lower header  206 , and a rotor  240  comprising a circular plate member which is rotated by the motor  208  relative to the stator  230 . With reference to  FIGS. 18 and 20 , the stator  230  includes a centrally disposed supply port  230   a , six output ports  230   b , six first ports  230   c , three exhaust ports  230   d , six second ports  230   e  and a sealing port  230   f , which axially extend through the plate member of the rotor  240 . The supply port  230   a  fluidly communicates with the supply passage  206   a  of the header  206 . The output ports  230   b  fluidly communicate with the output passage  206   e  through the output groove  206   g . The first ports  230   c  fluidly communicate with the second passages  206   d  of the lower header  206 . The exhaust ports  230   d  fluidly communicate with the exhaust passage  206   b  through the exhaust groove  206   f . The second ports  230   e  fluidly communicate with the first passages  206   c  of the lower header  206 . The sealing port  230   f  fluidly communicates with the exhaust passage  206   b  through the exhaust groove  206   f.    
         [0085]     With reference to  FIGS. 21-23 , the rotor  240  has a front face  241   a  contacting the stator  130  and an opposite rear face  241   b . On the front face  241   a , the rotor  240  defines two first recesses  240   c , two second recesses  240   e  which are fluidly connected to each other by a circular groove  240   f  and a circular sealing recess  240   i . The circular groove  240   f  is disposed to fluidly communicate with the three exhaust ports  230   d  of the stator  230 . On the rear face  241   b , the rotor  240  defines a receptacle  240   m  for receiving a cover  242 , an inner groove  240   j  and a outer groove  240   k . A flow passage  243  is defined between the cover  242  disposed in the receptacle  240   m  and the rotor  240 . The rotor  240  further includes a centrally disposed supply opening  240   a , two first openings  240   b , four second openings  240   d  and four third openings  240   g , which axially extend through the rotor.  
         [0086]     With reference to  FIGS. 26-28 , the operation of the oxygen concentrator  200  according the second embodiment will be described below. In the second embodiment, the oxygen concentrator  200  includes the six adsorption cylinders  102  the positions of which are indicated by reference numbers  1 - 6 , in  FIGS. 26-28 . In the following description, the operation of the oxygen concentrator  200  will be described in relation to one of the adsorption cylinders, cylinder  1  which is disposed at position  1 .  
         [0087]     Step I (Pressurization Step)  
         [0088]     The rotor  240  is at the home position shown in  FIG. 27  where the first opening  240   b  aligns with one of the second port  230   e  of the stator  230  so that the air is supplied to cylinder  1  from the compressor  12  through the air supply conduit  16 , the supply passage  206   a  of the lower header  206 , the supply port  230   a  of the stator  230   a , the supply opening  240   a  of the rotor  240 , the passage  243  defined between the stator  240  and the cover  242 , the first opening  240   b , the second port  230   e  and the lower orifice of cylinder  1 .  
         [0089]     Step II (Pressurization-Generation Step)  
         [0090]     The rotator  240  rotates to a rotational position at 15 degrees from the home position where the first opening  240   b  is still aligned with the second port  230   e  and, therefore, the compressed air is supplied to cylinder  1 . At the same time, the first recess  240   c  of the rotor  240  aligns with both the output port  230   b  and the first port  230   c  of the stator  230 . This rotational position of the rotor  240  allows the oxygen enriched gas to flow from cylinder  1  to the user through the upper orifice of cylinder  1 , the passage  204   a  of the upper header  204 , the connection conduit  216 , second passage  206   d  of the lower header  206 , the first ports  230   c  of the stator  230 , the first recess  240   c  of the rotor  240 , the output ports  230   b  of the stator  230 , the output groove  206   g , the output passage  206   e  of the lower header  206  and the output conduit  24 .  
         [0091]     Step III (Generation Step)  
         [0092]     The rotator  240  rotates to a rotational position at 30 degrees from the home position where the first opening  240   b  of the rotor  240  is not aligned with the second port, and therefore, the supply of the compressed to cylinder  1  is terminated. However, the first recesses  240   c  is still aligned with both the output ports  230   b  and the first ports  230   c  of the stator  230 . Therefore, the oxygen enriched gas is still supplied to the user from cylinder  1  as described above.  
         [0093]     Step IV (First Depressurization-Equalization Step)  
         [0094]     The rotor  240  rotates to a rotational position at 45 degrees from the home position where the second opening  240   d  of the rotor  240  aligns with the first port  230   c  communicating with cylinder  1  and, at the same time, the third opening  240   g  align with the first port  230   c  communicating with cylinder  3 . This rotational position of the rotor  240  allows the oxygen enriched gas to flow from cylinder  1  to cylinder  3  through the upper orifice of cylinder  1 , the passage  204   a  of the upper header  204 , the connection conduit  216 , the second passages  206   d  of the lower header  206 , the first port  230   c  of the stator  230 , the second opening  240   d , the outer groove  240   k , the third opening  240   g  of the rotor  240 , the first port  230   c  of the stator  230 , the second passage  206   d  of the lower header  206 , the connection conduit  216 , the passage  204   a  of the upper header  204  and the upper orifice of cylinder  3 . Thus, the pressure in cylinder  1  is reduced and the pressure in cylinder  3  is increased to equalize the pressure in cylinders  1  and  3 .  
         [0095]     Step V (Second Depressurization-Equalization Step)  
         [0096]     The rotor  240  rotates to a rotational position at 60 degrees from the home position where the second opening  240   d  align with the first port  230   c  communicating with cylinder  1  and at the same time the third opening  240   g  align with the first port  230   c  communicating with cylinder  4 . This rotational position of the rotor  240  allows the oxygen enriched gas to flow from cylinder  1  to cylinder  4   
         [0097]     through the upper orifice of cylinder  1 , the passage  204   a  of the upper header  204 , the connection conduit  216 , the second passages  206   d  of the lower header  206 , the first port  230   c  of the stator  230 , the second opening  240   d , the outer groove  240   k , the third opening  240   g  of the rotor  240 , the first port  230   c  of the stator  230 , the second passage  206   d  of the lower header  206 , the connection conduit  216 , the passage  204   a  of the upper header  204  and the upper orifice of cylinder  3 . Thus, the pressure in cylinder  1  is reduced and the pressure in cylinder  4  is increased to equalize the pressure in cylinders  1  and  4 .  
         [0098]     Step VI (Third Depressurization-Equalization Step)  
         [0099]     The rotor  240  rotates to a rotational position at 75 degrees from the home position where the second opening  240   d  align with the first port  230   c  communicating with cylinder  1  and at the same time the third opening  240   g  align with the first port  230   c  communicating with cylinder  5 . This rotational position of the rotor  240  allows the oxygen enriched gas to flow from cylinder  1  to cylinder  5   
         [0100]     through the upper orifice of cylinder  1 , the passage  204   a  of the upper header  204 , the connection conduit  216 , the second passages  206   d  of the lower header  206 , the first port  230   c  of the stator  230 , the second opening  240   d , the outer groove  240   k , the third opening  240   g  of the rotor  240 , the first port  230   c  of the stator  230 , the second passage  206   d  of the lower header  206 , the connection conduit  216 , the passage  204   a  of the upper header  204  and the upper orifice of cylinder  3 . Thus, the pressure in cylinder  1  is reduced and the pressure in cylinder  5  is increased to equalize the pressure in cylinders  1  and  5 .  
         [0101]     Step VII (Cocurrent Depressurization Step)  
         [0102]     The rotor  240  rotates to a rotational position at 90 degrees from the home position where the third openings  240   g  of the stator  240  align with the first ports  230   c  communicating with cylinders  1  and  6 . This rotational position of the rotor  240  allows the oxygen enriched gas to flow, as a purge gas, from cylinder  1  to cylinder  6  through the lower orifice of cylinder  1 , through the upper orifice of cylinder  1 , the passage  204   a  of the upper header  204 , the connection conduit  216 , the second passages  206   d  of the lower header  206 , the first port  230   c  of the stator  230 , the third opening  240   g , the third opening  240   h , the inner groove  240   j , the third opening  240   h , the third opening  240   g  of the stator  240 , the first port  230   c  of the stator  230  of the stator  230 , the second passages  206   d  of the lower header  206   d , the connection conduit  216 , the passage  204   a  of the upper header  204  and the upper orifice of cylinder  6 . At that time, a purge step, which will be described below, is conducted in cylinder  6 .  
         [0103]     Step VIII (Evacuation Step)  
         [0104]     The rotor  240  rotates to a rotational position at 105 degrees from the home position where the second port  230   e  of the stator  230  aligns with the second recess  240   e . This rotational position of the rotor  240  allows the gas in cylinder  1  to be evacuated by the vacuum pump  22  through the lower orifice of cylinder  1 , the first passage  206   c  of the lower header  206 , the second port  230   e  of the stator  230 , the second recess  240   e , the circular groove  240   f  of the rotor  240 , the exhaust ports  230   d  of the rotor  240 , the exhaust groove  206   f , the exhaust passage  206   b  of the lower header  206  and the exhaust conduit  22 .  
         [0105]     Step IX (Purge Step)  
         [0106]     The rotor  240  rotates to a rotational position at 120 degrees from the home position where the second port  230   e  of the stator  230  still aligns with the second recess  240   e  and the third openings  240   g  of the stator  240  align with the first ports  230   c  communicating with cylinders  1  and  2 . Therefore, the oxygen enriched gas is supplied to cylinder  1  from cylinder  2  as described in relation to Step VII while the gas in cylinder  1  is still evacuated as described above.  
         [0107]     Step X (Third Pressurization-Equalization Step)  
         [0108]     The rotor  240  rotates to a rotational position at 135 degrees from the home position where the third openings  240   g  align with the first ports  230   c  communicating with cylinders  1  and  3 . This rotational position of the rotor  240  allows the oxygen enriched gas to flow from cylinder  3  to cylinder  1  as described above in relation to Step VI.  
         [0109]     Step XI (Second Pressurization-Equalization Step)  
         [0110]     The rotor  240  rotates to a rotational position at 150 degrees from the home position where the second openings  240   d  align with the first ports  230   c  communicating with cylinders  1  and  4 . This rotational position of the rotor  240  allows the oxygen enriched gas to flow from cylinder  4  to cylinder  1  as described above in relation to Step V.  
         [0111]     Step XII (First Pressurization-Equalization Step)  
         [0112]     The rotor  240  rotates to a rotational position at 165 degrees from the home position where the second openings  240   d  align with the first ports  230   c  communicating with cylinders  1  and  5 . This rotational position of the rotor  240  allows the oxygen enriched gas to flow from cylinder  5  to cylinder  1  as described above in relation to Step IV.  
         [0113]     As shown in the drawings, in the second embodiment, the six output ports  230   b , the six first ports  230   c , the three exhaust ports  230   d  and the six second ports  230   e  are disposed along different circles about the rotational axis of the rotor  140 . Further, each of the ports fluidly communicating with each of the adsorption cylinders  202  are disposed at any one of (i)th point, (m+i)th point, (2m+i)th point, (3m+i)th point, . . . , ((n−1)m+i)th point (i: integer=1 to m) along the circle. Here, i is integer i=1 to m, m is number of the adsorption cylinders and n is the number of cycle of the above described process during one rotation of the rotor, that is 2 in the second embodiment. This arrangement prevents the concentrator  200  from executing the same steps of the above described process at a rotational position of the rotor  240 .  
         [0114]     Further, according to the second embodiment of the present invention, the supply passage  206   a , the exhaust passage  206   b  and the output passage  206   e  provide a common flow passages. The upper or first orifices of the adsorption cylinders  202  provide flow passages of a first subgroup of a selective flow passage group and the lower or second orifices of the adsorptions cylinders  202  provide flow passages of a second subgroup of the selective flow passage group.