Abstract:
The invention provides a hard seal plug valve, comprising a valve body, wherein a tapered plug is arranged in the valve body, a bonnet is arranged at an upper part of the valve body, a drive valve rod penetrates the bonnet, an elastic hold-down mechanism is sheathed on the drive valve rod and arranged on a plug bearing seat, the plug bearing seat is connected with the tapered plug, and the plug bearing seat is held down when the elastic hold-down mechanism extends; and the hard seal plug valve characterized in that a telescopic mechanism is sheathed on the drive valve rod, the plug bearing seat is pushed upward when the telescopic mechanism extends, a valve rod bearing seat is arranged at the bottom of the drive valve rod, ends of the valve rod bearing seat pass through a planetary reduction mechanism, and the tapered plug is connected with the planetary reduction mechanism and rotates with the drive valve rod by the planetary reduction mechanism. In the invention, the tapered plug can reliably float and rotate under any circumstances. The drive torque of the plug valve is at least 7 times less than that of a general plug valve, therefore, when a motor is used, a general valve requires 2 minutes from opening to closing, and the valve of the invention only requires 3.8 seconds.

Description:
FIELD OF THE INVENTION 
     The invention relates to a hard seal plug valve. 
     DESCRIPTION OF THE RELATED ART 
     Owning to simple structure, quick opening and closing and relatively small pressure drop, plug valves are widely applied to a certain extent. The plug valves are divided into hard seal plug valves and soft seal plug valves. 
     Sealing and lubricating films must be established between the tapered outer surface of an existing soft seal plug valve and the tapered inner surface of a valve cavity. Axial seal pressure is arranged at the large end of a tapered plug, and the tapered plug still keeps the same seal pressure during rotation, thus the rotating torque is large, and the sealing surface also suffers from serious wear. High-temperature impact and vibration will damage the lubricating film, so that the plug is attached to the valve cavity, and cannot be rotated, opened and closed. When in use, the tapered plug is off the valve cavity once because of high temperature and sudden pressure rise in the line, causing the medium in the line to flow into the seal cavity, possibly washing the seal film away. 
     Although the hard seal plug valve is not provided with a seal film, the rotating torque is very large, and the sealing surface suffers from more serious wear. 
     Plug valves with plug being lifted firstly and then pressed after rotation once occurred, such as lift plug valves and double-acting plug valves. However, both need more than two operating mechanisms or more than two actions, so that the valves are complex in structure and inconvenient to operate. Therefore, the improved plug valves are not widely applied. 
     Invention patent ZL200710046094 discloses a floating tapered plug valve with simple structure, and “lifting the plug firstly, and then pressing it after rotation” can be completed by only one action. Although the patent solves the sealing and switching problems well, but it also has the following problems: 
     Firstly, a compression spring is used as the device for floating the tapered plug before the valve switching. When the tapered plug is jammed (locked) by the sealing surface of the seal cavity, the compression spring has static elasticity only instead of impact force, and the jammed (locked) tapered plug can be removed from the valve cavity by a rising impact force, thus the use of compression spring cannot reliably float the tapered plug. Meanwhile, the spring is required to have certain elasticity to float the tapered plug, but the elasticity needs to be overcome while the tapered plug is pressed. If there is no spring causing the tapered plug to float, an axial force of 10000N is applied to press the tapered plug to the seal pressure. After the floating spring is arranged, if the elasticity of the compression spring is 20000N after compression, additional 20000N axial force plus 10000N axial force is required to overcome the elasticity of the spring. Total axial force of 30000N is thus required to press the tapered plug, and the force applied is 3 times of the original force, that is, the driving force required to drive the valve rod is increased by 2 times additionally. 
     Secondly, a torque limiter is used to rotate the tapered plug. That is, when the tapered plug floats, the torque for rotating the tapered plug is fixed. A higher torque will cause the drive valve rod to remove from the tapered plug and skid, and the drive valve rod continues rotation and presses the tapered plug. When the valve is switched to the closed condition from the open condition, a swirling moment occurs as dynamic pressure caused by the flow rate of the fluid will prevent change in direction of the channel of the tapered plug. The swirling moment is the resistance stopping rotation of the tapered plug, and is associated with the pressure and flow rate of the fluid. Therefore, the torque limiter with fixed torque cannot ensure reliable rotation of the tapered plug in general. 
     SUMMARY OF THE INVENTION 
     The purpose of the invention is to provide a plug valve capable of closing and opening the valve quickly and reliably. 
     In order to achieve the purpose above, the technical solution of the invention provides a hard seal plug valve. The hard seal plug valve comprises a valve body which comprises a first through channel and a second through channel for flowing of a medium, a tapered valve cavity communicated with the first through channel and the second through channel, and a plug through port communicated with the first through channel and the second through channel in an open condition. A rotatable tapered plug for blocking the first through channel and the second through channel in a closed condition is arranged in the tapered valve cavity. A bonnet assembly is arranged at the upper part of the valve body, and a drive valve rod penetrates the bonnet assembly. A valve rod bearing seat is arranged at the bottom of the drive valve rod. The hard seal plug valve is characterized in that a telescopic mechanism allowing the tapered plug to move upward and an elastic hold-down mechanism allowing the tapered plug to move toward the tapered valve cavity are sheathed on the drive valve rod. A plug bearing seat is connected with the tapered plug, and the telescopic mechanism extends when the elastic hold-down mechanism retracts due to rotation of the drive valve rod. The tapered plug is pushed upward by the plug bearing seat, and the telescopic mechanism retracts and the elastic hold-down mechanism extends due to continual rotation of the drive valve rod. The tapered plug is pressed toward the tapered valve cavity by the plug bearing seat to be under the seal pressure. The valve rod bearing seat is provided with an upper limiting shaft shoulder and a lower limiting shaft shoulder, and a part between the upper limiting shaft shoulder and the lower limiting shaft shoulder is tapped on the valve rod bearing seat. A sun gear is sheathed on the threads of the valve rod bearing seat, and an inner gear coplanar with the sun gear is connected to the upper part of the valve body. Two or three planet gears are arranged between the inner gear and the sun gear, and a planet gear rotating shaft at the middle of the planet gears is connected with the tapered plug. When the drive valve rod begins to rotate, the sun gear only rotates upward and downward, but does not transfer torque. Only after the tapered plug moves upward and the sun gear is limited by the upper limiting shaft shoulder or the lower limiting shaft shoulder, the drive valve rod drives the sun gear to rotate, and drives the tapered plug to rotate to a certain angle and limit the tapered plug. At this moment, the planet gears slip while the drive valve rod can continue to rotate till completion of opening and closing operation. 
     In the invention, the telescopic mechanism driven by threads is used to float the tapered plug. When the tapered plug is floating, a planetary reduction mechanism is used to rotate the tapered plug. After rotation, the tapered plug is pressed toward the valve cavity by the elastic hold-down mechanism and is under seal pressure, thus achieving reliable floating, rotation and sealing of the tapered plug in any case. The driving moment of the plug valve is at least 7 times less than that of a general plug valve. For example, a DN100 and 4.0 MPa common hard seal plug valve needs the driving moment of 150N·m generally, but the driving force of 20N·m is enough for the valve of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a hard seal plug valve in a closed condition; 
         FIG. 2  is a schematic diagram of fit between a drive valve rod and an inner screw rod of a telescopic mechanism; 
         FIG. 3  is a schematic diagram of the hard seal plug valve in an intermediate condition when the plug has been turned; 
         FIG. 4  is a schematic diagram of fit of an elastic hold-down mechanism; 
         FIG. 5A  is a sectional view of the telescopic mechanism; 
         FIG. 5B  is a schematic diagram of several assemblies of the telescopic mechanism; 
         FIG. 6A  is a front view of an orthohexagonal upper switching pin; 
         FIG. 6B  is a top view of the orthohexagonal upper switching pin; 
         FIG. 7A  is a front view of an orthohexagonal lower switching pin; 
         FIG. 7B  is a top view of the orthohexagonal lower switching pin; 
         FIG. 8A  is a front view of a circular upper switching pin; 
         FIG. 8B  is a top view of the circular upper switching pin; 
         FIG. 9A  is a front view of a circular lower switching pin; 
         FIG. 9B  is a top view of the circular lower switching pin; 
         FIG. 10  is a structural diagram of a planetary reduction mechanism when the valve is closed after the drive valve rod rotates clockwise; 
         FIG. 11  is a schematic diagram of a four-way plug valve with the telescopic mechanism arranged below the tapered plug; and 
         FIG. 12  is a schematic diagram of the four-way plug valve with the telescopic mechanism driven by magnetic induction arranged below the tapered plug. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention is further described in combination with examples as follows. 
     Example 1 
     The invention provides a hard seal plug valve, and the work process is generally as follows: a plug valve shown in  FIG. 1  is in off state, and a plug through port  30  at the middle of a tapered plug  2  is communicated with a first through channel  33  and a second through channel  24  of a valve body  1  at the moment. When the plug valve is opened, a drive valve rod  5  is rotated anticlockwise and an elastic hold-down mechanism retracts intermediately.  FIG. 2  shows that the drive valve rod  5  is in clearance fit with an inner screw rod  52  of a telescopic mechanism  15 . When elastic stroke of a disk spring  9  of the elastic hold-down mechanism extends to fully relaxed condition, the inner screw rod  52  of the telescopic mechanism  15  starts to rotate anticlockwise with the drive valve rod  5 , and the telescopic mechanism  15  starts to extend to push upward the plug bearing seat  14 , thus driving the tapered plug  2  upward. The drive valve rod  5  is continuously rotated anticlockwise when the tapered plug rises to a certain position, the tapered plug  2  is driven by a planetary reduction mechanism, both ends of the plug through port  30  are aligned with the first through channel  33  and the second through channel  24  respectively, the telescopic mechanism  15  retracts at the same time, while the elastic hold-down mechanism extends to press the plug bearing seat  14  so as to drive the tapered plug  2  down until the tapered plug  2  drops in place, then the valve is opened. The structure of the invention is further described below in combination with the drawings. 
       FIG. 1  and  FIG. 3  show that the hard seal plug valve of the invention comprises the valve body  1 . The first through channel  33  and the second through channel  24  for flow of the medium are arranged on the left and right sides of the valve body  1 , and a tapered valve cavity  32  communicated with the first through channel  33  and the second through channel  24  is arranged in the valve body  1 . A valve body bearing seat  3  is arranged on the top of the valve body  1  by bonnet locking screws  25  on both sides. A flange locking gasket  26  is arranged between the valve body  1  and the valve body bearing seat  3 . A valve body flange  28  is fixed at the bottom of the valve body  1  by a valve body flange locking screw  27 . A bonnet  6  is arranged on the valve body bearing seat  3 , a lock nut  4  is inserted into the top end of the bonnet  6 , and a seal assembly  7  is arranged between the lock nut  4  and the bonnet  6 . The tapered plug  2  is arranged in the tapered valve cavity  32  of the valve body  1 , and the plug through port  30  is arranged at the middle of the tapered plug  2 . The plug through port  30  is communicated with the first through channel  33  and the second through channel  24  when the valve is in open condition. Balance holes  29  are arranged on both sides of the plug through port  30 . The tapered plug  2  can float up and down and rotate in the tapered valve cavity  32 . The first through channel  33  and the second through channel  24  are blocked by the tapered plug  2  when the valve is in closed condition. The drive valve rod  5  is arranged in the valve body bearing seat  3  after passing through the lock nut  4 , the bonnet  6  and the seal assembly  7 . 
       FIG. 4  shows that the elastic hold-down mechanism is sheathed on the drive valve rod  5 . The elastic hold-down mechanism comprises an inner hold-down housing  11 . The inner hold-down housing  11  is sheathed on the drive valve rod  5 , and an outer hold-down housing  12  is sheathed on the inner hold-down housing  11 . The inner hold-down housing  11  is coordinated with the outer hold-down housing  12  by a thread pair. Needle bearings  10  are arranged on the inner hold-down housing  11  and the outer hold-down housing  12 . The needle bearings  10  are sheathed on the drive valve rod  5 . The disk spring  9  is arranged between the needle bearings  10  and the valve body bearing seat  3 . The inner hold-down housing  11  and the outer hold-down housing  12  are arranged on the plug bearing seat  14 , and the plug bearing seat  14  is connected with the tapered plug  2 . 
       FIG. 5A  and  FIG. 5B  show that the telescopic mechanism  15  is arranged outside the drive valve rod  5 . The telescopic mechanism  15  comprises a liner  51  with inner thread and outer thread on both sides, the inside and the outside of the liner  51  are provided with inner screw rods  52  and housings  48  respectively, and the liner  51  is arranged between the inner screw rod  52  and the housing  48  by a key. The inner screw rod  52  is sheathed on the drive valve rod  5 . The middle part of the inner screw rod  52  is an inner hole with a key slot in clearance fit with the drive valve rod  5  with a key pin. The inner screw rod  52  is driven to rotate with the drive valve rod  5 , but its axial movement is not limited. The first thread with an upper shaft shoulder  57  and a lower shaft shoulder  58  is arranged on the outside of the inner screw rod  52 . The first thread is a clockwise thread. The second thread with the upper and lower shaft shoulders are arranged on the inside of the housing  48 . The inside and the outside of the housing  51  are provided with inner thread and outer thread respectively. The outer housing  48  is sheathed on the liner  51  and coordinated with the outer thread of the liner  51 . The upper and lower shaft shoulders of the outer housing  48  can limit the movement range of the liner  51 . The length and pitch of the thread between the upper and lower shaft shoulders are equal to the length and pitch of the outer thread of the inner screw rod  52 . The inner thread of the liner  51  is coordinated with the first thread of the inner screw rod  52  and is short screw only moving between the upper shaft shoulder  57  and the lower shaft shoulder  58  of the inner screw rod  52 . The outer thread and the inner thread of the liner  51  have equal pitch but opposite rotation directions. Therefore, the first thread and the inner thread form a first thread pair, the second thread and the outer thread form a second thread pair, and the rotation directions of the first thread pair and the second thread pair are opposite. A rotating downward caging device  53  and a rotating upward caging device  54  are arranged between the outer housing  48  and the inner screw rod  52 . The rotating downward caging device  53  and the rotating upward caging device  54  are arranged above and blow the liner  51  respectively. The upper and lower ends of the inner part of the outer housing  48  are provided with key slots which are similar to the rotating downward caging device  53  and the rotating upward caging device  54  in shape, and cause the rotating downward caging device  53  and the rotating upward caging device  54  sheathed in the outer housing  48  to fail to relatively rotate. The shape of the outer part of the outer housing  48  can limit its rotation and prevent rotation of the outer housing  48  in coordination with the plug bearing seat  14 . The rotating downward caging device  53  and the rotating upward caging device  54  are two heads sheathed on the inner screw rod  52  and in the liner  51 . 
     The rotating downward caging device  53  comprises an upper switching pin  60 . The bottom of the upper switching pin  60  is provided with an upper fixture block  61 . An upper insertion slot  62  is arranged on the upper edge of the liner  51 . The upper insertion slot  62  is coordinated with the upper fixture block  61  so that the liner  51  can not rotate anticlockwise but can rotate clockwise. A first spring  50  is connected between the upper switching pin  60  and the inner screw rod  52 . The rotating upward caging device  54  comprises a lower switching pin  63 . The bottom of the lower switching pin  63  is provided with a lower fixture block  64 . A lower insertion slot  65  is arranged on the lower edge of the liner  51 . The lower insertion slot  65  is coordinated with the lower fixture block  64  so that the liner  51  can not rotate clockwise but can rotate anticlockwise. A second spring  55  is connected between the lower switching pin  63  and the inner screw rod  52 . Either of the upper switching pin  60  and the lower switching pin  63  of the rotating downward caging device  53  and the rotating upward caging device  54  is blocked in the slot of the liner  51  under the action of the first spring  50  and the second spring  55 . 
     The inner walls of the upper switching pin  60  and the lower switching pin  63  are a-step shape. The upper part of the inner screw rod  52  is provided with the upper shaft shoulder  57  which is coordinated with the step-shaped inner wall of the upper switching pin  60 . The lower shaft shoulder  58  is arranged on the lower part of the inner screw rod  52 , and the lower shaft shoulder  58  is coordinated with the step-shaped inner wall of the lower switching pin  63 . 
     If the first thread between the upper shaft shoulder  57  and the lower shaft shoulder  58  of the inner screw rod  52  is a clockwise thread with length L and the length of the liner  51  is T, the inner thread of the liner  51  is also a clockwise thread and the outer thread must be the anticlockwise thread, T must be less than L, and the pushed upward stroke S of the whole telescopic mechanism  13  is L−T. 
     When the telescopic mechanism  15  is in the condition as shown in  FIG. 5B , the upper fixture block  61  of the upper switching pin  60  is blocked in the upper insertion slot  62  of the liner  51 , and the step-shaped inner wall in the lower switching pin  63  is blocked by the inner screw rod  52 , so the lower fixture block  64  is separated from the lower insertion slot  65  of the liner  51 . And the drive valve rod  5  is rotated anticlockwise. When the drive valve rod  5  is in clearance fit with the inner screw rod  52  through rotation, the inner screw rod  52  is driven to rotate with the drive valve rod  5  anticlockwise. As the upper fixture block  61  is blocked in the upper insertion slot  62  of the liner  51  and the liner  51  rotates anticlockwise, the second thread pair does not work. At the same time, the inner screw rod  52  rises under the action of the first thread pair. The upper switching pin  60  is driven upward after the upper shaft shoulder  57  of the inner screw rod  52  contacts the step-shaped inner wall of the upper switching pin  60 . When the inner screw rod  52  rises until the lower end surface D of the liner  51  is in contact with the end surface of the lower shaft shoulder  58  of the inner screw rod  52 , the upper fixture block  61  is completely separated from the upper insertion slot  62 , the liner  51  can rotate anticlockwise, and the lower fixture block  64  can be blocked in the lower insertion slot  65  (ready for clockwise rotation of the drive valve rod  5 ). The drive valve rod  5  is continuously rotated. As movement of the first thread pair is limited by the end surface of a lower lug  58  of the inner screw rod  52 , the inner screw rod  52  drives the liner  51  to drop with the liner  51  under the action of the second thread pair until the lower end surface D of the liner  52  is in contact with the surface E of the lower shaft shoulder of the outer housing  48 . Then the inner screw rod  52  is flush with the outer housing  48  to complete an extension and retraction process. 
     In order to ensure that the upper switching pin  60  and the lower switching pin  63  will not rotate relative to the outer housing  48 , the outer walls of the upper switching pin  60  and the lower switching pin  63  can be designed to be regular polygon as shown in  FIG. 6A  to  FIG. 7B . Then the inner wall of the outer housing  48  without the second thread on both ends is a regular polygon which is coordinated with the shape of the outer walls of the upper switching pin  60  and the lower switching pin  63 . 
     If the outer walls of the upper switching pin  60  and the lower switching pin  63  are circular, as shown in  FIG. 8A  to  FIG. 9B , straight stroke groove is arranged on the outer walls of the upper switching pin  60  and the lower switching pin  63 , and one side of an outer housing transmission flat key  49  is arranged in the straight stroke groove, while the other side is fixed onto the inner wall of the outer housing  48 . 
       FIG. 1  and  FIG. 3  show that a valve rod bearing seat  16  is arranged at the bottom of the drive valve rod  5 , and a thread with an upper limiting shaft shoulder  17  and a lower limiting shaft shoulder  19  is set at the bottom of the valve rod bearing seat  16 . The thread passes through the planetary reduction mechanism. The tapered plug  2  is connected with the planetary reduction mechanism and rotates with the drive valve rod  5  along with the planetary reduction mechanism. When the drive valve rod  5  rotates until the elastic hold-down mechanism retracts entirely, the telescopic mechanism  15  totally extends and drives the tapered plug  2  upward to the highest position, and the upper limiting shaft shoulder  17  obstructs the sun gear  18  of the planetary reduction mechanism, thus driving the sun gear  18  to rotate. When the drive valve rod  5  rotates in an opposite direction until the elastic hold-down mechanism retracts entirely, the telescopic mechanism  15  totally extends and drives the tapered plug  2  upward to the highest position, and the lower limiting shaft shoulder  19  obstructs the sun gear  18  of the planetary reduction mechanism. 
     In combination with  FIG. 10 , the planetary reduction mechanism comprises the sun gear  18 . The sun gear  18  is sheathed on the thread between the upper limiting shaft shoulder  17  and the lower limiting shaft shoulder  19 . When the drive valve rod  5  starts rotation, the sun gear  18  rotates upward and downward only without torque transmission. Only when the rotation between the sun gear  18  and the drive valve rod  5  is limited by the upper limiting shaft shoulder  17 , the drive valve rod  5  drives the sun gear  18  to rotate. An inner gear  23  is fixedly arranged at the upper part of the valve body  1  coplanar with the sun gear  18 . Three planet gears  22  engaged with the inner gear  23  and the sun gear  18  are arranged between inner gear  23  and the sun gear  18 , and a planet gear rotating shaft  21  connected with the tapered plug  2  is arranged among the planet gears  22 . Three continuous tooth sections with the same stroke are arranged on the inner gear  23 , and a planet gear  22  is engaged onto each continuous tooth section which is provided with 2 movable tooth assemblies. 
     For the purpose of limiting, an arc stroke groove is arranged on the inner gear  23 , and a valve core limiting pin  31  fixed on the tapered plug  2  is arranged in the arc stroke groove. Radian of the arc stroke groove is equivalent to the rotation angle required for the tapered plug  2  from the open condition to the closed condition or from the closed condition to the open condition (generally 90°). 
     The movable tooth assembly comprises a first movable tooth  40  and a second movable tooth  37 . The first movable tooth  40  is arranged symmetrical with the second movable tooth  37 . The first movable tooth  40  and the second movable tooth  37  rotate around a movable gear shaft  39 . A first movable tooth spring  42  and a second movable spring  38  are connected with the first movable tooth  40  and the second movable tooth  37  separately. A first limit stop  41  and a second limit stop  43  are arranged above and below the ends of the first movable tooth  40  and the second movable tooth  37  separately. 
     The drive valve rod  5  drives the sun gear  18  to rotate clockwise, and the sun gear  18  drives the planet gears  22  to rotate anticlockwise and the tapered plug  2  to rotate clockwise to point A. Then the teeth of planet gears  22  and the first movable tooth  40  slip, and planet gears  22  only rotate without driving the tapered plug  2 . Similarly, the second movable tooth  37  slips while the drive valve rod  5  drives the tapered plug  2  to point B when the sun gear  18  to rotates anticlockwise. 
     In combination with the drawings, the whole process from the open to closed condition of the hard seal plug valve provided by the invention is described below: as shown in  FIG. 1 , after the drive valve rod  5  is rotated clockwise to the bottom, the plug valve is in off condition. The inner hold-down housing  11  and the outer hold-down housing  12  then stagger and extend, while the outer housing  48  is level with the inner screw rod  52 , and a certain stroke is reserved between the lower limiting shaft shoulder  19  and the sun gear  18 . After the drive valve rod  5  is rotated anticlockwise, driven by the drive valve rod  5 , the inner hold-down housing  11  rotates upward relative to the outer hold-down housing  12 , and the elastic hold-down mechanism retracts, while the inner screw rod  52  rotates upward by the drive valve rod  5  and push upward the plug bearing seat  14 , thus driving the tapered plug  2  to move upward. When the drive valve rod  5  is rotated until the elastic hold-down mechanism retracts entirely, the inner screw rod  52  rotates upward and drives the tapered plug  2  to the highest position. The lower limiting shaft shoulder  19  obstructs the sun gear  18  so as to drive the sun gear  18  to rotate anticlockwise and drive the planet gears  22  to rotate clockwise and revolves anticlockwise around the sun gear  18 , thus driving the tapered plug  2  to rotate. The tapered plug  2  is rotated from point A to point B. The valve core limiting pin  31  fixed onto the tapered plug  2  is moves to the position due to limitation by the arc stroke groove arranged on the inner gear  23 . Then the plug through port  30  on the tapered plug  2  is aligned with the first through channel  33  and the second through channel  24  on both ends. As shown in  FIG. 3 , the plug valve is opened, the teeth of the planet gears  22  and the second movable tooth  37  slip, and the plant gears  22  rotate only without driving the tapered plug  2 . Meanwhile, the lower lug of the inner screw rod  52  is obstructed by the lower end surface D of the liner  51 . The inner screw rod  52  drives the liner  51  to rotate downward, and the telescopic mechanism  15  starts retraction and the elastic hold-down mechanism starts extension again until the inner screw rod  52  is level with the outer housing  48  and the inner hold-down housing  11  and the outer hold-down housing  12  stagger and extend to the maximum position. Then the tapered plug  2  is totally blocked in the tapered valve cavity  32  of the valve body  1 . If the plug valve needs to be closed, the drive valve rod  5  is rotated clockwise according to the same principle to open the valve. 
     Example 2 
       FIG. 11  is a schematic diagram of a four-way plug valve when a telescopic mechanism is arranged below the tapered plug. The difference between the plug valve in this example and the plug valve in example 1 is that the telescopic mechanism  15  is arranged below the tapered plug  2  while the tapered plug  2  has a four-way channel in coordination with the valve body  1 . Other mechanisms and their principles are the same as example 1. 
     Example 3 
     As shown in  FIG. 12 , the difference between this example and example 2 is that the mechanism is driven by magnetic induction, that is, a ring of magnet  66  is arranged around the drive valve rod  5  at the top end of the drive valve rod  5  and is covered by a shielding cover  67 . The shielding cover  67  is made of a nonmagnetic material like stainless steel, copper or plastic so that the magnetic force of the magnet  66  will not be obstructed. In use, a ring of magnet is arranged outside the shielding cover  67 . The magnet inside the shielding cover  67  corresponds to the magnet outside the shielding cover but they have opposite polarity. When the magnet outside the shielding cover  67  rotates, it drives the magnet  66  in the shielding cover  67  to rotate, thus driving the drive valve rod  5  to rotate and achieve magnetic induction. Other mechanisms of this example and their principles are the same as example 1.