Abstract:
A pressure control valve, which has a main valve for control, capable of opening and closing a valve hole by means of a diaphragm, and controls the pressure of a fluid by the agency of the main valve for control, comprises a non-return auxiliary valve located around the main valve for control so as to be coaxial therewith. The non-return auxiliary valve includes a cylindrical portion to be guided by a valve guard body having the valve hole therein and an annular rib extending outward from one end of the cylindrical portion. The rib can engage an auxiliary-valve seat on an outlet-side case.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a pressure control valve, and more specifically, to a pressure control valve in the form of a composite valve that includes a check valve incorporated in a valving element of the pressure control valve.  
           [0003]    2. Description of the Prior Art  
           [0004]    Conventionally, pressure control valves are frequently used in a refrigerating cycle of the vapor-pressure compression type. In a pressure control valve described in Japanese Patent Application Laid-open No. 2000-230650, for example, a coil spring that applies a force to enlarge the opening of a valve port to a valving element is formed of a shape-memory alloy. In this case, the valve opening can be restrained from becoming smaller than a given value, and the refrigerant pressure on the outlet side of a radiator can be prevented from increasing excessively. Thus, apparatuses that are located on the high-pressure side of the radiator and a supercritical refrigerating cycle of a compressor can be prevented from being damaged.  
           [0005]    In a pressure control valve described in Japanese Patent Application Laid-open No. 2000-81157, a temperature sensor of a control valve body is situated in a first refrigerant passage that connects the outlet side of a radiator and the inlet side of an internal heat exchanger, and a second refrigerant passage that guides a refrigerant flowing out of the heat exchanger to the upper-stream side is formed in a casing body. Thus, a delay of temperature change in a closed space (control chamber) behind the refrigerant temperature change on the outlet side of the radiator can be lessened, so that the temperature response of the pressure control valve can be improved.  
           [0006]    In a pressure control valve described in Japanese Patent Application Laid-open No. 2001-82835, a noncondensable gas and a refrigerant with given density are sealed into a closed space in order to lessen fatigue breakage of a joint between a diaphragm and a valving element. The diaphragm is displaced by the difference between the internal pressure of the closed space and the refrigerant pressure on the outlet side of a radiator through all the area from a supercritical area to a condensation area. By doing this, stress can be prevented from being concentrated on the joint between the diaphragm and the valving element.  
           [0007]    In general, according to these conventional pressure control valves, check valves are frequently used in a refrigeration system. For ease of installation of the refrigeration system, it is to be desired that various valves including pressure control valves should be readily installed even in a narrow space. In view of the durability or maintenance of the pressure control valves or manufacturing costs, moreover, the valves should preferably be simple in construction.  
         OBJECT AND SUMMARY OF THE INVENTION  
         [0008]    The present invention has been contrived in order to solve the problems of the prior art, and its object is to propose a technique for a pressure control valve that incorporates a check valve. More specifically, the object of the invention is to provide a pressure control valve, in which a check valve is incorporated so that the pressure control valve or the check valve can be used alternatively, and which can be suitably used in a narrow space and is easy to manufacture and highly maintainable.  
           [0009]    In order to achieve the above object, a pressure control valve according to the present invention has a main valve for control, capable of opening and closing a valve hole by means of a diaphragm, and controls the pressure of a fluid by the agency of the main valve for control. The valve comprises a non-return auxiliary valve located on the extension of the main valve for control in the direction of operation thereof or located around the main valve for control so as to be coaxial therewith.  
           [0010]    The invention may be arranged in the following manner.  
           [0011]    The non-return auxiliary valve includes a cylindrical portion to be guided by a valve guard body having the valve hole therein and an annular rib extending outward from one end of the cylindrical portion.  
           [0012]    The rib can engage an auxiliary-valve seat on an outlet-side case having therein a spring chamber for a main valve-closing spring.  
           [0013]    The outlet-side case is formed having a plurality of auxiliary-valve working holes opening in the auxiliary-valve seat and communicating with the spring chamber for the main valve-closing spring.  
           [0014]    A bleed port is formed in the rib or between the spring chamber and a refrigerant inlet in an inlet-side case.  
           [0015]    Constructed in this manner, the pressure control valve of the invention has the following effects.  
           [0016]    The pressure control valve can be reduced in general size. More specifically, the non-return auxiliary valve and an auxiliary valve spring are arranged around the main valve for control so as to be coaxial therewith, so that no housing is needed to hold the auxiliary valve. Thus, the pressure control valve can be reduced in size and weight, and its manufacturing cost can be lowered.  
           [0017]    The auxiliary-valve seat of the non-return auxiliary valve must only be formed on the upper surface of the outlet-side case in the shape of a ring that surrounds the valve guard body. Thus, the valve seat can be worked easily, so that its cost can be lowered.  
           [0018]    Since a receiving frame and the valve guard body are formed integrally, moreover, the number of indispensable parts can be reduced, and there are no dimensional errors that are attributable to combination. Thus, a high-accuracy, high-reliability pressure control valve can be provided.  
           [0019]    Metal seals are used for sealing between a temperature sensor lid and an inner seal portion of the inlet-side case and between the valve guard body and an inner seal portion of the outlet-side case. Further, screw clamping torque with which the inlet-side case and the outlet-side case are screwed to each other is converted into abutting load on each metal seal, whereby the metal seal surface is fixed. Thus, the temperature sensor lid need not be provided with any O-ring groove or O-ring. Furthermore, the valve guard body and the outlet-side case need not be threaded for connection, so that the cost can be lowered.  
           [0020]    Further, the inlet-side case and the outlet-side case are sealed in a manner such that the respective outer peripheries of their screwed portions are grooved and welded together after they are screwed to each other. Thus, the O-rings and their corresponding grooves can be omitted, so that the cost can be lowered. Since welding is used for external sealing, moreover, a leakage to the outside can be reduced to zero.  
           [0021]    Since the bleed port is formed in the outlet-side case or the non-return auxiliary valve, furthermore, it can be worked with ease. In some conventional pressure control valves, a bleed port is formed in a portion corresponding to a valve guard body. In this case, however, much air flows out through the bleed port during air setting operation, so that the setting operation takes time. If the bleed port is formed in the outlet-side case, as in the present invention, however, the air setting operation can be adjusted with use of a dedicated jig for an internal assembly (assembly of the temperature sensor lid, valve guard body, diaphragm, main valve for control, etc.) only, so that the operation can be performed speedily or efficiently without any outflow from the bleed port. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is a longitudinal sectional view of a pressure control valve according to a first embodiment of the present invention; and  
         [0023]    [0023]FIG. 2 is a longitudinal sectional view of a pressure control valve according to a second embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    A pressure control valve according to a first embodiment of the present invention will first be described with reference to FIG. 1.  
         [0025]    This pressure control valve comprises an inlet-side case  10 , a housing  60 , and an outlet-side case  80 , which constitutes an outside frame. The following is a description of various components of the pressure control valve with the inlet- and outlet-side cases  10  and  80  located above and below, respectively.  
         [0026]    The inlet-side case  10 , which is situated at the top portion of the pressure control valve, has a substantially cylindrical shape as a whole, and a first inlet  11  is formed in the upper part of the case  10 . An internal thread portion  12  for connection to a conduit (not shown) of a refrigeration system is formed on the inner peripheral portion of the first inlet. Further, an outlet  13  and a second inlet  14  are formed in the flank of the inlet-side case  10 . An inlet and an outlet of a heat exchanger (not shown) in the refrigeration system, for example, are coupled to the outlet  13  and the second inlet  14 , respectively. Further, an internal thread portion  16  for connection to a housing  60  (mentioned later) is formed on the inner periphery of the lower end portion of the inlet-side case  10 .  
         [0027]    Below the outlet  13 , a temperature sensor lid  20  is attached to the inner wall of the inlet-side case  10  through an O-ring  33 . A capillary tube  21  and a main valve  70  for control are attached to the top and bottom, respectively, of the sensor lid  20 . A diaphragm  30  and a reinforcing plate  31  are embedded in a ring-shaped protrusion  70   a ′ on a main valve head portion  70   a  of the main valve  70 . The valve  70  is formed having these members welded together.  
         [0028]    A ring-shaped receiving frame  40  underlies the main valve head portion  70   a . The temperature sensor lid  20 , a peripheral pendent end portion of the diaphragm  30  that is welded together with the valve head portion  70   a , and the receiving frame  40  are welded to form a closed space  22 . Carbon dioxide is sealed in the space  22 .  
         [0029]    The main valve  70  for control is passed for vertical movement through the central portion of the lower part of the receiving frame  40  with the aid of an O-ring  42 . The O-ring  42  is fixed to the frame  40  by caulking the lower end of the receiving frame  40  with a washer  52 . Further, the receiving frame  40  is formed having an introduction hole  41  that causes a fluid pressure in a main valve chamber  55  to act on a pressure receiving surface at the lower part of the diaphragm  30 . Suitable gaps are defined individually between the receiving frame  40  and the diaphragm  30 , between the frame  40  and the main valve head portion  70   a , and between the diaphragm  30  and the temperature sensor lid  20 .  
         [0030]    A valve guard body  50  is attached to the lower part of the receiving frame  40 . The valve guard body  50  is substantially in the shape of a cup, and has a valve hole  53  in its base portion through which the main valve  70  for control passes. A plurality of passage holes  51  are formed in the peripheral wall of the flank of the valve guard body  50 . Further, a valve seat  53   a  is formed at the inlet of the valve hole  53 . Further, a spring bearing portion  54  of a main valve-closing spring  73  (mentioned later) is formed on the lower surface of the base portion of the valve guard body  50 .  
         [0031]    The main valve  70  for control has the shape of a column as a whole and comprises the main valve head portion  70   a  provided with the diaphragm  30 , a valve portion  70   b  that engages the valve seat  53   a  of the valve guard body  50  for valve operation, and a valve column portion  70   c . An adjust screw  71  is attached to the lower part of the valve column portion  70   c . The screw  71  is provided with a spring bearing  72 . The main valve-closing spring  73  is located between the spring bearing  72  and the spring bearing portion  54  of the valve guard body  50 . The spring  73  serves to press the main valve  70  downward, thereby causing the valve portion  70   b  to engage the valve seat  53   a  (or to close the valve hole  53 ).  
         [0032]    The housing  60  is coupled to the lower part of the inlet-side case  10  with an O-ring  61  between them. The temperature sensor lid  20 , diaphragm  30 , receiving frame  40 , main valve  70  for control, and valve guard body  50  are arranged in a space that is defined by the inlet-side case  10  and the housing  60 . The upper part of the housing  60  forms a spring chamber  66  for the main valve-closing spring  73 . The outlet-side case  80  (mentioned later) is coupled to the lower part of the housing  60  with an O-ring  82  between them.  
         [0033]    A regular passage  64  is formed in the base portion of the housing  60  so as to connect the spring chamber  66  and a regular passage  84  of the outlet-side case  80 . A circular hole  65  for auxiliary valve is formed having a given depth in the center of the base portion of the housing  60 . First and second non-return passages  62  and  63  that connect the auxiliary-valve hole  65  and the second inlet  14  are formed in the lateral portion and base portion, respectively, of the housing  60 .  
         [0034]    A non-return auxiliary valve  90  (mentioned later) is attached to the auxiliary-valve hole  65  in the housing  60 . A thread portion  87  is formed on the outer periphery of the upper part of the outlet-side case  80  that is coupled to the lower part of the housing  60 , and a thread portion  88  for conduit attachment on the lower part. The regular passage  84  that communicates with the regular passage  64  is formed in the upper part of the outlet-side case  80 . An auxiliary-valve working hole  85  is formed in the center of the upper part of the outlet-side case  80 . The upper end portion of the working hole  85  forms a valve seat  86  for auxiliary valve. Further, a main passage  83  that communicates with the regular passage  84  and the auxiliary-valve working hole  85  is formed in the center of the lower part of the outlet-side case  80 .  
         [0035]    The non-return auxiliary valve  90  is fitted in the auxiliary-valve hole  65  on the extension of the main valve  70  for control in the direction of its operation. As shown in FIG. 1, the auxiliary valve  90  has the shape of a cylindrical cup. When its base portion is pressed to engage the auxiliary-valve seat  86  by means of an auxiliary valve spring  91  and the pressure of a fluid from the second inlet  14 , the fluid cannot pass through the non-return auxiliary valve  90 , so that it never flows. A communication hole  93  is bored through the sidewall of the non-return auxiliary valve  90 .  
         [0036]    The following is a description of the operation of the first embodiment. The operation of a temperature sensor will be described first. A fluid that is introduced into the pressure control valve through the first inlet  11  flows out through the outlet  13 . As this is done, carbon dioxide that is sealed in the closed space  22  is expanded or contracted depending on the temperature of the fluid introduced through the first inlet  11 , and causes the diaphragm  30  to press the main valve  70  for control downward. In other words, if carbon dioxide in the closed space  22  is expanded depending on the temperature of the fluid, the main valve  70  is moved downward depending on the degree of the expansion, thereby closing the valve hole  53 .  
         [0037]    When the valve portion  70   b  is not in engagement with the valve seat  53   a  (i.e., when the valve hole  53  is open), the fluid that is introduced into the main valve chamber  55  through the second inlet  14  gets into the spring chamber  66  through the valve hole  53 . Then, the fluid flows out from the regular passages  64  and  84  and the main passage  83 . As this is done, the valve hole  53  is opened and closed for pressure control by means of the valve portion  70   b  of the main valve  70  for control. Thus, the fluid that flows into the first inlet  11  is a fluid that is pressure-controlled according to the fluid temperature.  
         [0038]    Some of the fluid that is introduced through the second inlet  14  enters the first non-return passage  62 , and then gets into the auxiliary-valve hole  65  through the second non-return passage  63  and the communication hole  93 , thereby causing the non-return auxiliary valve  90  to close.  
         [0039]    If the flow of the fluid is then changed so that the fluid flows back from the outlet-side case  80  toward the second inlet  14 , the fluid that ascends in the auxiliary-valve working hole  85  pushes the non-return auxiliary valve  90  open by means of its pressure, and passes through the second non-return passage  63 . Then, the fluid passes through the first non-return passage  62  and flows out through the second inlet  14 . As this is done, the valve portion  70   b  of the main valve  70  for control is closed by means of the main valve-closing spring  73 , so that the fluid never flows forward in the valve hole  53 .  
         [0040]    According to the first embodiment, the non-return auxiliary valve  90  is located right under the main valve  70  for control, so that the housing  60  is needed to hold the auxiliary valve  90 . In consequence, the number of indispensable parts increases, and the overall length of the pressure control valve also increases. However, the valve can be reduced in general size.  
         [0041]    A second embodiment of the pressure control valve of the present invention will now be described with reference to FIG. 2. The valve of the second embodiment is more compact than the valve of the first embodiment. The pressure control valves of the first and second embodiments are constructed basically in the same manner, having the first inlet  11 , internal thread portion  12 , outlet  13 , second inlet  14 , and internal thread portion  16  that are formed in the inlet-side case  10 .  
         [0042]    A capillary tube  21 ′ that is attached to a temperature sensor lid  20  in the inlet-side case  10  is longer than that of the first embodiment. A closed space  22  that is formed in the temperature sensor lid  20  shares its construction with that of the first embodiment. In the second embodiment, the tube  21 ′ is lengthened so that the sealing effect of a sealed portion can be improved when the distal end of the capillary tube  21 ′ filled with carbon dioxide is sealed by cold welding. Further, the tube  21 ′ is fixed to the side face of a cylindrical portion of the temperature sensor lid  20  by brazing. In consequence, the capillary tube  21 ′ is wound around the cylindrical portion of the lid  20 , so that the long tube  21 ′ can be held even in a narrow space with good room in the axial direction of the inlet-side case  10 .  
         [0043]    As in the case of the first embodiment, a diaphragm  30  is attached to a reinforcing plate  31 . Further, the temperature sensor lid  20  is fixed in the inlet-side case  10  in a manner such that it is supported by means of a valve guard body  50  when an outlet-side case  80 ′ (mentioned later) is coupled to the lower part of the inlet-side case  10  by means of an internal thread portion  16 .  
         [0044]    The pressure control valve of the present embodiment is provided with no single member that is equivalent to the receiving frame  40  of the first embodiment.  
         [0045]    The valve guard body  50  is supported from below by means of the outlet-side case  80 ′ that is coupled to the lower part of the inlet-side case  10  by means of the internal thread portion  16 . A main valve  70  for control is located in the central portion of the valve guard body  50 . A plurality of communication holes  56  are formed in the vertically middle part of the valve guard body  50 . A valve hole  53  is formed in the center of the lower part of the valve guard body  50 , and a valve seat  53   a  is formed on the peripheral portion of the inlet of the hole  53 . The valve hole  53  communicates with a main valve chamber  55  that is formed in the center of the valve guard body  50 .  
         [0046]    Further, the valve guard body  50  is formed having an inlet hole  59  through which a fluid pressure from the communication holes  56  acts on a pressure receiving surface of the lower part of the diaphragm  30 . A spring bearing portion  54  of a main valve-closing spring  73  is formed in that region of the lower surface of the valve guard body  50  which surrounds the valve hole  53 . Furthermore, an auxiliary-valve spring bearing portion  57  is formed on the upper part of the valve guard body  50 .  
         [0047]    The pressure control valve of the second embodiment is provided with no single member that is equivalent to the housing  60  of the first embodiment.  
         [0048]    The main valve  70  for control of the second embodiment is constructed basically in the same manner as that of the first embodiment. More specifically, the main valve  70  is an integral component that has the shape of a column as a whole and comprises a main valve head portion  70   a  provided with the diaphragm  30 , a valve portion  70   b  that touches and leaves the valve seat  53   a  of the valve guard body  50  for valve operation, and a valve column portion  70   c  at the lower part. A spring bearing  72  is mounted on the main valve  70  through an adjust screw  71  that is attached to the lower part of the valve column portion  70   c . The main valve-closing spring  73  is located between the spring bearing  72  and the spring bearing portion  54  that is formed on the valve guard body  50 . The spring  73  serves to press the main valve  70  downward, thereby causing the valve portion  70   b  to engage the valve seat  53   a  (or to close the valve).  
         [0049]    In the present embodiment, the outlet-side case  80 ′ has the shape of a cylinder as a whole, and the valve guard body  50  is coupled to the central portion of its upper part. The outer periphery of the case  80 ′ is formed having a external thread portion  87 ′ that mates with the internal thread portion  16  of the inlet-side case  10 . A spring chamber  83 ′ is formed in the middle part of the outlet-side case  80 ′. A main passage  83  is formed in the lower part of the case  80 ′.  
         [0050]    A passage groove portion  85   a  is formed like a ring on the sidewalls of the outlet-side case  80 ′ that define the spring chamber  83 ′. The groove portion  85   a  communicates with the respective lower ends of a plurality of auxiliary-valve working holes  85  that are formed in the outlet-side case  80 ′. The respective upper ends of the working holes  85  communicate with the second inlet  14 . Further, the case  80 ′ is formed having a bleed port  89  that connects the spring chamber  83 ′ and the inlet  14 .  
         [0051]    An auxiliary-valve seat  86 ′ is formed on the upper surface of the outlet-side case  80 ′. It is a ring that surrounds the valve guard body  50 . An upper opening of each auxiliary-valve working hole  85  can be closed by placing a non-return auxiliary valve  90 ′ on the valve seat  86 ′. On the other hand, a thread portion  88  is formed on the outer periphery of the lower part of the outlet-side case  80 ′.  
         [0052]    After the outlet-side case  80 ′ is screwed the inlet-side case  10 , these cases are coupled to each other by welding. For this welding, a groove is formed in the mating area between the inlet-side case  10  and the outlet-side case  80 ′. The resulting weld is denoted by numeral  100  in FIG. 2.  
         [0053]    The non-return auxiliary valve  90 ′ is located around the main valve  70  for control so as to be coaxial with the valve  70 . The auxiliary valve  90 ′ is composed of a cylindrical portion  94  and an annular rib  95 . The cylindrical portion  94  is fitted on the valve guard body  50  and can vertically slide on the outer peripheral surface of the body  50 . The rib  95  extends outward from the lower end of the cylindrical portion  94 . It can engage the auxiliary-valve seat  86 ′ that is formed on the outlet-side case  80 ′.  
         [0054]    An auxiliary valve spring  91 ′ is interposed between the non-return auxiliary valve  90 ′ and the auxiliary-valve spring bearing portion  57  that is formed on the upper part of the valve guard body  50 . Normally, the rib  95  of the auxiliary valve  90 ′ is brought into contact with the auxiliary-valve seat  86 ′ by means of the elastic force of the spring  91 ′, thereby closing the auxiliary-valve working hole  85 . Instead of forming the bleed port  89  in the outlet-side case  80 ′, a bleed port  90 ′ a  may be formed in a part (corresponding to the opening of the auxiliary-valve working hole  85 ) of the auxiliary valve  90 ′.  
         [0055]    The non-return auxiliary valve  90 ′ can be formed by press molding or resin molding and can reduce parts cost. If the auxiliary valve  90 ′ is formed by working a metallic material, its seal surface may be coated or printed with resin or rubber.  
         [0056]    The following is a description of the operation of the second embodiment. According to the present embodiment, the temperature sensor operates in the same manner as that of the first embodiment, depending on the temperature of a fluid that flows into the pressure control valve through the first inlet  11  and flows out through the outlet  13 .  
         [0057]    When the valve portion  70   b  of the main valve  70  for control is not in engagement with the valve seat  53   a  (or when the valve hole  53  is not closed), the fluid that is introduced again into the main valve chamber  55  through the second inlet  14  of the pressure control valve gets into the spring chamber  83 ′ through the valve hole  53 . Then, the fluid flows out from the main passage  83 . As this is done, the valve hole  53  is opened and closed for pressure control by means of the main valve  70  for control. Thus, the fluid that flows into the first inlet  11  is a fluid that is pressure-controlled according to the fluid temperature.  
         [0058]    While the fluid enters through the second inlet  14  and flows out from the main passage  83 , as described above, the rib  95  of the non-return auxiliary valve  90 ′ closes the auxiliary-valve working hole  85  by means of the pressure of the fluid that acts on the rib  95  in contact with the auxiliary-valve seat  86 ′ and the spring load of the auxiliary valve spring  91 ′.  
         [0059]    If the flow of the fluid is then changed so that the fluid flows back from the outlet-side case  80 ′ toward the second inlet  14 , the fluid that passes through the passage groove portion  85   a  and flows in through the auxiliary-valve working hole  85  pushes the non-return auxiliary valve  90 ′ open by means of its pressure, passes through the working hole  85 , and flows out through the second inlet  14 . As this is done, the valve portion  70   b  of the main valve  70  for control is closed by means of the main valve-closing spring  73 , so that the fluid cannot pass through the valve hole  53 .  
         [0060]    The pressure control valve of the second embodiment described above can be made smaller than that of the first embodiment in general size. According to the first embodiment, the non-return auxiliary valve  90  is located under the main valve  70  for control, so that the housing  60  is needed to hold the auxiliary valve  90  between the inlet-side case  10  and the outlet-side case  80 ′. In consequence, the number of indispensable parts increases, and the overall length of the pressure control valve also increases, so that the valve is large-sized inevitably. According to the second embodiment, on the other hand, the non-return auxiliary valve  90 ′ and the auxiliary valve spring  91 ′ are located around the main valve  70  for control so as to be coaxial with the valve  70 , so that the housing  60  that is required by the first embodiment is omitted. Thus, the pressure control valve of the second embodiment can be made smaller in size and lighter in weight than that of the first embodiment, its manufacturing cost can be lowered further.  
         [0061]    Since the non-return auxiliary valve  90 ′ of the second embodiment can be formed by press molding or resin molding, its manufacturing cost can be lowered. If the auxiliary valve  90 ′ is formed by working a metallic material, its seal surface may be coated or printed with resin or rubber. According to the first embodiment, moreover, the auxiliary-valve seat  86  of the non-return auxiliary valve  90  is formed on the outlet-side case  80  by cutting. According to the second embodiment, on the other hand, the auxiliary-valve seat  86 ′ of the non-return auxiliary valve  90 ′ must only be formed on the upper surface of the outlet-side case  80 ′ in the shape of a ring that surrounds the valve guard body  50 . Thus, the valve seat  86 ′ can be worked relatively easily, so that its cost can be lowered.  
         [0062]    According to the first embodiment, the receiving frame  40  and the valve guard body  50  are manufactured separately and screwed to each other, so that the number of indispensable parts and the necessary man-hour increase inevitably. Possibly, moreover, dimensional errors may be caused when the receiving frame  40  and the valve guard body  50  are combined together. According to the second embodiment, on the other hand, the valve guard body  50  also has the function of the receiving frame  40 , so that the receiving frame  40  need not be used separately. Thus, the second embodiment, unlike the first embodiment, is not subject to the problem of dimensional errors that are caused when the receiving frame  40  and the valve guard body  50  are combined, so that a high-accuracy pressure control valve can be provided.  
         [0063]    According to the first embodiment, the outer periphery of the temperature sensor lid  20  is sealed by means of the O-ring  33 . Therefore, the lid  20  must be formed having a groove for the O-ring  33 , and the O-ring  33  to be fitted in the groove is required separately.  
         [0064]    According to the first embodiment, moreover, the valve guard body  50  and the housing  60  are internally sealed by being screwed to each other. Therefore, an external thread and an internal thread must be formed on the valve guard body  50  and the housing  60 , respectively. Since the sealing properties must be secured by controlling the clamping torque, the manufacturing cost is high.  
         [0065]    According to the second embodiment, on the other hand, metal seals are used for sealing between the temperature sensor lid  20  and the inlet-side case  10  and between the valve guard body  50  and the outlet-side case  80 ′. Further, screw clamping torque with which the inlet-side case  10  and the outlet-side case  80 ′ are screwed to each other is converted into abutting load on each metal seal, whereby the metal seal surface is fixed. Thus, the temperature sensor lid  20  need not be provided with any groove for the O-ring, and the O-ring  33  can be omitted. Furthermore, the valve guard body  50  and the outlet-side case  80 ′ need not be threaded for connection, so that the cost can be lowered.  
         [0066]    According to the first embodiment, moreover, the O-rings  61  and  82  are used for sealing, so that gas transmission through the O-ring members may possibly cause a slow leakage to the outside. According to the second embodiment, on the other hand, the inlet-side case  10  and the outlet-side case  80 ′ are sealed in a manner such that the respective outer peripheries of their screwed portions are grooved and welded together after they are screwed to each other. Thus, the O-rings and their corresponding grooves can be omitted, so that the cost can be lowered. Since welding is used for sealing, moreover, a leakage to the outside can be reduced to zero.  
         [0067]    According to the second embodiment, furthermore, the bleed port  89  is formed in the outlet-side case  80 ′, so that it can be worked with ease. Accordingly, air setting operation can be adjusted with use of a dedicated jig for an internal assembly (assembly of the temperature sensor lid  20 , valve guard body  50 , diaphragm  30 , main valve  70  for control, etc.) only, so that the operation can be performed speedily or efficiently without any outflow from the bleed port  89 . The same effect can be obtained if the bleed port  89  of the outlet-side case  80 ′ is replaced with the bleed port  90 ′ a  of the auxiliary valve  90 ′.  
         [0068]    According to the second embodiment, moreover, carbon dioxide is sealed in the elongated capillary tube  21 ′, and the distal end of the tube  21 ′ is sealed by cold welding, whereby the sealing effect is improved. Furthermore, the capillary tube  21 ′ can be wound around the cylindrical portion on the upper part of the temperature sensor lid  20  in a manner such that it is fixed to the side face of the cylindrical portion by brazing. Even in a narrow space, therefore, the long tube  21 ′ can be held with good room in the axial direction of the inlet-side case  10 .