Patent Publication Number: US-2023139315-A1

Title: Gate valve

Description:
TECHNICAL FIELD 
     The present invention relates to a gate valve to be disposed between a pair of chambers in, for example, a semiconductor manufacturing apparatus. More specifically, the present invention relates to a gate valve to be disposed between a first chamber such as a process chamber and a second chamber such as a transfer chamber, the first chamber and the second chamber being adjacent to each other, the gate valve being usable for causing a first opening communicating with the first chamber and a second opening communicating with the second chamber to communicate with each other and for opening and closing the first opening and the second opening separately. 
     BACKGROUND ART 
     Known examples of such a gate valve include gate valves disclosed in PTL 1 and PTL 2. The existing gate valves include a valve assembly including a pair of valve plates, a valve shaft having a tip end portion to which the valve assembly is attached, and a drive mechanism connected to the valve shaft. Then, by operation of the valve shaft driven by the drive mechanism, the existing gate valves are capable of moving the valve assembly sequentially to a retracted position where such a first opening and such a second opening communicate with each other, and a first closed position and a second closed position where the pair of valve plates come into contact with the first opening and the second opening separately to airtightly close the openings. 
     Meanwhile, the drive mechanism of each existing gate valve guides the operation of the valve shaft for moving the valve assembly to each position from both the left and right sides. Thus, one cam groove is provided on each of both the left and right sides of the valve shaft so as to extend in an up-down direction, that is, the height direction along the axis of the valve shaft. 
     However, to enable the valve assembly to move sequentially to each position by using the one cam groove extending in the up-down direction in this manner, the drive mechanism is increased in height, thus increasing the height of the entire gate valve. 
     When the height of the entire gate valve is increased in this manner, there may be a case in which the gate valve cannot be installed due to the space, between a pair of chambers, for installing the gate valve. Thus, also in terms of reducing the size of the entire equipment, it is desirable to minimize the height of the entire gate valve. 
     CITATION LIST 
     Patent Literature 
     [PTL 1]: Japanese Unexamined Patent Application Publication No. 2004-197769 
     [PTL 2]: Japanese Unexamined Patent Application Publication No. 2015-017655 
     SUMMARY OF INVENTION 
     Technical Problem 
     Thus, a technical object of the present invention is to provide a gate valve to be disposed between chambers adjacent to each other, the gate valve being usable for causing openings communicating with the respective chambers to communicate with each other and for opening and closing the openings separately by operation of a valve shaft driven by a drive mechanism to move a pair of valve plates attached to the valve shaft, the height of the entire gate valve being able to be reduced. 
     Solution to Problem 
     To solve the problem, a gate valve according to the present invention is disposed between a first chamber and a second chamber adjacent to each other, the gate valve being usable for causing a first opening communicating with the first chamber and a second opening communicating with the second chamber to communicate with each other and for opening and closing the first opening and the second opening separately. The gate valve includes: a bonnet partitioning off an upper side and a lower side; a valve shaft passing through the bonnet in a direction along an axis extending in an up-down direction, the valve shaft having a tip end portion disposed above the bonnet and a base end portion disposed below the bonnet; a valve assembly formed by attaching a first valve plate and a second valve plate back to back to the tip end portion of the valve shaft; and a valve drive mechanism connected to the base end portion of the valve shaft, the valve drive mechanism being configured to move the valve assembly by operation of the valve shaft. The valve drive mechanism includes an air cylinder including a first drive rod and a second drive rod capable of being driven separately, the air cylinder being fixedly provided to the bonnet, and a power transmission mechanism connecting the valve shaft and both the first drive rod and the second drive rod, the power transmission mechanism being configured to transmit driving force of the air cylinder to the valve shaft and is thus capable of moving the valve assembly in the direction along the axis and a thickness direction orthogonal to the axis to move the valve assembly to a first closed position for closing the first opening with the first valve plate, a second closed position for closing the second opening with the second valve plate, and a retracted position for causing the openings to communicate with each other. The power transmission mechanism includes a first cam frame connected to the first drive rod to operate together with the first drive rod, a second cam frame connected to the second drive rod to operate together with the second drive rod, a lever member attached to the base end portion of the valve shaft, and a first opening and closing mechanism and a second opening and closing mechanism configured to separately cause the valve assembly to reciprocate in the thickness direction. The first opening and closing mechanism includes a first cam groove provided in one of the first cam frame and the lever member, and a first cam roller provided on another of the first cam frame and the lever member, the first cam roller being slidably fitted into the first cam groove, and the second opening and closing mechanism includes a second cam groove provided in one of the second cam frame and the lever member, and a second cam roller provided on another of the second cam frame and the lever member, the second cam roller being slidably fitted into the second cam groove. The first cam roller reciprocates together with reciprocation of the first drive rod so as to follow the first cam groove, thus causing the valve assembly to reciprocate between a position occupied by the retracted position and a position occupied by the first closed position in the thickness direction, and the second cam roller reciprocates together with reciprocation of the second drive rod so as to follow the second cam groove, thus causing the valve assembly to reciprocate between the position occupied by the retracted position and a position occupied by the second closed position in the thickness direction. 
     In the present invention, preferably, the gate valve has a width direction orthogonal to both the direction along the axis and the thickness direction, and at the first opening and closing mechanism and the second opening and closing mechanism, the first and second cam frames are disposed on both sides of the lever member in the width direction and are provided on both the sides of the lever member so as to be adjacent to each other in the thickness direction. More preferably, the first cam groove has a first recess for letting the first cam roller therein when the valve assembly is moved to the second closed position, and the second cam groove has a second recess for letting the second cam roller therein when the valve assembly is moved to the first closed position. 
     In addition, in the present invention, for example, the valve assembly may be capable of further moving to an intermediate position located between the position occupied by the retracted position and the position occupied by the first and second closed positions in the direction along the axis, the power transmission mechanism may further include a first spring member and a second spring member provided between the lever member and both the first drive rod and the second drive rod to transmit driving force of the first drive rod to the lever member through the first spring member and to transmit driving force of the second drive rod to the lever member through the second spring member, the power transmission mechanism may further include a stopper configured to, when the valve assembly reaches the intermediate position from the retracted position by driving of the air cylinder, stop operation of the lever member in the direction along the axis and allow the lever member to be operated in the thickness direction by the opening and closing mechanisms, and in a state in which the operation of the lever member in the direction along the axis is stopped by the stopper, the opening and closing mechanisms may be configured to separately cause the valve assembly to reciprocate between the intermediate position and the first and second closed positions when the first and second drive rods are separately driven. 
     Then, preferably, the intermediate position is located at the position occupied by the first and second closed positions in the direction along the axis. In addition, preferably, the gate valve has a width direction orthogonal to both the direction along the axis and the thickness direction, at the first opening and closing mechanism and the second opening and closing mechanism, the first and second cam frames are disposed on both sides of the lever member in the width direction and are provided on both the sides of the lever member so as to be adjacent to each other in the thickness direction, and a first support frame and a second support frame relatively movably connected to the lever member are respectively attached to the first drive rod and the second drive rod, and a pair of the first cam frames are provided upright in the direction along the axis from the first support frame, the first support frame and the lever member being connected by the first spring member between the pair of the first cam frames in the width direction, and a pair of the second cam frames are provided upright in the direction along the axis from the second support frame, the second support frame and the lever member being connected by the second spring member between the pair of the second cam frames in the width direction. 
     Then, more preferably, the first cam groove has a first recess for letting the first cam roller therein when the valve assembly is moved from the intermediate position to the second closed position, and the second cam groove has a second recess for letting the second cam roller therein when the valve assembly is moved from the intermediate position to the first closed position. 
     In addition, in the present invention, the power transmission mechanism may further include a guide frame fixedly provided to the bonnet, and first and second guide mechanisms provided between the guide frame and the first and second cam frames, the first and second guide mechanisms being configured to guide the cam frames so as to move in the direction along the axis, and the first guide mechanism may include a first guide groove provided, along the axis, in one of the guide frame and the first cam frame, and a first guide roller provided on another of the guide frame and the first cam frame, the first guide roller being slidably fitted into the first guide groove, and the second guide mechanism may include a second guide groove provided, along the axis, in one of the guide frame and the second cam frame, and a second guide roller provided on another of the guide frame and the second cam frame, the second guide roller being slidably fitted into the second guide groove. 
     Then, preferably, the guide frame is disposed on both the sides of the lever member in the width direction so as to be located outside, in the width direction, the first and second cam frames provided adjacent to each other in the thickness direction. In addition, more preferably, the air cylinder is disposed on both the sides of the lever member in the width direction so as to be drooped from the bonnet along the axis, and the guide frame is disposed inside each air cylinder in the width direction, the first drive rod and the second drive rod are provided to each of a pair of the air cylinders so as to be adjacent to each other in the thickness direction, and the first drive rods of the pair of the air cylinders are attached to respective end portions of the first support frame, and the second drive rods of the pair of the air cylinders are attached to respective end portions of the second support frame. 
     Advantageous Effects of Invention 
     The gate valve according to the present invention includes the first opening and closing mechanism and the second opening and closing mechanism including the respective separate cam grooves to separately cause the valve assembly to reciprocate, in the thickness direction, between the position occupied by the retracted position and the position occupied by the first closed position and between the position occupied by the retracted position and the position occupied by the second closed position. Thus, the present invention enables a reduction in the height of the first and second cam frames including the respective cam grooves and thus enables a reduction in the height of the entire gate valve. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is an external view illustrating an embodiment of a gate valve according to the present invention. 
         FIG.  2    is an exploded perspective view in which a valve drive mechanism is divided into air cylinders and a power transmission mechanism. 
         FIG.  3    is a sectional view of a main part of the air cylinder in  FIG.  2   . 
         FIG.  4    is an exploded perspective view of the power transmission mechanism in  FIG.  2   . 
         FIG.  5    is a schematic view illustrating the relationship between guide rollers and guide grooves when a valve assembly is located at a retracted position. 
         FIG.  6    is a schematic view illustrating the positional relationship between cam rollers and cam grooves when the valve assembly is located at the retracted position. 
         FIG.  7    is a schematic view illustrating the relationship between the guide rollers and the guide grooves when the valve assembly is located at an intermediate position. 
         FIG.  8    is a schematic view illustrating the positional relationship between the cam rollers and the cam grooves when the valve assembly is located at the intermediate position. 
         FIG.  9    is a schematic view illustrating the relationship between the guide rollers and the guide grooves when the valve assembly is located at a first closed position. 
         FIG.  10    is a schematic view illustrating the positional relationship between the cam rollers and the cam grooves when the valve assembly is located at the first closed position. 
         FIG.  11    is a schematic view illustrating the relationship between the guide rollers and the guide grooves when the valve assembly is located at a second closed position. 
         FIG.  12    is a schematic view illustrating the positional relationship between the cam rollers and the cam grooves when the valve assembly is located at the second closed position. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     As illustrated in  FIGS.  5  to  12   , a gate valve  1  illustrated in  FIG.  1   , which is an embodiment of the present invention, is disposed, in, for example, a semiconductor manufacturing apparatus, between a process chamber (first chamber)  2  and a transfer chamber (second chamber)  3 , the first chamber  2  and the second chamber  3  being adjacent to each other. Thus, the gate valve  1  is usable for causing a first opening  4   a,  which communicates with the first chamber  2 , and a second opening  4   b,  which communicates with the second chamber  3 , to communicate with each other and for opening and closing the first opening  4   a  and the second opening  4   b  separately. 
     The gate valve  1  includes a bonnet  5 , which forms the boundary between an upper region U and a lower region B to partition off the regions U and B, a valve shaft  6 , which passes through the bonnet  5  in the direction along an axis L extending in an up-down direction and which has a tip end portion  6   a  disposed in the upper region U above the bonnet  5  and a base end portion  6   b  disposed in the lower region B below the bonnet  5 , a valve assembly  10 , which is formed by providing a first valve plate  11  and a second valve plate  12  back to back to the tip end portion  6   a  of the valve shaft  6  so as to be adjacent to each other, and a valve drive mechanism  20 , which is connected to the base end portion  6   b  of the valve shaft  6  and which is configured to move the valve assembly  10  by operation of the valve shaft  6 . 
     The bonnet  5  is made of a metal plate having a substantially rectangular shape that is long in a width direction W orthogonal to the axis L. The bonnet  5  has a first surface (upper surface)  5   a,  which faces the upper region U, a second surface (lower surface)  5   b,  which faces the lower region B, and a through hole  5   c,  into which the valve shaft  6  is inserted. As illustrated in  FIGS.  5  to  12   , the bonnet  5  forms a bottom wall of a valve casing  7 , which has a hollow shape whose lower side is open. The valve casing  7  has side walls  8 , which surround the four sides around the axis L. A lower end opening of the side walls  8  can be airtightly closed by detachably attaching the bonnet  5  to a lower end portion of each of the side walls  8  in the direction along the axis L. 
     In this manner, the bonnet  5  is attached to the valve casing  7 . Thus, the valve assembly  10  attached to the tip end portion  6   a  of the valve shaft  6  is configured to be accommodated in the valve casing  7 . In addition, the through hole  5   c  allows the valve assembly  10  to move in the direction along the axis L and in a thickness direction D orthogonal to the direction along the axis L and the width direction W (that is, in the direction in which the first valve plate  11  and the second valve plate  12  of the valve assembly  10  are provided adjacent to each other). Thus, the through hole  5   c  has an inner diameter slightly larger than the outer diameter of the valve shaft  6  and is provided at the center of the bonnet  5  so as to pass therethrough. 
     The valve assembly  10  includes the first valve plate  11  and the second valve plate  12 , which have a substantially rectangular shape that is long in the width direction W, and first clamp members  13  and second clamp members  14  for detachably fixing the valve plates  11  and  12  to the tip end portion  6   a  of the valve shaft  6 . The first valve plate  11  and the second valve plate  12  are located back to back in the thickness direction D and respectively have a first sealing surface  11   a  and a second sealing surface  12   a,  which are parallel to each other. Valve sealing members lib and  12   b,  which are, for example, O-rings having an annular shape, are attached to the peripheries of the sealing surfaces  11   a  and  12   a,  respectively. In addition, the pair of valve sealing surfaces  11   a  and  12   a  do not necessarily have to be parallel to each other. 
     The first clamp members  13  are engaged, from above, with respective two parts of the valve assembly  10  at the center thereof in the width direction W so as to be fitted thereinto and to extend between the first valve plate  11  and the tip end of the valve shaft  6  and between the second valve plate  12  and the tip end of the valve shaft  6 . In addition, the second clamp members  14  are engaged, from above, with respective end portions of the valve assembly  10  in the width direction W so as to be fitted thereinto and to extend between the first valve plate  11  and the second valve plate  12 . Then, spacer members  15  are held, by inner surfaces of the pair of valve plates  11  and  12 , between the first valve plate  11  and the second valve plate  12  and below the second clamp members  14  ( FIGS.  5  to  12   ). 
     Then, when the first clamp members  13  are fixed to the tip end of the valve shaft  6  with fastening bolts  13   a  from above in a state in which the first valve plate  11  and the second valve plate  12  are engaged, from above, with respective end portions of the tip end portion  6   a  closer to the base end so as to be fitted thereinto, inclined surfaces having different inclinations of the parts that are engaged so as to be fitted to each other are in pressure contact with each other. As a result, at the center of the valve assembly  10  in the width direction W, in a state in which the tip end portion  6   a  of the valve shaft  6  is held by the inner surfaces of the first valve plate  11  and the second valve plate  12 , the valve shaft  6  and the valve plates  11  and  12  are fastened to each other in the thickness direction D. 
     On the other hand, at the respective end portions of the valve assembly  10  in the width direction W, when the second clamp members  14  are fixed to the respective tip ends of the spacer members  15  with fastening bolts  14   a  from above in a state in which the first valve plate  11  and the second valve plate  12  are engaged, from above, with respective end portions of the second clamp members  14  closer to the base end so as to be fitted thereinto, inclined surfaces having different inclinations of the parts that are engaged so as to be fitted to each other are in pressure contact with each other. As a result, at the respective end portions of the valve assembly  10  in the width direction W, in a state in which the spacer members  15  are held by the inner surfaces of the first valve plate  11  and the second valve plate  12 , the spacer members  15  and the valve plates  11  and  12  are fastened to each other in the thickness direction D. 
     In this connection, such a specific structure in which the first valve plate  11  and the second valve plate  12  are attached to the valve shaft  6  is described in a prior Japanese patent application (Japanese Patent Application No. 2021-168188) by the present applicant. In addition, in the present application, the structure of the valve assembly  10  and the structure in which the valve plates  11  and  12  are attached to the valve shaft  6  are not limited to the structures described above, and it is possible to adopt various commonly known structures. Thus, more specific descriptions related thereto are omitted here. 
     Meanwhile, as illustrated in  FIGS.  5  to  12   , the valve casing  7  is attached between the first chamber  2  and the second chamber  3  and is formed by detachably attaching, to an upper end opening of the side walls  8  in the direction along the axis L, a top wall  9 , which airtightly closes the opening. By detachably attaching the top wall  9  to the side walls  8  in this manner, various operations such as detachment of the valve plates  11  and  12  can be performed through the upper end opening of the side walls  8  during maintenance of the valve assembly  10  such as replacement of the valve sealing members  11   b  and  12   b  of the valve plates  11  and  12 . 
     In addition, the side walls  8  of the valve casing have a first inner side surface  8   a  and a second inner side surface  8   b,  which face parallel to each other with the axis L interposed therebetween in the thickness direction D. The first inner side surface  8   a  has the first opening  4   a,  which is open and communicates with the first chamber  2 . The second inner side surface  8   b  has the second opening  4   b,  which is open and communicates with the second chamber  3 . The first opening  4   a  and the second opening  4   b  are disposed so as to face each other in the thickness direction D. In addition, valve seats  4   c  for coming into contact with and separating from each valve sealing member  11   b ,  12   b  of the first and second sealing surfaces  11   a ,  12   a  of the valve assembly  10  are formed around the first opening  4   a  and the second opening  4   b  of the first inner side surface  8   a  and the second inner side surface  8   b  so as to surround the openings  4   a  and  4   b.    
     Then, by operation of the valve shaft  6  driven by the valve drive mechanism  20 , the gate valve  1  mounted on such a valve casing  7  is capable of moving the valve assembly  10  in the valve casing  7  to a retracted position ( FIGS.  5  and  6   ) located on the axis L for causing the first opening  4   a  and the second opening  4   b  to communicate with each other, a first closed position ( FIGS.  9  and  10   ) for airtightly closing the first opening  4   a  with the first valve plate  11 , a second closed position ( FIGS.  11  and  12   ) for airtightly closing the second opening  4   b  with the second valve plate  12 , and an intermediate position ( FIGS.  7  and  8   ) set to the same height position, on the axis L, as the height position occupied by the first and second closed positions. In this connection, the valve assembly  10  located at the intermediate position is separated from both the first opening  4   a  and the second opening  4   b.    
     As illustrated in  FIGS.  1  to  3   , the valve drive mechanism  20  configured to operate the valve assembly  10  in this manner includes air cylinders  21 , each of which includes a first drive rod  22   a  and a second drive rod  23   a  capable of being driven separately, and a power transmission mechanism  30 , which connects the base end portion of the valve shaft  6  and the first drive rod  22   a  and the second drive rod  23   a  and which is configured to transmit driving force of the air cylinders  21  to the valve shaft  6 . 
     As illustrated in  FIG.  3   , the air cylinder  21  includes a cylinder body  24 , a first cylinder hole  22   b  and a second cylinder hole  23   b,  which are provided in the cylinder body  24  so as to extend along the axis L, and a pair of pistons  22   c  and  23   c,  which are slidably provided in the pair of cylinder holes  22   b  and  23   b , respectively. Respective base end portions of the first drive rod  22   a  and the second drive rod  23   a  are fixed to the pair of pistons  22   c  and  23   c.  Then, the air cylinder  21  is drooped from the bonnet  5  along the axis L by fixedly attaching an end portion of the cylinder body  24  closer to the head to the second surface  5   b  of the bonnet  5 , the second surface  5   b  facing downward. 
     Thus, the tip end side of each of the first drive rod  22   a  and the second drive rod  23   a  extends downward from an end portion of the cylinder body  24  closer to the rods so as to be capable of advancing and retracting. In addition, it is possible to supply and discharge air separately into and from the first cylinder hole  22   b  and the second cylinder hole  23   b.  Thus, it is possible to drive the first drive rod  22   a  and the second drive rod  23   a  separately. 
     As illustrated in  FIGS.  2  and  4   , the power transmission mechanism  30  includes a first support frame  31  and a second support frame  32 , which are respectively attached to the first drive rod  22   a  and the second drive rod  23   a , first cam frames  33  and second cam frames  34 , which are fixedly attached to the first support frame  31  and the second support frame  32 , respectively, and which extend along the axis L, a lever member  35 , which is fixedly attached to the base end portion  6   b  of the valve shaft  6  and which is configured to operate together with the valve shaft  6 , and a first spring member  36  and a second spring member  37 , which connect the lever member  35  and both the first support frame  31  and the second support frame  32 , respectively, so as to be capable of being relatively displaced. Then, as described below, in particular, the power transmission mechanism  30  is formed symmetrically in the thickness direction D relative to a central plane that includes the axis L and that extends in the width direction W. In addition, the power transmission mechanism  30  is formed symmetrically in the width direction W relative to a central plane that includes the axis L and that extends in the thickness direction D. Furthermore, in the present embodiment, similarly, the entire gate valve  1  is formed substantially symmetrically in the width direction W and the thickness direction D. 
     In this manner, the first spring member  36  and the second spring member  37  are provided (specifically, provided in a compressed state) between the lever member  35  and both the first support frame  31  and the second support frame  32 , respectively. Thus, driving force of the first drive rod  22   a  and the second drive rod  23   a  is transmitted separately to the lever member  35  through the first spring member  36  and the second spring member  37 . As a result, it is possible to relatively operate the lever member  35  and each of the first drive rod  22   a  and the second drive rod  23   a.    
     More specifically, in the present embodiment, the air cylinder  21  is fixedly attached to the bonnet  5  in a state in which the first cylinder hole  22   b,  the piston  22   c,  and the first drive rod  22   a  are disposed closer to the first closed position and in which the second cylinder hole  23   b,  the piston  23   c,  and the second drive rod  23   a  are disposed closer to the second closed position. That is, the first drive rod  22   a  and the second drive rod  23   a  are adjacent to each other in the thickness direction D such that the first drive rod  22   a  is disposed closer to the first closed position and the second drive rod  23   a  is disposed closer to the second closed position. Then, the pair of air cylinders  21  formed in this manner are disposed on respective sides between which the valve shaft  6  (that is, the axis L) is interposed in the width direction W. However, the number and the disposition of the air cylinders  21  are not limited to those in the present embodiment. 
     The first support frame  31  and the second support frame  32  are each made of a metal plate that is long in the width direction W. Tip end portions of the first drive rods  22   a  of the pair of air cylinders  21  are attached to respective end portions of the first support frame  31  between which the axis L is interposed in the width direction W. Tip end portions of the second drive rods  23   a  of the pair of air cylinders  21  are attached to respective end portions of the second support frame  32  between which the axis L is interposed in the width direction W. 
     Thus, the first support frame  31  and the second support frame  32  are provided adjacent to each other in the thickness direction D such that the first support frame  31  is disposed closer to the first closed position and the second support frame  32  is disposed closer to the second closed position. In addition, spring seats  31   a  and  32   a,  which are recessed, are provided at the respective centers of the support frames  31  and  32  in the width direction W. The spring seats  31   a  and  32   a  receive respective lower end portions of the first spring member  36  and the second spring member  37  in the direction along the axis L. 
     The first cam frame  33  and the second cam frame  34  are each made of a metal plate. The first cam frame  33  has an inner surface  33   a  and an outer surface  33   b,  which are located back to back so as to extend in the direction along the axis L and the thickness direction D. The second cam frame  34  has an inner surface  34   a  and an outer surface  34   b,  which are located back to back so as to extend in the direction along the axis L and the thickness direction D. Then, a pair of the first cam frames  33  are fixedly provided upright, between the pair of air cylinders  21 , from respective sides of the first support frame  31  between which the axis L is interposed. Similarly, a pair of the second cam frames  34  are fixedly provided upright, between the pair of air cylinders  21 , from respective sides of the second support frame  32  between which the axis L is interposed. 
     Thus, the first cam frame  33  and the second cam frame  34  are provided adjacent to each other in the thickness direction D such that the first cam frame  33  is disposed closer to the first closed position and the second cam frame  34  is disposed closer to the second closed position. Then, the cam frames  33  and  34  adjacent to each other are formed symmetrically in the thickness direction D relative to a central plane that includes the axis L and that extends in the width direction W. On the other hand, of the pair of first cam frames  33 , the inner surfaces  33   a  face each other, and the outer surfaces  33   b  are located back to back. In addition, of the pair of second cam frames  34 , the inner surfaces  34   a  face each other, and the outer surfaces  34   b  are located back to back. Then, the pair of first cam frames  33  are disposed symmetrically in the width direction W relative to a central plane that includes the axis L and that extends in the thickness direction D. In addition, the pair of second cam frames  34  are disposed symmetrically in the width direction W relative to a central plane that includes the axis L and that extends in the thickness direction D. 
     The lever member  35  is made of a metal block having an H shape in front view. The lever member  35  has an upper recess  35   a,  which is closer to the upper end in the direction along the axis L and which is formed at the center thereof in the width direction W, a pair of upper projections  35   b,  which project from respective side portions thereof, a lower recess  35   c,  which is closer to the lower end in the direction along the axis L and which is formed at the center thereof in the width direction W, and a pair of lower projections  35   d,  which project from the respective side portions thereof. In addition, the lever member  35  has a pair of side surfaces  35   e,  which are located back to back at respective ends thereof in the width direction W. 
     Then, the base end portion  6   b  of the valve shaft  6  is fixedly attached to the upper recess  35   a.  A bellows  6   c,  which has a cylindrical shape, airtightly surrounds the valve shaft  6  between the upper recess  35   a  of the lever member  35  and the through hole  5   c  of the bonnet  5 . In addition, an upper end portion of each of the first spring member  36  and the second spring member  37  in the direction along the axis L is attached to the lower recess  35   c.    
     The first spring member  36  and the second spring member  37  are each made of a metal coil spring and have spring force (spring stiffness) sufficient to support the weight of each of the valve assembly  10  and the lever member  35 . Thus, in the process of moving the assembly  10  along the axis L from the retracted position ( FIGS.  5  and  6   ) to the intermediate position ( FIGS.  7  and  8   ), spring force of the spring members  36  and  37  enables the valve assembly  10  and the drive rods  22   a  and  23   a  of the air cylinder  21  to operate together. 
     Then, in the process in which opening and closing mechanisms  40  and  45 , which will be described later, move the assembly  10  in the thickness direction D from the intermediate position to the first and second closed positions, the spring members  36  and  37  are compressed and deformed by driving force of the drive rods  22   a  and  23   a.  As a result, it is possible to move the valve assembly  10  relative to the drive rods  22   a  and  23   a  and to thus move the valve assembly  10  in the thickness direction D, which is orthogonal to the direction in which the drive rods  22   a  and  23   a  operate (direction along the axis L). 
     In addition, the power transmission mechanism  30  includes first opening and closing mechanisms  40  and second opening and closing mechanisms  45 , which serve for operation of the valve shaft  6  and the valve assembly  10  in the thickness direction D and which separately cause the valve assembly  10  to reciprocate, in the thickness direction D, between the position occupied by the retracted position and the position occupied by the first closed position and between the position occupied by the retracted position and the position occupied by the second closed position, first guide mechanisms  50  and second guide mechanisms  55 , which serve for guiding the first cam frames  33  and the second cam frames  34  so as to reciprocate in the direction along the axis L and which guide the cam frames  33  and  34  so as to reciprocate between the position occupied by the retracted position and the position occupied by the intermediate position in the direction along the axis L, and stoppers  60 , which cause the lever member  35  to be in contact with the second surface  5   b  of the bonnet  5  at the intermediate position to prevent the valve shaft  6  and the valve assembly  10  together with the lever member  35  from moving in the direction along the axis L and to allow the valve shaft  6  and the valve assembly  10  together with the lever member  35  to move in the thickness direction D. 
     The first opening and closing mechanisms  40  and the second opening and closing mechanisms  45  are formed so as to extend between the first and second cam frames  33  and  34  and the lever member  35  disposed between the cam frames  33  and  34 . Specifically, the first opening and closing mechanisms  40  and the second opening and closing mechanisms  45  are provided between the respective inner surfaces  33   a  and  34   a  of the first and second cam frames  33  and  34  and the side surfaces  35   e  of the lever member  35 , the side surfaces  35   e  facing the inner surfaces  33   a  and  34   a.  In addition, the opening and closing mechanisms  40  and  45  are provided adjacent to each other in the thickness direction D such that the first opening and closing mechanism  40  is disposed closer to the first closed position and the second opening and closing mechanism  45  is disposed closer to the second closed position. 
     The first opening and closing mechanism  40  includes first cam grooves  41 , which are recessed and provided in the inner surface  33   a  of the first cam frame  33 , and first cam rollers  42 , which are provided on the side surface  35   e  of the lever member  35 , the side surface  35   e  facing the first cam grooves  41 , and which are slidably fitted into the respective first cam grooves  41 . On the other hand, the second opening and closing mechanism  45  includes second cam grooves  46 , which are recessed and provided in the inner surface  34   a  of the second cam frame  34 , and second cam rollers  47 , which are provided on the side surface  35   e  of the lever member  35 , the side surface  35   e  facing the second cam grooves  46 , and which are slidably fitted into the respective second cam grooves  46 . In the present embodiment, the first opening and closing mechanisms  40  and the second opening and closing mechanisms  45  formed in this manner are provided so as to form pairs located closer to respective side surfaces  35   e  of the lever member  35 . 
     The first cam groove  41  has a beginning end position S 1 , which is closer to the upper end in the direction along the axis L, and a terminal end position E 1 , which is closer to the lower end in the direction along the axis L. The terminal end position E 1  is located closer than the beginning end position S 1  to the first closed position in the thickness direction D. That is, the first cam groove  41  has a profile inclined toward the first closed position in a direction from the beginning end position S 1  closer to the upper end toward the terminal end position E 1  closer to the lower end. Then, when the first cam roller  42  is located at the beginning end position S 1 , the valve assembly  10  is disposed on the axis L. When the first cam roller  42  is located at the terminal end position E 1 , the valve assembly  10  is disposed at the first closed position. In the present embodiment, the two first cam grooves  41  having the same shape are formed at an upper end portion and a lower end portion of the first cam frame  33 . One of the two first cam grooves  41  that is disposed closer to the upper end is open in an upper end face of the first cam frame  33  at the beginning end position S 1 . 
     On the other hand, the second cam groove  46  has a beginning end position S 2 , which is closer to the upper end in the direction along the axis L, and a terminal end position E 2 , which is closer to the lower end in the direction along the axis L. The terminal end position E 2  is located closer than the beginning end position S 2  to the second closed position in the thickness direction D. That is, the second cam groove  46  has a profile inclined toward the second closed position in a direction from the beginning end position S 2  closer to the upper end toward the terminal end position E 2  closer to the lower end. Then, when the second cam roller  47  is located at the beginning end position S 2 , the valve assembly  10  is disposed on the axis L. When the second cam roller  47  is located at the terminal end position E 2 , the valve assembly  10  is disposed at the second closed position. In the present embodiment, the two second cam grooves  46  having the same shape are formed at an upper end portion and a lower end portion of the second cam frame  34 . One of the two second cam grooves  46  that is disposed closer to the upper end is open in an upper end face of the second cam frame  34  at the beginning end position S 2 . 
     In this manner, when one of the first cam frame  33  and the second cam frame  34  moves upward in the direction along the axis L relative to the lever member  35 , the cam rollers fitted into the cam grooves of the moved cam frame move from the beginning end position S to the terminal end position E so as to follow the cam grooves. Then, the lever member  35  is displaced in the thickness direction D toward one of the first closed position and the second closed position. Simultaneously with this, the cam rollers fitted into the other remaining cam frame also have to be displaced by the same length in the thickness direction D. 
     Thus, in the gate valve  1 , all the (two upper and lower) cam grooves  41  formed in the first cam frame  33  have a first recess  41   a,  which is provided so as to be recessed in the thickness direction D from the beginning end position S 1  toward the second closed position, and all the (two upper and lower) cam grooves  46  formed in the second cam frame  34  have a second recess  46   a,  which is provided so as to be recessed in the thickness direction D from the beginning end position S 2  toward the first closed position. 
     In addition, sliding members  33   c  and  34   c  that are made of a resin material and that are usable for sliding relative to both side surfaces  35   e  of the lever member  35  are respectively provided on the inner surfaces  33   a  and  34   a  of the first cam frame  33  and the second cam frame  34 , the sliding members  33   c  being arranged in the up-down direction, the sliding members  34   c  being arranged in the up-down direction. On the other hand, similarly, sliding members  33   c  and  34   c  that are made of a resin material and that are usable for sliding relative to guide surfaces  25   a  of guide frames  25  described later are respectively provided on the outer surfaces  33   b  and  34   b  of the first cam frame  33  and the second cam frame  34 , the sliding members  33   c  being arranged in the up-down direction, the sliding members  34   c  being arranged in the up-down direction. However, the number and the positions of the sliding members  33   c  and  34   c  are not limited thereto. 
     Furthermore, the power transmission mechanism  30  includes the guide frames  25 , each of which is fixedly attached to the bonnet  5  between the air cylinder  21  and the cam frames  33  and  34  and which are drooped from the second surface  5   b  of the bonnet  5 . The guide frame  25  has the guide surface  25   a,  which faces the outer surfaces  33   b  and  34   b  of the cam frames  33  and  34 . In the present embodiment, the pair of guide frames  25  formed in this manner are disposed on the respective sides between which the axis L is interposed in the width direction W. The guide frame  25  is integrally formed with the cylinder body  24  of the air cylinder  21  adjacent to the guide frame  25  in the width direction W. 
     Then, the first guide mechanisms  50  and the second guide mechanisms  55  are formed so as to extend between the guide frames  25  and the first and second cam frames  33  and  34  adjacent to the guide frames  25 . Specifically, the first guide mechanisms  50  and the second guide mechanisms  55  are provided between the respective guide surfaces  25   a  of the guide frames  25  and the outer surfaces  33   b  and  34   b  of the first and second cam frames  33  and  34 , the outer surfaces  33   b  and  34   b  facing the guide surfaces  25   a.  That is, the guide mechanisms  50  and  55  are provided adjacent to each other in the thickness direction D such that the first guide mechanism  50  is disposed closer to the first closed position and the second guide mechanism  55  is disposed closer to the second closed position. 
     The first guide mechanism  50  includes a first guide groove  51 , which is recessed and provided in the outer surface  33   b  of the first cam frame  33 , and first guide rollers  52 , which are provided on the guide surface  25   a  of the guide frame  25 , the guide surface  25   a  facing the first guide groove  51 , and which are slidably fitted into the first guide groove  51 . On the other hand, the second guide mechanism  55  includes a second guide groove  56 , which is recessed and provided in the outer surface  34   b  of the second cam frame  34 , and second guide rollers  57 , which are provided on the guide surface  25   a  of the guide frame  25 , the guide surface  25   a  facing the second guide groove  56 , and which are slidably fitted into the second guide groove  56 . In the present embodiment, the first guide mechanisms  50  are provided closer to the respective outer surfaces  33   b  of the pair of first cam frames  33 , and the second guide mechanisms  55  are provided closer to the respective outer surfaces  34   b  of the pair of second cam frames  34 . 
     The first guide groove  51  is provided so as to extend straight along the axis L from the upper end portion to the lower end portion of the first cam frame  33 . In the present embodiment, the upper end of the guide groove  51  is open in the upper end face of the first cam frame  33 . In addition, similarly, the second guide groove  56  is provided so as to extend straight along the axis L from the upper end portion to the lower end portion of the second cam frame  34 . In the present embodiment, the upper end of the guide groove  56  is open in the upper end face of the second cam frame  34 . Then, the guide grooves  51  and  56  have the same length in the direction along the axis L. In addition, the cam grooves  41  and  46  and the guide grooves  51  and  56  are disposed so as to partially overlap each other in the thickness direction D such that the sum of the depths of the cam groove  41  and the guide groove  51  formed in the cam frame  33  and the sum of the depths of the cam groove  46  and the guide groove  56  formed in the cam frame  34  are respectively smaller than the length between the inner surface  33   a  and the outer surface  33   b  of the cam frame  33  and the length between the inner surface  34   a  and the outer surface  34   b  of the cam frame  34 . Thus, the valve drive mechanism  20  and the power transmission mechanism  30  are inhibited from increasing in size in the thickness direction D. 
     The two first guide rollers  52  arranged in the up-down direction along the axis L are provided at respective positions, closer to the first closed position, in the guide surface  25   a  of the guide frame  25 . Similarly, the two second guide rollers  57  arranged in the up-down direction along the axis L are provided at respective positions, closer to the second closed position, in the guide surface  25   a.  Then, the distance between the pair of upper and lower first guide rollers  52  in the direction along the axis L is smaller than the length of the first guide groove  51  in the direction along the axis L. Similarly, the distance between the pair of upper and lower second guide rollers  57  in the direction along the axis L is smaller than the length of the second guide groove  56  in the direction along the axis L. In addition, the length of the first guide groove  51  and the second guide groove  56  in the direction along the axis L is larger than the sum of the distance between the retracted position and the intermediate position in the direction along the axis L and the distance, in the direction along the axis L, between the beginning end positions S 1  and S 2  and the terminal end positions E 1  and E 2  in the cam grooves  41  and  46 . 
     The stoppers  60  are provided on respective upper end faces  35   f  of the pair of upper projections  35   b  of the lever member  35 . The stoppers  60  each include a stop roller  61 , which is capable of rolling in the thickness direction D, and a cushion  62  ( FIGS.  5  and  6   ), which is provided on the part, facing the stop roller  61 , of the second surface (lower surface) of the bonnet  5 . That is, pairs of the stop roller  61  and the cushion  62  are provided on the respective left and right sides between which the valve shaft  6  is interposed in the width direction W. Thus, when the stop roller  61  comes into contact with the bonnet  5 , the cushion  62  can absorb the shock. 
     Then, as illustrated in  FIGS.  5  to  12   , when the valve assembly  10  is moved upward along the axis L from the retracted position to the intermediate position by upward retracting operation of the first drive rod  22   a  or the second drive rod  23   a,  the stop roller  61  provided at the upper end of the lever member comes into contact with the cushion  62  provided on the second surface  5   b  of the bonnet  5 , thus stopping upward movement along the axis L of the valve assembly  10 . Subsequently, when the valve assembly  10  is moved in the thickness direction D from the intermediate position to the first closed position or the second closed position by the first opening and closing mechanism  40  or the second opening and closing mechanism  45 , the stop roller  61  in contact with the cushion  62  rolls on the cushion  62  in the thickness direction D together with the movement. 
     In this manner, in the gate valve  1 , the first opening and closing mechanism  40 , which includes the first cam grooves  41  and the first cam rollers  42  and which causes the valve assembly  10  to reciprocate between the intermediate position and the first closed position, and the second opening and closing mechanism  45 , which includes the second cam grooves  46  and the second cam rollers  47  and which causes the valve assembly  10  to reciprocate between the intermediate position and the second closed position, are disposed adjacent to each other in the thickness direction D. The gate valve  1  according to the present embodiment capable of moving the valve assembly  10  separately to the first closed position and the second closed position by using the two pairs of cam grooves  41  and  46  and cam rollers  42  and  47  in this manner enables a reduction in the height of the cam frames  33  and  34  compared with an existing one configured to move a valve assembly sequentially to the first closed position and the second closed position by using a pair of a cam groove and a cam roller. As a result, it is possible to reduce the height of the valve drive mechanism  20  and to thus reduce the height of the entire gate valve  1 . 
     The operation of the gate valve  1  having such a configuration will be described. As illustrated in  FIGS.  5  and  6   , when the valve assembly  10  is located at the retracted position, both the first drive rod  22   a  and the second drive rod  23   a  of the air cylinder  21  advance to the lower stroke end. In this state, the lever member  35  is integrally supported on the first support frame  31  and the second support frame  32  by spring force (spring stiffness) of the first spring member  36  and the second spring member  37 , and the first cam rollers  42  and the second cam rollers  47  are respectively disposed at the beginning end positions S 1  and S 2  in the first cam grooves  41  and the second cam grooves  46  by the spring force of the spring members  36  and  37 . Thus, the valve assembly  10  and the drive rods  22   a  and  23   a  are integrally connected via the support frames  31  and  32 , the cam frames  33  and  34 , and a lever member  35 . In addition, of the pair of upper and lower first guide rollers  52  and the pair of upper and lower second guide rollers  57 , only the guide rollers  52  and  57  disposed on a lower part are respectively fitted into the first guide groove  51  and the second guide groove  56 . 
     Next, from this state, when air is supplied into the first cylinder hole  22   b  of the air cylinder  21  to drive the first drive rod  22   a  to retract upward in the direction along the axis L, a “rod-side assembly”, which is formed by each first drive rod  22   a,  each second drive rod  23   a,  the first support frame  31 , the second support frame  32 , each first cam frame  33 , and each second cam frame  34 , and a “shaft-side assembly”, which is formed by the lever member  35 , the valve shaft  6 , and the valve assembly  10 , move upward in the direction along the axis L together. Then, the valve assembly  10  moves upward on the axis L from the retracted position and reaches the intermediate position illustrated in  FIGS.  7  and  8    (the position where the first valve plate  11  and the second valve plate  12  respectively face the first opening  4   a  and the second opening  4   b  of the valve casing  7  and where the valve sealing members  11   b  and  12   b  of the valve plates are separated from respective valve seats  4   c  of the openings  4   a  and  4   b ). 
     Meanwhile, as illustrated in  FIG.  5   , both the first cam frame  33  and the second cam frame  34  are guided along the axis L by the lower first guide roller  52  and the lower second guide roller  57  fitted into the first guide groove  51  and the second guide groove  56 . Thus, it is possible to move the valve shaft  6  upward along the axis L without being inclined relative to the axis L. Then, as illustrated in  FIG.  7   , when the valve assembly  10  reaches the intermediate position, the first guide roller  52  and the second guide roller  57  disposed on an upper part are also fitted into the first guide groove  51  and the second guide groove  56  from the upper end openings thereof. Simultaneously, the stop roller  61  of the lever member  35  comes into contact with the cushion  62  of the bonnet  5 , thus stopping, at the position, upward movement in the direction along the axis L of the “shaft-side assembly”. As a result, upward movement in the direction along the axis L from the retracted position of the valve assembly  10  is stopped at the intermediate position. 
     Thus, when air supply into the first cylinder hole  22   b  continues in such a state in which the valve assembly  10  is located at the intermediate position, a “first assembly”, which is formed by each first drive rod  22   a,  the first support frame  31 , and each first cam frame  33 , of the “rod-side assembly” further continues to move upward while compressing the first spring member  36 . On the other hand, a “second assembly”, which is formed by each second drive rod  23   a,  the second support frame  32 , and each second cam frame  34 , of the “rod-side assembly” stops at the position. 
     Then, the pair of upper and lower first cam grooves  41  formed in the first cam frame  33  move upward relative to the pair of upper and lower first cam rollers  42  fitted thereinto until the first drive rod  22   a  reaches the upper stroke end. Then, as illustrated in  FIG.  10   , in the pair of upper and lower first cam grooves  41 , the pair of upper and lower first cam rollers  42  located at the beginning end position S 1  move to the terminal end position E 1 . Then, the first cam rollers  42  move toward the first closed position in the thickness direction D orthogonal to the direction along the axis L so as to follow the respective cam grooves  41 . 
     As a result, as illustrated in  FIGS.  9  and  10   , the entire “shaft-side assembly” including the valve assembly  10  is displaced in the thickness direction D orthogonal to the axis L from the intermediate position to the first closed position where the first opening  4   a  of the valve casing  7  is closed by the first valve plate  11 . Then, the pair of upper and lower second cam rollers  47  provided on the lever member  35  also move toward the first closed position together with the movement of the “shaft-side assembly” and, as described above, move, in the second cam grooves  46 , from the beginning end position S 2  to the second recesses  46   a  provided so as to be recessed from the beginning end position S 2  toward the first closed position. 
     On the contrary, when air is supplied into the second cylinder hole  23   b  to drive the second drive rod  23   a  to retract upward in the direction along the axis L, the valve assembly  10  moves from the retracted position of the valve assembly  10  illustrated in  FIGS.  5  and  6    to the intermediate position illustrated in  FIGS.  7  and  8    as in the case in which the first drive rod  22   a  is driven to retract. Then, when air supply into the second cylinder hole  23   b  continues in the state in which the valve assembly  10  is located at the intermediate position, the “second assembly” of the “rod-side assembly” further continues to move upward while compressing the second spring member  37 . On the other hand, the “first assembly” of the “rod-side assembly” stops at the position. 
     Then, the pair of upper and lower second cam grooves  46  formed in the second cam frame  34  move upward relative to the pair of upper and lower second cam rollers  47  fitted thereinto until the second drive rod  23   a  reaches the upper stroke end. Then, as illustrated in  FIG.  12   , in the pair of upper and lower second cam grooves  46 , the pair of upper and lower second cam rollers  47  located at the beginning end position S 2  move to the terminal end position E 2 . Then, the second cam rollers  47  move toward the second closed position in the thickness direction D orthogonal to the direction along the axis L so as to follow the respective cam grooves  46 . 
     As a result, as illustrated in  FIGS.  11  and  12   , the entire “shaft-side assembly” including the valve assembly  10  is displaced in the thickness direction D orthogonal to the axis L from the intermediate position to the second closed position where the second opening  4   b  of the valve casing  7  is closed by the second valve plate  12 . Then, the pair of upper and lower first cam rollers  42  provided on the lever member  35  also move toward the second closed position together with the movement of the “shaft-side assembly” and, as described above, move, in the first cam grooves  41 , from the beginning end position S 1  to the first recesses  41   a  provided so as to be recessed from the beginning end position S 1  toward the second closed position. 
     In addition, an operation in which the process described above is reversed is performed to return the valve assembly  10  from the first closed position or the second closed position ( FIGS.  9  to  12   ) to the retracted position ( FIGS.  5  and  6   ) via the intermediate position ( FIGS.  7  and  8   ). 
     In this manner, in particular, when the valve assembly  10  is displaced from the intermediate position to the second closed position, the gate valve  1  is capable of directly displacing the valve assembly  10  to the second closed position without passing through the first closed position as ever. Thus, the gate valve  1  is also extremely excellent in the operability of the valve assembly  10 . In addition, when the valve assembly  10  is displaced from the intermediate position to the first closed position and the second closed position, the entire “shaft-side assembly” moves in the thickness direction D orthogonal to the axis L. Thus, when the first valve plate  11  and the second valve plate  12  come into contact with and are separated from the first opening  4   a  and the second opening  4   b  of the valve casing  7 , respectively, it is possible to inhibit, for example, twisting of the valve sealing members  11   b  and  12   b  and generation of abrasion powder. 
     The embodiment of the present invention has been specifically described above, but the present invention is not limited thereto. Needless to say, various design changes can be made without departing from the gist of the present invention. 
     For example, in the present embodiment, the “first assembly”, which is formed by each first drive rod  22   a,  the first support frame  31 , and each first cam frame  33 , and the “second assembly”, which is formed by each second drive rod  23   a,  the second support frame  32 , and each second cam frame  34 , are disposed adjacent to each other in the thickness direction D such that the “first assembly” is disposed closer to the first closed position and the “second assembly” is disposed closer to the second closed position. On the contrary, the “first assembly” may be disposed closer to the second closed position, and the “second assembly” may be disposed closer to the first closed position. 
     In addition, in the present embodiment, the first cam grooves  41  and the second cam grooves  46  are provided in the first cam frame  33  and the second cam frame  34 , and the first cam rollers  42  and the second cam rollers  47  are provided on the lever member  35 . On the contrary, the cam grooves  41  and  46  may be provided in the lever member  35 , and the cam rollers  42  and  47  may be provided on the cam frames  33  and  34 . Then, in the present embodiment, the first guide groove  51  and the second guide groove  56  are provided in the cam frames  33  and  34 , and the first guide rollers  52  and the second guide rollers  57  are provided on the guide frame  25 , which is integrally formed with the cylinder body  24 . On the contrary, the guide grooves  51  and  56  may be provided in the guide frame  25 , and the guide rollers  52  and  57  may be provided on the cam frames  33  and  34 . In addition, the guide frame  25  can be formed separately from the cylinder body  24 . 
     Furthermore, in the present embodiment, the pairs of upper and lower cam grooves  41  and  46  formed in the cam frames  33  and  34  have the same profile, and the entire “shaft-side assembly” is thus moved in the thickness direction D orthogonal to the axis L when the valve assembly  10  is displaced from the intermediate position to the first closed position and the second closed position. However, each upper one and each lower one of the pairs of upper and lower cam grooves  41  and  46  may have different profiles, and the “shaft-side assembly” may thus be inclined relative to the axis L when the valve assembly  10  is displaced from the intermediate position to the first closed position and the second closed position. 
     In addition, the materials forming the respective components of the gate valve  1  according to the present embodiment are not necessarily limited to the materials described above, and appropriate materials therefor can be adopted as needed. 
     Furthermore, in the present embodiment, components such as the power transmission mechanism  30  and the first and second cam frames  33  and  34  are formed symmetrically in the thickness direction D and the width direction W. As a result, the entire gate valve  1  is also formed substantially symmetrically in the thickness direction D and the width direction W. However, each configuration thereof is not necessarily limited thereto and may be asymmetrical. 
     REFERENCE SIGNS LIST 
       1  gate valve 
       5  bonnet 
       6  valve shaft 
       6   a  tip end portion 
       6   b  base end portion 
       10  valve assembly 
       11  first valve plate 
       12  second valve plate 
       20  valve drive mechanism 
       21  air cylinder 
       22   a  first drive rod 
       23   a  second drive rod 
       25  guide frame 
       30  power transmission mechanism 
       31  first support frame 
       32  second support frame 
       33  first cam frame 
       34  second cam frame 
       35  lever member 
       36  first spring member 
       37  second spring member 
       40  first opening and closing mechanism 
       41  first cam groove 
       41   a  first recess 
       42  first cam roller 
       45  second opening and closing mechanism 
       46  second cam groove 
       46   a  second recess 
       47  second cam roller 
       50  first guide mechanism 
       51  first guide groove 
       52  first guide roller 
       55  second guide mechanism 
       56  second guide groove 
       57  second guide roller 
       60  stopper 
     S 1 , S 2  beginning end position 
     E 1 , E 2  terminal end position 
     L axis