Abstract:
A gear case part ( 70 ), which has an upper aperture that opens upward and which forms a recess that houses a portion of a drive gear device ( 63 ) and for which the drive gear device ( 63 ) can be inserted from the upper aperture and assembled, is provided integrally on the upper part of a first or second divided case ( 21, 22 ); a cover ( 66 ) that blocks the upper aperture of the gear case part ( 70 ) is fastened to the gear case part ( 70 ); an operating part ( 67 ) protrudes upward from a through-hole ( 66   a ) that vertically penetrates the cover ( 66 ); and by removing the cover ( 66 ) from the gear case part ( 70 ), the drive gear device ( 63 ) can be extracted from the gear case part ( 70 ) through the upper aperture.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a branching unit for flow-undisrupted boring (for boring without stopping a passage of fluid) suitable for providing a branch off of an existing pipe of water or gas. 
       BACKGROUND ART 
       [0002]    There are known processes in the art for boring a portion of an existing pipe without disrupting the water supply using a boring machine having a hole saw (see the first patent document). 
       Citation List  
     Patent Document  
       [0003]    [FIRST PATENT DOCUMENT] Japanese Laid-Open Patent Publication No. 2002-321109 
         [0004]    Basic procedures, etc., of boring operations of this type will be described briefly. 
         [0005]    First, as shown in  FIG. 12A , a portion of an existing pipe  1  is covered by a sealing case  2  composed of a pair of separate cases  21  and  22 . A valve body  100  of a gate valve is provided in the first separate case  21 . Then, a boring machine  3  is attached to the first separate case  21 . 
         [0006]    In this state, the boring machine  3  is operated so as to bore a circular opening  11  in the existing pipe  1  with a hole saw  4  at the tip by spinning the main shaft, as shown in  FIG. 12B . Then, the hole saw  4  is retracted and then the valve body  100  is closed, as shown in  FIG. 12C . After the boring operation is finished as described above, the boring machine  3  is removed, and a predetermined branch pipe is connected to the first separate case  21 , after which the valve body  100  is opened, thus completing the branching operation. 
       SUMMARY OF INVENTION 
       [0007]    With such a conventional unit, however, a large valve housing (valve casing) is additionally needed for accommodating the valve body  100  which moves up and down. This leads to an increase in the cost. 
         [0008]    Moreover, the valve body  100  moves up and down at a position away from the existing pipe  1 , which increases the stroke by which the hole saw  4  is advanced/retracted. This leads to an increase in the size of the boring machine  3 . 
         [0009]    Furthermore, since the valve body  100  moves up and down, a valve operation cap  101  is positioned high, thus requiring deeper earth covering. 
         [0010]    The second patent document and the third patent document identified below each disclose a branching unit having an arc-shaped valve body accommodated between a saddle having a branch hole and an existing pipe. The valve body moves in the circumferential direction in one separate case to shut the branch hole. 
         [0011]    [SECOND PATENT DOCUMENT] Japanese Laid-Open Patent Publication No. 6-74387 
         [0012]    [THIRD PATENT DOCUMENT] Japanese Laid-Open Patent Publication No. 2006-207747 
         [0013]    With these conventional techniques, however, if the saddle becomes bigger, it is necessary to install the valve body after installing the driving means from the rear surface of the heavy saddle, thus complicating the operation. 
         [0014]    Thus, in view of the problems in the prior art, a primary object of the present invention is to provide a branching unit for flow-undisrupted boring which is inexpensive and capable of performing the operation with a short boring stroke and even with shallow earth covering. A further object of the present invention is to provide a branching unit which is easy to assemble. 
         [0015]    In order to achieve the object set forth above, a branching unit of the present invention is a branching unit for flow-undisrupted boring suitable for boring a portion of a pipe wall of an existing pipe to form an opening in the pipe wall with a boring machine having a hole saw so as to connect a branch pipe to the existing pipe, including; a sealing case including first and second separate cases separated from each other in a circumferential direction of the existing pipe and enclosing a portion of the existing pipe, wherein a branch pipe portion to be branching off of the existing pipe by protruding in a radial direction of the existing pipe is formed integral with the first separate case; a valve body including a portion having an arc-shaped lateral cross section for opening/closing a branch hole of the branch pipe portion by rotating in the circumferential direction of the existing pipe between an inner periphery surface of the sealing case and an outer periphery surface of the existing pipe; a valve seat provided on the inner periphery surface of the first separate case with which the valve body contacts in a valve-closed state; and a rotation mechanism for rotating the valve body, the rotation mechanism including: an operation portion rotated outside the sealing case; a driving gear unit which rotates by (following) the rotation of the operation portion; and a driven gear provided on the valve body for rotating the valve body in the circumferential direction of the existing pipe following the rotation of the driving gear unit, wherein: a gear case portion is formed integral with an upper portion of the first or second separate case, the gear case portion having a lower opening which opens in a downward direction, allowing for a portion of the driving gear unit to mesh with the driven gear, and an upper opening which opens in an upward direction, wherein the gear case portion forms a depressed portion accommodating a portion of the driving gear unit, and allows the driving gear unit to be inserted and assembled through the upper opening; a cover which shuts the upper opening of the gear case portion is fastened to the gear case portion; the operation portion protrudes in the upward direction through a through hole vertically running through the cover; and the cover can be removed from the gear case portion so as to allow the driving gear unit to be taken out from the gear case portion through the upper opening. 
         [0016]    With the present invention, since the portion of the valve body having an arc-shaped lateral cross section rotates along the existing pipe in the gap between the sealing case and the existing pipe, it is not necessary to separately provide a portion for accommodating the valve body such as a valve housing and a valve cover. Therefore, the unit is inexpensive and small. 
         [0017]    Moreover, an arc-shaped valve body has a greater flexural strength than a flat plate-shaped valve body. Therefore, the valve body can be made thinner. 
         [0018]    It is not necessary to separately provide a portion for accommodating the valve body. Therefore, the boring stroke is shorter. 
         [0019]    Moreover, instead of moving up and down, the valve body rotates along the outer periphery surface of the existing pipe. Therefore, the valve height is lower. As a result, it is possible to perform the operation even with shallow earth covering. 
         [0020]    On the other hand, with the provision of the gear case portion forming the depressed portion, the branching unit can be assembled by inserting the driving gear unit through the upper opening of the gear case portion and shutting the gear case portion with the cover. Therefore, it is no longer necessary to insert and assemble the driving gear unit from the rear side of the heavy separate case. That is, it is possible to install the driving gear unit through the upper opening. This significantly facilitates the operation of assembling the branching unit. 
         [0021]    In the present invention, it is preferred that the first and second separate cases each include a curved surface portion extending along the existing pipe; and the gear case portion includes a side wall rising in the upward direction from the curved surface portion, and a flange which is formed integral with an upper end of the side wall and to which the cover is fastened. 
         [0022]    With the present invention, a flange to which the cover is fastened is formed in an upper end of the side wall of the gear case portion, thereby facilitating the attachment and removal of the cover from above. 
         [0023]    In the present invention, it is preferred that the driving gear unit includes a worm which rotates integral with the operation portion, and a worm wheel which rotates by (following) the rotation of the worm. 
         [0024]    Here, if the valve body moves in the circumferential direction during the installment operation, the working efficiency of the installment decreases. There are vibrations from vehicles passing on the road surface after the completion of the boring operation, and if the valve body moves in the circumferential direction due to these vibrations, the branch hole may shut inadvertently. 
         [0025]    In the present embodiment, the valve body does not move inadvertently by using a pair of gears including an irreversible worm and a worm wheel. 
         [0026]    In the present invention, it is preferred that a bearing portion rotatably supporting the worm wheel is formed integral with the cover. 
         [0027]    In the present embodiment, by attaching the worm wheel to the bearing portion which is formed in advance in the cover, it is possible to attach the cover and install the worm wheel simultaneously, thus significantly improving the working efficiency during assembly. Moreover, it is no longer necessary to separately provide a support member, or the like, for rotatably supporting the worm wheel, thereby simplifying the structure. 
         [0028]    In the present invention, it is preferred that the gear case portion further includes a bottom wall portion rotatably supporting a lower end of the worm. 
         [0029]    In the present embodiment, since the lower end of the worm is rotatably supported by contacting the bottom wall portion, it is no longer necessary to separately use a support member, or the like, for supporting the lower end of the worm, thus making it possible to form the gear case portion with a simple structure and improving the working efficiency of the installment because the worm does not fall in the downward direction. 
         [0030]    In the present invention, it is preferred that the valve body has a concave surface curved along the outer periphery surface of the existing pipe, and a convex surface opposing the branch hole in the valve-closed state; and in the valve-closed state, a contact portion of the convex surface which is in contact with the valve seat protrudes past a surface of the driven gear in the radial direction of the existing pipe. 
         [0031]    In the present embodiment, since the contact surface contacting the valve seat protrudes past the surface of the driven gear in the radial direction of the existing pipe, the gear will not bite into the valve seat, and the valve body can be moved smoothly. 
         [0032]    In a preferred embodiment of the present invention, the contact portion is formed in a loop shape; the driven gear is formed on the valve body in an inner first region surrounded by the loop-shaped contact portion; and the valve seat is formed in a loop shape, and the branch hole and the lower opening are formed in the first separate case in an inner second region surrounded by the loop-shaped valve seat. 
         [0033]    Here, in a water-undisrupted operation, disruption (stopping) of water supply is not acceptable even in the event of an unexpected incident. For example, there may be an event where the valve body which is closed after the completion of boring does not open due to a failure of the driving gear unit. 
         [0034]    In such an event, the driven gear is formed in the inner region surrounded by the loop-shaped contact portion in the present embodiment. Therefore, in the valve-closed state, water pressure is not applied to the space inside the gear case portion. Therefore, water does not gush out even when the cover is removed, thereby allowing the cover to be removed for replacement of the driving gear unit. 
         [0035]    A branching unit of the present invention is a branching unit for flow-undisrupted boring suitable for boring a portion of a pipe wall of an existing pipe to form an opening in the pipe wall with a boring machine having a hole saw so as to connect a branch pipe to the existing pipe, including; a sealing case including first and second separate cases separated from each other in a circumferential direction of the existing pipe and enclosing a portion of the existing pipe, wherein a branch pipe portion to be branching off of the existing pipe by protruding in a radial direction of the existing pipe is formed integral with the first separate case; a valve body including a portion having an arc-shaped lateral cross section for opening/closing a branch hole of the branch pipe portion by rotating in the circumferential direction of the existing pipe between an inner periphery surface of the sealing case and an outer periphery surface of the existing pipe; a valve seat provided on the inner periphery surface of the first separate case with which the valve body contacts in a valve-closed state; and a rotation mechanism for rotating the valve body, the rotation mechanism including: an operation portion rotated outside the sealing case; a driving gear unit which rotates following the rotation of the operation portion; and a driven gear provided on the valve body for rotating the valve body in the circumferential direction of the existing pipe following the rotation of the driving gear unit, wherein: the valve body is made of ductile cast iron, and a groove for attachment of the driven gear is formed in the valve body, extending in a circumferential direction of the valve body; and the driven gear made of stainless steel is attached to the groove. 
         [0036]    Here, where the driven gear is made of ductile cast iron, the anticorrosive applied on the surface of the driven gear may be rubbed off as the driving gear unit meshes with the driven gear, thereby allowing the formation of rust. 
         [0037]    In contrast, in the present embodiment, the driven gear is made of stainless steel, and therefore the anticorrosive effect does not deteriorate even if the surface of the driven gear is rubbed off. 
         [0038]    As the valve body is formed by ductile cast iron and only the driven gear is formed by stainless steel, it is possible to significantly reduce the cost as compared with a case where the entire valve body is formed by stainless steel. 
         [0039]    Here, for a valve unit used in a water pipe, or the like, the specification of whether the operation portion is rotated counterclockwise or clockwise in order to close the valve body is prescribed for each orderer, and orders are made based on the specification. 
         [0040]    The teeth of the worm wheel are helical teeth, and therefore the driven gear of the valve body employs helical teeth so as to mesh with the worm wheel. Thus, the inclination of the helical teeth forming the worm wheel is reversed depending on the specification of whether the rotation for closing the valve body is counterclockwise or clockwise. 
         [0041]    Thus, the inclination of the driven gear which meshes the worm wheel differs depending on whether the valve is left-handed or right-handed. 
         [0042]    For this, by selecting the driven gear to be attached depending on the valve specification, it is possible to accommodate both the left-handed and right-handed specifications. 
         [0043]    In a preferred embodiment of the present invention, the driven gear is formed by a stainless steel cast product. 
         [0044]    In a preferred embodiment of the present invention, the driven gear includes a plurality of through holes formed in parallel to one another in a stainless steel plate material, forming the driven gear. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0045]      FIG. 1  is an exploded perspective view showing a branching unit according to Embodiment 1 of the present invention. 
           [0046]      FIG. 2  is a schematic cross-sectional view showing the branching unit. 
           [0047]      FIG. 3  is an exploded schematic cross-sectional view showing a first separate case. 
           [0048]      FIG. 4  is an exploded schematic side view showing how a worm wheel is attached to a cover. 
           [0049]      FIG. 5  is a schematic side view showing a first separate case. 
           [0050]      FIG. 6A  is a schematic side view showing a valve body,  FIG. 6B  is a schematic perspective view showing how a rubber ring is fixed. 
           [0051]      FIGS. 7A and 7B  are schematic cross-sectional views of the branching unit, etc., showing a flow-undisrupted boring method. 
           [0052]      FIGS. 8A and 8B  are schematic cross-sectional views of the branching unit, etc., showing the flow-undisrupted boring method. 
           [0053]      FIGS. 9A and 9B  are schematic cross-sectional views of the branching unit, etc., showing the flow-undisrupted boring method. 
           [0054]      FIGS. 10A and 10B  are schematic cross-sectional views of the branching unit, etc., showing the flow-undisrupted boring method. 
           [0055]      FIG. 11  is a schematic cross-sectional view showing a branching unit illustrating Embodiment 2. 
           [0056]      FIGS. 12A ,  12 B and  12 C are schematic cross-sectional views of a unit, etc., showing a conventional flow-undisrupted boring method. 
           [0057]      FIGS. 13A ,  13 B and  13 C are front views showing driving gear units of Embodiments 3, 4 and 5, respectively. 
           [0058]      FIGS. 14A ,  14 B and  14 C are partial cross-sectional views showing the operation of a valve-opening assisting mechanism according to Embodiment 6. 
           [0059]      FIGS. 15A to 15G  are directed to Embodiment  7 , wherein  FIGS. 15A and 15B  are a side view and a front view, respectively, of a driven gear,  FIGS. 15C and 15D  are a side view and a front view, respectively, of a valve body,  FIGS. 15E and 15F  are a side view and a front view, respectively, of the valve body where the driven gear is attached to the valve body, and  FIG. 15G  is a front view showing a left-handed valve body. 
           [0060]      FIG. 16  is a schematic perspective view showing a plate material of Embodiment 8 flattened out. 
           [0061]      FIGS. 17A to 17E  are directed to Embodiment  8 , wherein  FIG. 17A  is a side view of a driven gear made of a plate material,  FIGS. 17B and 17C  are a side view and a front view, respectively, of a valve body to which the plate material is not attached,  FIG. 17D  is a side view of the valve body to which the plate material is attached, and  FIG. 17E  is a partially-cross-sectional side view showing worm teeth. 
           [0062]      FIGS. 18A and 18B  are schematic end view in which the plate material is attached to the valve body. 
           [0063]      FIG. 19  is a schematic perspective view showing the flattened-out plate material as seen from the rear surface. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0064]    The present invention will be understood more clearly from the following description of preferred embodiments taken in conjunction with the accompanying documents. However, the embodiments and the drawings are merely illustrative, and shall not be relied upon in defining the scope of the present invention. The scope of the present invention shall be defined only by the appended claims. In the accompanying drawings, like reference numerals denote like components throughout the plurality of figures. 
         [0065]    Embodiments of the present invention will now be described with reference to the drawings. 
       Embodiment 1 
       [0066]      FIGS. 1 to 11  show Embodiment 1. 
         [0067]    First, the general configuration of the present branching unit will be described. 
         [0068]    Branching Unit  2 : 
         [0069]    A branching unit  2  shown in  FIGS. 1 and 2  is used in flow-undisrupted boring, in which a branch is provided off of an existing pipe  1  while a fluid (e.g., water, etc.) is flowing through the inside of the existing pipe  1 . That is, the branching unit  2  is for boring a portion of a pipe wall  12  of the existing pipe  1  with a boring machine  3  having a hole saw  4 , as shown in  FIG. 8A . 
         [0070]    As shown in  FIG. 2 , the branching unit  2  includes a sealing case  20  for enclosing the existing pipe  1 . The sealing case  20  includes first and second separate cases  21  and  22  which are separated from each other in the circumferential direction R of the existing pipe  1 . A branch pipe portion  27  to be branching off of the existing pipe  1  by protruding in the radial direction C of the existing pipe  1  is formed integral with the first separate case  21 . 
         [0071]    Separate Cases  21  and  22 : 
         [0072]    The first and second separate cases  21  and  22  are separated from each other along a virtual plane H which is generally orthogonal to an axis  27 L of the branch pipe portion  27 . The pair of separate cases  21  and  22  are attached from outside to the existing pipe  1  from opposite sides in the radial direction C of the existing pipe  1  and are assembled together by fastening coupling portions  25  thereof to each other by assembling bolts (not shown). 
         [0073]    As shown in  FIGS. 1 and 2 , the separate cases  21  and  22  each have an inner periphery surface  29  which is curved generally along an outer periphery surface  13  of the existing pipe  1 . As shown in  FIGS. 1 ,  2  and  5 , groove-shaped gasket attachment portions  24  are formed along the coupling portions  25  and opposite end portions of the inner periphery surface  29  in the pipe axis direction L of the existing pipe  1  of the separate cases  21  and  22 . Rubber gaskets  26  are attached to the gasket attachment portions  24 , thereby sealing between the existing pipe  1  and the branching unit  2  and between the first separate case  21  and the second separate case  22 . 
         [0074]    Note that bolt insertion holes (not shown) may be further provided in the opposite end portions of the separate cases  21  and  22  in the pipe axis direction L, and the opposite end portions may be fastened together by assembling bolts. 
         [0075]    Branch Pipe Portion  27 : 
         [0076]    As shown in  FIG. 7A , the boring machine  3  is attached to a joint portion  81 , which is like a plate-shaped flange, for example, of the branch pipe portion  27 . As the hole saw  4 , while spinning, is passed toward the radial direction C of the existing pipe  1  through a branch hole  28  of the branch pipe portion  27 , the pipe wall  12  of the existing pipe  1  is cut as shown in  FIG. 8A , thereby boring the opening  11  in the existing pipe  1  as shown in  FIG. 8B . Note that a center drill  41  for positioning the hole saw  4  is provided at the center of rotation of the hole saw  4  so as to protrude toward the existing pipe  1 , as shown in  FIG. 7B . 
         [0077]    Valve Body  5 : 
         [0078]    As shown in  FIG. 2 , first and second spaces S 1  and S 2  are provided between the existing pipe  1  and the first and second separate cases  21  and  22 , respectively. The first space S 1  and the second space S 2  communicate with each other in the circumferential direction R, and accommodate a valve body  5  which has an arc-shaped lateral cross section so that the valve body  5  can be moved between the two separate cases  21  and  22 . The valve body  5  opens/closes the branch hole  28  of the branch pipe portion  27  by rotating along the inner periphery surfaces  29  of the separate cases  21  and  22  and the outer periphery surface  13  of the existing pipe  1  and in the circumferential direction R of the existing pipe  1 . 
         [0079]    That is, the majority of the valve body  5  is accommodated in the second space S 2  in the valve-open state of  FIG. 7A  and the boring state of  FIG. 8A , whereas the majority of the valve body  5  is accommodated in the first space S 1 , thus shutting the branch hole  28 , in the valve-closed state of  FIGS. 9A and 9B  after being rotated by a rotation mechanism  6 . 
         [0080]    A guide portion  55  (see  FIG. 5 ) for guiding the rotation of the arc-shaped valve body  5  is provided integral with the separate cases  21  and  22 . 
         [0081]    By rotating the valve body  5  in the circumferential direction R of the existing pipe  1 , it is possible to rotationally move the valve body  5  between the valve-open position shown in  FIG. 7A  and the valve-closed position shown in  FIG. 9A . 
         [0082]    A sealing rubber ring (an example of the valve seat)  56  is attached, in a generally circumferential pattern, to a rubber ring attachment groove  57  in the first separate case  21  having the branch pipe portion  27  shown in  FIG. 2  along the perimeter around the branch hole  28  of the branch pipe portion  27  and a gear case portion  70  thereof to be described later. 
         [0083]    As the valve body  5  is rotationally moved to the valve-closed position shown in  FIG. 9A  a first contact portion  5   f  indicated by a dotted area in the valve body  5  of  FIG. 6  comes into close contact with a second contact portion  56   f  of the rubber ring  56  indicated by a dotted area of  FIG. 5 . This shuts the branch hole  28 , as shown in  FIG. 9A , thus sealing the space around the opening  11  of the existing pipe  1  with the separate cases  21  and  22  and the valve body  5 . 
         [0084]    It is preferred that a dovetail groove  21   a  is formed in the first separate case  21  and a protruding portion  56   a  which fits into the dovetail groove  21   a  is formed integral with the rubber ring  56 , as shown in  FIG. 6B . In such a case, it is possible to prevent the rubber ring  56  from being taken off by the strong water flow when the closed valve body  5  is opened. 
         [0085]    Through holes (not shown) are formed in opposite end portions of the valve body  5 . The provision of the through holes in the valve body  5  allows for powder coating while hanging the valve body  5  with hooks through the through holes, and also reduces the weight of the valve body  5 . 
         [0086]    Next, important parts of the present invention will be described in greater detail. 
         [0087]    Rotation Mechanism  6 : 
         [0088]    The rotation mechanism  6  for rotating the valve body  5  is provided in the sealing case  20  shown in  FIG. 2 . 
         [0089]    The rotation mechanism  6  includes an operation portion  67  rotated outside the sealing case  20 , a driving gear unit  63  which rotates following the rotation of the operation portion  67 , and a driven gear  51  provided on the valve body  5  for rotating the valve body  5  along the circumferential direction R of the existing pipe  1  following the rotation of the driving gear unit  63 . 
         [0090]    The driving gear unit  63  includes a worm  61  which rotates integral with the operation portion  67 , and a worm wheel  62  which rotates following the rotation of the worm  61 . The worm  61  and the worm wheel  62  mesh with each other, and the driven gear  51  meshes with the worm wheel  62 . Note that the axial direction of the worm  61  is set to the vertical direction. 
         [0091]    On the other hand, as shown in  FIG. 6A , the driven gear  51  is provided generally at the center of the valve body  5  in the pipe axis direction L. As shown in  FIG. 2 , the worm wheel  62  protrudes from a depressed portion  73  ( FIG. 3 ) to be described later into the first space S 1 . The driven gear  51  meshes with the worm wheel  62 , and rotates in the circumferential direction R following the rotation of the worm wheel  62 , thereby rotating the valve body  5 . 
         [0092]    That is, when an operator rotates the operation portion  67 , the driven gear  51  is rotated via the worm  61  and the worm wheel  62 , thereby rotating the valve body  5 . 
         [0093]    Therefore, the operation portion  67 , the driving gear unit  63  (the worm  61 , the worm wheel  62 ) and the driven gear  51  together form the rotation mechanism  6  for rotating the valve body  5 . 
         [0094]    Gear Case Portion  70 : 
         [0095]    The gear case portion  70  is formed integral with the first separate case  21  in an upper portion of the first separate case  21 . As shown in  FIG. 3 , the gear case portion  70  has a lower opening  74   d  which opens in the downward direction Z 2 , allowing for the worm wheel  62  to mesh with the driven gear  51 , and an upper opening  74   u  which opens in the upward direction Z 1 . The gear case portion  70  forms the depressed portion  73  accommodating a portion of the driving gear unit  63 . The driving gear unit  63  can be inserted and assembled through the upper opening  74   u.    
         [0096]    As shown in  FIGS. 1 and 2 , the first and second separate cases  21  and  22  each have a curved surface portion  30  extending along the existing pipe  1 . As shown in  FIG. 1 , the gear case portion  70  includes a side wall  71  rising in the upward direction from the curved surface portion  30  of the first separate case  21 , and a flange  72  which is formed integral with the upper end of the side wall  71  and to which the cover  66  is fastened. Therefore, the cover  66  is fastened to the gear case portion  70  by bolts (not shown) via the flange  72 , thereby shutting the upper opening  74   u  of the gear case portion  70 . Note that a rubber gasket (not shown) is interposed between the cover  66  and the flange  72 . 
         [0097]    Attachment of Driving Gear Unit  63  to Cover  66 : 
         [0098]    As shown in  FIG. 3 , the operation portion  67  is formed integral with an upper portion of the worm  61 . 
         [0099]    On the other hand, as shown in  FIG. 4 , a support portion  66   b  is formed integral with a lower portion of the cover  66 , and a bearing portion (hole)  65  is formed in the support portion  66   b.  A rotation shaft  64  for rotatably supporting the worm wheel  62  is inserted through the bearing portion  65 . 
         [0100]    With the rotation shaft  64  inserted through the worm wheel  62  and the bearing portion  65 , the worm wheel  62  is rotatably attached to the cover  66 , as shown in  FIG. 2 . 
         [0101]    On the other hand, a through hole  66   a  vertically running through the cover  66  is formed in the cover  66  shown in  FIG. 3 . The worm  61  is rotatably attached to the through hole  66   a  of the cover  66  so as to mesh with the worm wheel  62 , as shown in  FIG. 2 . With the worm  61  attached to the cover  66 , the operation portion  67  formed in an upper portion of the worm  61  protrudes in the upward direction Z 1  through the through hole  66   a.    
         [0102]    Thus, the driving gear unit  63  composed of the worm  61  and the worm wheel  62  and the operation portion  67  can be attached in advance to the cover  66 . This attachment is done during shipment, but may be done on site. 
         [0103]    Installation of Cover  66 : 
         [0104]    As shown in  FIG. 3 , the lower opening  74   d  which opens in the downward direction Z 2  is formed in the depressed portion  73 . As shown in  FIG. 2 , when inserting and assembling the driving gear unit  63  into the depressed portion  73  through the upper opening  74   u,  a portion of the worm wheel  62  protrudes toward the valve body  5  through the lower opening  74   d,  thus meshing the worm wheel  62  with the driven gear  51  of the valve body  5 . 
         [0105]    On the other hand, as shown in  FIGS. 2 and 3 , a bottom wall portion  75  for rotatably supporting a lower end  61   d  of the worm  61  is formed integral with the gear case portion  70 . 
         [0106]    Therefore, when the cover  66  is installed on the gear case portion  70 , the worm wheel  62  is meshed with the driven gear  51 , and the lower end  61   d.  of the worm  61  is rotatably supported by the bottom wall portion  75  of the first separate case  21 . 
         [0107]    In the present embodiment, the worm wheel  62  is rotatably supported by the rotation shaft  64  inserted through the bearing portion  65 , and the lower end  61   d  of the worm  61  is rotatably supported by the bottom wall portion  75  of the first separate case  21 . Therefore, the driving gear unit  63  (the worm  61 , the worm wheel  62 ) does not fall through the lower opening  74   d.    
         [0108]    On the other hand, when the driving gear unit  63  (the worm  61 , the worm wheel  62 ) shown in  FIG. 2  is taken out from the sealing case  20 , the cover  66  is taken out in the upward direction Z 1 . Since the driving par unit  63  is attached to the cover  66 , as described above, when the cover  66  is taken out from the gear case portion  70 , the driving gear unit  63  is taken out from the gear case portion  70  through the upper opening  74   u  above. 
         [0109]    Valve Body  5  and Rubber Ring  56 : 
         [0110]    The valve body  5  has a concave surface  53  curved along the outer periphery surface  13  of the existing pipe  1 , and a convex surface  52  opposing the branch hole  28  in the valve-closed position shown in  FIGS. 9A and 9B . 
         [0111]    In the valve-closed position shown in  FIG. 2 , the first contact portion  5   f  of the convex surface  52  of the valve body  5  which is in contact with the second contact portion  56   f  of the rubber ring  56  protrudes past the surface of the driven gear  51  in the radial direction C of the existing pipe  1 . 
         [0112]    As shown in  FIG. 6 , in the valve-closed position ( FIG. 2 ), the first contact portion  5   f  (the portion indicated by a dotted area) with which the rubber ring  56  ( FIG. 5 ) contacts is formed in a loop shape. The driven gear  51  is formed on the valve body  5  in a region  5   a  inside the loop-shaped first contact portion  5   f  (the portion indicated by a dotted area). 
         [0113]    As shown in  FIG. 4 , the worm wheel  62  is formed by helical teeth  62   a  which are formed inclined with respect to the pipe axis direction L of the existing pipe  1  ( FIG. 2 ) so as to mesh with the worm  61 . On the other hand, as shown in  FIG. 6 , the driven gear  51  of the valve body  5  is formed by helical teeth so as to mesh with the worm wheel  62  ( FIG. 4 ). 
         [0114]    The driven gear  51  formed on the valve body  5  is formed in an inclined direction. Therefore, as the driven gear  51  meshes with the worm wheel  62 , a rotational force acts upon the cover  66 . In order to prevent the rotation of the cover  66 , it is preferred that the support portion  66   b  of the cover  66 , etc., engage with the depressed portion  73 . 
         [0115]    For example, a tar epoxy resin, or the like, is applied on the surface of the driven gear  51 , and powder coating is applied on a portion of the valve body  5  excluding the driven gear  51 . 
         [0116]    Flow-Undisrupted Boring Method (Boring Method Without Stopping A Passage of Fluid): 
         [0117]    First, with a fluid flowing inside the existing pipe  1  of  FIG. 2 , the branching unit  2  is attached so as to enclose the outer periphery surface  13  of the existing pipe  1 . After the attachment, the operator assembles together the separate cases  21  and  22  with the assembling bolts. 
         [0118]    Note that the valve body  5  is first set to the valve-closed position where the branch hole  28  of the branch pipe portion  27  is closed. A waterproof test may be performed for checking whether there is no water leak by injecting water between the sealing case  20  in the valve-closed state and the existing pipe  1 . 
         [0119]    Then, the valve is opened as shown in  FIG. 7A , and the operator further attaches a joint portion  31  of the boring machine  3  to the joint portion  81  of the branch pipe portion  27  using bolts. Thus, the branching unit  2  airtightly encloses a portion of the existing pipe  1 . 
         [0120]    After the enclosure, as the hole saw  4  is moved in the boring direction C 1  toward the existing pipe  1  while spinning the hole saw  4  as shown in  FIG. 7B , the center drill  41  cuts the pipe wall  12  of the existing pipe  1 , thereby positioning the hole saw  4  spinning about the center drill  41  with respect to the existing pipe  1 . Then, as shown in  FIG. 8A , a portion of the pipe wall  12  of the existing pipe  1  is cut off by the hole saw  4 , thus forming the opening  11 . 
         [0121]    After boring by the center drill  41  and the hole saw  4 , the hole saw  4  is moved in the retracting direction C 2  as shown in  FIG. 8B . 
         [0122]    Then, as the operator rotates the operation portion  67 , the worm wheel  62  which meshes with the worm  61  rotates, and the valve body  5  is guided by the guide portion  55  ( FIG. 5 ) by means of the driven gear  51  which meshes with the worm wheel  62  so as to be rotated in the valve-closing direction R 1  of the branch hole  28 , thus moving the valve body  5  in the valve-open position to the valve-closed position shown in  FIG. 9A . As the valve body  5  moves into the valve-closed position, the valve body  5  closely contacts the surface of the rubber ring  56 , thus shutting the branch hole  28 . 
         [0123]    After the shutting, the boring machine  3  is taken out from the branching unit  2  as shown in  FIG. 9B . After the boring machine  3  is taken out, a joint portion  91  of a branch pipe  90  is connected to the joint portion  81  of the branch pipe portion  27  as shown in  FIG. 10A  using bolts (not shown). 
         [0124]    After the branch pipe is completely finished (installed), the operator rotates the operation portion  67  in the valve-opening direction so as to rotate the valve body  5  in the valve-opening direction R 2  to the valve-open position shown in  FIG. 10B , thus allowing water through the branch pipe  90 . 
         [0125]    Note that if the driving gear unit  63  malfunctions, and the valve body  5  cannot be rotated in the valve-opening direction R 2 , the cover  66  can be removed and the driving gear unit  63  can be taken out. 
         [0126]    Next, other embodiments will be described. Each of the embodiments below will be described while focusing on the difference from Embodiment 1 described above. 
       Embodiment 2 
       [0127]    In Embodiment 2, a branch pipe portion  27 A is formed in a hemispherical shape as shown in  FIG. 11  for the connection of a branch pipe whose tip portion is formed in a hemispherical shape (so called an earthquake-proof joint). 
       Embodiment 3 
       [0128]    In Embodiment 3, as shown in  FIG. 13A , the driving gear unit  63  is formed by a pair of bevel gears  63   a  and  63   b  and a spur wheel  63   c.    
       Embodiment 4 
       [0129]    In Embodiment 4, as shown in  FIG. 13B , the driving gear unit  63  is formed by a single spur wheel. 
         [0130]    Incidentally, the driven gear may be provided in an outside region that is not surrounded by the loop-shaped contact portion. In such a case, the driven gear may be provided at one end of the valve body in the pipe axis direction. 
         [0131]    In such a case, however, the rotational force of the valve body from the driven gear is applied to one end portion of the valve body. Therefore, the valve body may not rotate smoothly. 
       Embodiment 5 
       [0132]    In view of this, in Embodiment 5, as shown in  FIG. 13C , the driven gears  51  are provided on opposite sides of the valve body  5  in the pipe axis direction. In such a case, however, a long shaft  63   d  is needed in the pipe axis direction in order to transfer rotation to the pair of driven gears  51  and  51 . 
         [0133]    Such a problem is solved when the driven gear  51  is formed in the region inside the contact portion  5   f  of the valve body  5 . 
         [0134]    Note that in the embodiments above, the valve body  5  including the driven gear  51  is formed as an integral part by stainless steel or ductile cast iron. Where the valve body  5  is formed by ductile cast iron, the valve body  5  is subjected to an appropriate coating such as powder coating. 
       Embodiment 6 
       [0135]    In Embodiment 6, as shown in  FIG. 14A , a pusher  40  is provided which threadedly engages with a through hole  21   h  formed in the first separate case  21 . A male screw is formed around the pusher  40 , and a female screw which threadedly engages with the male screw of the pusher  40  is formed on the through hole  21   h.    
         [0136]    A hemispherical pusher head  40   h  is formed integral with the pusher  40  on one side of the pusher  40  that is closer to the valve body  5 . 
         [0137]    When the valve body  5  is closed and a water pressure is applied after the opening  11  is formed in the existing pipe  1 , as shown in  FIG. 9B , the water pressure acts only upon the concave surface of the valve body  5 , and it may become difficult to open the valve body  5  of  FIG. 14B . 
         [0138]    In such a case, after the valve body  5  is pushed by the pusher head  40   h  of the pusher  40  as shown in  FIG. 14C  by rotating the pusher  40  of  FIG. 14B , the valve body  5  is turned in the opening direction. 
         [0139]    Note that the pusher  40  and the through hole  21   h  of the first separate case  21  with which the pusher  40  threadedly engages form a valve-opening assisting mechanism. 
       Embodiment 7 
       [0140]      FIGS. 15A to 15G  show Embodiment 7. 
         [0141]    As shown in  FIGS. 15A to 15D , the valve body  5  and a driven gear  51 A are formed separately. The driven gear  51 A shown in  FIGS. 15A and 15B  is formed by a stainless steel cast product. The driven gear  51 A is arc-shaped and strip-shaped. 
         [0142]    The valve body  5  shown in  FIGS. 15C and 15D  is made of ductile cast iron, and a groove  50  for the attachment of the driven gear  51 A is formed in the valve body  5 , extending in the circumferential direction R of the valve body  5 . As shown in  FIGS. 15E and 15F , the driven gear  51 A is attached to the groove  50  of the valve body  5 . 
         [0143]    Incidentally, as shown in  FIG. 4 , the helical teeth  62   a  of the worm wheel  62  are formed inclined with respect to the pipe axis direction L of the existing pipe  1  so as to mesh with the worm  61 . Therefore, as shown in  FIG. 15F , each tooth of the driven gear  51 A is formed inclined with respect to the pipe axis direction L. The driven gear  51 A of  FIG. 15F  and the worm  61  of  FIG. 2  illustrate the case of the right-handed thread. 
         [0144]    Here, if the “left-handed” specification where the valve body  5  closes when the operation portion  67  of  FIG. 2  is turned counterclockwise is employed, the members are formed as follows. The thread of the worm  61  is formed left-handed, and the helical teeth  62   a  of the worm wheel  62  which mesh with the worm  61  are formed with an inclination with respect to the pipe axis direction L that is opposite to that shown in  FIG. 4 . As shown in  FIG. 15G , the helical teeth of the driven gear  51 A are also formed with an inclination opposite to the driven gear  51 A shown in  FIG. 15F . 
         [0145]    Therefore, the left-handed and right-handed specifications can be accommodated while using the large valve body  5  as a common member. 
       Embodiment 8 
       [0146]      FIGS. 16 to 19  show Embodiment 8. 
         [0147]    As shown in  FIG. 16 , the driven gear  51 A is obtained by forming a plurality of through holes  7   c  in a plate material  7  made of stainless steel. The through holes  7   c  are formed inclined with respect to the pipe axis direction L, and are formed in parallel to one another. As shown in  FIGS. 16 and 17A , the plate material  7  is arc-shaped and strip-shaped. 
         [0148]    Note that the plate material  7  is bent so that the upper surface in  FIG. 16  is the convex surface  52 . 
         [0149]    The valve body  5  shown in  FIGS. 17B and 17C  is made of ductile cast iron, first and second attachment grooves  50   a  and  50   b  for the attachment of the driven gear  51 A are formed in the valve body  5  so as to extend in the circumferential direction R of the valve body  5 . 
         [0150]    As shown in  FIG. 17D , the plate material  7  is attached to the valve body  5 . 
         [0151]    As shown in  FIG. 16 , bolt insertion holes  7   a  are formed along the peripheral portion of the plate material  7 . As shown in  FIGS. 18A and 18B , the peripheral portion of the plate material  7  is attached to the first attachment groove  50   a,  and the plate material  7  is fixed to the first attachment groove  50   a  by bolts  7   b.    
         [0152]    On the other hand, as shown in  FIG. 18B , the second attachment groove  50   b  is formed deeper than the first attachment groove  50   a,  thereby allowing the tooth of the worm wheel  62  indicated by a two-dot chain line to enter the through hole  7   c  of the plate material  7  and mesh with the driven gear  51 A. Therefore, as shown in  FIG. 17E , the tooth  62   a  of the worm wheel  62  meshes with the driven gear  51 A. 
         [0153]    Here, as the plate material  7  shown in  FIG. 16  is reversed as shown in  FIG. 19 , the inclination of the driven gear  51 A with respect to the pipe axis direction L is reversed. Thus, the driven gear  51 A can mesh with the teeth  62   a  of the worm wheel  62  which are formed left-handed. 
         [0154]    Thus, the left-handed and right-handed specifications can both be accommodated by selectively using the front surface or the rear surface of the plate material  7 . 
         [0155]    While preferred embodiments have been described above with reference to the drawings, various obvious changes and modifications will readily occur to those skilled in the art upon reading the present specification. 
         [0156]    While the sealing case is divided into two pieces of the first and second separate cases in the embodiments described above, the sealing case may be divided into three or more pieces. 
         [0157]    The sealing case may be a cast product or may be formed by a steel plate. Where the sealing case is formed by a steel plate, the two separate cases may be integrated together into the sealing case by welding the first and second separate cases which are tentatively assembled together. 
         [0158]    Moreover, it is not necessary to provide the rubber gasket on the separate cases, but the rubber gasket may be provided on the valve body. 
         [0159]    The gear case portion may be provided on the side of the second separate case. 
         [0160]    Thus, such changes and modifications are deemed to fall within the scope of the present invention, which is defined by the appended claims. 
       INDUSTRIAL APPLICABILITY 
       [0161]    The branching unit for flow-undisrupted boring of the present invention can be used in providing a branch off of an existing pipe of water, gas, etc. 
       Description of Reference Numerals  
       [0162]      1 : Existing pipe 
         [0163]      2 : Branching unit 
         [0164]      3 : Boring machine 
         [0165]      4 : Hole saw 
         [0166]      5 : Valve body 
         [0167]      6 : Rotation mechanism 
         [0168]      7 : Plate material 
         [0169]      11 : Opening 
         [0170]      12 : Pipe wall 
         [0171]      20 : Sealing case 
         [0172]      21 : First separate case 
         [0173]      22 : Second separate case 
         [0174]      28 : Branch hole 
         [0175]      30 : Curved surface portion 
         [0176]      50 : Groove 
         [0177]      50   a:  First attachment groove 
         [0178]      50   b:  Second attachment groove 
         [0179]      51 : Driven gear 
         [0180]      52 : Convex surface 
         [0181]      53 : Concave surface 
         [0182]      56 : Rubber ring (an example of the valve seat) 
         [0183]      61 : Worm 
         [0184]      62 : Worm wheel 
         [0185]      63 : Driving gear unit 
         [0186]      65 : Bearing portion 
         [0187]      66 : Cover 
         [0188]      66   a:  Through hole 
         [0189]      67 : Operation portion 
         [0190]      70 : Gear case portion 
         [0191]      71 : Side wall 
         [0192]      72 : Flange 
         [0193]      73 : Depressed portion 
         [0194]      74   u:  Upper opening 
         [0195]      75   d:  Lower opening 
         [0196]      90 : Branch pipe 
         [0197]    R: Circumferential direction