Patent Publication Number: US-2023160481-A1

Title: Check valve unit and air-conditioning apparatus, and method for manufacturing check valve unit

Description:
TECHNICAL FIELD 
     The present disclosure relates to a check valve unit used in a refrigeration cycle of an air-conditioning apparatus, for example, and to a method for manufacturing a check valve unit. 
     BACKGROUND ART 
     An air-conditioning apparatus includes a refrigeration cycle through which refrigerant cycles, the refrigeration cycle being formed of a compressor, a condenser, an expansion valve, an evaporator, and the like. In such a refrigeration cycle, a check valve may be further installed to cause refrigerant to flow through the refrigeration cycle only in one direction (see Patent Literature 1, for example). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2013-44418 
     SUMMARY OF INVENTION 
     Technical Problem 
     As disclosed in Patent Literature 1, a related-art check valve includes a large diameter portion, small diameter portions, and tapered portions, the large diameter portion forming a tubular body and housing a valve assembly, the small diameter portions being located on both sides of the large diameter portion and forming an inlet port and an outlet port, the tapered portion being formed between each small diameter portion and the large diameter portion. Therefore, a check valve per se has a long dimension. Particularly, when a plurality of check valves are used in combination, an assembly of the check valves increases in size and hence, there is a problem that restrictions are imposed on the arrangement of the assembly when the assembly is mounted on an air-conditioning apparatus. 
     The present disclosure has been made to solve the above-mentioned problem, and it is an object of the present disclosure to provide a check valve unit in which minimal restrictions are imposed on the arrangement of the check valve unit due to a reduction in size when the check valve unit is mounted on an air-conditioning apparatus. 
     Solution to Problem 
     A check valve unit of an embodiment of the present disclosure includes: a container body including a valve body housing portion, a valve seat, and a protruding portion, the valve body housing portion having a cylindrical shape, the valve seat being formed at one end portion of the valve body housing portion and protruding from an inner peripheral surface of the valve body housing portion, the protruding portion being formed at the other end portion of the valve body housing portion and protruding from the inner peripheral surface of the valve body housing portion; and a valve body including a valve portion and a guide portion and disposed in the container body, the valve portion coming into contact with the valve seat at a time of preventing backflow of refrigerant, the guide portion including a plurality of blades. 
     Advantageous Effects of Invention 
     The check valve unit of the embodiment of the present disclosure is reduced in size compared with a related-art check valve, thus giving the higher degree of freedom in arrangement than the related-art check valve unit at the time of being mounted on an air-conditioning apparatus. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a cross-sectional view showing a state where a check valve unit according to Embodiment 1 of the present disclosure is mounted in a refrigerant pipe. 
         FIG.  2   a    is a cross-sectional view showing one of steps of manufacturing the check valve unit according to Embodiment 1 of the present disclosure. 
         FIG.  2   b    is a cross-sectional view showing one of the steps of manufacturing the check valve unit according to Embodiment 1 of the present disclosure. 
         FIG.  2   c    is a cross-sectional view showing one of the steps of manufacturing the check valve unit according to Embodiment 1 of the present disclosure. 
         FIG.  2   d    is a cross-sectional view showing one of the steps of manufacturing the check valve unit according to Embodiment 1 of the present disclosure. 
         FIG.  2   e    is a cross-sectional view showing one of the steps of manufacturing the check valve unit according to Embodiment 1 of the present disclosure. 
         FIG.  2   f    is a cross-sectional view showing one of the steps of manufacturing the check valve unit according to Embodiment 1 of the present disclosure. 
         FIG.  2   g    is a cross-sectional view showing one of the steps of manufacturing the check valve unit according to Embodiment 1 of the present disclosure. 
         FIG.  3    is a cross-sectional view of a check valve unit according to Embodiment 2 of the present disclosure. 
         FIG.  4    is a cross-sectional view of a check valve unit according to Embodiment 3 of the present disclosure. 
         FIG.  5    is a cross-sectional view of a check valve unit according to Embodiment 4 of the present disclosure. 
         FIG.  6    is a cross-sectional view showing a state where a check valve unit according to Embodiment 5 of the present disclosure is mounted in a refrigerant pipe. 
         FIG.  7    is a cross-sectional view showing a state where a plurality of check valve units according to the present disclosure are mounted in a refrigerant pipe. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a check valve unit and a method for manufacturing a check valve unit according to embodiments of the present disclosure will be described with reference to drawings and the like. In the respective drawings, identical or corresponding components are given the same reference symbols, and the description of such components is omitted or simplified when appropriate. The shapes, the sizes, the arrangement, and the like of the components described in the respective drawings may be suitably changed within the scope of the present disclosure. 
     Embodiment 1 
       FIG.  1    is a cross-sectional view showing a state where a check valve unit according to Embodiment 1 of the present disclosure is mounted in a refrigerant pipe. A check valve unit  1  according to the present disclosure is mounted in a refrigerant pipe  10  forming the refrigeration cycle of an air-conditioning apparatus, and has a function of restricting the flow of refrigerant to only one direction by preventing backflow of refrigerant. An example of a method for mounting the check valve unit  1  in the refrigerant pipe  10  is that, at positions in front and in rear of where the check valve unit  1  is mounted, a plurality of protrusions  11  are formed from the outer side of the refrigerant pipe  10  by dimpling or the like to fix the check valve unit  1  in the refrigerant pipe  10 . For the method for mounting the check valve unit  1  in the refrigerant pipe  10 , a related-art method may be adopted where drawing is applied to the refrigerant pipe  10  at positions in front and in rear of where the check valve unit  1  is mounted. 
     The check valve unit  1  includes a container body  2  and a valve body  3 . The container body  2  is an inner pipe having a cylindrical shape. The valve body  3  is disposed in the container body  2  and is movable in the axial direction. 
     The container body  2  is formed of a tube stock made of copper, and forms the body of the check valve unit  1 . The container body  2  includes a valve body housing portion  21 , a valve seat  22 , and a protruding portion  23 . The valve body housing portion  21  has a cylindrical shape and houses the valve body  3 . The valve seat  22  is formed at one end portion of the valve body housing portion  21 , and protrudes from the inner peripheral surface of the valve body housing portion  21 . The protruding portion  23  is formed at the other end portion of the valve body housing portion  21 , and protrudes from the inner peripheral surface of the valve body housing portion  21 . 
     The valve body housing portion  21  houses the valve body  3  therein, and has a certain length to allow the valve body  3  to move in the axial direction according to the flow direction of refrigerant. 
     The valve seat  22  is formed at one end portion of the valve body housing portion  21  in the longitudinal direction, and protrudes from the inner peripheral surface of the valve body housing portion  21 . The valve seat  22  forms an inlet for refrigerant when the refrigerant flows through the check valve unit  1  as shown by arrows in  FIG.  1   . The valve seat  22  is formed to have an inner diameter smaller than the inner diameter of the valve body housing portion  21 , and is closed by the valve body  3  at the time of preventing backflow of refrigerant. The valve seat  22  is integrally formed with the valve body housing portion  21  by hydroforming, which will be described later. 
     The protruding portion  23  is formed at the other end portion of the valve body housing portion  21  in the longitudinal direction, and protrudes from the inner peripheral surface of the valve body housing portion  21 . The protruding portion  23  forms an outlet for refrigerant when the refrigerant flows through the check valve unit  1  as shown by the arrows in  FIG.  1   . The protruding portion  23  is formed to have an inner diameter smaller than the inner diameter of the valve body housing portion  21 , and has a function of confining the valve body  3  in the valve body housing portion  21  when refrigerant flows through the check valve unit  1 . 
     The valve body  3  is disposed between the valve seat  22  and the protruding portion  23  in the container body  2 , and moves in the axial direction in the valve body housing portion  21  according to the flow direction of refrigerant. When refrigerant flows from the valve seat  22  toward the protruding portion  23 , the valve body  3  moves toward the protruding portion  23  in the valve body housing portion  21  to allow the refrigerant to pass through the check valve unit  1 . 
     In contrast, when refrigerant flows from the protruding portion  23  toward the valve seat  22 , the valve body  3  moves toward the inflow side in the valve body housing portion  21  and comes into contact with the valve seat  22 , thus preventing the refrigerant from flowing back in the check valve unit  1 . 
     The valve body  3  includes a valve portion  31  and a guide portion  32 . The valve portion  31  is made of a resin, and comes into contact with the valve seat  22  at the time of preventing backflow of refrigerant. The guide portion  32  includes a plurality of blades. The valve portion  31  comes into contact with the valve seat  22  to close the opening port of the valve seat  22  at the time of preventing refrigerant from flowing back from the protruding portion  23  toward the valve seat  22 . The guide portion  32  has a function of guiding the valve body  3  when the valve body  3  moves in the axial direction in the valve body housing portion  21 , and the outer diameter of the guide portion  32  is substantially equal to the inner diameter of the valve body housing portion  21 . The guide portion  32  includes the plurality of blades, and refrigerant flows through between the blades when the refrigerant flows from the valve seat  22  toward the protruding portion  23 . In Embodiment 1, the guide portion  32  includes four blades arranged at equal angular intervals of 90 degrees. However, the number of blades is not limited to four. 
     Next, a method for manufacturing the check valve unit  1  according to Embodiment 1 will be described.  FIG.  2    is a cross-sectional view showing each of steps of manufacturing the check valve unit  1  according to Embodiment 1 of the present disclosure. 
     As shown in  FIG.  2   a   , first, a tube stock  20  haying a cylindrical shape and forming the container body  2  is disposed in a state of being clamped by outer dies  4 . In Embodiment 1, a hollow pipe made of copper and haying a thickness of approximately 1.5 mm is used as the tube stock  20 . The reason why copper is adopted as a material for forming the container body  2  is that copper has high workability and high durability, thus being suitable for hydroforming, which will be described later. A material is not limited to copper as long as the material can be worked by hydroforming. 
     Next, the tube stock  20  is fixed by pushing shaft pushing tools  5  into the tube stock  20  from both ends of the tube stock  20  as shown in  FIG.  2   b   . Each shaft pushing tool  5  includes an insertion portion  51 , a pressing portion  52 , and a nozzle hole  53 . The insertion portion  51  is inserted into the tube stock  20 . The pressing portion  52  is pressed against the end surface of the tube stock  20 . Fluid, such as water, is fed into the tube stock  20  through the nozzle hole  53 . The insertion portion  51  has a shape where the outer diameter of the insertion portion  51  is substantially equal to the inner diameter of the tube stock  20 . Therefore, when the insertion portions  51  of the shaft pushing tools  5  are inserted into the tube stock  20  from both ends of the tube stock  20 , the outer surfaces of the insertion portions  51  are brought into contact with the inner surface of the tube stock  20 , and the tube stock  20  is clamped by the insertion portions  51  and the outer dies  4 . In this step, the shaft pushing tools  5  are pushed into the tube stock  20  until the pressing portions  52  are brought into contact with the end surfaces of the tube stock  20 . 
     Next, as shown in  FIG.  2   c   , the tube stock  20  is filled with fluid, such as water through the nozzle hole  53  to apply internal pressure. Arrows in  FIG.  2   c    show a state where fluid passes through the nozzle holes  53  and flows into the tube stock  20 . 
     Next, from a state in the step shown in  FIG.  2   b   , the shaft pushing tools  5  are further pushed into the tube stock  20  from both ends of the tube stock  20  as shown in  FIG.  2   d    while a state is maintained where the inside of the tube stock  20  is filled with fluid. The tube stock  20  is pushed from both ends by the pressing portions  52  and hence, the tube stock  20  gathers at a portion that is not brought into contact with the insertion portions  51 , so that the valve seat  22  is formed. At this point of operation, by pushing the shaft pushing tools  5  into the tube stock  20  from both ends in a state where internal pressure is applied to the tube stock  20  from the inside by fluid, the valve seat  22  can be formed while buckling is prevented. Applying the process by using fluid as described with reference to  FIG.  2   c    and  FIG.  2   d    is referred to as hydroforming or the hydroform process. By forming the valve seat  22  on the inner peripheral surface of the tube stock  20  by hydroforming, it is possible to form the opening port of the valve seat  22  coaxially with the tube stock  20 . With such a configuration, it is possible to suppress leakage of refrigerant that may occur at the time of manufacture or due to deterioration over time. 
     After the valve seat  22  is formed, the tube stock  20  is removed from the outer dies  4  and the shaft pushing tools  5  and, as shown in  FIG.  2   e   , one side of the tube stock  20  is cut to cause the valve seat  22  to form one end portion. In Embodiment 1, the tube stock is cut off from the base of the valve seat  22 . However, the tube stock may also be cut off from an intermediate portion of the valve seat  22  provided that the valve seat  22  can ensure a required width w. For example, when a valve seat having a width  2   w  or more is formed in the above-mentioned step of forming the valve seat  22  by pushing the shaft pushing tools  5  into the tube stock  20  from both ends of the tube stock  20  and when the formed valve seat is then cut at the center, it is possible to form a tube stock  20  including two valve seats  22  at one time. In this case, wasted portions are not formed when the tube stock is cut and hence, it is possible to reduce a material cost. 
     After the one side of the tube stock  20  is cut off, as shown in  FIG.  2   f   . the valve body  3  is inserted into the tube stock  20  with the valve portion  31  being inserted first. 
     Lastly, as shown in  FIG.  2   g   , the protruding portion  23  protruding inward is formed on the tube stock  20  at the other end portion, the other end portion being on a side opposite to the valve seat  22 . For a method for forming the protruding portion  23 , it is sufficient to adopt a method that causes the end portion of a pipe to protrude inward. An example of such a method includes terminal processing where a rotating roller is caused to come into contact with the tube stock  20  from the outside and pressure is applied to the tube stock  20 , thus drawing the tube stock  20  inward. By performing the manufacturing steps shown in  FIG.  2   a    to  FIG.  2   g    as described above, the check valve unit  1  according to Embodiment 1 is obtained. 
     The check valve unit  1  according to the present disclosure includes neither the small diameter portions nor the tapered portions that are included in the related-art check valve, the small diameter portions forming the inlet port and the outlet port, each tapered portion being formed between the small diameter portion and the large diameter portion. Therefore, in the above-mentioned manufacturing method, the check valve unit  1  according to the present disclosure can be reduced in size. Further, the valve seat  22  is integrally formed with the valve body housing portion  21  by hydroforming and hence, the check valve unit  1  can be formed of two components, that is, the container body  2  and the valve body  3 . Compared with the related-art check valve, the check valve unit  1  can reduce the number of parts and can simplify manufacturing steps, thus achieving a reduction in manufacturing cost. 
     A width w and a thickness t of the valve seat  22  can be adjusted by the degree at which the shaft pushing tools  5  are pushed into the tube stock  20  and by the length of the insertion portion  51  of each shaft pushing tool  5 . The width w of the valve seat  22  is equal to a separation between the distal ends of the insertion portions  51  of two shaft pushing tools  5  when the shaft pushing tools  5  are pushed into the tube stock  20  as shown in  FIG.  2   d   . The thickness t of the valve seat  22  is determined based on the width w and the degree at which the shaft pushing tools  5  are pushed into the tube stock  20  in the step shown in  FIG.  2   d   . In other words, the volume of the tube stock  20  does not change between before and after the step shown in  FIG.  2   d   . Therefore, the tube stock  20  gathers at a portion that is not brought into contact with the insertion portions  51  by an amount corresponding to the degree at which the shaft pushing tools  5  are pushed into the tube stock  20 , so that the valve seat  22  is formed. Accordingly, the width w and the thickness t of the valve seat  22  can be adjusted by the degree at which the shaft pushing tools  5  are pushed into the tube stock  20  and by the length of the insertion portion  51  of each shaft pushing tool  5 . 
     In the above-mentioned Embodiment 1, the step shown in  FIG.  2   d    of further pushing the shaft pushing tools  5  into the tube stock  20  from both ends of the tube stock  20  is performed after the step shown in  FIG.  2   c    of filling the tube stock  20  with fluid. However, the order of steps is not limited to such an order. It is sufficient to prevent a case where the shaft pushing tools  5  are pushed into the tube stock  20  from both ends of the tube stock  20  without applying pressure to the tube stock  20  from the inside. For example, the step of filling the tube stock  20  with fluid may be performed simultaneously with the step of further pushing the shaft pushing tools  5  into the tube stock  20  from both ends of the tube stock  20 . 
     The check valve unit  1  manufactured by the above-mentioned manufacturing method is mounted in the refrigerant pipe  10  forming the refrigeration cycle of an air-conditioning apparatus as shown in  FIG.  1   . The air-conditioning apparatus includes a refrigeration cycle including at least a compressor, a condenser, an expansion valve, and an evaporator. The check valve unit  1  can be mounted at any desired position in the refrigeration cycle. Further, the check valve unit  1  is reduced in size compared with the related-art check valve, thus giving the higher degree of freedom in arrangement than the related-art check valve unit at the time of being mounted on an air-conditioning apparatus. 
     As described above, the check valve unit  1  according to Embodiment 1 includes the container body  2  and the valve body  3 . The container body  2  includes the valve body housing portion  21 , the valve seat  22 , and the protruding portion  23 , the valve body housing portion  21  having a cylindrical shape, the valve seat  22  being formed at one end portion of the valve body housing portion  21  and protruding from the inner peripheral surface of the valve body housing portion  21 , the protruding portion  23  being formed at the other end portion of the valve body housing portion  21  and protruding from the inner peripheral surface of the valve body housing portion  21 . The valve body  3  includes the valve portion  31  and the guide portion  32 , and is disposed in the container body  2 , the valve portion  31  coming into contact with the valve seat  22  at the time of preventing backflow of refrigerant, the guide portion  32  including a plurality of blades. 
     With such a configuration, it is possible to achieve a reduction in size compared with the related-art check valve. 
     In the check valve unit  1  according to Embodiment 1, the valve seat  22  is integrally formed with the valve body housing portion  21  by hydroforming. Compared with the related-art check valve, such a configuration can reduce the number of parts and can simplify manufacturing steps, thus achieving a reduction in manufacturing cost. 
     The method for manufacturing the check valve unit  1  according to Embodiment 1 includes the step of disposing the tube stock  20  in a state of being damped by the outer dies  4 , the step of fixing the tube stock  20  by pushing the shaft pushing tools  5  into the tube stock  20  from both ends of the tube stock  20 , the step of filling the tube stock  20  with fluid, the step of forming the valve seat  22  on the inner peripheral surface of the tube stock  20  by further pushing the shaft pushing tools  5  into the tube stock  20  from both ends of the tube stock  20 , the step of cutting the tube stock  20  to cause the valve seat  22  to form one end portion, the step of inserting the valve body  3  into the tube stock  20 , and the step of forming the protruding portion  23  protruding inward at the other end portion, the other end portion being on a side opposite to the valve seat  22 . 
     The check valve unit  1  manufactured by such a manufacturing method includes neither the small diameter portions nor the tapered portions that are included in the related-art check valve, the small diameter portions forming the inlet port and the outlet port, the tapered portion being formed between each small diameter portion and the large diameter portion. Therefore, the check valve unit  1  can be reduced in size. Further, the valve seat  22  is integrally formed with the valve body housing portion  21  by hydroforming and hence, the check valve unit  1  can be formed by two components, that is, the container body  2  and the valve body  3 . Compared with the related-art check valve, the check valve unit  1  can reduce the number of parts and can simplify manufacturing steps, thus achieving a reduction in manufacturing cost. 
     In the method for manufacturing the check valve unit  1  according to Embodiment 1, each shaft pushing tool  5  includes the insertion portion  51 , the pressing portion  52 , and the nozzle hole  53 . The insertion portion  51  is inserted into the tube stock  20 . The pressing portion  52  is pressed against the end surface of the tube stock  20 . Fluid is fed into the tube stock  20  through the nozzle hole  53 . The insertion portion  51  has a shape where the outer diameter of the insertion portion  51  is substantially equal to the inner diameter of the tube stock  20 . With such a manufacturing method, the valve seat  22  can be integrally formed with the valve body housing portion  21  by hydroforming. 
     In the method for manufacturing the check valve unit according to Embodiment 1, the step of filling the tube stock  20  with fluid is performed simultaneously with the step of forming the valve seat  22  on the inner peripheral surface of the tube stock  20  by further pushing the shaft pushing tools  5  into the tube stock  20  from both ends of the tube stock  20 . With such a manufacturing method, the valve seat  22  can be formed while buckling is prevented. 
     Embodiment 2 
     A check valve unit of Embodiment 2 of the present disclosure will be described.  FIG.  3    is a cross-sectional view of the check valve unit according to Embodiment 2 of the present disclosure. A check valve unit  1   a  of Embodiment 2 differs from the check valve unit  1  of Embodiment 1 in that the valve seat  22  has an oblique side portion  24  obtained by cutting off an outer corner that does not come into contact with the valve body  3 . In the description for the check valve unit  1   a  according to Embodiment 2, components identical to the corresponding components of the check valve unit  1  according to Embodiment 1 are given the same reference symbols, and the description of such components is omitted. The description will be made mainly for a point that makes the check valve unit  1   a  according to Embodiment 2 different from the check valve unit  1  according to Embodiment 1. 
     The valve seat  22  of Embodiment 2 has the oblique side portion  24  obtained by cutting off the outer corner that does not come into contact with the valve body  3 . By cutting off the outer corner of the valve seat  22  as described above to form a slope such that the diameter of an opening port, which is an inlet for refrigerant, gradually reduces, it is possible to reduce pressure loss when refrigerant flows into the check valve unit  1   a.    
     For a method for forming the oblique side portion  24  on the valve seat  22 , a related-art method may be adopted where an outer corner that does not come into contact with the valve body  3  is cut off or shaved off. It is sufficient to perform, after the step of cutting the tube stock  20  to cause the valve seat  22  to form one end portion, the step of forming the oblique side portion  24  by cutting off the outer corner of the valve seat  22  that does not come into contact with the valve body  3 . 
     As described above, the valve seat of the check valve unit  1   a  according to Embodiment 2 has the oblique side portion  24  obtained by cutting off the outer corner that does not come into contact with the valve body  3 . With such a configuration, it is possible to reduce pressure loss when refrigerant flows into the check valve unit  1 . 
     Embodiment 3 
     A check valve unit of Embodiment 3 of the present disclosure will be described.  FIG.  4    is a cross-sectional view of the check valve unit according to Embodiment 3 of the present disclosure. A check valve unit  1   b  of Embodiment 3 differs from the check valve unit  1  of Embodiment 1 in that the valve seat  22  has a cut-away portion  25  obtained by cutting off an inner corner that comes into contact with the valve body  3 . In the description for the check valve unit  1   b  according to Embodiment 3, components identical to the corresponding components of the check valve unit  1  according to Embodiment 1 are given the same reference symbols, and the description of such components is omitted. The description will be made mainly for a point that makes the check valve unit  1   b  according to Embodiment 3 different from the check valve unit  1  according to Embodiment 1. 
     The valve seat  22  of Embodiment 3 has the cut-away portion  25  obtained by cutting off the inner corner that comes into contact with the valve body  3 . The cut-away portion  25  is formed such that the portion that comes into contact with the valve portion  31  at the time of preventing backflow of refrigerant has a highly accurate roundness. By cutting off the inner corner of the valve seat  22  as described above, it is possible to reduce a gap formed between the valve seat  22  and the valve body  3  at the time of preventing backflow of refrigerant and hence, leakage of refrigerant can be reduced. 
     For a method for forming the cut-away portion  25  on the valve seat  22 , a related-art method may be adopted where an inner corner that comes into contact with the valve body  3  is cut off or shaved off. It is sufficient to perform, after the step of cutting the tube stock  20  to cause the valve seat  22  to form one end portion, the step of forming the cut-away portion  25  by cutting off the inner corner of the valve seat  22  that comes into contact with the valve body  3 . 
     As described above, the valve seat  22  of the check valve unit  1   b  according to Embodiment 3 has the cut-away portion  25  obtained by cutting off the inner corner that comes into contact with the valve body  3 . The cut-away portion  25  is formed such that the portion that comes into contact with the valve portion  31  at the time of preventing backflow of refrigerant has a highly accurate roundness. With such a configuration, it is possible to reduce a gap formed between the valve seat  22  and the valve body  3  at the time of preventing backflow of refrigerant and hence, leakage of refrigerant can be reduced. 
     Embodiment 4 
     A check valve unit of Embodiment 4 of the present disclosure will be described.  FIG.  5    is a cross-sectional view of the check valve unit according to Embodiment 4 of the present disclosure. A check valve unit  1   c  of Embodiment 4 differs from the check valve unit  1  of Embodiment 1 in that the check valve unit  1   c  further includes a valve body confining portion  26  that confines the valve body  3  when refrigerant flows. In the description for the check valve unit  1   c  according to Embodiment 4, components identical to the corresponding components of the check valve unit  1  according to Embodiment 1 are given the same reference symbols, and the description of such components is omitted. The description will be made mainly for a point that makes the check valve unit  1   c  according to Embodiment 4 different from the check valve unit  1  according to Embodiment 1. 
     The check valve unit  1   c  of Embodiment 4 further includes the valve body confining portion  26  provided on the inner peripheral surface of the valve body housing portion  21  at a position in contact with the protruding portion  23  and configured to confine the valve body  3  when refrigerant flows. In each of the check valve units of Embodiments 1 to 3, the valve body  3  is confined in the valve body housing portion  21  by the protruding portion  23  when refrigerant flows through the check valve unit. In the case of such a configuration, the valve body  3  collides with the protruding portion  23  made of metal, thus causing a large impact sound. In view of the above, the valve body confining portion  26  that confines the valve body  3  when refrigerant flows is additionally mounted. With such a configuration, it is possible to suppress an impact sound caused when the valve body  3  collides with the valve body confining portion  26 . By using a resin material, such as polyphenylene sulfide (PPS), polyacetal (POM), or nylon, as a material for forming the valve body confining portion  26 , impact sound can be suppressed. 
     For a method for mounting the valve body confining portion  26 , a method is adopted where, after the valve body  3  is inserted into the tube stock, the valve body confining portion  26  is mounted on the inner peripheral surface of the tube stock by welding or other methods at a position on a side opposite to the valve seat  22  as viewed from the valve body  3 . Alternatively, a method may be adopted where the valve body confining portion  26  is fixed by forming a step portion by shaving the inner peripheral surface of the tube stock. After the valve body confining portion  26  is mounted in the tube stock, the protruding portion  23  is formed to be in contact with the valve body confining portion  26 . 
     As described above, the check valve unit  1   c  according to Embodiment 4 further includes the valve body confining portion  26  provided on the inner peripheral surface of the valve body housing portion  21  at a position in contact with the protruding portion  23  and configured to confine the valve body  3  when refrigerant flows. With such a configuration, when refrigerant flows through the check valve unit  1   c,  the valve body  3  is confined by the valve body confining portion  26  instead of the protruding portion  23  and hence, it is possible to improve durability of a component. 
     Embodiment 5 
     A check valve unit of Embodiment 5 of the present disclosure will be described.  FIG.  6    is a cross-sectional view showing a state where the check valve unit according to Embodiment 5 of the present disclosure is mounted in a refrigerant pipe. A check valve unit  1   d  of Embodiment 5 differs from the check valve unit  1  of Embodiment 1 in that the outer peripheral surface of the valve seat  22  of the container body  2  has a recessed portion  27  into which a ring-shaped resin is inserted. In the description for the check valve unit  1   d  according to Embodiment 5, components identical to the corresponding components of the check valve unit  1  according to Embodiment 1 are given the same reference symbols, and the description of such components is omitted. The description will be made mainly for a point that makes the check valve unit  1   d  according to Embodiment 5 different from the check valve unit  1  according to Embodiment 1. 
     In the container body  2  of the check valve unit  1   d  of Embodiment 5, the outer peripheral surface of the valve seat  22  has the recessed portion  27  into which a ring-shaped resin is inserted. By inserting the ring-shaped resin into the recessed portion  27  when the check valve unit  1   d  is mounted in the refrigerant pipe  10 , it is possible to suppress refrigerant flowing through a gap formed between the check valve unit  1   d  and the refrigerant pipe  10 . The recessed portion  27  is formed on the outer peripheral surface of the valve seat  22  having a larger thickness than the valve body housing portion  21  and hence, there is no possibility for reduction in the strength of the container body  2 . 
     For a method for forming the recessed portion on the outer peripheral surface of the valve seat  22  of the container body  2 , a related-art method, such as shaving, may be adopted. It is sufficient to perform the step of forming the recessed portion after the step of forming the valve seat  22  on the inner peripheral surface of the tube stock  20  by hydroforming. 
     As described above, in the valve seat of the check valve unit  1   d  according to Embodiment 5, the outer peripheral surface of the valve seat  22  of the container body  2  has the recessed portion  27  into which a ring-shaped resin is inserted. With such a configuration, by mounting the check valve unit  1   d  in the refrigerant pipe  10  with the ring-shaped resin being inserted into the recessed portion  27 , it is possible to suppress refrigerant flowing through a gap formed between the check valve unit  1   d  and the refrigerant pipe  10 . 
     Embodiment 6 
     Embodiment 6 of the present disclosure will be described.  FIG.  7    is a cross-sectional view showing a state where a plurality of check valve units according to Embodiment 1 of the present disclosure are mounted in a refrigerant pipe. Embodiment 6 differs from Embodiment 1 in that a plurality of check valve units  1  according to Embodiment 1 are mounted in one refrigerant pipe  10 . The check valve unit  1  according to Embodiment 6 is identical to the check valve unit  1  according to Embodiment 1 and hence, the description of the check valve unit  1  according to Embodiment 6 is omitted, and the description will be made mainly for a point that makes the check valve unit  1  according to Embodiment 6 different from the check valve unit  1  according to Embodiment 1. 
     In Embodiment 6, two check valve units  1  are mounted in series in one refrigerant pipe  10 . An opening port  13  is formed in the refrigerant pipe  10  by burring or other processing at a position between the check valve units  1 , and a refrigerant pipe  12  is connected to the opening port  13  by brazing or other methods. The check valve unit according to the present disclosure is reduced in size, thus allowing mounting of the check valve unit at any desired position in a refrigeration cycle. Therefore, even when a plurality of check valve units are used in combination, the plurality of check valve units as a whole are made compact, thus giving the higher degree of freedom in arrangement than the related-art check valve unit at the time of being mounted on an air-conditioning apparatus. Further, in the case of forming an assembly by using a plurality of related-art check valves, joint pipes are used between the check valves and hence, the number of portions where brazing is applied increases. However, when the check valve units of the present disclosure are used, it is possible to reduce the number of portions where brazing is applied. For a method for mounting the check valve unit  1  in the refrigerant pipe  10 , the method described in Embodiment 1 may be adopted. 
     As described above, Embodiment 6 is directed to the air-conditioning apparatus where the plurality of check valve units are mounted in one refrigerant pipe. The check valve unit according to the present disclosure is reduced in size and hence, even when the plurality of check valve units are mounted in one refrigerant pipe, the plurality of check valve units as a whole are made compact, thus giving the higher degree of freedom in arrangement than the related-art check valve unit at the time of being mounted on an air-conditioning apparatus. 
     In Embodiment 6, the check valve unit  1  described in Embodiment 1 is used. However, the check valve unit is not limited to such a check valve unit, and the check valve unit of any one of Embodiments 2 to 6 or a check valve unit obtained by combining some check valve units may be used. 
     The present disclosure has been described heretofore by using the above-mentioned Embodiments. However, some of these Embodiments may be performed in combination. Further, the technical scope of the present disclosure is not limited to the scope described in the above-mentioned Embodiments. Various changes or modifications may be applied to each of the above-mentioned Embodiments without departing from the gist of the disclosure, and Embodiments to which such changes or modifications are applied also fall within the technical scope of the present disclosure. 
     REFERENCE SIGNS LIST 
       1 ,  1   a,    1   b,    1   c,    1   d:  check valve unit,  2 : container body,  3 : valve body,  4 : outer die,  5 : shaft pushing tool,  10 : refrigerant pipe,  11 : protrusion,  12 : refrigerant pipe,  13 : opening port,  20 : tube stock,  21 : valve body housing portion,  22 : valve seat,  23 : protruding portion,  24 : oblique side portion,  25 : cut-away portion,  26 : valve body confining portion,  27 : recessed portion,  31 : valve portion,  32 : guide portion,  51 : insertion portion,  52 : pressing portion,  53 : nozzle hole, w: width, t: thickness