Patent Publication Number: US-2017360278-A1

Title: Conduit switching piston, and endoscope

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of PCT/JP2016/080314 filed on Oct. 13, 2016 and claims benefit of Japanese Application No. 2016-033400 filed in Japan on Feb. 24, 2016, the entire contents of which are incorporated herein by this reference. 
    
    
     BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a conduit switching piston that is fitted and inserted in an advanceable and retractable manner into a cylinder to which a plurality of conduits are connected, and is configured to switch communication states of the plurality of conduits, and also relates to an endoscope. 
     2. Description of the Related Art 
     By inserting an elongated insertion portion of an endoscope into a subject, the endoscope can observe an inside of the subject using an observation lens provided at a distal end of the insertion portion. 
     Further, a configuration is known in which an air/water feeding nozzle is provided at the distal end of the insertion portion. The air/water feeding nozzle is a component that removes dirt on an observation lens by supplying a fluid to the observation lens and, for example, in the case of an endoscope for medical use, supplies a gas into a body cavity to expand the inside of the body cavity and secure an observation field of view within the body cavity. 
     The air/water feeding nozzle is connected to a distal end of an air/water feeding conduit provided inside the insertion portion. The air/water feeding conduit, for example, is branched into an air feeding conduit and a water feeding conduit inside the insertion portion. The air feeding conduit is connected to a gas supply source and a liquid supply source, respectively. The water feeding conduit is connected to a liquid supply source. 
     A configuration is also known in which a conduit switching piston is provided in an operation portion that is connected to the proximal end of the insertion portion of an endoscope. 
     The conduit switching piston is configured to switch a fluid to be supplied from the air/water feeding nozzle between a gas and a liquid, and also switches between a state in which fluid is supplied from the air/water feeding nozzle and a state in which the supply of fluid from the air/water feeding nozzle is cut off. 
     Inside the operation portion, the conduit switching piston is fitted and inserted in an advanceable and retractable manner into a cylinder that is connected at a position that is partway along the air feeding conduit and the water feeding conduit. 
     An upstream side and a downstream side of the air feeding conduit are each connected to the cylinder, and an upstream side and a downstream side of the water feeding conduit are each connected to the cylinder. 
     The conduit switching piston is configured to switch a communication state between the upstream side and downstream side of the air feeding conduit between a state in which communication is allowed and a state in which communication is cut off, and also switch the communication state between the upstream side and downstream side of the water feeding conduit between a state in which communication is allowed and a state in which communication is cut off. 
     Specifically, the conduit switching piston has a configuration that includes a shaft member, and a plurality of seal portions that are covered over the outer circumferential face of the shaft member and are configured to butt against the inner circumferential face of the cylinder in a watertight and airtight manner. 
     As is known, the conduit switching piston changes the contact positions of the plurality of seal portions with respect to the inner circumferential face of the cylinder by causing the shaft member to advance or retract with respect to the cylinder. 
     Thus, the conduit switching piston has a configuration that switches the communication state between the upstream side and downstream side of the air feeding conduit between a state in which communication is allowed and a state in which communication is cut off, and also switches the communication states between the upstream side and downstream side of the water feeding conduit between a state in which communication is allowed and a state in which communication is cut off. 
     More specifically, a through-hole is formed in the radial direction in the shaft member. Further, in the shaft member, a communication passage that communicates with the through-hole and also communicates with a leak hole provided in an upper portion of the shaft member is formed along the extending direction of the shaft member. 
     In a fluid cut-off state in which communication between the air feeding conduit and the water feeding conduit is cut off by the plurality of seal portions, because gas that is supplied to the cylinder from the upstream side of the air feeding conduit is released to the atmosphere via the through-hole, the communication passage and the leak hole, the supply of fluid from the air/water feeding nozzle is cut off. 
     In a leak-hole blockage state which is entered at a time that the leak hole is blocked by an operator when in the fluid cut-off state, a seal portion that blocks communication between the upstream side and downstream side of the air feeding conduit inside the cylinder is deformed by gas supplied into the cylinder from the upstream side of the air feeding conduit. 
     As a result, because the seal portion that blocks communication between the upstream side and downstream side of the air feeding conduit does not contact against the inner circumferential face of the cylinder, the upstream side and downstream side of the air feeding conduit communicate, and hence gas is discharged from the air/water feeding nozzle. 
     In a state in which the shaft member was moved inside the cylinder from the leak-hole blockage state, the contact positions of the plurality of seal portions with respect to the inner circumferential face of the cylinder change. 
     Consequently, as a result of the seal portion that blocks communication between the upstream side and downstream side of the water feeding conduit inside the cylinder separating from the cylinder inner circumferential face, the upstream side and downstream side of the water feeding conduit communicate with each other. 
     In addition, inside the cylinder, communication between the upstream side and downstream side of the air feeding conduit is cut off by a seal portion that blocks communication between the upstream side and the downstream side of the air feeding conduit. 
     As a result, because gas is supplied to the liquid supply source, a liquid that is pushed out from the liquid supply source by the gas is discharged from the air/water feeding nozzle through the water feeding conduit that is caused to communicate therewith. 
     In this case, generally a seal portion is used that has a configuration in which an O-shaped ring or the like is covered over the outer circumferential face of a shaft member made of stainless steel or the like. 
     However, because the O-shaped ring slidingly moves over the inner circumferential face of the cylinder accompanying movement of the shaft member, the position of the O-shaped ring is liable to be displaced with respect to the outer circumferential face of the shaft member. 
     Hence, a configuration is known in which a mounting-strength reinforcement portion for an O-shaped ring is provided on an outer circumferential face of a shaft member. 
     In U.S. Pat. No. 9,161,680 a configuration of a conduit switching piston is disclosed in which a shaft member is injection molded from resin or the like, a groove portion is formed along the shaft member in the outer circumferential face of the shaft member, and a sealing unit made of resin or the like is injection molded using a mold in the groove portion. 
     Note that the sealing unit includes a plurality of seal portions and a connecting portion configured to connect the seal portions along the extending direction thereof. 
     Because the sealing unit is formed integrally with the shaft member by being injection molded in the groove portion of the shaft member, the fixing strength with respect to the outer circumferential face of the shaft member is improved without using a strength reinforcement portion. 
     SUMMARY OF THE INVENTION 
     A conduit switching piston according to one aspect of the present invention is a conduit switching piston that is fitted and inserted in an advanceable and retractable manner into a cylinder to which a plurality of conduits are connected, the conduit switching piston being configured to switch communication states of the plurality of conduits, the conduit switching piston including: a shaft member having a cross-section in a radial direction that is formed in a circular shape; a plurality of seal portions formed having a set interval with respect to each other along an extending direction of the shaft member on an outer circumferential face of the shaft member, and having an outer circumference that elastically contacts an inner circumferential face of the cylinder; a pair of flat portions formed by cutting out a part of the outer circumferential face along the extending direction on each of two sides of the outer circumferential face with a central axis of the shaft member being interposed between the two sides, and having two edge portions facing each other on the outer circumferential face and extending along the extending direction; and a connecting portion configured to connect two seal portions among the plurality of seal portions which are adjacent along the extending direction, and formed on the pair of flat portions integrally with the seal portions. 
     Further, an endoscope according to one aspect of the present invention is equipped with the conduit switching piston according to claim  1 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view that schematically illustrates an endoscope apparatus including an endoscope in which a conduit switching piston of the present embodiment is provided; 
         FIG. 2  is a view that schematically illustrates a conduit configuration that communicates with an air/water feeding nozzle in the endoscope in  FIG. 1 , together with an air/water feeding switching apparatus and a water feeding tank; 
         FIG. 3  is a partial cross-sectional view that schematically illustrates the configuration of a conduit switching apparatus shown in  FIG. 2 ; 
         FIG. 4  is a partial cross-sectional view that schematically illustrates a state in which a leak hole of an air/water feeding button shown in  FIG. 3  is blocked, and a downstream-side air feeding conduit and an upstream-side air feeding conduit inside a cylinder are caused to communicate; 
         FIG. 5  is a partial cross-sectional view that schematically illustrates a state in which an air/water feeding button shown in  FIG. 3  is pushed down to thereby cut off communication between the downstream-side air feeding conduit and the upstream-side air feeding conduit inside the cylinder and to also cause a downstream-side water feeding conduit and an upstream-side water feeding conduit to communicate; 
         FIG. 6  is a perspective view illustrating a piston main body and a sealing unit in the conduit switching piston shown in  FIG. 3 ; 
         FIG. 7  is a perspective view in which, relative to  FIG. 6 , the sealing unit is removed and only the piston main body is illustrated; 
         FIG. 8  is a top view of the conduit switching piston in  FIG. 6  as seen from a VIII direction in  FIG. 6 ; 
         FIG. 9  is a side view of the conduit switching piston in  FIG. 6  as seen from an IX direction in  FIG. 6 ; 
         FIG. 10  is a view illustrating the conduit switching piston along an X-X line in  FIG. 8 , and which illustrates a cross-section of only one half of the conduit switching piston; 
         FIG. 11  is a cross-sectional view of the conduit switching piston along an XI-XI line in  FIG. 10 ; 
         FIG. 12  is a cross-sectional view of the conduit switching piston along an XII-XII line in  FIG. 10 ; 
         FIG. 13  is a cross-sectional view of the conduit switching piston along an XIII-XIII line in  FIG. 10 ; 
         FIG. 14  is a cross-sectional view of the conduit switching piston along an XIV-XIV line in  FIG. 10 ; 
         FIG. 15  is a top view of the piston main body in  FIG. 7  as seen from an XV direction in  FIG. 7 ; 
         FIG. 16  is a side view of the piston main body in  FIG. 7  as seen from an XVI direction in  FIG. 7 ; 
         FIG. 17  is a view illustrating the piston main body along an XVII-XVII line in  FIG. 15 , and which illustrates a cross-section of only one half of the piston main body; 
         FIG. 18  is a cross-sectional view of the piston main body along an XVIII-XVIII line in  FIG. 17 ; 
         FIG. 19  is a cross-sectional view of the piston main body along an XIX-XIX line in  FIG. 17 ; 
         FIG. 20  is a view illustrating a modification of the conduit switching piston in which the shape of a through-hole formed in the piston main body in  FIG. 10  is made elliptical, and which illustrates a cross-section of only one half of the conduit switching piston; and 
         FIG. 21  is an exploded perspective view of a piston main body on which a sealing unit of the conduit switching piston shown in  FIG. 3  is formed, an enclosing member, an urging spring and an air/water feeding button. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Embodiments of the present invention are described hereunder with reference to the accompanying drawings. It should be noted that the drawings are schematic ones in which the relationship between the thickness and width of each member, the thickness ratios of the members and the like are different from those of actual members. Naturally, the drawings include portions in which the dimensional relationships and ratios are different from one another.  FIG. 1  is a view that schematically illustrates an endoscope apparatus including an endoscope in which a conduit switching piston of the present embodiment is provided, and  FIG. 2  is a view that schematically illustrates a conduit configuration that communicates with an air/water feeding nozzle in the endoscope in  FIG. 1 , together with an air/water feeding switching apparatus and a water feeding tank. 
     As illustrated in  FIG. 1 , a principal part of an endoscope apparatus  101  is configured by including an endoscope  102  and peripheral apparatuses  100 . 
     The peripheral apparatuses  100  include a light source apparatus  133 , a video processor  134 , a monitor  136  and a water feeding tank  137  which are placed on a rack  130 . 
     A gas supply pump  133 P (see  FIG. 2 ) is provided inside the light source apparatus  133 . 
     A principal part of the endoscope  102  is configured by including an insertion portion  104  configured to be inserted into a subject, an operation portion  103  that is connected to a proximal end of the insertion portion  104 , a universal cord  105  that is extended from the operation portion  103 , and a connector  132  provided at an extending end of the universal cord  105 . The connector  132  is detachably attachable to the light source apparatus  133 . 
     The connector  132  and the video processor  134  are electrically connected by a connection cable  135 . 
     A tube  138  that is extended from the water feeding tank  137  is inserted through the inside of the connector  132  through a pipe sleeve  132   k  (see  FIG. 2 ) of the connector  132 . 
     The insertion portion  104  includes a distal end portion  106  that is located on a distal end side of the insertion portion  104 , a bending portion  107  that is operated to bend in, for example, the four directions of upward, downward, left and right by a bending operation knob  109  provided in the operation portion  103 , and a flexible tube portion  108  that is connected to a proximal end of the bending portion  107 . 
     An opening  110  of an unshown treatment instrument insertion channel that is provided inside the endoscope  102 , an observation lens  121 , an air/water feeding nozzle  123  and an illuminating window  125  and the like are provided in a distal end face  106   s  of the distal end portion  106 . 
     The air/water feeding nozzle  123  is configured to remove dirt adhering to the observation lens  121  by supplying a liquid toward the observation lens  121  upon an air/water feeding button  63  provided in the operation portion  3  being operated. 
     In addition, the air/water feeding nozzle  123  is configured to supply a gas into a subject to expand the inside of the subject to secure the observation field of view of the observation lens  121 . 
     The illuminating window  125  is configured to supply an illuminating light into the subject. Note that, instead of the illuminating window  125 , a light emitting device such as an LED may be provided in the distal end face  106   s.    
     As illustrated in  FIG. 2 , a distal end of an air/water feeding conduit  30  is connected to the air/water feeding nozzle  123 . 
     Inside the insertion portion  104 , the air/water feeding conduit  30  is branched into a downstream-side air feeding conduit (hereunder, referred to simply as “air feeding conduit”)  36  and a downstream-side water feeding conduit (hereunder, referred to simply as “water feeding conduit”)  38 . 
     Further, the proximal ends of the respective conduits  36  and  38  are connected to a cylinder  35  in the conduit switching apparatus  13  provided in the operation portion  3 . 
     A distal end of an upstream-side air feeding conduit (hereunder, referred to simply as “air feeding conduit”)  37  and a distal end of a downstream-side water feeding conduit (hereunder, referred to simply as “water feeding conduit”)  39  are connected to the cylinder  35 . 
     When the connector  132  is mounted to the light source apparatus  133 , a proximal end of the air feeding conduit  37  is connected to the gas supply pump  133   p  provided inside the light source apparatus  133 . 
     Inside the connector  132 , the tube  138  that is extended from the water feeding tank  137  is connected to the air feeding conduit  37 . That is, the air feeding conduit  37  is connected to the water feeding tank  137  through the tube  138 . 
     The proximal end of the water feeding conduit  39  is positioned inside the water feeding tank  137  by inserting the proximal end side of the water feeding conduit  39  through the tube  138 . 
     A principal portion of the conduit switching apparatus  13  is configured by including the cylinder  35 , and a conduit switching piston  10  that is fitted and inserted in an advanceable and retractable manner into the cylinder  35 . 
     Further, the conduit switching apparatus  13  is configured to switch a communication state between the air feeding conduit  37  and the air feeding conduit  36  between a state in which communication is allowed and a state in which communication is cut-off, and is configured to switch a communication state between the water feeding conduit  38  and the water feeding conduit  39  between a state in which communication is allowed and a state in which communication is cut-off. 
     Next, the configuration of the conduit switching apparatus  13  illustrated in  FIG. 2  will be described using  FIG. 3  to  FIG. 5 .  FIG. 3  is a partial cross-sectional view that schematically illustrates the configuration of the conduit switching apparatus illustrated in  FIG. 2 .  FIG. 4  is a partial cross-sectional view that schematically illustrates a state in which a leak hole in an air/water feeding button shown in  FIG. 3  is blocked to thereby cause a downstream-side air feeding conduit and an upstream-side air feeding conduit in the cylinder to communicate.  FIG. 5  is a partial cross-sectional view that schematically illustrates a state in which an air/water feeding button shown in  FIG. 3  is pushed down to thereby cut off communication between the downstream-side air feeding conduit and the upstream-side air feeding conduit in the cylinder, and cause a downstream-side water feeding conduit and an upstream-side water feeding conduit to communicate. 
     As illustrated in  FIG. 3  to  FIG. 5 , a mounting hole  34  is formed in an outer sheathing member  33  configuring the operation portion  103  so as to penetrate through the outer sheathing member  33  in an extending direction E, described later, and the cylinder  35  is fixed in the mounting hole  34 . 
     The cylinder  35  is formed in a substantially cylindrical shape having steps which, for example, is made from metal. In a side wall of the cylinder  35 , the aforementioned air feeding conduit  37 , water feeding conduit  39 , air feeding conduit  36  and water feeding conduit  38  are connected so as to communicate inside the cylinder  35  in the order of the air feeding conduit  36 , the air feeding conduit  37 , the water feeding conduit  38  and the water feeding conduit  39  from the upper side in  FIG. 3  toward the lower side. 
     A threaded portion is formed in the outer circumferential face of an opening portion of the cylinder  35 . The cylinder  35  is fixed to the outer sheathing member  33  so as to sandwich the outer sheathing member  33  from the inner and outer sides by screwing a pipe sleeve  41  into the threaded portion of the cylinder  35  from the outer side of the outer sheathing member  33 . 
     Note that a jig hole  42  into which a jig is inserted for rotating the pipe sleeve  41  when mounting the pipe sleeve  41  to the threaded portion of the cylinder  35  is provided in the outer circumference of the pipe sleeve  41 . 
     The pipe sleeve  41  has an upper flange  41   a  and a lower flange  41   b . The pipe sleeve  41  is fixed to the cylinder  35  in which the mounting hole  34  is sealed by an O-shaped ring  44  inside an annular groove  43  formed in the inner circumferential face of the mounting hole  34  being compressed by the lower flange  41   b . By this means, entry of a gas or a liquid into the operation portion  103  is prevented. 
     The conduit switching piston  10 , for example, includes a piston main body  45  that is a shaft member made from a resin. The piston main body  45  is formed, for example, by injection molding. 
     Inside the piston main body  45 , a communication passage  46  is formed along the extending direction E of the piston main body  45 . 
     Further, at the lower end in the extending direction E of the communication passage  46  of the piston main body  45  (hereunder, referred to simply as “lower end”), a through-hole  47  is formed that communicates with the communication passage  46  and also penetrates through the piston main body  45  in a radial direction K of the piston main body  45 . 
     On an outer circumferential face  45   g  of the piston main body  45 , a ring-shaped seal portion  54  of a sealing unit  50  (see  FIG. 6 ) is formed integrally with the piston main body  45  by injection molding at a position in the vicinity of an upper portion in the extending direction E of the through-hole  47  (hereunder, referred to simply as “upper portion”). The seal portion  54  is made, for example, from a resin and is configured to elastically contact an inner circumferential face  35   n  of the cylinder  35 . 
     Further, on the outer circumferential face  45   g  of the piston main body  45 , a slider  45   w  having a face that butts against the inner circumferential face  35   n  is formed integrally with the piston main body  45  at a position that is upward in the extending direction E relative to the seal portion  54  (hereunder, referred to simply as “upward”). 
     Note that the slider  45   w  is a member configured to prevent the piston main body  45  from becoming misaligned with respect to the cylinder  35  by butting against the inner circumferential face  35   n.    
     In addition, on the outer circumferential face  45   g , a ring-shaped seal portion  53  of the sealing unit  50  (see  FIG. 6 ) that, for example, is made from a resin and is configured to elastically contact the inner circumferential face  35   n  of the cylinder  35  is formed integrally with the piston main body  45  by injection molding at an upper portion of the slider  45   w . That is, the seal portion  53  is disposed at a position that is separated by a set interval E 1  (see  FIG. 6 ) in the upward direction from the seal portion  54  in the extending direction E. 
     On the outer circumferential face  45   g  of the piston main body  45 , a ring-shaped seal portion  55  of the sealing unit  50  (see  FIG. 6 ) is formed integrally with the piston main body  45  by injection molding at a position in the vicinity of a lower portion in the extending direction E of the through-hole  47  (hereunder, referred to simply as “lower portion”). 
     The seal portion  55 , for example, is made from a resin and is configured to elastically contact the inner circumferential face  35   n  of the cylinder  35 . That is, the seal portion  55  is disposed at a position that is separated in a downward direction in the extending direction E (hereunder, referred to simply as “downward”) by a set interval E 2  (see  FIG. 6 ) from the seal portion  54  in the extending direction E. 
     Further, on the outer circumferential face  45   g  of the piston main body  45 , a slider  45   v  having a face that butts against the inner circumferential face  35   n  is formed integrally with the piston main body  45  in the vicinity of the lower portion of the seal portion  55 . 
     Note that the slider  45   v  is a member configured to prevent the piston main body  45  from becoming misaligned with respect to the cylinder  35  by butting against the inner circumferential face  35   n.    
     In addition, on the outer circumferential face  45   g  of the piston main body  45 , a ring-shaped seal portion  56  of the sealing unit  50  (see  FIG. 6 ) is formed integrally with the piston main body  45  by injection molding at a position that is downward relative to the slider  45   v.    
     The seal portion  56  is made, for example, from a resin and is configured to elastically contact the inner circumferential face  35   n  of the cylinder  35 . That is, the seal portion  56  is disposed at a position that is separated by a set interval E 3  in the downward direction from the seal portion  55  (see  FIG. 6 ) in the extending direction E. 
     Further, a cylindrical piston stopper  60  that is made, for example, from a rigid member is provided at the outer circumference on the upper portion side of the piston main body  45 . 
     The piston stopper  60  has an inward flange portion  60   a , and an outward flange portion  45   a  provided at an upper portion relative to the seal portion  53  on the outer circumferential face  45   g  of the piston main body  45  freely butts against the inward flange portion  60   a.    
     An urging spring  61  configured by a coil spring is interposed between a top face in the extending direction E of the inward flange portion  60   a  (hereunder, referred to simply as “top face”) and a bottom face in the extending direction E of the air/water feeding button  63  (hereunder, referred to simply as “bottom face”) that is screwingly attached to a top end in the extending direction E of the piston main body  45  (hereunder, referred to simply as “top end”). 
     The urging force of the urging spring  61  urges the air/water feeding button  63  upward and urges the piston stopper  60  downward. 
     As illustrated in  FIG. 3 , in a natural state, the top face of the outward flange portion  45   a  is butted against the bottom face of the inward flange portion  60   a , and as a result the piston main body  45  is locked. 
     In addition, at the outer circumference of the piston stopper  60 , an enclosing member  62  that is made, for example, from rubber, is provided integrally with the piston stopper  60 . 
     An inward protrusion portion  62   a  provided at the lower end of the enclosing member  62  is engaged with the bottom face of the upper flange  41   a  of the pipe sleeve  41 . Further, a leak hole  64  that communicates with the communication passage  46  is formed at a center portion of the air/water feeding button  63 . 
     Next, an operation for switching the communication state of the air feeding conduit and an operation for switching the communication state of the water feeding conduit using the conduit switching apparatus  13  configured as described above will be briefly described. 
     First, as illustrated in  FIG. 3 , in a natural state the piston main body  45  is being pushed upward in the extending direction E by the urging force of the urging spring  61 . At this time, an upward position of the piston main body  45  is defined by the top face of the outward flange portion  45   a  being butted against the bottom face of the inward flange portion  60   a.    
     Further, communication between the water feeding conduit  39  and the water feeding conduit  38  inside the cylinder  35  is cut off by the seal portion  56 . 
     In addition, communication between the air feeding conduit  37  and the air feeding conduit  36  inside the cylinder  35  is cut off by the seal portions  54  and  55 . 
     Therefore, a gas that is supplied into the cylinder  35  through the air feeding conduit  37  from the gas supply pump  133 P flows into the through-hole  47  and passes through the communication passage  46  and flows out into the atmosphere from the leak hole  64 . 
     Next, as illustrated in  FIG. 4 , when the leak hole  64  is blocked by a finger F of an operator, the seal portion  54  is bent upward by the gas that is supplied into the cylinder  35 , and the seal portion  54  separates from the inner circumferential face  35   n  of the cylinder  35 . 
     As a result, because the air feeding conduit  37  and the air feeding conduit  36  communicate, the gas flows into the air feeding conduit  36  through the cylinder  35  from the air feeding conduit  37 , and thereafter the gas flows into the air/water feeding conduit  30  from the air feeding conduit  36  and is discharged from the air/water feeding nozzle  123 . 
     Note that, in the state illustrated in  FIG. 4 , communication between the water feeding conduit  39  and the water feeding conduit  38  inside the cylinder  35  remains cut off by the seal portion  56 . 
     Next, as illustrated in  FIG. 5 , when an operation is performed to push the air/water feeding button  63  downward in a state in which the leak hole  64  is blocked by the finger F of the operator, inside the cylinder  35  the piston main body  45  is moved downward in the extending direction E against the urging force of the urging spring  61 , and the outward flange portion  45   a  separates from the inward flange portion  60   a  in the downward direction. 
     As a result, because the seal portion  54  is pressed against a tapered face  35   a  formed in the inner circumferential face  35   n  of the cylinder  35  and elastically deforms and is flattened, communication between the air feeding conduit  37  and the air feeding conduit  36  inside the cylinder  35  is cut off. 
     In addition, accompanying downward movement of the piston main body  45 , the seal portion  56  separates from the inner circumferential face  35   n  of the cylinder  35 . As a result, the water feeding conduit  39  and the water feeding conduit  38  communicate with each other. 
     Hence, because the leak hole  64  is blocked and communication between the air feeding conduit  37  and the air feeding conduit  36  is cut off by the seal portion  54 , the gas supplied from the gas supply pump  133 P is supplied into the water feeding tank  137  through the tube  138  as illustrated in  FIG. 2 . 
     Consequently, the liquid inside the water feeding tank  137  is pushed out, and liquid that flowed into the cylinder  35  from the water feeding conduit  39  flows into the water feeding conduit  38  and furthermore flows into the air/water feeding conduit  30  and is thereafter discharged from the air/water feeding nozzle  123 . 
     Next, the specific configuration of the conduit switching piston  10  illustrated in  FIG. 2  to  FIG. 5  is described using  FIG. 6  to  FIG. 19 . 
       FIG. 6  is a perspective view illustrating a piston main body and a sealing unit in the conduit switching piston illustrated in  FIG. 3 , and  FIG. 7  is a perspective view in which, relative to  FIG. 6 , the sealing unit is removed and only the piston main body is illustrated; 
       FIG. 8  is a top view of the conduit switching piston in  FIG. 6  as seen from a VIII direction in  FIG. 6 ,  FIG. 9  is a side view of the conduit switching piston in  FIG. 6  as seen from an IX direction in  FIG. 6 , and  FIG. 10  is a view illustrating the conduit switching piston along an X-X line in  FIG. 8 , and which illustrates a cross-section of only one half of the conduit switching piston. 
     In addition,  FIG. 11  is a cross-sectional view of the conduit switching piston along an XI-XI line in  FIG. 10 ,  FIG. 12  is a cross-sectional view of the conduit switching piston along an XII-XII line in  FIG. 10 ,  FIG. 13  is a cross-sectional view of the conduit switching piston along an XIII-XIII line in  FIG. 10 , and  FIG. 14  is a cross-sectional view of the conduit switching piston along an XIV-XIV line in  FIG. 10 . 
       FIG. 15  is a top view of the piston main body in  FIG. 7  as seen from an XV direction in  FIG. 7 ,  FIG. 16  is a side view of the piston main body in  FIG. 7  as seen from an XVI direction in  FIG. 7 , and  FIG. 17  is a view illustrating the piston main body along an XVII-XVII line in  FIG. 15 , and which illustrates a cross-section of only one half of the piston main body. 
     In addition,  FIG. 18  is a cross-sectional view of the piston main body along an XVIII-XVIII line in  FIG. 17 , and  FIG. 19  is a cross-sectional view of the piston main body along an XIX-XIX line in  FIG. 17 . 
     As illustrated in  FIG. 7  and  FIG. 15  to  FIG. 17 , a flat portion  20  is formed on the outer circumferential face  45   g  of the piston main body  45 . 
     The flat portion  20  has two edge portions  21  and  22  that face each other on the outer circumferential face  45   g  and extend along the extending direction E, and is formed from the outward flange portion  45   a  to the lower end of the piston main body  45  along the extending direction E. 
     Specifically, as illustrated in  FIG. 7  and  FIG. 15  to  FIG. 19 , the flat portion  20  is formed with respect to the outer circumferential face  45   g  of the piston main body  45  by one part of the outer circumferential face  45   g  of the piston main body  45  whose cross-section in a radial direction K was formed in an approximately circular shape being cut out so that the flat portion  20  is parallel with a penetrating direction T of the through-hole  47 . 
     Further, the flat portion  20  is formed at a position on the outer circumferential face  45   g  that is deviated by approximately 90° in the circumferential direction of the piston main body  45  from the through-hole  47 . 
     Note that the flat portion  20  need not necessarily be formed at a position that is deviated by 90° in the circumferential direction from the through-hole  47 . However, as described later, forming the flat portion  20  at a position that is deviated by 90° is preferable because, when the sealing unit  50  is injection molded using a mold on the outer circumferential face  45   g  of the piston main body  45 , the piston main body  45  on which the sealing unit  50  is integrally formed can be easily taken out from the mold. 
     The flat portion  20  is also formed at the above described positions of the sliders  45   w  and  45   v  that butt against the inner circumferential face  35   n  of the cylinder  35 , and needless to say the flat portion  20  is formed on the inner side in the radial direction K relative to the faces of the sliders  45   w  and  45   v  that butt against the inner circumferential face  35   n . That is, regions of the sliders  45   w  and  45   v  at which the flat portion  20  is formed do not butt against the inner circumferential face  35   n.    
     Further, as illustrated in  FIG. 16  to  FIG. 19 , with respect to the outer circumferential face  45   g  of the piston main body  45 , the flat portion  20  is formed on two sides with a central axis J along the extending direction E of the piston main body  45  being interposed between the two sides. 
     The sealing unit  50  is configured to have an elastic force by including the above described plurality of ring-shaped seal portions  53  to  56 , and a connecting portion  59  that is formed integrally with the seal portions  53  to  56  and connects the seal portions  53  and  54 , the seal portions  54  and  55 , and the seal portions  55  and  56  that are respectively adjacent along the extending direction E. 
     Note that the sealing unit  50  is integrally formed on the outer circumferential face  45   g  of the piston main body  45  by injection molding a resin or the like into a mold with respect to the piston main body  45  that is formed from resin that was inserted into the mold. 
     Note that a material having self-adhesiveness with respect to the piston main body  45  is preferable as the material forming the sealing unit  50 . 
     For example, in a case where the piston main body  45  is formed from polycarbonate, the sealing unit  50  is preferably formed from a polyester-based elastomer resin. 
     Further, in a case where the piston main body  45  is formed from polypropylene, the sealing unit  50  is preferably formed from a styrene-based thermoplastic elastomer resin. 
     In addition, in a case where the piston main body  45  is formed from a polysulfone, it has been found based on experimental results that the sealing unit  50  is preferably formed from silicon. 
     Consequently, since an adhesive need not be used for forming the sealing unit  50  on the outer circumferential face  45   g  of the piston main body  45 , the molding cost and processing cost of the conduit switching piston  10  can be reduced. 
     Note that the material forming the sealing unit  50  is not limited to the above described materials, and may be any material that has self-adhesiveness with respect to the piston main body  45  and also has an elastic force. 
     As described above, the connecting portion  59  is a part that connects the plurality of seal portions  53  to  56  in the sealing unit  50 , and as illustrated in  FIG. 6  and  FIG. 8  to  FIG. 14 , is formed with respect to the flat portion  20 . 
     That is, by means of the flat portion  20 , the connecting portion  59  is formed on the outer circumferential face  45   g  with a large contact area with respect to the outer circumferential face  45   g , and hence the adhesiveness of the connecting portion  59  is enhanced. 
     Note that, as illustrated in  FIG. 11  to  FIG. 14 , the connecting portion  59  is formed so as to be located within cut-out regions L, M, N and O formed with respect to the flat portion  20  by cutting out part of the outer circumferential face  45   g  of the piston main body  45 . 
     Further, because the connecting portion  59  is formed in the flat portion  20 , as illustrated in  FIG. 9 , the connecting portion  59  is formed so as to have a clearance between the inner circumferential face  35   n  of the cylinder  35  and the connecting portion  59 . 
     Note that, as described above, on the outer circumferential face  45   g  of the piston main body  45 , the sliders  45   v  and  45   w  are members configured to butt against the inner circumferential face  35   n  of the cylinder  35 . 
     However, because the flat portion  20  is formed at the sliders  45   v  and  45   w  also, as illustrated in  FIG. 9 , the connecting portion  59  formed at the flat portion  20  of the sliders  45   v  and  45   w  is also formed at the flat portion  20  so as to have respective clearances P and Q with respect to the inner circumferential face  35   n.    
     Thus, the connecting portion  59  is prevented from inhibiting the slidability of the sliders  45   v  and  45   w  with respect to the inner circumferential face  35   n.    
     Furthermore, as illustrated in  FIG. 13  and  FIG. 14 , the cross-sectional shape of the connecting portion  59  formed at the flat portion  20  of the sliders  45   v  and  45   w  preferably has a rectangular shape. 
     This is because, if the cross-sectional shape of the connecting portion  59  has a rectangular shape, as illustrated in  FIG. 11  and  FIG. 12 , in comparison to a case where the cross-sectional shape is formed in a semicircular shape, places that have a thin edge cannot arise in the connecting portion  59  after being formed in the flat portion  20 . It is therefore difficult for the connecting portion  59  to detach from the flat portion  20 . 
     Note that, with regard to the cross-sectional shape of the connecting portion  59  to be formed in the flat portion  20  at regions other than the sliders  45   v  and  45   w  also, the connecting portion  59  may be formed to be a rectangular shape. 
     Further, as described above, on the outer circumferential face  45   g  of the piston main body  45 , the flat portion  20  is formed at a position that is deviated in the circumferential direction relative to the through-hole  47 . 
     Consequently, when the connecting portion  59  is injection molded with respect to the flat portion  20 , the material forming the sealing unit  50  is prevented from leaking out from the through-hole  47 , and furthermore the shape of the mold can be made a simple shape since there is no necessity to form the mold in a shape that avoids the through-hole  47 . 
     For these reasons, the occurrence of molding defects or burrs in the sealing unit  50  can be prevented, and the mold can be manufactured at a low cost. 
     In addition, because the flat portion  20  is formed on two sides of the outer circumferential face  45   g  of the piston main body  45  with the central axis J being interposed between the two sides, the connecting portion  59  is also formed on both sides with the central axis J being interposed between the two sides. 
     That is, since the material forming the connecting portion  59  can be filled into the mold from both sides, the filling property is enhanced, and in addition, because it is difficult for molding defects to occur in the connecting portion  59 , the manufacturing yield of the conduit switching piston  10  increases. 
     Note that, if the aforementioned advantage is to be disregarded, the connecting portion  59  and the flat portion  20  may be formed at one place on only one side with respect to the outer circumferential face  45   g  of the piston main body  45  as in the conventional configuration. 
     The remaining configuration of the conduit switching apparatus  13  is the same as the configuration of the conventional conduit switching apparatus  13 . 
     Thus, in the present embodiment a configuration has been described in which, in the conduit switching piston  10 , the flat portion  20  is formed along the extending direction E on the outer circumferential face  45   g  of the piston main body  45 . 
     Further, it has been described that after the sealing unit  50  is injection molded onto the outer circumferential face  45   g , the connecting portion  59  configured to connect the plurality of ring-shaped seal portions  53  to  56  along the extending direction E is formed on the flat portion  20 . 
     Consequently, it is not necessary to form a groove portion for forming the sealing unit  50  in the outer circumferential face  45   g  as in the conventional configuration. 
     Therefore, the shape of a mold to be used when forming the sealing unit  50  is simple and the sealing unit  50  can be formed inexpensively, and furthermore a large contact area of the connecting portion  59  with respect to the flat portion  20  can be secured. Consequently, the sealing unit  50  can be injection molded so that the sealing unit  50  is firmly bonded to the outer circumferential face  45   g.    
     Further, because the flat portion  20  is formed at a position on the outer circumferential face  45   g  that is deviated in the circumferential direction of the piston main body  45  from the through-hole  47 , the shape of a mold for forming the sealing unit  50  can be simplified and the mold can be made at a low cost. 
     In addition, it has been described that the connecting portion  59  is formed on the flat portion  20  so as to have a clearance with respect to the inner circumferential face  35   n  of the cylinder  35 , and that a cross-section of the connecting portion that is formed on the flat portion  20  of the sliders  45   v  and  45   w  is formed in a rectangular shape. 
     Therefore, because the connecting portion  59  does not contact the inner circumferential face  35   n , the sliding resistance of the piston main body  45  is not increased by the connecting portion  59 . 
     As described in the foregoing, the conduit switching piston  10  and the endoscope  102  can be provided in which the conduit switching piston  10  has a configuration in which the plurality of seal portions  53  to  56  are integrally formed with respect to the outer circumferential face  45   g  of the piston main body  45  inexpensively and with an enhanced fixing strength. 
     A modification will now be described using  FIG. 20 .  FIG. 20  is a view illustrating a modification of the conduit switching piston in which the shape of a through-hole formed in the piston main body in  FIG. 10  is made elliptical, and which illustrates a cross-section of only one half of the conduit switching piston. 
     As illustrated in  FIG. 20 , the shape of the through-hole  47  may be made an elliptical shape that has the same area as a circle and in which the long axis is along the extending direction E. 
     According to this configuration, while keeping the same amount with respect to the air feeding amount for which the through-hole  47  is used, as illustrated in  FIG. 10  and  FIG. 20 , it is possible to secure a wall thickness Y 2  in the radial direction K of a region in which the through-hole  47  is formed in the piston main body  45  that is greater than a wall thickness Y 1  in the case of the circular through-hole  47  (Y 2 &gt;Y 1 ). Thus, the strength of the piston main body  45  can be further improved. 
     Another modification will be described hereunder using  FIG. 21 .  FIG. 21  is an exploded perspective view of a piston main body on which the sealing unit of the conduit switching piston shown in  FIG. 3  is formed, an enclosing member, an urging spring and an air/water feeding button. 
     In the present embodiment described above, it is described that the air/water feeding button  63  is fixed by being screwingly attached to the outer circumference of the top end of the piston main body  45 . 
     Regardless of the above description, as illustrated in  FIG. 21 , after the piston main body  45  on which the sealing unit  50  is formed, the enclosing member  62 , the urging spring  61  and the air/water feeding button  63  are assembled, the air/water feeding button  63  may be fixed by ultrasound welding to the top end of the piston main body  45 . 
     According to this configuration, not only is it not necessary to use an adhesive for fixing the air/water feeding button  63 , the number of components can also be reduced relative to a structure in which the air/water feeding button  63  is fixed via an unshown plurality of components to the top end of the piston main body  45 , and hence the manufacturing cost can be reduced. 
     Note that, in the foregoing present embodiment, it is described that the conduit switching piston  10  switches communication states of air feeding conduits and water feeding conduits. 
     Regardless of the above description, it is needless to say that the conduit switching piston  10  is also applicable to a configuration that switches communication states of other conduits, and is also applicable to a configuration that switches communication states of three or more conduits.