Patent Publication Number: US-11041575-B2

Title: Magnetically latched pneumatic valve

Description:
TECHNICAL FIELD 
     This invention relates to a valve device, especially to a valve device as a color-change valve to supply each selected color paint that is being transported from a color-paint source to a coating machine or the like. 
     TECHNICAL BACKGROUND 
     Demand for vehicle-color variation from users has recently diversified, and it is now necessary to coat many different colors onto the same model of car. Especially, recent car bodies that need to be coated with different colors are mixed and carried onto a car-coating line. Thus, it is needed to coat such a car body by changing the color coating in accordance with the body type. 
     As shown in  FIG. 12 , the color-change device  101  is used, for example, to change a color coating. Conventionally, the general type of color-change device  101  has a structure of which multiple color-change valves  104  and a cleaning-liquid valve  105  and a cleaning-air valve  106  or the like are provided on a manifold block  103 , therein a color-paint passage  102  is formed. These multiple color-change valves  104  are connected respectively to each color paint source P 1  to P 4 . The cleaning-liquid valve  105  is connected to the cleaning-liquid source  107 , and the cleaning-air valve  106  is connected to the pressed-air source  108 . Using such a color-change device  101  allows the color-change device  101  to select any color paint from among many color paints, which makes it possible to supply such a selected paint to the coating machine  109 , thus aiding in coating the car body. 
       FIG. 13  shows an example of the conventional type of valve device wherein the color-change valve  104  is used for this type of color-change device. This color-change valve  104  is a pilot-type 2-port valve that has the driving means of a piston cylinder made of the valve-driving part  112  located atop of the drawing, and the valve-main body  113  located at the bottom of the drawing. 
     The piston housing  121  making the valve-driving part  112  has a piston-housing space  122  inside and a rod-insertion hole  123  passing through the piston-housing space  122  at the bottom. The valve housing  131  is provided at the bottom-end face of the piston housing  121 . The input port  132  is formed on the side of the valve housing  131 , and the output port  133  is formed at the bottom face. These ports  132 ,  133  are communicated with the passage  134  provided within the valve housing  131 . The valve seat  135  is formed within the opening of the output port  133 . A support assembly  138 , including the packing  136 ,  137  or the like, is installed in the valve housing  131 . 
     This color-change valve  104  has a valve rod  141  as a mobile body  141  having a rod part  142 , a piston part  143  and a valve part  144 . The piston part  143  is secured on the base end of the rod part  142  and is also slidably stored within the piston housing space  122 . The tip of the rod part  142  protrudes out of the piston-housing space  122  through the rod-insertion hole  123  and the support assembly  138 . Then, such protrusion reaches the vicinity of the valve seat  135  of the valve housing  131 . The valve part  144  is integrally formed at the tip of the rod part  142  and can be contacted to and separated from the valve seat  135 . 
     The piston-housing space  122  within the piston housing  121  is divided by the piston part  143  into the first chamber  151  and second chamber  152 . The pilot port  153  is formed in the first chamber  151  of the piston housing  121 , which drives the piston part  143  upward to supply the pilot air. A biasing means  154  is stored in the second chamber  152  of the piston housing  121 , which presses the piston part  143  downward all the time. Such a mechanism of the color-change valve  104  makes it possible to drive the valve rod  141  vertically by the supply and discharge of the pilot air, with the valve part  144  being contacted or separated from the valve seat  135 , subsequently controlling the opening and closing of the valve. 
     Besides this type of valve device, the valve as shown in Patent Document 1, for example, is conventionally suggested. 
     PRIOR ARTS 
     Patent Documents 
     Patent Document 1: Japanese Patent No. 5511339 
     Patent Document 2: Unexamined Japanese Patent Application No. 2017-2939 
     SUMMARY OF THE INVENTION 
     Problems to Be Solved By the Invention 
     The above conventional valve device is installed into a driving part such as the arm of the coating machine or the like. Therefore, such a valve device is required to be as small as possible. However, if the valve device is downsized, the diameter of the piston should be smaller, thus decreasing the pressurized area of the piston part. To activate the piston part under a similar power, as usual, it is necessary to increase the pressure of the pilot air (e.g. 0.4 MPa should be increased up to 0.8 MPa). Therefore, the compressed pressure to supply the air should be increased. 
     Under such circumstance, a valve device is conventionally suggested such that the piston-drive force based on the pilot air should be supported by magnetic force (e.g. see Patent Document 2). However, the conventional device has a complicated structure and may make noise, because the magnet stored within the housing directly contacts a partition wall, and there is also the concern about low durability, since the magnet is made of parts that are not so strong against an impact or the like, thus being liable to damage. 
     This invention was made in the light of the above-mentioned problems. The aim of the invention is to provide a durable valve device to be activated by pilot air that is of comparatively light pressure regardless of it being small in size. 
     Means for Solving the Problems 
     To solve the above problems, the first aspect of this invention refers to a valve device comprising a housing having a piston-storing space; a valve rod of which a piston part is provided at the position within the piston-storing space and a valve part is formed at the tip protruding outside the piston-storing space; a pilot port that is provided on the first chamber of the first and second chambers that are dividedly formed on the piston part within the housing, so as to supply pilot air, thus activating the piston part in the first direction, along the axial line of the valve rod; and a biasing means, which is provided on the second chamber of the housing, to bias the piston part in the second direction that is the opposite direction of the first direction, so that valve part makes contact with or separates from the valve seat by supplying or discharging the pilot air, thus controlling the opening and closing of the valve, characterized in that the valve comprises a first-magnetic member provided on the valve-rod side and a second-magnetic member facing the first magnetic member provided on the housing side, therein at least one magnetic member, either of the first or second magnetic member is a permanent magnet, so that a magnetic attraction is generated between both magnetic members to activate the piston part in the first direction, thus increasing the magnetic attraction by the approach of both magnetic members, therein an arrangement-relation facing each magnetic member through an air gap is set even when making its closest approach. 
     Therefore, the first aspect of this invention generates the effect between both magnetic members to activate the piston part in the first direction and to increase the magnetic attraction by the mutual approach of both magnetic members. As such, the valve rod is activated in the first direction by the effect of the magnetic attraction as well as by the pressure of the pilot air while the pilot air is being supplied. Therefore, even if the pressurized area of the piston part is small, the opening and closing of the valve can be controlled by the comparatively low pressured pilot air. The arrangement relation of which both magnetic members face each other through an air gap is set between both magnetic members even as they approach each other the closest, so that the contact of both magnetic members can be avoided when activating the valve rod, and that the contact of the magnetic member with the inner wall of the housing can also be avoided, which may decrease noise or damage by the contact of the magnetic members, thus increasing the durability of the magnetic members. 
     The second aspect of this invention refers to a valve device according to the first aspect of this invention, characterized in that the magnetic attraction that works on the piston part while the pilot air is not being supplied is less than the biasing force of the bias means, and that the total amount of the pressing force of the magnetic attraction and of the pilot air that work on the piston part while the pilot air is being supplied is greater than the biasing force of the bias means. 
     The third aspect of this invention refers to a valve device according to the first aspect or the second aspect, characterized in that the first magnetic member and the second magnetic member are both permanent magnets, and that the proximity-fixing member, to hold firmly the first permanent magnet as the first magnetic member, is provided on the valve rod side in a state being close to the second permanent magnet as the second magnetic member. 
     As such, the third aspect of this invention allows the first permanent magnet to come close to the second permanent magnet, thus efficiently utilizing the magnetic attraction of both permanent magnets. 
     The fourth aspect of this invention refers to a valve device according to the first aspect or the second aspect, characterized in that the first magnetic member and the second magnetic member are both permanent magnets, and that the proximity-fixing member, to hold firmly the second permanent magnet as the second magnetic member, is provided on the housing side in a state being close to the first permanent magnet as the first magnetic member. 
     As such, the fourth aspect of this invention allows the second permanent magnet to come close to the first permanent magnet, thus efficiently utilizing the magnetic attraction of both permanent magnets. 
     The fifth aspect of this invention refers to a valve device according to the first aspect or the second aspect of this invention, characterized in that the first permanent magnetic member and the second permanent magnetic member are both permanent magnets, and that the piston part has a place where the first permanent magnet as the first magnetic member does not exist, and a stopper-step is provided within the housing side to avoid a collision of both permanent magnets in making contact at the place where the first permanent magnet does not exist. 
     As such, the fifth aspect of this invention allows the said place to first contact the stopper-step to avoid contacting or the like of both permanent magnets, thus reducing the possibility of noise and damage. 
     The sixth aspect of this invention refers to a valve device according to the first aspect or the second aspect of this invention, characterized in that the first permanent magnetic member and the second permanent magnetic member are both permanent magnets, and that the housing has a place where the second permanent magnet as the second magnetic member does not exist, and a stopper member is provided on the valve rod within the housing to avoid the collision of both permanent magnets in making contact at the place where the second permanent magnet does not exist. 
     As such, the sixth aspect of this invention allows the said place to first contact the stopper member to avoid contacting or the like of both permanent magnets, thus reducing the possibility of noise and damage. 
     Effects of the Invention 
     As described above, the first to sixth aspects of this invention make it possible to activate the valve device with pilot air of comparatively low pressure, even though the valve device is small, thus providing a valve device that is excellent in durability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1( a ) and 1( b )  show the schematic drawings of the valve device as the first embodiment of this invention, showing the longitudinal section of such a valve device. 
         FIG. 2  is the schematic drawing of the valve device as the first embodiment being used. 
         FIGS. 3( a ) and 3( b )  show the schematic drawings of the valve device as the second embodiment of this invention, showing the longitudinal sectional view of such a valve device. 
         FIGS. 4( a ) and 4( b )  show the schematic drawings of the valve device as the third embodiment of this invention, showing the longitudinal sectional view of such a valve device. 
         FIGS. 5( a ) and 5( b )  show the schematic drawings of the valve device as the fourth embodiment of this invention, showing the longitudinal sectional view of such a valve device. 
         FIGS. 6( a ) and 6( b )  show the schematic drawings of the valve device as the fifth embodiment of this invention, showing the longitudinal sectional view of such a valve device. 
         FIG. 7  is the schematic drawing of the valve device as the sixth embodiment of this invention, showing the longitudinal sectional view of such a valve device. 
         FIG. 8  is the schematic drawing of the valve device as the sixth embodiment being used. 
         FIGS. 9( a ) and 9( b )  show the schematic drawings of the valve device as another embodiment of this invention. 
         FIGS. 10( a ) and 10( b )  show the schematic drawings of the valve device as yet another embodiment of this invention, showing the longitudinal sectional view of such a valve device. 
         FIGS. 11( a ) and 11( b )  show the schematic drawings of the valve device as yet another embodiment of this invention, showing the longitudinal sectional view of such a valve device. 
         FIG. 12  is the schematic drawing explaining the structure of the color-change device using the valve device. 
         FIG. 13  is the schematic drawing of the conventional valve device, showing the longitudinal sectional view of such a valve device. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     Hereinafter the color-change valve  11  as an embodiment of the invention is described in reference to  FIG. 1  and  FIG. 2 . Drawings (a) and (b) of  FIG. 1  show the schematic longitudinal sectional view of the color-change valve  11 .  FIG. 2  shows the schematic view when the color-change valve  11  is being used as part of the color-change device CV 1 . 
     As shown in  FIG. 1 , the color-change valve  11  as an embodiment of this invention is a pilot type of a 2-port valve having a piston cylinder as a drive means, making of the valve-driving part  12  located atop the drawing and the valve-main body  13  located at the bottom of the drawing. 
     The piston housing  21  that forms the valve-driving part  12  has a piston-housing space  22  inside. A rod-insertion hole  23  is provided in the center of the lower part of the piston-housing space  21  that communicates the piston-housing space  22 . A valve housing  31  is provided on the lower-end part of the piston housing  21 . An input port  32  is formed on the side of the valve housing  31 , and an output port  33  is formed in the center of the lower part. Also, a passage  34  to let the paint flow within the valve housing  31  and the input port  32  and the output port  33  are respectively communicated to the passage  34 . A valve seat  35  that is sectionally tapered is formed inside the opening of the output port  33 . Furthermore, within the valve housing  31 , a cylindrical support assembly  38  including a sealing material  36 ,  37  or the like is arranged in an area (communication space) that connects the passage  34  to the rod insertion hole  23  of the piston housing  21 . Therein, the sealing material  36  prevents the pilot air from leaking into the passage  34  from the piston-housing space  22  through the communication space. The sealing material  37  prevents the paint, the cleaning liquid or the like that is being led to the passage  34  from leaking to the piston-housing space  22  through the communication space. 
     The color-change valve  11  comprises a valve rod  41  as a mobile body having a rod part  42 , a piston part  43  and a valve part  44 . The valve rod  41  is slidably inserted into the rod-insertion hole  23 . The rod part  42  of the embodiment of this invention is made of a bottom-half part that is relatively large in diameter and of an upper-half part that is relatively small in diameter. The disk-shaped piston part  43  is firmly attached to the small-diameter part of the rod part  42 , i.e. at the position within the piston-housing space  22 . The piston part  43  is placed within the piston-housing space  22 , allowing the piston part  43  to slide vertically. A recess part for the housing packing is provided on the outer-peripheral surface of the piston part  43 . Therein, a ring-seal packing  45  is placed. 
     The bottom end (head end) of the rod part  42  protrudes into the outer area of the piston housing space  22  through the rod-insertion hole  23 . The bottom end (head end) of the rod part  42  goes through the center hole of the support assembly  38  to be exposed in the passage  34  within the valve housing  31 . The valve part  44 , having a tapered section, is integrally formed on the head end of the rod part  42 , thus making contact with or separating from the valve seat  35  with the vertical motion of the valve rod  41 . In addition,  FIG. 1( a )  shows the valve part  44  making contact with the valve seat  35 , and  FIG. 1( b )  shows the valve part  44  separating from the valve seat  35 . 
     The piston-housing space  22  within the piston housing  21  is divided into the first chamber  51  of the lower side and the second chamber  52  of the upper side through the piston part  43 . The pilot port  53  is formed in the first chamber  51  of the piston housing  21  so that the pilot air is supplied therein so as to move vertically the piston part  43 . The pilot port  53  opens on the side of the piston housing  21 , thus communicating the first chamber  51  with the atmospheric pressure region. 
     The second chamber  52  of the piston housing  21  is communicated with the atmospheric-pressure region through a rod-release hole  25  provided in the center of the ceiling part  24 . The upper end of the small diameter of the rod part  42  is always inserted into the rod-release hole  25  without making contact. A coil spring  54  in a compressed state as the bias means is stored in the second chamber  52 . One end of the coil spring  54  makes contact with the upper end if the piston part  43  and the other end of the coil spring  54  makes contact with the inner wall of the ceiling part  24  within the piston housing  21 , thus allowing the effect of the bias force always to press the piston part  43  downward. 
     Hereinafter, the mechanical structure to support the piston-driving force based on pilot air using magnetic force is described. The color-change valve  11  of the embodiment of this invention comprises a first permanent magnet  56  as the first magnetic member and a second permanent magnet  57  as the second magnetic member within its valve-driving part  12 . 
     The second permanent magnet  57  is ring shaped and installed in a mounting recess formed on the inner-end opening of the rod-release hole  25  of the ceiling part  24 . On the other hand, the first permanent magnet  56  is also a ring-shaped magnet and has the size to be engaged with the small diameter of the rod part  42 . This first permanent magnet  56  is formed slightly smaller than the diameter of the coil spring  54 , so as to be arranged in a state not being contacted with the coil spring  54  within the inner region of the coil spring  54 . The second permanent magnet  57  is also formed almost the same size as the first permanent magnet  56 . It is possible to use a conventional permanent magnet for the first permanent magnet  56  and for the second permanent magnet  57 . However, a strong neodymium magnet of strong magnetic force is used for the embodiment of this invention. It is also possible to use, e.g. samarium cobalt magnets, ferrite magnets, alnico magnets or the like. 
     A cylindrically shaped sleeve  55  (proximity-fixing member) is mounted in the position of the base-end side rather than that of the piston part  43  on the smaller diameter part of the rod part  42 . This sleeve  55  is of a non-magnetic material (made of non-magnetic metal e.g. synthetic resin, aluminum) and is of a predetermined length. Thereof, one end contacts the center of the upper surface of the piston part  43 , and the first permanent magnet  56  is fixed on the other end by adhesion or the like. As such, compared to the condition that the first permanent magnet  56  is directly attached onto the top surface of the piston part  43 , the first permanent magnet  56  approaching the second permanent magnet is firmly fixed in a state of both magnets facing each other. 
     Between the first permanent magnet  56  and the second permanent magnet  57 , there is an arrangement relation of the magnetic force to drive the piston part  43  in the upper direction A 1  (first direction) as shown in  FIG. 1 , i.e. an arrangement relation whereby the magnetic attraction works. Thus, the first permanent magnet  56  and the second permanent magnet  57  are facing each other with different electrodes. In this case, the magnetic attraction increases as the first permanent magnet  56  and the second permanent magnet  57  approach each other, thus maximizing the magnetic attraction in the state of the closest approach of both magnets, as shown in  FIG. 1( b ) . 
     The stopper-step  58  is provided on the inner-wall surface of the side wall of the second chamber  52  within the piston housing  21 , thus avoiding a collision of the first permanent magnet  56  and the second permanent magnet  57 . This stopper-step  58  makes contact at the place of the piston part  43  where the first permanent magnet  56  does not exist, specifically at the place of the outer-peripheral part of the upper-end surface of the piston part  43 . As a result of such contact, the upward movement of the piston part  43  is controlled (see  FIG. 1( b ) ). As shown in  FIG. 1( b ) , when the first permanent magnet  56  approaches closest to the second permanent magnet  57 , an arrangement relation whereby the first permanent magnet  56  stops in a state with a slight air gap (e.g. 1 to 5 mm) before the second permanent magnet  57  is set between them (magnets  56  and  57 ). Specifically, such an arrangement relation as described above is set by adjusting the length of the sleeve  55  at the most appropriate value. 
     Hence, the inner state of the first chamber  15  and of the second chamber  52  become an atmospheric-pressure region, respectively, when the pilot air is not being supplied, as shown in  FIG. 1( a ) . At this time, the pressurizing force by the atmospheric pressure working the first direction A 1  and the second direction A 2  through the piston part  43  is offset. Then, the biasing force of the coil spring  54  that presses the piston part  43  into the second direction A 2  works on the piston part  43  at the same time that magnetic attraction is being generated to press the piston part  43  into the first direction A 1 . However, the value of the magnetic attraction at this time is the least as the first permanent magnet  56  and the second permanent magnet  57  are separated the farthest from each other. Furthermore, the magnetic attraction is set so as to be less than the biasing force of the coil spring  54 , thus causing the piston part  43  to move in the second direction A 2 . As such, the valve rod  41  moves downward so that the valve part  44  contacts the valve seat  35  to become closed, thus forming the passage  34 . In other words, in regard to the color-change valve  11  as the embodiment of this invention, the valve is completely closed by the biasing force of the coil spring  54  even when such coil spring  54  is blocking the pilot air. 
     As shown in  FIG. 1( b ) , when the pilot air is being supplied, inside of the second chamber  52  there is still an atmospheric-pressure region. On the other hand, the pilot air being pressurized in the pilot port  53  is introduced into the first chamber  51 . As such, the pressure of the pilot air works at the bottom side of the piston part  43  so that the force to press the piston part  43  is in the first direction A 1 . The total amount of the pressuring force by the pilot air and of the above magnetic attraction is set in advance so as to become greater than the biasing force of the coil spring  54 . Thus, the pressurizing force by the pilot air and of the above magnetic attraction work at the same time. Then, the piston part  43  moves into the first direction A 1  against the biasing force of the coil spring  54 . Thus, the piston part  43  stops being in contact with the stopper-step part  58 . As a result, the valve rod  41  moves upward so that the valve part  44  separates from the valve seat  35  to become closed, thus forming the passage  34 . 
     The mechanical motion whereby the color-change valve  11  as the embodiment of this invention is used as part of the color-change device CV 1  is described hereinafter. As shown in  FIG. 2 , the color-change valve  11  as the embodiment of this invention is used in a state, e.g. to be multiply provided in the manifold block M 1 . The main passage R 1  as the paint-flow passage is formed within the manifold block M 1 . Besides, multiple sub-passages R 2  are branched from there and formed. The main passage R 1  is connected to a coating machine (not described in the drawings). Each color-change valve  11  is mounted such that the opening of each sub-passage R 2  is communicated with each output port  33  in a state that the valve housing  31  contacts the manifold block M 1 . Also, an input port  32  of each color-change valve  11  is separately connected to an individual-paint supplying source (drawing omitted). The pilot port  53  of each color-change valve  11  is connected to an air compressor (drawing omitted) for supplying the pilot air through a fluid controller such as a solenoid valve or the like (drawing omitted). The embodiment of this invention is designed such that air of comparatively low pressure e.g. 0.4 MPa is supplied. 
     In the initial stage that the pilot air is not being supplied to each color-change valve  11 , the passage  34  of each color-change valve  11  is closed. Thus, the paint is not being supplied then to the sub-passage R 2  and to the main passage R 1 . At this time, if the pilot air is being supplied to the specified color-change valve  11 , the valve rod  41  of the color-change valve  11  is driven to the position as shown in  FIG. 1( b )  from the position as shown in  FIG. 1( a ) . As such, the valve part  44  is separated from the valve seat  35 , thus forming an opening to communicate the input port  32  with the output port  33  through the passage  34 . Then, the predetermined paint is flown into the manifold block M 1  from the color-change valve  11 , thus supplying the appropriate paint into the coating machine. Also, if the supply of pilot air into the color-change valve  11  is suspended, the valve rod  41  of the color-change valve  11  is returned to the position as shown in  FIG. 1( a )  from the position as shown in  FIG. 1( b ) . As such, the valve part  44  is closed as being in contact with the valve seat  35 , so as to shut off the relation between the input port  32  and the output port  33 . Therefore, the predetermined paint will not be flown into the manifold block M 1  from the color-change valve  11 , thus suspending the paint being supplied to the coating machine. 
     Therefore, the embodiment of this invention realizes the following effects. 
     (1) The color-change valve  11  as the embodiment of this invention generates the magnetic attraction between the first permanent magnet  56  and the second permanent magnet  57 , which is increased by the approach of each magnet when driving the piston part  43  in the first direction A 1 . As such, when the pilot air is being supplied, the magnetic attraction works with the pilot air, thus driving the valve rod  41  in the first direction A 1 . Therefore, even if the pressurized area of the piston part  43  is small, the closing and opening of the valve can be controlled by using the comparatively low pressured-pilot air. Also, an arrangement-relation facing the first permanent magnet  56  and the second permanent magnet  57  through an air gap is set between them when making its closest approach, so that the contact of both the first permanent magnet  56  and the second permanent magnet  57  can be avoided when activating the valve rod  41 , and that the contact of the first permanent magnet  56  and the second permanent magnet  57  with the inner wall of the housing can also be avoided, which may decrease noise or damage by such contact of the permanent magnets, thus increasing the durability of the magnetic members. The aforementioned embodiment of this invention makes it possible to provide a color-change valve  11  that can be activated by pilot air of comparatively low pressure, even though such color-change valve is small and light, thus providing such a color-change valve  11  that is excellent in durability. 
     (2) In the case of this color-change valve  11  when the pilot air is not being supplied, the magnetic attraction that works on the piston part  43  is set so as to become less than the biasing force of the coil spring  54 . Such a biasing force of the coil spring  54  makes the valve rad  41  move to the position whereat the valve part  44  contacts the valve seat  35 , thus keeping the valve completely closed. Also, the total amount of the magnetic attraction that works on the piston part  43 , and the total amount of the pressing force by the pilot air while the pilot air is being supplied, is set to be greater than the biasing force of the bias means. Therefore, the resultant force of the magnetic attraction and of the pressing force by the pilot air makes the valve rod  41  move to the position whereat the valve part  44  is separated from the valve seat  35 , thus keeping the valve completely closed. Also, this embodiment provides a normal closed type of valve of which the valve is closed by the biasing force of the coil spring  54  when the pilot air is not being supplied. Therefore, it is possible to reduce the amount of the supply of the pilot air necessary to activate the color-change device CV 1  that makes most units of the multiple color-change valves  11  closed. 
     (3) About this color-change valve  11 , the first permanent magnet  56  is used as the first magnetic member, and the second permanent magnet  57  is used as the second magnetic member, which makes it possible to generate magnetic attraction greater than if either one of them is not a magnet. Also, the sleeve  55  is provided on the valve rod  55  to hold firmly the first permanent magnet  56  in the state of being close to the second permanent magnet  57 , thus making it possible for the magnet attraction to be greater and more efficient. 
     About this color-change valve  11 , the stopper-step  58  is provided on the piston housing  21  that makes contact with the outer-peripheral part of the upper-end surface whereat the first permanent magnet  56  does not exist on the piston part  43  within the piston housing  21 . As such, when the valve rod  41  moves in the first direction A 1 , the stopper-step part first contacts the stopper-step  58  to avoid contact or the like of the first permanent magnet  56  with the second permanent magnet  57 , thus reducing the possibility of noise and damage. 
     (5) About this color change valve  11 , the first permanent magnet  56  is used as the first magnetic member, and the second permanent magnet  57  is used as the second magnetic member. On the other hand, non-magnetic members are used for other components (e.g. piston housing  21 , valve housing  31 , rod part  42 , piston part  43 , support assembly  38  or the like). Therefore, there is no magnetic force generated between such non-magnetic components; magnetic attraction is only generated between the first permanent magnet  56  and the second permanent magnet  57 . 
     Second Embodiment 
     Hereinafter, the color-change valve  11 A as the second embodiment of this valve-device invention is described in reference to  FIG. 3 .  FIGS. 3( a ) and ( b )  are the schematic longitudinal sectional view of the color-change valve  11 A. In this section of the second embodiment, only aspects different from the first embodiment are mainly described, and the description of the common aspects is omitted only by showing the same part numbers. 
     As shown in  FIGS. 3( a ) and ( b ) , this color-change valve  11 A comprises a first permanent magnet  66  as the first magnetic member and a second permanent magnet  67  as the second magnetic member within its valve-driving part  12 . The first permanent magnet  66  and the second permanent magnet  67  are both ring-shaped magnets but different in size, and the mounting place is different from that of the first embodiment. The first permanent magnet  66  is almost of the same outer diameter as the piston part  43  and is attached to the mounting recess that is formed on the upper-peripheral part of the upper-end surface of the piston part  43 . The second permanent magnet  67  is almost of the same outer diameter as the first permanent magnet  66 . A mounting recess is formed on the stair-member located on the side-inner wall of the second chamber  52  within the piston housing  21  and the second permanent magnet  67  is attached to the mounting recess. Thus, the first permanent magnet  66  and the second permanent magnet  67  are facing each other with different electrodes. 
     About this embodiment, a cylindrically shaped non-magnetic stopper member  68  is firmly mounted in the position of the base-end side rather than that of the piston part  43  on the smaller-diameter part of the cylindrical-rod part  42 . This stopper member  68  makes contact with the place of the upper-end side whereat the first permanent magnet  66  does not exist within the piston housing  21 . Specifically, it makes contact with the inner-wall surface of the ceiling part  24 . As a result of such contact, the upward movement of the piston part  43  is controlled (see  FIG. 3( b ) ). As shown in  FIG. 3( b ) , when the first permanent magnet  66  approaches closest to the second permanent magnet  67 , an arrangement relation whereby the first permanent magnet  66  stops in a state with a slight air gap (e.g. 1 to 5 mm) before the second permanent magnet  67 , is set between the magnets  66  and  67 . 
     Even the color-change valve  11 A, as structured above, makes it possible to drive the valve rod  41  vertically by supplying and discharging the pilot air and to make contact with and to separate the valve part  44  from the valve seat  35 , thus opening and closing the valve. The color-change valve  11 A can also be activated by pilot air of comparatively low pressure, even though the size of such valve  11 A is small, thus providing a valve device that is excellent in durability. 
     Third Embodiment 
     Hereinafter, the color-change valve  11 B as the third embodiment of this valve-device invention is described in reference to  FIG. 4 .  FIGS. 4( a ) and ( b )  are the schematic longitudinal sectional views of the color-change valve  11 B. In this section of the third embodiment, only aspects different from the first embodiment are mainly described, and the description of the common aspects is omitted only by showing the same part numbers. 
     As shown in  FIGS. 4( a ) and ( b ) , this color-change valve  11 B comprises the first permanent magnet  56  as the first magnetic member and the second permanent magnet  57  as the second magnetic member within its valve-driving part  12 . The first permanent magnet  56  and the second permanent magnet  57  are both ring-shaped magnets but different in size, and the mounting place is different from that of the first embodiment. The first permanent magnet  56  is inserted into the small diameter part of the rod part  42  and is fixed so as to make contact with the center of the upper-end surface of the piston part  43 . On the other hand, the second permanent magnet  57  is mounted in the piston housing  21  through the cylindrically shaped and non-magnetic sleeve  59  (proximity-fixing member). Specifically, this sleeve  59  is installed in the rod-release hole  25  of which one end is on the ceiling  24  and the other end extends in the direction of the piston part  43 . And the second permanent magnet  57  is fixed on the end surface of the other end with an adhesive or the like. As a result, compared to the case that the second permanent magnet  57  is directly fixed on the ceiling part, the second permanent magnet  57  approaches to the first permanent magnet  56  to be firmly fixed in a state of both magnets facing each other. The first permanent magnet  56  and the second permanent magnet  57  are facing each other with different electrodes, thus generating the magnetic attraction between them. Also, the sleeve  59  and the second permanent magnet  57  have a hole in the middle that is larger in diameter than the outer diameter of the small-diameter part of the rod part  42 , thus keeping the state of non-contact with the rod part  42 . 
     Even the color-change valve  11 B, as structured above, makes it possible to drive the valve rod  41  vertically by supplying and discharging the pilot air and to make contact to with and to separate the valve part  44  from the valve seat  35 , thus opening and closing the valve. The color-change valve  11 B can also be activated by pilot air of comparatively low pressure, even though the size of such valve  11 B is small, thus providing a valve device that is excellent in durability. 
     Fourth Embodiment 
     Hereinafter, the color-change valve  11 C as the fourth embodiment of this valve-device invention is described in reference to  FIG. 5 .  FIGS. 5( a ) and ( b )  are the schematic longitudinal sectional views of the color-change valve  11 C. In this section of the fourth embodiment, only aspects different from the first embodiment are mainly described, and the description of the common aspects is omitted only by showing the same part numbers. 
     As shown in  FIGS. 5( a ) and ( b ) , about this color-change valve  11 C, a cylindrically shaped sleeve  55  (proximity-fixing member) is mounted in the position of the base-end side rather than the piston part  43  on the small-diameter part of the rod part  42 . The first permanent magnet  56  is arranged on the upper side of the sleeve  55 . Furthermore, a fastening member such as a nut  69  or the like made of a non-magnetic material is arranged above the first permanent magnet  56 . Fastening the nut  69  fixes the first permanent magnet  56  onto the sleeve  55 . Even the color-change valve  11 C, as structured above, makes it possible to drive the valve rod  41  vertically by supplying and discharging the pilot air and by making contact with and by separating the valve part  44  from the valve seat  35 , thus opening and closing the valve. The color-change valve  11 C can also be activated by pilot air of comparatively low pressure, even though the size of such valve  11 C is small, thus providing a valve device that is excellent in durability. 
     Fifth Embodiment 
     Hereinafter, the color-change valve  11 D as the fifth embodiment of this valve device invention is described in reference to  FIG. 6 .  FIGS. 6( a ) and ( b )  are the schematic longitudinal sectional views of the color-change valve  11 D. In this section of the fifth embodiment, only aspects different from the first embodiment are mainly described, and the description of the common aspects is omitted only by showing the same part numbers. 
     About this embodiment, other members except for the permanent magnets are used for the second magnetic member. As shown in  FIGS. 6( a ) and ( b ) , a disk-shaped magnetic-lid member  70  is screwed into the place that is to be the ceiling part of the piston housing  21 , thus letting such a lid member to work as the second magnetic member. In other words, the piston part  43  is pressured in the first direction A 1  with the effect of the magnetic attraction that generates between the lid member  70  and the first permanent magnet  56 . Such a lid member  70  is formed using an alloy or the like that is a magnetic body, such as an iron-based metal or stainless steel. 
     Sixth Embodiment 
     Hereinafter, the color-change valve  11 E as the fifth embodiment of this valve-device invention is described in reference to  FIGS. 7 and 8 .  FIGS. 7( a ) and ( b )  are the schematic longitudinal sectional views of the color-change valve  11 E.  FIG. 8  is a schematic view of the color-change valve  11 E being used as part of the color-change device CV 2 . In this section of the sixth embodiment, only aspects different from the first embodiment are mainly described, and the description of the common aspects is omitted only by showing the same part numbers. 
     As shown in  FIGS. 7( a ) and ( b ) , this color-change valve  11 E comprises a valve-driving part  12 . However, it does not comprise a valve housing  31  making the valve-main unit  13 . Therefore, the tip of the valve rod  41  protrudes from the piston housing  21  and is exposed outside of the color-change valve  11 E. About this color-change valve  11 E, the diaphragm  71  as the separation member is provided in the insertion hole  23  that is open at the bottom face of the piston housing  21 . The diaphragm  71  plays the role to in preventing paint, cleaning liquid or the like from flowing into the passage  34  through the communication space or from leaking into the piston-housing space  22 . Also, an opening is formed on the top surface of the piston housing  21 , and therein the U-shaped lid member  73  is cross-sectionally screwed, thus forming the piston housing space  22 . A mounting recess is formed in the inner-end opening of the rod-release hole  25  of the lid member  73 . Then the first permanent magnet  57  is installed in the mounting recess. A pair of packing-housing recesses is provided at the upper and lower position of the pilot port  53  within the lower side of the piston housing  21 , thus installing the packing  72  individually in the packing-housing recess. 
     On the other hand, as shown in  FIG. 8 , the manifold block M 2  of this embodiment functions as the valve housing. The multiple valve-mounting recesses  74  are formed in multiple places. The bottom-side region of each valve-mounting recess  74  is a passage  34  wherein the paint or the like flows. The input port  32  and the output  33  are formed in communication with this passage  34 . The output port  33 , located on the bottom-center part of each valve mounting recess  74 , is connected to each sub-passage R 2  provided on the manifold block M 2 , and the valve seat  35  is formed in its connection part. Also, multiple pilot-air inlets  75  are provided on the manifold block M 2 , and each pilot-air inlet  75  is open at the inner side of each valve mounting recess  74 . Mounting the color-change valve  11 E in each valve-mounting recess  74  achieves the color-change device CV 2 . 
     Even the color-change device CV 2 , as structured above, makes it possible to move the valve rod  41  vertically by supplying and discharging the pilot air in regard to the color-change valve  11 E, so as to make the valve part  44  contact and separate from the valve seat  35  of the manifold block M 2 , thus controlling the opening and closing of the valve. The color-change valve  11 E can also be activated by pilot air of comparatively low pressure, even though the size of such valve  11 E is small, thus providing a valve device that is excellent in durability. 
     It is also possible to modify the embodiments of this invention as follows. 
     As another embodiment of the color-change valve  11 F, as shown in  FIG. 9 , for example, it is possible to cover the piston-housing space  22  with a non-magnetic disk-shaped lid member  81 , so as to attach the second permanent magnet  57  to the lid member  81 . Furthermore, it is possible, as well as the color-change valve  11 G, as shown in  FIG. 10 , to cover the piston-housing space  22  with a non-magnetic disk-shaped lid member  82 . In other words, the ceiling part of the piston housing  21  is not necessarily to be integrally structured with the piston housing  21 , but possible to be structured separately. 
     The first embodiment, as described above, prevents paint, cleaning liquid or the like from leaking into the piston-housing space  22  through the communication space by using a seal  37  at the lower side of the support assembly  38 . However, it is also possible to provide a diaphragm  71 , instead. 
     The coil spring  54  is used for each embodiment, as described above. However, it is also possible to use a spring of a shape other than the coil spring  54 , as well as using another biasing means other than a spring. 
     About each embodiment, as described above, the first permanent magnet  56 ,  66  and the second permanent magnet  57 ,  67  are all ring-shaped. However, they are not limited to being that shape; it is possible to use a magnet of any shape. 
     About each embodiment, as described above, the biasing force of the biasing means works in the direction to close the valve, and the pilot-air pressure and the magnetic attraction of the permanent magnets work in the direction to open the valve. However, it is not limited to such a structure. In other words, it is possible to have a structure such that the biasing force of the biasing means works in the direction to open the valve, and the pilot-air pressure and the magnetic attraction of the permanent magnets work in the direction to close the valve. 
     About the fifth embodiment, as described above, the first permanent magnet  56  is provided on the valve rod  41  that is the mobile body, and the second magnetic member (lid member  70 ), which is not a permanent magnet, is provided in the piston housing  21  that is the fixed body. However, it is possible to reverse such a structure. That is, it is possible to provide a non-magnetic first-magnetic member on the valve rod  41  and to provide a non-magnetic second-permanent magnet  57  on the piston housing  21 . 
     About each embodiment, as described above, the proximity-fixing member is separated from the rod part  42  and from the piston part  43  or from the piston housing  21 . However, it is also possible to be integrally structured with the rod part  42 , with the piston part  43  or with the piston housing  21 . The stopper member can also be integrally structured with the rod part  42  and with the piston part  43  or with the piston housing  21 . 
     About each embodiment, as described above, the valve device of this invention is used as the color-change valve  11  to  11 H, so as to make the color-change device CV 1 , CV 2  for the coating machine. However, it is not limited to that; it is possible to use such valve device for another purpose. 
     Besides the technical ideas of this invention, as described above, other technical ideas to be understood are described hereinafter. 
     (1) A valve device according to any of the first to sixth aspects of this invention, characterized in that the biasing force of the biasing means works in the direction to close the valve. Contrarily, the pilot air pressure and the magnetic attraction work in the direction to open the valve. 
     (2) A valve device according to any of the first to sixth aspects of this invention, characterized in that the valve components, except for the first magnetic member and the second magnetic member, are non-magnetic members. 
     DESCRIPTION OF THE REFERENCE NUMERALS 
     
         
           11 ,  11 A,  11 B,  11 C,  11 D,  11 E,  11 F,  11 G and  11 H: Color-change valve as the valve device 
           21 : Housing (for the piston) 
           22 : Piston-housing space 
           35 : Valve seat 
           41 : Valve rod 
           43 : Piston part 
           51 : First chamber 
           52 : Second chamber 
           53 : Pilot port 
           56 ,  66 : First permanent magnet as the first magnetic member 
           57 ,  67 : Second permanent magnet as the second magnetic member 
           70 : Magnetic-lid member as the second magnetic member 
           55 ,  59 : Sleeve as the adjacent-securing member 
           58 : Stopper step 
           68 : Stopper member 
         A 1 : First direction 
         A 2 : Second direction