Abstract:
A flow control device is capable of performing accurate flow control over a wide pressure range. The flow control device includes: a housing; a diaphragm splitting the housing into a gas chamber side to which gas is introduced and a fluid chamber side through which fluid passes, and being activated by the differential pressure generated between the gas chamber side and the fluid chamber side; and a valve body which operates in integration with the diaphragm to regulate the flow of the fluid introduced to the fluid chamber side. The diaphragm includes: a base part provided in a substantially central part of the diaphragm; and a thin film part provided on the outer rim of the base part. An opposing surface which is provided on the fluid chamber side to oppose the diaphragm includes a retaining form which retains the shape of the thin film part deformed by the differential pressure.

Description:
TECHNICAL FIELD 
     The present invention relates to a flow control device which controls the flow of chemical solution, purified water, or the like. 
     BACKGROUND ART 
     Generally, as disclosed in Patent Literature 1, a flow control device used to regulate the flow of fluid such as chemical solution and purified water used in manufacturing a semiconductor or the like includes: a housing which is formed of a resin material such as a fluororesin having superior chemical resistance so that the fluid would flow in a flow passage provided in the flow control device; a diaphragm which splits the housing in half; and a valve body which is linked with the movement of the diaphragm. In such a flow control device, one of the housing halves split by the diaphragm corresponds to a fluid chamber in which flow-controlled fluid flows while another housing half corresponds to a gas chamber to which control air is supplied, whereby the diaphragm is activated by the differential pressure generated between the fluid chamber and the gas chamber. The flow control device which activates the diaphragm by the differential pressure regulates the flow of the fluid flowing in the fluid chamber by making the valve body work with the movement of the diaphragm. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Application, Publication No. 2004-162774 
     SUMMARY OF INVENTION 
     Technical Problem 
     When the flow of high pressure fluid is to be regulated by the flow control device described in Patent Literature 1, it is required that the control air having high pressure be supplied into the gas chamber, whereby it has been concerned that, when the high pressure control air is acted upon the diaphragm, the diaphragm would be deformed to a great extent toward the fluid chamber side and that a thin film part constituting the diaphragm would break. 
     An object of the present invention is to provide a flow control device capable of performing accurate flow control over a wide pressure range. 
     Solution to Problem 
     A flow control device according to the present invention includes: a housing; a diaphragm splitting the housing into a gas chamber side to which gas is introduced and a fluid chamber side through which fluid passes, and being activated by the differential pressure generated between the gas chamber side and the fluid chamber side; and a valve body which operates in integration with the diaphragm to regulate the flow of the fluid introduced to the fluid chamber side. The diaphragm includes: a base part provided in a substantially central part of the diaphragm; and a thin film part provided on the outer rim of the base part. An opposing surface which is provided on the fluid chamber side to oppose the diaphragm includes a retaining form which retains the shape of the thin film part deformed by the differential pressure. 
     According to the flow control device of the present invention including the diaphragm activated by the differential pressure between the gas pressure on the gas chamber side and the fluid pressure on the fluid chamber side, the thin film part of the diaphragm would be deformed toward the fluid chamber side when the gas pressure is higher than the pressure on the fluid chamber side, and would be deformed toward the gas chamber side when the fluid pressure is higher than the pressure on the gas chamber side. When the flow of the high pressure fluid is regulated by such a flow control device, the gas having the pressure higher than that of the fluid acting upon the diaphragm would be acted upon the diaphragm to regulate the movement of the valve body. 
     Now, the deformation of the thin film part of the diaphragm which is activated by the differential pressure between the two chambers formed in the housing is retained by the retaining form provided on the opposing surface which is provided on the fluid chamber side and opposite to the diaphragm. The deformation of the thin film part of the diaphragm caused by the gas pressure can thus be retained by the retaining form on the opposing surface on the fluid chamber side when regulating the flow of the high pressure fluid. Accordingly, the deformation of the thin film part would stop at some point so that the breakage of the diaphragm can be prevented. The flow of the high pressure fluid can thus be regulated accurately. 
     The flow control device according to the present invention may also be configured such that the gas chamber side includes a holding member which holds the diaphragm between itself and the opposing surface and that a surface of the holding member opposing the diaphragm includes a retaining form which retains the shape of the thin film part deformed by the differential pressure. 
     When the flow of the high pressure fluid is regulated by the flow control device including the diaphragm which is activated by the differential pressure between the gas pressure on the gas chamber side and the fluid pressure on the fluid chamber side, it is concerned that, in the case where the fluid having the pressure higher than that of the gas is acted upon the diaphragm, the thin film part would be continuously deformed toward the gas chamber side until the diaphragm breaks. 
     Now, in the aforementioned configuration, the deformation of the thin film part of the diaphragm which is activated by the differential pressure between the two chambers formed in the housing is retained by the retaining form provided on the surface of the holding member opposing the diaphragm, the holding member being provided on the gas chamber side and holding the diaphragm between itself and the opposing surface. The deformation of the thin film part of the diaphragm caused by the fluid pressure can thus be retained by the retaining form provided on the surface of the holding member when regulating the flow of the high pressure fluid. Accordingly, the deformation of the thin film part would stop at some point so that the breakage of the diaphragm can be prevented. The flow of the high pressure fluid can thus be regulated accurately. 
     The flow control device according to the present invention may also be configured such that the surface of the holding member opposing the diaphragm includes a projection to hold the diaphragm. 
     According to the aforementioned configuration, the diaphragm can be securely brought into contact with the holding member by including the projection on the surface of the holding member opposing the diaphragm. As a result, the diaphragm can be securely held between the holding member and the opposing surface on the fluid chamber side, whereby a seal structure on a contact surface (seal surface) between the opposing surface on the fluid chamber side and the diaphragm can be securely maintained. The flow of the high pressure fluid can thus be regulated accurately and soundly. 
     Advantageous Effects of Invention 
     The deformation of the thin film part of the diaphragm which is activated by the differential pressure between the two chambers formed in the housing is retained by the retaining form which is provided on the opposing surface on the fluid chamber side and opposite to the diaphragm. The deformation of the thin film part of the diaphragm caused by the gas pressure can thus be retained by the retaining form on the opposing surface on the fluid chamber side when regulating the flow of the high pressure fluid. Accordingly, the deformation of the thin film part would stop at some point so that the breakage of the diaphragm can be prevented. The flow of the high pressure fluid can thus be regulated accurately. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an exploded view illustrating a structure of a flow control device according to an embodiment of the present invention. 
         FIG. 2  is a schematic block diagram of a vertical section of the flow control device where the valve opening of the flow control device illustrated in  FIG. 1  is in a fully-closed state. 
         FIG. 3  is a schematic block diagram of a vertical section of the flow control device where the valve opening of the flow control device illustrated in  FIG. 1  is in a fully-open state. 
         FIG. 4  is a partially enlarged block diagram illustrating a portion A of the flow control device, the valve opening of which illustrated in  FIG. 2  is in the fully-closed state. 
         FIG. 5  is an enlarged view of a diaphragm illustrated in  FIG. 1 . 
         FIG. 6  is a schematic block diagram of a vertical section of a flow control device according to a modification of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A structure of a flow control device according to an embodiment of the present invention will now be described with reference to an exploded view illustrated in  FIG. 1 , schematic block diagrams of a vertical section illustrated in  FIGS. 2 and 3 , a partially enlarged block diagram illustrated in  FIG. 4 , and an enlarged view of a diaphragm illustrated in  FIG. 5 . Here, the valve opening of the flow control device is in the fully-closed state in the case illustrated in  FIG. 2  and in the fully-open state in the case illustrated in  FIG. 3 . 
     As illustrated in  FIG. 1 , a flow control device  1  is used to regulate the flow of fluid such as chemical solution and purified water used in manufacturing a semiconductor or the like, is provided to a supply line (not shown) of the fluid, and is generally referred to as a regulator as well. 
     A housing  10  forming the external shape of the flow control device  1  is configured by combining each of three housings  10   a ,  10   b , and  10   c , which are fastened by a through-bolt  17  (refer to  FIG. 2 ). The housing  10   b among them is formed of a fluororesin such as PTFE or PFA having superior chemical resistance. A material such as PVDF or PFA is used to form the housings  10   a and  10   c . 
     Each housing  10   a ,  10   b , and  10   c  constituting the housing  10  will be described. The lower housing  10   a  formed of PVDF or PFA corresponds to a base part of the flow control device  1 . The middle housing  10   b  arranged above the lower housing  10   a  and formed of PTFE or PFA resin with superior chemical resistance corresponds to a middle part of the flow control device  1  and includes an inlet port  21 , an outlet port  24 , a first space  22 , a second space  23 , a flow passage including a middle flow passage  25 , and the like. 
     The upper housing  10   c  arranged above the middle housing  10   b  and formed of PVDF or PFA resin corresponds to an upper part of the flow control device  1 . The upper housing  10   c  presses down a support nut (a holding member)  41 , which fixes a diaphragm  35  to the middle housing  10   b , to the side of the middle housing  10   b  and includes, above the support nut  41  and a cap nut  42  provided on the inner peripheral side of the support nut, a pressure chamber (a gas chamber side)  12 , a control port  13  which supplies control air (gas) to the pressure chamber  12 , and the like. 
     As illustrated in  FIG. 2 , the middle housing  10   b  mainly includes therein: a valve seat  11  which has an aperture  11   a  communicating with the inlet port  21 ; a valve body  31  which moves perpendicularly (a vertical direction in  FIG. 2 ) to the aperture  11   a  of the valve seat  11 ; the diaphragm  35  which is fitted to a support nut housing part  40  (refer to  FIG. 1 ) formed at the upper end of the middle housing  10   b ; and a spring  36  which presses the valve body  31  against the valve seat  11 . 
     The flow passage provided in the middle housing  10   b  includes: the first space  22  (typically referred to as a “valve chamber”) which communicates from the inlet port  21  to the valve body  31 ; the second space  23  which is positioned between the valve seat  11  and a bottom surface  40   a  of the support nut housing part  40 ; a fluid-side space (on a fluid chamber side)  29  formed between the bottom surface  40   a  of the support nut housing part  40  and the bottom surface of the diaphragm  35 ; the middle flow passage  25  which communicates from the fluid-side space  29  to the outlet port  24 ; and a connecting flow passage  30  which is provided at a part of the middle housing  10   b  between the second space  23  and the middle flow passage  25  to connect the second space  23  and the middle flow passage  25 . 
     Provided on the upper end surface of the middle housing  10   b  is the support nut housing part  40  (refer to  FIG. 1 ) which is depressed downward from the upper end of the middle housing  10   b  and in which the support nut  41  is housed. The diaphragm is provided between the lower end surfaces of the support nut  41  and the cap nut  42  and the bottom surface  40   a  of the support nut housing part  40 . 
     The support nut  41  housed in the support nut housing part  40  is ring-shaped. The cap nut  42  is housed on the inner peripheral side of the ring-shaped support nut  41 . Moreover, a screw (now shown) is formed on the outer peripheral wall of the support nut  41  to be screwed together with a screw (not shown) provided on the inner peripheral wall of the support nut housing part  40  described above. Here, it is preferred that the support nut  41  be formed of a resin material such as PFA, PCTFE, and PEEK which have superior temperature and mechanical characteristics. 
     A depression  42   a  (refer to  FIG. 1 ) capable of housing the projection  35   a  provided to the diaphragm  35  is formed on the lower end surface of the cap nut  42  which is housed on the inner peripheral side of the support nut  41 . A screw (now shown) provided on the inner peripheral wall of the depression  42   a  can be screwed together with a screw (not shown) provided on the outer peripheral wall of the projection  35   a.    
     Here, the height of the cap nut  42  (the length in the axial direction of the flow control device  1 ) is set shorter than the depth of the support nut housing part  40  (the length in the axial direction of the flow control device  1 ). As a result, as illustrated in  FIG. 2 , a gas-side space (a gas chamber side)  28  is formed between the upper end surface of the cap nut  42  and the lower end surface of the upper housing  10   c . The gas-side space  28  communicates with the pressure chamber  12  when the upper housing  10   c  is provided on top of the middle housing  10   b.    
     The structure of the diaphragm  35  in the present embodiment will now be described in detail with reference to  FIGS. 4 and 5 . 
     As illustrated in  FIG. 4 , the diaphragm  35  is positioned between the lower end surfaces of the support nut  41  and the cap nut  42  and the bottom surface  40   a  of the support nut housing part  40  (refer to  FIG. 1 ) and is sized to be housed in the support nut housing part  40 . 
     Moreover, a permeation protection sheet  43  to be described later is provided on the top surface of the diaphragm  35 . 
     When the differential pressure is generated between the fluid-side space  29  and the gas-side space  28  described above, the external force is applied to the top surface of the diaphragm  35 , thereby causing a thin film part  35   c  to be described later to be displaced and a diaphragm base (a base part)  35   b  to be moved in a perpendicular direction (a vertical direction in  FIG. 4 ). The valve body  31  in contact with the diaphragm  35  would accordingly move in the perpendicular direction by the movement of the diaphragm base  35   b . As a result, the flow of the fluid passing through the flow passage in the flow control device  1  would be regulated. 
     The diaphragm  35  is formed of the resin material or the like of PTFE or PFA, for example, and is substantially disc-shaped with an outer diameter thereof approximately equal to an inner diameter of the support nut housing part  40  (refer to  FIG. 1 ). As illustrated in  FIG. 5 , the diaphragm  35  includes: the diaphragm base  35   b  which is provided in the substantially central part; the thin film part  35   c  which is ring-shaped and provided on the outer rim of the diaphragm base  35   b ; and a thick outer peripheral edge  35   d  provided at the outer peripheral edge of the thin film part  35   c . Note that the thin film part  35   c  is thinner than the diaphragm base  35   b  while the outer peripheral edge  35   d  is thicker than the thin film part  35   c.    
     The projection  35   a  which is projected upward is provided on the top surface side of the diaphragm base  35   b  in the substantially central part thereof. Moreover, a recess  35   e , which is concave upward and to which a protrusion  31   a  (refer to  FIG. 4 ) of the valve body  31  can be inserted, is formed on the bottom surface side of the projection  35   a  provided to the diaphragm base  35   b.    
     As illustrated in  FIG. 4 , for example, the bottom surface of the outer peripheral edge  35   d  of the diaphragm  35  is in contact with a part of the bottom surface  40   a  of the support nut housing part  40  (refer to  FIG. 1 ). An annular projection  35   f  which is projected downward is provided on the bottom surface of the outer peripheral edge  35   d . The annular projection  35   f  is fitted to an annular recess  40   b  (refer to  FIG. 1 ) which is provided on the outer peripheral edge of the bottom surface  40   a . Moreover, the top surface of the outer peripheral edge  35   d  is in contact with the bottom surface of the permeation protection sheet  43 . 
     When the valve opening of the flow control device  1  is in the fully-open state, the bottom surface of the diaphragm base  35   b  of the diaphragm  35  is in contact with the bottom surface  40   a  so that the fluid-side space  29  is not formed between the bottom surface of the diaphragm base  35   b  and the bottom surface  40   a  as illustrated in  FIG. 3 , for example. 
     Here, as illustrated in  FIG. 4 , a step  40   c  is provided on the approximately outer side of the bottom surface  40   a  of the support nut housing part  40  along the radial direction, and the bottom surface  40   a  provided on the approximately inner side of the step  40   c  along the radial direction is recessed below the bottom surface  40   a  on the approximately outer side of the step  40   c.    
     A protective form (a retaining form)  40   d  is formed on the bottom surface  40   a  on the approximately inner side of the step  40   c  along the radial direction. When the thin film part  35   c  of the diaphragm  35  is deformed (bent) downward by the pressure of the control air introduced to the gas-side space  28 , the protective form (retaining form)  40   d  can retain the shape of the thin film part  35   c  by suppressing further downward deformation thereof. The protective form also has a smooth shape along the shape of the thin film part  35   c.    
     Moreover, a gas vent hole  35   g  passing through from the inner side to the outer side (from the right side to the left side in  FIG. 5 ) along the radial direction is provided to a part of the thick outer peripheral edge  35   d  forming the diaphragm  35 , as illustrated in  FIG. 5 . As illustrated in  FIG. 4 , an end of the gas vent hole  35   g  is communicated with a permeating gas vent hole  26  passing through from the support nut housing part  40  toward the outer side of the middle housing  10   b  along the radial direction. 
     The gas vent hole  35   g  is provided to exhaust, to the outside of the flow control device  1 , a corrosive gas passing through the thin film part  35   c  of the diaphragm  35  when a chemical solution such as hydrofluoric acid or nitric acid having gas permeability is fed, the corrosive gas being produced by the volatilization of the fluid passing through the fluid-side space  29 . 
     The top surface of the diaphragm  35  is provided with the permeation protection sheet  43  which is formed along the shape of the thin film part  35   c  to reinforce the thin film part  35   c  made into a thin film. The permeation protection sheet  43  formed of a highly flexible rubber sheet has a role of preventing the corrosive gas from flowing into the gas-side space  28  from the fluid-side space  29  when the corrosive gas produced from the fluid (a chemical solution such as hydrofluoric acid or nitric acid) flowing in the fluid-side space  29  has permeated the thin film part  35   c . Moreover, the permeation protection sheet  43  has a role of sufficiently securing the deformation of the thin film part  35   c  caused by the pressure of the fluid flowing in the fluid-side space  29  while keeping the strength of the thin film part  35   c  high against the deformation. 
     The permeation protection sheet  43  is disc-shaped with no center part to match the shape of the diaphragm  35 , while the outer peripheral edge and the inner peripheral edge on the top surface side of the permeation protection sheet  43  are brought into contact with the lower end surface of each of the support nut  41  and the cap nut  42 , respectively. The outer peripheral edge on the bottom surface side of the permeation protection sheet  43  is brought into contact with the top surface of the outer peripheral edge  35   d  of the diaphragm  35 . Accordingly, the outer peripheral edge of the permeation protection sheet  43  and the outer peripheral edge  35   d  of the diaphragm  35  are held between the support nut  41  and the bottom surface  40   a  of the support nut housing part  40 . 
     An edge (an annular projection)  41   b  provided on the lower end surface (a surface opposing the diaphragm  35 ) of the support nut  41  is bit into the top surface of the outer peripheral edge of the permeation protection sheet  43 , while an edge  42   b  provided on the lower end surface of the cap nut  42  is bit into the top surface of the inner peripheral edge of the permeation protection sheet  43 . 
     Each of edge receiving parts  43   b  and  43   c  is formed into a ring shape across the circumferential direction of the outer peripheral edge and the inner peripheral edge (partially) of the permeation protection sheet  43 , respectively, and has a substantially V-shaped cross section. 
     The edge receiving parts  43   b  and  43   c  are cut into the top surface of the permeation protection sheet  43  while the cap nut  42  is screwed together with the projection  35   a  of the diaphragm  35  and the support nut  41  is screwed together with the support nut housing part  40 . As a result, the lower end surfaces of the outer peripheral edge of the support nut  41  and the inner peripheral edge of the cap nut  42  can be securely sealed with the top surface of the outer peripheral edge and the inner peripheral edge of the permeation protection sheet  43 , respectively. 
     A smooth protective form (a retaining form)  41   a  along the shape of the thin film part  35   c  and the permeation protection sheet  43  is formed on the lower end surface of the support nut  41 . When the thin film part  35   c  of the diaphragm  35  and the permeation protection sheet  43  provided on the top surface of the thin film part  35   c  are deformed upward (bent) by the pressure of the fluid flowing into the fluid-side space  29 , the protective form can retain the shapes of the thin film part  35   c  and the permeation protection sheet  43  by suppressing further upward deformation thereof. 
     As illustrated in  FIG. 2 , the sealed gas-side space  28  and the pressure chamber  12  can be formed by providing the upper housing  10   c  above the support nut  41  and the cap nut  42  on the side opposite to where the diaphragm  35  is held between the upper end of the middle housing  10   b  and the support nut  41  and the cap nut  42 . The gas-side space  28  communicates with the pressure chamber  12  formed in the upper housing  10   c , whereas the pressure chamber  12  communicates with the control port  13  formed on the side wall of the upper housing  10   c.    
     As illustrated in  FIG. 1 , a diaphragm  45  is integrally provided to the outer periphery of the valve body  31  near the tip (the lower end) thereof, the valve body being provided in the middle housing  10   b . In addition, the protrusion  31   a  is provided at the upper end of the valve body  31  into which the diaphragm is integrated. 
     The diaphragm  45  integrally provided to the valve body  31  includes: a thin film part  45   c  provided outward in the radial direction from the valve body  31 ; an outer peripheral edge  45   d  which is thicker than the thin film part  45   c  and provided on the outer peripheral edge thereof; and an annular projection  45   f  which is provided on the top surface of the outer peripheral edge  45   d  and projected upward. 
     The outer diameter of the diaphragm  45  is approximately equal to the inner diameter of a diaphragm insertion groove  46  formed at the lower end of the middle housing  10   b . When the diaphragm  45  is inserted from the bottom part of the middle housing  10   b  to be housed in the diaphragm insertion groove  46 , the annular projection  45   f  provided in the diaphragm  45  is fitted to an annular recess  46   b  provided on the top surface of the diaphragm insertion groove  46  across the outer peripheral edge thereof. 
     A spring folder  47  is provided to the tip of the valve body  31  from below. Provided on the top surface of the spring folder  47  is a protective form  47   a  which can retain the shape of the thin film part  45   c  by suppressing further deformation of the thin film part  45   c  of the diaphragm  45  when the diaphragm  45  integrally provided to the valve body  31  is deformed by the fluid flowing in the first space  22 . 
     A recess  47   b  which is depressed downward and into which the tip of the valve body  31  can be inserted is formed in the substantially central part of the spring folder  47  on the top surface side thereof. Moreover, the spring folder  47  includes, in the middle of the side wall thereof, a step  47   c  where the outer diameter of the side wall below the step  47   c  is smaller than the outer diameter of the side wall above the step  47   c . A spring  36  is provided on the outer periphery of the spring folder  47  below the step  47   c.    
     While the spring  36  is provided on the outer periphery of the side wall of the spring folder  47  below the step  47   c , a valve body binding member  49  is provided to the spring folder  47  from the lower end side thereof. It is preferred that the valve body binding member  49  be formed of a resin material with the temperature and mechanical characteristics superior to that of the lower housing  10   a , the resin material preferably being PFA, PCTFE, PEEK or the like in this case. 
     The spring  36  can be retained between the inner peripheral wall of the cylindrical valve body binding member  49  and the spring folder  47  provided on the inner peripheral wall, while a step  49   a  is provided in the middle of the outer peripheral wall of the valve body binding member  49 . The outer diameter of the valve body binding member  49  above the step  49   a  is smaller than below the step  49   a . The valve body binding member  49  above the step  49   a  is inserted into the diaphragm insertion groove  46  from below to be housed therein after the diaphragm  45  is housed in the diaphragm insertion groove  46  of the middle housing  10   b.    
     A screw (not shown) is provided on the outer peripheral wall of the valve body binding member  49  below the step  49   a . The valve body binding member  49  can be housed inside an annular lower screwing part  48  by screwing together the screw provided on the outer peripheral wall of the valve body binding member  49  and a screw (not shown) provided on the inner peripheral wall of the lower screwing part  48  which is connected to the lower end of the middle housing  10   b.    
     The lower housing  10   a  is provided upward to the lower end of the middle housing  10   b . A recess  50  which is depressed downward is provided on the top surface of the lower housing  10   a . The inner diameter of the recess  50  is approximately equal to the outer diameter of the lower screwing part  48  provided at the lower end of the middle housing  10   b . Also provided in a substantially central part of a bottom surface  50   a  of the recess  50  is a spring groove  51  which can house the lower end of the spring  36  when the spring  36  is housed in the inner peripheral side of the valve body binding member  49 . 
     The lower housing  10   a  is provided at the lower end of the middle housing  10   b  by housing the lower screwing part  48  of the middle housing  10   b  in the recess  50  of the lower housing  10   a  and housing the lower end of the spring  36  projected below the valve body binding member  49  into the spring groove  51  provided on the bottom surface  50   a  of the recess  50 . 
     By providing the lower housing  10   a  to the middle housing  10   b  in the aforementioned manner, the spring  36  would be disposed between the step  47   c  of the spring folder  47  and the bottom surface  50   a  of the lower housing  10   a  as described above, whereby the valve body  31  can be pressed upward toward the valve seat  11  as illustrated in  FIGS. 2 and 3 . 
     A method of regulating the flow of the fluid by the flow control device  1  configured in the aforementioned manner will be described with reference to  FIGS. 2 to 5 . 
     First, as illustrated in  FIG. 2 , the fluid is introduced to the inlet port  21  of the flow control device  1  from the fluid supply line while the valve opening of the flow control device  1  is in the fully-closed position. The fluid introduced to the inlet port  21  fills the first space  22  because the valve body  31  is in contact with the valve seat  11 . 
     Next, the control air is supplied from the control port  13  provided in the upper housing  10   c . As a result, the pressure chamber  12  formed in the upper housing  10   c  as well as the gas-side space  28  communicating with the pressure chamber  12  are pressurized. By pressurizing the pressure chamber  12  and the gas-side space  28 , the diaphragm  35  having acquired the force surpassing the elastic force of the spring  36  provided at the lower part of the middle housing  10   b  is pressed down. As a result, the valve body  31  is separated from the valve seat  11  through the diaphragm  35 . Once the valve body  31  is separated from the valve seat  11 , the aperture  11   a  of the valve seat  11  is opened so that the fluid in the first space  22  would flow into the second space  23 . 
     The distance travelled by the valve body  31  in the perpendicular direction would vary according to the degree of pressure applied to the pressure chamber  12  and the gas-side space  28 . The valve opening of the flow control device  1  would thus be adjusted according to the degree of pressurization. As a result, the flow of the fluid passing through the aperture  11   a  of the valve seat  11  would change by adjusting the valve opening. 
     As described above, the diaphragm  35  is pressed down when adjusting the flow of the fluid by pressurizing the pressure chamber  12  and the gas-side space  28 . That is, the diaphragm base  35   b  and the thin film part  35   c  would move downward by the pressure of the control air acting upon the top surface of the diaphragm base  35   b  and the thin film part  35   c  of the diaphragm  35  illustrated in  FIG. 4 . Here, the protective form  40   d  formed on the bottom surface  40   a  of the support nut housing part  40  (refer to  FIG. 1 ) would suppress further downward deformation of the thin film part  35   c.    
     The fluid having passed through the aperture  11   a  would flow from the second space  23  into the fluid-side space  29 , as illustrated in  FIG. 3 . The fluid having flowed into the fluid-side space  29  would further flow into the middle flow passage  25 . Here, the connecting flow passage  30  is provided between the second space  23  and the middle flow passage  25  in the middle housing  10   b  as described above. 
     The connecting flow passage  30  is provided to pass through between a part of the circumferential direction of the second space  23  formed annularly on the outer periphery of the valve body  31  and the middle flow passage  25 . The length of the connecting flow passage  30  in the axial direction of the flow control device  1  is approximately equal to the length of the second space  23  in the axial direction of the flow control device  1 . A part of the fluid having flowed into the second space  23  would flow out therefrom into the middle flow passage  25  through the connecting flow passage  30 . 
     The fluid having flowed into the middle flow passage  25  from the fluid-side space  29  and the connecting flow passage  30  would flow out toward the outlet port  24 . Accordingly, the flow of the fluid in the flow control device  1  can be regulated. 
     Now,  FIG. 3  will be used to describe a case where the valve opening of the flow control device  1  is increased to be in the fully-open state. 
     As illustrated in  FIG. 3 , when the valve opening of the flow control device  1  is in the fully-open state, the diaphragm base  35   b  of the diaphragm  35  is in contact with the bottom surface  40   a  of the middle housing  10   b.    
     The second space  23  and the fluid-side space  29  would not be communicated with each other since the diaphragm base  35   b  is in contact with the bottom surface  40   a . As a result, the fluid would not flow into the fluid-side space  29  or from the fluid-side space  29  to the middle flow passage  25 . 
     However, the connecting flow passage  30  provided in a part of the middle housing  10   b  in the flow control device  1  would allow the fluid having flowed into the second space  23  to flow from the second space  23  to the middle flow passage  25  through the connecting flow passage  30 . Therefore, the fluid can flow with the maximum flow (the flow of the fluid when the valve opening is in the fully-open state) toward the outlet port  24  and out by way of the connecting flow passage  30  even when the valve opening of the flow control device  1  is in the fully-open state and the diaphragm base  35   b  is in contact with the bottom surface  40   a.    
     The following effect can be attained by the flow control device  1  according to the present embodiment. 
     The deformation of the thin film part  35   c  of the diaphragm  35  which is activated by the differential pressure between the gas-side space (the gas chamber side)  28  and the fluid-side space (the fluid chamber side)  29  that are formed in the housing  10  (the differential pressure between the two chambers) is retained by the protective form (the retaining form)  40   d  provided on the bottom surface  40   a  of the support nut housing part  40  formed in the middle housing  10   b  (the opposing surface of the fluid-side space  29  opposite to the diaphragm  35 ). The deformation of the thin film part  35   c  of the diaphragm  35  caused by the pressure of the control air (gas) can thus be retained by the protective form  40   d  provided on the bottom surface  40   a  when regulating the flow of the high pressure fluid. Accordingly, the deformation of the thin film part  35   c  would stop at some point so that the breakage of the diaphragm  35  can be prevented. The flow of the high pressure fluid can thus be regulated accurately. 
     The deformation of the thin film part  35   c  of the diaphragm  35  which is activated by the differential pressure between the gas-side space  28  and the fluid-side space  29  is retained by the protective form (the retaining form)  41   a  provided on the lower end surface (the surface opposing the diaphragm  35 ) of the support nut (the holding member)  41  holding the diaphragm  35  between itself and the bottom surface  40   a  of the support nut housing part  40 . The deformation of the thin film part  35   c  caused by the fluid pressure can thus be retained by the protective form  41   a  provided on the bottom surface of the support nut  41  when regulating the flow of the high pressure fluid. Accordingly, the deformation of the thin film part  35   c  would stop at some point so that the breakage of the diaphragm  35  can be prevented. The flow of the high pressure fluid can thus be regulated accurately. 
     The annular edge (projection)  41   b  provided on the lower end surface of the support nut  41  is bit into the outer peripheral edge of the permeation protection sheet  43  across the circumferential direction, the permeation protection sheet being provided on the top surface of the diaphragm  35 . The diaphragm  35  can thus be securely brought into contact with the support nut  41  through the permeation protection sheet  43 . As a result, the diaphragm  35  and the permeation protection sheet  43  can be securely held between the support nut  41  and the outer peripheral edge of the bottom surface  40   a  of the support nut housing part  40  forming the fluid-side space  29 , whereby the seal structure between the bottom surface  40   a  and the diaphragm  35  can be securely maintained. The flow of the high pressure fluid can thus be regulated accurately and soundly. 
     While it has been described in the present embodiment that the housing  10  is formed of the resin material such as PVDF, PFA, and PTFE, the present invention may also employ a resin material such as PPS or P.P. 
     Moreover, as a modification of the present embodiment, a control means for controlling the upward movement of the valve body  31  may be provided to slightly open the aperture  11   a  of the valve seat  11  when the valve opening of the flow control device  1  is in a closed state, so that dust (particles) would not be produced by bringing the valve body  31  and the valve seat  11  into contact with each other. 
     A flow control device  100  according to the modification of the present invention is illustrated in  FIG. 6 . 
     The flow control device  100  is provided with a cap nut (a control means)  62  which controls the upward movement of the valve body  31  to prevent the generation of dust. The cap nut  62  is different from the cap nut  42  (refer to  FIG. 2 ) of the aforementioned embodiment in terms of the height only. That is, the height of the cap nut  62  of the present modification is greater (longer) than that of the cap nut  42  illustrated in  FIG. 2 . 
     The bottom surface of the upper housing  10   c  is brought into contact with the top surface of the cap nut  62  by making the cap nut  62  tall as illustrated in  FIG. 6 , so that the gas-side space  28  (refer to  FIG. 2 ) is not formed between the bottom surface of the upper housing  10   c  and the top end surface of the cap nut  62 . As a result, the valve body  31  would be slightly moved upward in the perpendicular direction with respect to the aperture  11   a  of the valve seat  11  so that the valve body  31  and the valve seat  11  are not in contact with each other even when the control air is not supplied to the pressure chamber  12  (when the valve opening of the flow control device  100  is in the closed state). 
     Since the valve body  31  and the valve seat  11  are not in contact with each other, there can be prevented the dust (particles) generated by bringing the valve body  31  and the valve seat  11  into contact with each other as illustrated in  FIG. 2  of the aforementioned embodiment. 
     REFERENCE SIGNS LIST 
     
         
           1  flow control means 
           10   b  housing (middle housing) 
           23  flow passage (second space) 
           28  gas chamber side (gas-side space) 
           29  fluid chamber side (fluid-side space) 
           31  valve body 
           35  diaphragm 
           35   b  base part (diaphragm base) 
           35   c  thin film part 
           40   a  opposing surface (bottom surface) 
           40   d  retaining form (protective form)