Abstract:
A fluid control valve for a pipeline pig includes a main valve and a mechanism for operating the main valve. The main valve comprises a valve body communicated to a fluid pipe, a main valve core movably disposed in the inner chamber of the valve body, and a main valve stem connected to the main valve core. The operating mechanism includes a hydrocylinder, which comprises a piston disposed in the cylinder, and a piston rod connected to the piston. The piston rod is transmissibly connected with the main valve stem so as to drive the main valve core by the main valve stem. A valve device includes a pilot valve, positioned in the pipeline which communicates the fluid pipe with the hydrocylinder, and an operator for controlling the actuation of the pilot valve so as to enable the piston to move reciprocally by the pressure of fluid in the fluid pipe.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a fluid-controlled valve, and in particular to a fluid-controlled valve for pipeline pig, which is capable of allowing a pipeline pig to pass through. 
     BACKGROUND OF THE INVENTION 
     A pipeline for transferring fluid, especially a pipeline having deposit sediment and exfoliation corrosion, needs to be cleaned through running a pipeline pig in the pipeline to resume the transfer performance of the pipeline. Generally, since the pipeline pig has to closely match the hole of the pipe, the pipeline pig can only be used to clean a section of pipeline provided with fluid control valves and associated means capable of allowing the pipeline pig to pass through. Thus, the pipe-cleaning work is difficult to do and takes a long period of time, resulting in much labor and high cost. A fluid control valve which can both control the fluid and allow a pipeline pig to pass is known in the art. A known sluice valve, for example, capable of allowing a pipeline pig to pass includes a through hole, which matches the hole of the pipe, formed on a plate valve clack. The blind flange portion of the valve clack is used to realize the function of a gate valve, and the through hole in the valve clack is used to let a pipeline pig to pass through. This arrangement only solves the problem of the passage of a pipeline pig through a ram valve, but not other valves. And when cleaning the pipe, the valves are controlled manually or by external hydraulic means. As a result, the valve has the disadvantages that it is inconvenient to control and requires an external energy source. 
     SUMMARY OF THE INVENTION 
     In view of this, the object of the present invention is to provide a fluid-controlled valve for pipeline pig which is capable of allowing a pipeline pig to pass through, and the working state of the fluid-controlled valve can be controlled by the fluid to be controlled. 
     To achieve the object of the invention, there is provided in an embodiment of the present invention a fluid-controlled valve for pipeline pig which comprises a main valve and a controlling device. The main valve comprises a valve body connected with a fluid pipe, a main valve core movably disposed in the inner cavity of the valve body and a main valve stem connected with the main valve core. The controlling device comprises a hydraulic cylinder having a piston disposed therein and a piston rod connected with the piston, where the piston rod is operationally connected with the main valve stem so as to control the main valve core through the main valve stem. Valve means includes a pilot valve provided in a pipeline which communicates the fluid pipe and the hydraulic cylinder. A controller controls the actuation of the pilot valve so as to control the reciprocating movement of the piston by the pressurized fluid in the fluid pipe. 
     The main valve of the present invention can be a self-operated valve, such as an adjustable differential flow shuttle valve, a check valve, a shuttle check valve, and a shuttle type pipeline-bursting-protection valve. The main valve can also be an external-operated valve, such as a ball valve, a control valve, a shuttle control valve, a stop valve, and a shuttle stop valve. 
     The fluid-controlled valve for pipeline pig of the present invention has following advantages and effects.
         1. With the arrangement of the present invention in which the hydraulic cylinder is transmissibly coupled with the main valve and the pilot valve cooperates with the fluid pipe, the pressurized fluid in the fluid pipe can be introduced into and discharged from the hydraulic cylinder, and the kinetic energy of the fluid itself is used to drive the piston of the hydraulic cylinder, thereby controlling the movement of the valve core of the main valve through the valve stem, opening the main valve to cause its flow path to coincide and communicate with the fluid pipe, so that the pipeline pig can pass through the main valve smoothly;   2. In the present invention, different kinds of controllers are used to control the pilot valve. A controller may include, for example, an electromagnetic switch and an electric controller; an electromagnetic switch, a sensor and an electric controller; a hydraulic pressure-holding cylinder and a restoring valve; or a lever. All of these controllers are capable of utilizing the moving pipeline pig to keep the main valve in a state of allowing the pipeline pig to pass until the pipeline pig has passed through the valve and then causing the main valve to return to the normal operating state, thereby having an advantage of ensuring that the pipeline pig can pass through the main valve smoothly. Among these controllers, the controller comprising a hydraulic pressure-holding cylinder and a restoring valve is particularly suitable for the applications where there is no power, such as electricity and the like, or no available human operator;   3. With the controller comprising an electromagnetic switch and an electric controller, the main valve is controlled via the electric controller, the pilot valve and the hydraulic cylinder. This arrangement not only has the advantage of being capable of causing the main valve to move to a state of allowing the pipeline pig to pass through, keeping the state by a time delay and returning to the normal operation state, but also has the advantage of being capable of controlling the fluid by operating the main valve. This is particularly suitable for applications where there is no power, such as electricity and the like, or no available human operator.   4. With the two-way control valve of the invention, it is possible to adjust the flow rate of the fluid introduced into and discharged from the hydraulic cylinder, thereby having the advantage of adjusting the moving speed of the main valve.   5. The main valve of the invention may present different configurations. The main valve can be constructed as follows: (1) the main valve stem is coaxial connected with the piston rod of the hydraulic cylinder, and the main valve core reciprocates in the cavity of the main valve; (2) the main valve stem is rotatably coupled with the main valve core and is perpendicularly connected with the piston rod of the hydraulic cylinder through a gear-rack pair, so that the main valve stem reciprocates while rotating; (3) the valve core of the main valve reciprocates in the main valve cavity; (4) or the valve core of the main valve rotates in the main valve cavity.       

    
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
       The preferred embodiments of the invention will be described in detail in connection with accompanying drawings, in which 
         FIG. 1  is a schematic view showing the structure of a fluid-controlled valve for pipeline pig in accordance with the first embodiment of the invention, wherein the main valve is in a normal working state for controlling the fluid; 
         FIG. 2  is a schematic view showing the structure of a fluid-controlled valve for pipeline pig in accordance with the first embodiment of the invention, wherein the main valve is in a state for allowing a pipeline pig to pass; 
         FIG. 3  is a schematic view showing the structure of a fluid-controlled valve for pipeline pig in accordance with the second embodiment of the invention; 
         FIG. 4  is a schematic view showing the structure of a fluid-controlled valve for pipeline pig in accordance with the third embodiment of the invention, wherein the main valve is in a normal working state for controlling the fluid; 
         FIG. 5  is a schematic view showing the structure of a fluid-controlled valve for pipeline pig in accordance with the third embodiment of the invention, wherein the main valve is in a state for allowing a pipeline pig to pass; 
         FIG. 6  is a partial view, wherein a restoring valve is pushed to its upper position by a pipeline pig; 
         FIG. 7  is a schematic view showing the structure of a fluid-controlled valve for pipeline pig in accordance with the fourth embodiment of the invention; 
         FIG. 8  is a schematic view showing the structure of a fluid-controlled valve for pipeline pig in accordance with the fifth embodiment of the invention, wherein the main valve is in a normal working state for controlling the fluid; 
         FIG. 9  is a schematic view showing the structure of a fluid-controlled valve for pipeline pig in accordance with the fifth embodiment of the invention, wherein the main valve is in a state for allowing a pipeline pig to pass; 
         FIG. 10  is a schematic view showing the structure of a fluid-controlled valve for pipeline pig in accordance with the sixth embodiment of the invention; 
         FIG. 11  is a schematic view showing the structure of a fluid-controlled valve for pipeline pig in accordance with the seventh embodiment of the invention, wherein the main valve is in a normal working state for controlling the fluid; 
         FIG. 12  is a schematic view showing the structure of a fluid-controlled valve for pipeline pig in accordance with the seventh embodiment of the invention, wherein the main valve is in a state for allowing a pipeline pig to pass; and 
         FIG. 13  is a schematic view showing the structure of a fluid-controlled valve for pipeline pig in accordance with the eighth embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
       FIGS. 1 and 2  illustrate the first embodiment of the fluid-controlled valve for pipeline pig in accordance with the present invention. As shown in  FIGS. 1 and 2 , the fluid-controlled valve for pipeline pig of this embodiment is comprised of a main valve  1  and a controlling device, where the controlling device is comprised of a hydraulic cylinder  6 , a pilot valve  11  and a controller. 
     The main valve  1  comprises a valve body  2  having a cavity of a conventional shape and is connected to a fluid pipe  3  in a conventional manner. The main valve is formed with a flow path which matches with the flow path of the fluid pipe so as to allow a pipeline pig  19  to pass. In other words, the shape and size of the flow path of the main valve are substantially the same as the shape and size of the flow path of the fluid pipe. On the upper end of the valve body  2  there is a valve cover  4 . The valve body can be integral with the valve cover as shown in the figures, or they can be separate members and coupled with each other through a flange. The valve stem  5  of the main valve can be fixedly secured to, or rotatably connected to the valve core (not shown) of the main valve. The valve core of the main valve can reciprocate in the valve body  2 , and thus the main valve can be a gate valve, a sluice valve or a plunger valve. 
     The hydraulic cylinder  6  is a conventional cylinder which is integrated with the main valve  1 . A piston  7  reciprocates in the hydraulic cylinder and is fixedly secured to a piston rod  8 . The chamber of the hydraulic cylinder is divided by the piston  7  into an upper chamber  9  and a lower chamber  10 . The valve stem  5  of the main valve extends through the valve cover  4  and is integrally coupled with the piston rod  8  coaxially. 
     The pilot valve  11  is a conventional two-position multi-way piston valve, and can be installed by means of a support on the fluid pipe  3  on the upstream side of the main valve. In the case  12  of the pilot valve there are formed an upper chamber connection port  13 , a lower chamber connection port  14 , a fluid pipe connection port  15  and an atmosphere connection port  16 . The pilot valve core  17  inside the valve case is fixedly coupled to the pilot valve stem  18 , and the lower end of the pilot valve stem extends into the fluid pipe  3  by an appropriate depth such that a running pipeline pig  19  can push upward the pilot valve stem and hence the pilot valve core. The upper end of the pilot valve stem  18  extends out of the valve case and connects with a disk  30 . Between the pilot valve stem and the fluid pipe there should be disposed sealing means. The pilot valve core  17  is formed with a passage way  20  and a release passage way  21 , when the core is at its upper position inside the case, the passage way  20  connects the lower chamber connection port  14  and the fluid pipe connection port  15 , and the release passage way  21  connects the upper chamber connection port  13  and the atmosphere connection port  16 . The pilot valve core  17  is also formed with a restoring passage way  22  and a release passage way  23 . When the core is at its lower position inside the case, the restoring passage way  22  connects the upper chamber connection port  13  and the fluid pipe connection port  15 , and the release passage way  23  connects the lower chamber connection port  14  and the atmosphere connection port  16 . The upper chamber connection port  13  is connected with the upper chamber  9  of the hydraulic cylinder  6  via a pipeline  24 , and the lower chamber connection port  14  is connected with the lower chamber  10  of the hydraulic cylinder via a pipeline  25 . The fluid pipe connection port  15  is connected with the fluid pipe  3  via a pipeline; and the atmosphere connection port  16  can be opened to atmosphere via a pipeline, and a reservoir  26  can be disposed under the pipeline outlet. Two-way control valves  27  and  28  are respectively provided in pipelines  24  and  25 . The inventor&#39;s adjustable differential flow shuttle valve (Chinese Patent No. 87103004.7 granted to the inventor and filed in 1987) can be used as the two-way control valves to control the flow of fluid in two directions in pipelines. A two-position multi-way valve with a rotating valve core can also be used as the pilot valve, and when using such a valve, a corresponding driving mechanism for the valve core should be used. 
     The controller is comprised of an electromagnetic switch  29 , a sensor  31 , an electric controller  32  and the like. An electromagnetic switch with a conventional structure can be used as the electromagnetic switch  29 . Under the control of the electric controller, the electromagnetic switch can attract and engage or release the disk  30  which is connected with the upper end of the pilot valve stem  18 . The electromagnetic switch can be formed such that it shares a common case with the pilot valve. A conventional inductance sensor, which can cooperate with the pipeline pig  19 , can be used as the sensor  31  and is mounted to the fluid pipe  3  on the downstream side of the main valve. As the electric controller  32 , a conventional electric controller can be used, and the electric controller is mounted at such a place that it is easy to operate. Wires  33  and  34  are used to electrically connect the electric controller with the electromagnetic switch  29  and the sensor  31  respectively. 
     When the fluid-controlled valve for pipeline pig of this embodiment is in a set, normal working state, e.g. for controlling the fluid, the pilot valve stem  18  of the pilot valve  11  extends into the fluid pipe  3 , as shown in FIG.  1 . The pilot valve core  17  is at its lower position in the case such that the passage way  20  and the release passage way  21  in the pilot valve core are cut off simultaneously, whereas the restoring passage way  22  connects the upper chamber connection port  13  and the fluid pipe connection port  15 , while the release passage way  23  connects the lower chamber connection port  14  and the atmosphere connection port  16 . The pressurized fluid in the fluid pipe  3  enters the upper chamber  9  of the hydraulic cylinder  6  through fluid pipe connection port  15  of pilot valve  11 , restoring passage way  22 , upper chamber connection port  13 , pipeline  24  and two-way control valve  27  such that the fluid pressure in the upper chamber of the hydraulic cylinder is substantially equal to the fluid pressure in the fluid pipe  3 . The lower chamber  10  of the hydraulic cylinder is opened to the atmosphere through pipeline  25 , lower chamber connection port  14  of pilot valve  11 , release passage way  23  and atmosphere connection port  16  such that the pressure in the lower chamber  10  of the hydraulic cylinder is equal to the air pressure. That is, the pressure in the upper chamber of hydraulic cylinder  6  is greater than that in the lower chamber. Under the action of the fluid pressure, the piston  7  in hydraulic cylinder  6  is pushed to the lower portion of the hydraulic cylinder, and the main valve core is pushed to its lower position by the piston via the piston rod  18  and the main valve stem  5  such that the fluid-controlled valve is in the normal working state. 
     At the time of using the pipeline pig  19  to clean the fluid pipe  3 , as shown in  FIG. 2 , when the pipeline pig  19  comes to the pilot valve  11  at the upstream side of the main valve  1 , the pilot valve stem  18  is pushed upward, causing the pilot valve core  17  to ascend to the upper portion of the case. At this time, the disk  30  engages the electromagnetic switch  29  and the electromagnetic switch is energized to attractively engage the disk, causing (1) the restoring passage way  22  and the release passage way  23  of the pilot valve core  17  to be cut off simultaneously, (2) the passage way  20  to connect the lower chamber connection port  14  and the fluid pipe connection port  15 , and at the same time (3) the release passage way  21  to connect the upper chamber connection port  13  and the atmosphere connection port  16 . The pressurized fluid in the fluid pipe  3  enters the lower chamber  10  of the hydraulic cylinder  6  through fluid pipe connection port  15  of pilot valve  11 , passage way  20 , lower chamber connection port  14 , pipeline  25  and two-way control valve  28 , such that the fluid pressure in the lower chamber is substantially equal to the fluid pressure in the fluid pipe  3 . Upper chamber  9  of the hydraulic cylinder  6  is opened to the atmosphere through pipeline  24 , upper chamber connection port  13  of pilot valve  11 , release passage way  21  and atmosphere connection port  16  such that the pressure in the upper chamber  9  of the hydraulic cylinder is the air pressure. That is, the pressure in the lower chamber of the hydraulic cylinder is greater than that in the upper chamber. Under the action of the electromagnetic switch  29 , the pilot valve core  17  of the pilot valve  11  remains at its ascended position such that the flow path from the fluid pipe  3  to the lower chamber  10  of hydraulic cylinder  6  is in an open state, and the pressurized fluid in the fluid pipe  3  continuously enters the lower chamber of the hydraulic cylinder such that the piston  7  is pushed upward to its upper position in the hydraulic cylinder. Thus, the main valve core is lifted through the main valve stem  5  of the main valve and the piston rod  8 , and the main valve  1  presents a fully opened state with its flow path coinciding and communicating with the flow path of the fluid pipe, so that the running pipeline pig  19  can pass through smoothly, and the fluid-controlled valve is in a state of allowing the pipeline pig to pass. 
     When the pipeline pig  19  comes to the sensor  31  on the downstream side of the main valve  1 , the sensor  31  sends to the electric controller  32  via the wire  33  a signal indicative of the passage of the pipeline pig through the main valve. After receiving the signal transmitted by the sensor  31  indicating that the pipeline pig has passed through the main valve, the electric controller cuts off the power to the electromagnetic switch so as to release the disk  30  and hence the pilot valve core  17 . The pilot valve core descends and returns to its original position under the action of gravity of the pilot valve core or a biasing device otherwise provided. The pressurized fluid in the fluid pipe  3  again enters the upper chamber  9  of the hydraulic cylinder  6  via the pilot valve  11 . At the same time, the fluid in the lower chamber  10  of the hydraulic cylinder is discharged to the atmosphere or the reservoir  26  via the pilot valve, and the piston  7  descends and returns to its original position. Thus, the fluid-controlled valve returns to its normal working state. 
     When the present fluid-controlled valve is in its normal working state for fluid control, the pilot valve  11  can be controlled by the electric controller  32  through the electromagnetic switch  29  to selectively communicate the fluid pipe  3  or the atmosphere with the upper or lower chamber  9  or  10  of the hydraulic cylinder according to requirements, so as to control the ascension or descension of the piston  7  in the hydraulic cylinder, and then to control the opening, closing and degree of openness of the main valve through the piston rod  8  and the main valve stem  5 , thereby realizing the control of the fluid. 
     Embodiment 2 
       FIG. 3  illustrates the second embodiment of the fluid-controlled valve for pipeline pig in accordance with the present invention. As shown in  FIG. 3 , the embodiment&#39;s general arrangement is substantially the same as that of embodiment 1, except that the pilot valve  11  is not provided with a pilot valve stem  18  extendable into the fluid pipe, and the sensor  31  fitted onto the fluid pipe and the wire  33  connecting the sensor are omtined. 
     In the fluid-controlled valve for pipeline pig of the second embodiment, the electric controller is used to control the operation of the pilot valve and then to control the piston  7  in the hydraulic cylinder and hence the ascension and descension of the main valve core of the main valve  1 , thereby achieving the fluid control function and the pig passage function of the main valve. The fluid-controlled valve for pipeline pig of this embodiment has the advantage of a simple arrangement. 
     Embodiment 3 
       FIGS. 4 ,  5  and  6  illustrate the third embodiment of the fluid-controlled valve for pipeline pig in accordance with the present invention. As shown in  FIGS. 4 ,  5  and  6 , the main valve  1  and the hydraulic cylinder  6  and the pilot valve  11  of the controlling device in the third embodiment are the same as those in embodiment 1, but the controller of the controlling device is comprised of a hydraulic pressure-holding cylinder  35 , a restoring valve  41 , etc. 
     The hydraulic pressure-holding cylinder  35  is a conventional piston hydraulic cylinder and can be superposed on the top of the pilot valve  11  to be integral with the pilot valve such that the cylinder  35  and the valve  11  are separated by a partition  36 . The hydraulic pressure-holding cylinder and the pilot valve can also, however, be separate components. In the chamber above a holding piston  37  of the hydraulic pressure-holding cylinder there is provided a restoring spring  38 . The piston rod  39  of the holding piston extends through the partition  36  to connect with the valve core  17  of the pilot valve, and between the piston rod and the partition there is provided a sealing means. 
     The restoring valve  41  is a conventional two-position three-way piston valve and can be installed on the fluid pipe  3  on the downstream side of main valve  1  with a support. In the restoring valve there is provided a restoring valve core  42 , and the lower end of a restoring valve stem  43  connected with the restoring valve core  42  extends into the fluid pipe  3  by an appropriate depth such that a running pipeline pig  19  can push upward the restoring valve stem and hence the restoring valve core. Between the restoring valve stem and the fluid pipe there is provided a sealing means. At the lower portion of the case  44  of the restoring valve there is formed an atmosphere connection port  45  which is open to the valve cavity. At the upper portion of the case  44  there is formed an inlet  46  open to the valve cavity, and at the middle portion of the case there is formed an outlet  47  open to the valve cavity. The inlet  46  is connected to the lower chamber  10  of the hydraulic cylinder  6  via a pipeline  48 . Inlet  46  can also be directly connected to the lower chamber connection port  14  of the pilot valve  11  via pipeline  48 . The outlet  47  is connected to the chamber under the holding piston  37  of the hydraulic pressure-holding cylinder  35  via a pipeline  49 . In the valve cavity above the restoring valve core  42  of the restoring valve there is provided a restoring spring  50 . Under the atmosphere connection port  45  there can be provided a reservoir  51 . 
     When the fluid-controlled valve for pipeline pig of the third embodiment is in the normal working state as shown in  FIG. 4 , the operating mode of the pilot valve  11 , the hydraulic cylinder  6  and the main valve  1  is the same as that in embodiment 1. At this time, the restoring valve core  42  in the restoring valve  41  is located at the lower portion of the valve case  44  under the action of the spring  50 , and the restoring valve stem  43  extends into the fluid pipe  3 . The hydraulic pressure-holding cylinder  35  is connected with the lower chamber  10  of the hydraulic cylinder  6  via pipeline  49 , outlet  47  of the restoring valve, the valve cavity above the restoring valve core, inlet  46  and pipeline  48 . Furthermore, hydraulic pressure-holding cylinder  35  is opened to the atmosphere via pipeline  25 , two-way control valve  28 , lower chamber connection port  14  of the pilot valve  11 , release passage way  23  and atmosphere connection port  16 . The holding piston  37  in the hydraulic pressure-holding cylinder  35  is at the lower portion of the hydraulic pressure-holding cylinder under the action of the spring  38 , causing the pilot valve core  17  of the pilot valve  11  to be held at the lower portion of the valve body through the piston rod  39  of the holding piston. Under the action of the fluid pressure, the piston  7  in the hydraulic cylinder  6  is at the lower portion of the hydraulic cylinder, and at the same time, the main valve core is pushed to its lower working position to control the flow of the fluid. 
     When using a pipeline pig to clean the fluid pipe such that the pipeline pig  19  comes to the pilot valve  11 , as shown in  FIG. 5 , the pilot valve  11 , the hydraulic cylinder  6  and the main valve  1  operate in the same way as that described in connection with Embodiment 1. At this time, the restoring valve stem  43  of the restoring valve  41  remains extended into the fluid pipe  3 , and the restoring valve core  42  remains at the lower portion of the case. Part of the pressurized fluid, which has entered the lower chamber  10  of the hydraulic cylinder  6 , enters the cylinder chamber under the holding piston  37  of the hydraulic pressure-holding cylinder  35  via pipeline  48 , inlet  46  of the restoring valve  41 , the valve cavity above the restoring valve core, outlet  47  and pipeline  49 . This keeps holding piston  37  and pilot valve core  17  ( FIG. 1 ) of the pilot valve  11  at the ascended position, thus keeping the flow path from the fluid pipe  3  to the lower chamber  10  of the hydraulic cylinder  6  in an open state. Therefore, the pressurized fluid in the fluid pipe  3  continuously enters the lower chamber of the hydraulic cylinder to push piston  7  upwards to the upper portion of the hydraulic cylinder and thereby lift the main valve core such that the flow path of the main valve coincides with and communicates with the flow path of the fluid pipe to let the pipeline pig pass through smoothly. That is, the fluid-controlled valve is now in the state allowing the pipeline pig to pass. 
     When the pipeline pig  19  comes to the restoring valve  41 , as shown in  FIG. 6 , the pipeline pig  19  pushes the restoring valve stem  43  of the restoring valve  41  upward against the biasing force of the spring  50 , causing the restoring valve core  42  to move upward to the upper portion of the case  44 . The inlet  46  in the case is blocked by the restoring valve core  42 , and the outlet  47  is connected with the atmosphere connection port  45  via the valve cavity under the restoring valve core. The fluid in the cylinder chamber under the holding piston  37  in the hydraulic pressure-holding cylinder  35  is discharged from the atmosphere connection port  45  or is discharged into the reservoir  51  under the atmosphere connection port via pipeline  49 , outlet  47  of the restoring valve and the valve cavity. The hydraulic pressure-holding cylinder is released from pressure, and the holding piston  37  returns to its original position under the action of the spring  38 , thereby pushing the piston rod  39  together with the pilot valve core  17  of the pilot valve  11  downward to make them return to the original position. Correspondingly, the hydraulic cylinder  6  and the main valve  1  also return to their original position, and the fluid-controlled valve returns to its normal working state. 
     Moreover, as in the first embodiment, the controller of the fluid-controlled valve for pipeline pig of this embodiment can also be provided with an electromagnetic switch  29  and an electric controller  32 . Correspondingly, the disk  30  cooperating with the electromagnetic switch  29  is connected with the holding piston  37  through a connecting rod  40 . Therefore, it is possible to control the working state of the main valve  1  by operating the controller, as shown in  FIGS. 4 and 5 . 
     Embodiment 4 
     The fluid-controlled valve for pipeline pig in accordance with the fourth embodiment of the invention is shown in FIG.  7 . Except as discussed below, its general arrangement is substantially the same as that in Embodiment 3. 
     The hydraulic cylinder  6  is secured to the valve body  2  of the main valve  1  transversely by means of a support. The piston rod  8  and the main valve stem  5  are perpendicular to each other, and the piston rod  8  of the hydraulic cylinder has a rack  52  formed on its end which extends beyond the hydraulic cylinder. 
     A gear  53 , which meshes with the rack  52 , is fixedly mounted on the main valve stem  5  of the main valve  1  so that the main valve stem  5  rotates as the piston rod  8  reciprocates. The main valve stem is secured to the main valve core. Correspondingly, a valve with a rotating valve core, e.g. a ball valve, is used as the main valve. 
     As an alternative, axial sliding grooves  54  may be formed on the main valve stem  5  such that the main valve stem has a structure similar to that of a spline shaft, and a gear  53  is mounted slidingly on the main valve stem. The lower end of the main valve stem is rotably connected with the main valve core, and the main valve stem and the valve cover  4  are connected with each other and form a screw pair. Thus, when the piston rod  8  of the hydraulic cylinder reciprocates, the main valve stem moves up and down while rotating, thereby driving the main valve core to move reciprocally up and down. Therefore, the main valve can be a gate valve, a sluice valve, a plunger valve, etc. 
     The operation of this valve is substantially the same as that of Embodiment 3. 
     Embodiment 5 
       FIGS. 8 and 9  illustrate the fifth embodiment of the fluid-controlled valve for pipeline pig in accordance with the present invention. As shown in  FIGS. 8 and 9 , the fluid-controlled valve for pipeline pig of this embodiment is also comprised of a main valve  1  and a controlling device, wherein the controlling device is comprised of a hydraulic cylinder  6 , a pilot valve  56 , a controller and the like. 
     The structure of the main valve  1  is the same as that of the main valve described in Embodiment 1. 
     Except as described below, the hydraulic cylinder  6  is substantially the same as that described in Embodiment 1. On the valve cover  4  of the main valve in this embodiment, however, there is formed a through hole which communicates the lower chamber  10  of the hydraulic cylinder and the valve cavity of the main valve  1 , and in the through hole there is mounted a conventional two-way control valve  55  which is capable of controlling the flow in two directions. The lower chamber  10  of the hydraulic cylinder is communicated with the fluid pipe  3  via the two-way control valve and the valve cavity of the main valve  1 . The inventor&#39;s adjustable differential flow shuttle valve noted above can be used as the two-way control valve. 
     The pilot valve  56  is a conventional piston valve and can be installed on the fluid pipe  3  by means of a support, although the pilot valve can also be installed on the main valve  1  or integrated with the main valve. At the upper portion of the valve cavity of the pilot valve there is formed a port which can connect with the fluid pipe  3  through a pipeline. At the lower portion of the valve cavity there is formed a port which is open to the atmosphere or is connected with the reservoir  57  through a pipeline, and at the middle of the valve cavity of the pilot valve there is formed a port which is connected with the upper chamber  9  of the hydraulic cylinder  6  through a pipeline  58 . When the pilot valve core  59  of the pilot valve moves to the lower portion of the valve cavity, the upper chamber  9  of the hydraulic cylinder is connected with the fluid pipe  3  via a pressurized chamber  60  formed above the valve core  59  of the pilot valve. When the pilot valve core moves to the upper portion of the valve cavity, the upper chamber  9  of the hydraulic cylinder is open to the atmosphere via a release chamber  61  formed under the valve core  59  of the pilot valve. The valve stem  40  connected with the pilot valve core extends out of the valve case upward. Sealing means is provided between the valve stem and the valve case, and a disk  30  is provided at the upper end of the valve stem. 
     As in the first embodiment, the controller is comprised of an electromagnetic switch  29 , an electric controller  32  and a connecting wire  34 . 
     For the fluid-controlled valve for pipeline pig of this embodiment, during the normal operation for controlling the fluid or when cleaning the fluid pipe with a pipeline pig, the electric controller  32  is used to control the pilot valve  56  by means of the electromagnetic switch  29 . When it is necessary to clean the fluid pipe, the electric controller  32  is activated so that the electromagnetic switch  29  attracts and engages the disk  30 , thereby lifting the pilot valve core  59 . At this time, the upper chamber  9  of the hydraulic cylinder  6  is open to the atmosphere via pipeline  58  and the release chamber  61  of the pilot valve. Pressurized fluid in the fluid pipe  3  enters the .lower chamber  10  of the hydraulic cylinder  6  via the valve cavity of the main valve  1  and the two-way control valve  55  and pushes the piston  7  and hence the main valve core upwards, causing the flow path of the main valve to coincide and communicate with the flow path of the fluid pipe. When the electric controller  32  is deactivated to cause the electromagnetic switch  29  to release the disk  30 , the pilot valve core  59  moves downward under the action of gravity or a biasing device otherwise provided, and upper chamber  9  of the hydraulic cylinder  6  is connected with the fluid pipe  3  via the pipeline  58  and the pressurized chamber  60  of the pilot valve. The pressurized fluid in the fluid pipe  3  enters the upper chamber  9  of the hydraulic cylinder under the combined action of the pressurized fluid in upper chamber  9  and the gravity of piston  7 , piston rod  8 , main valve stem  5  and the main valve core or under the action of a biasing device otherwise provided. Piston  7  and hence the main valve core move downward, causing the fluid in the lower chamber  10  to return to the fluid pipe  3  via the two-way control valve  55  and the valve cavity of the main valve  1 . As a result, the main valve  1  returns to its normal working state. When the fluid-controlled valve of this embodiment is in the normal working state, it is possible to control the opening, closing and degree of openness of the main valve through the pilot valve and the hydraulic cylinder by operating the electric controller so as to control to the flow of the fluid. 
     Embodiment 6 
       FIG. 10  illustrates the sixth embodiment of the fluid-controlled valve for pipeline pig in accordance with the invention. As shown in  FIG. 10 , the fluid-controlled valve for pipeline pig of this embodiment is substantially the same in structure as that of Embodiment 5. The controller is further provided, however, with two sensors  62  and  63 , which are respectively mounted on the fluid pipe  3  on the upstream side and the downstream side of the main valve  1 . The two sensors are respectively electrically connected with the electric controller  32  through wires  64  and  65 . A conventional inductance sensor, which can cooperate with the pipeline pig  19 , can be used as the sensor. 
     The two sensors  62  and  63  respectively transmit to the electric controller the signals indicative of the arrival of the running pipeline pig at the upstream side and at the downstream side of the main valve, and the electric controller controls the pilot valve  56  and the hydraulic cylinder  6  responsive to the signals received to thereby control the main valve  1 . The automatic control of the main valve  1  can be realized with the fluid-controlled valve for pipeline pig of this embodiment. 
     Embodiment 7 
       FIGS. 11 and 12  illustrate the seventh embodiment of the fluid-controlled valve for pipeline pig of the invention. As shown in  FIGS. 11 and 12 , the arrangement of the fluid-controlled valve for pipeline pig of this embodiment is substantially the same as that of Embodiment 5, except that the controller is further provided with a lever mechanism. 
     The lever mechanism comprises a lever  66  extending along the fluid pipe  3  and pivotally mounted on a support  67  which can be secured on the fluid pipe  3 . The front end and the rear end of the lever, which are located respectively on the front side and on the rear side of the pivoting point of the lever, are respectively pivotally connected with a push rod  68  and a push rod  69 , each of which are extendable into the fluid pipe  3  by an appropriate depth on the upstream side of the main valve  1 . A sealing means is provided between the push rods and the fluid pipe. The distance between the two push rods is determined by the running speed of the pipeline pig and the moving speed of the piston  7  of the hydraulic cylinder to ensure that piston  7  has enough time to reach its upper position. Furthermore, the distance between the push rod  69  and the main valve should also be determined by the running speed of the pipeline pig and the moving speed of the piston of the hydraulic cylinder to ensure that there is enough time for the pipeline pig to pass through the main valve. 
     A pilot valve stem  70  is fixedly connected with the valve core of the pilot valve  56  and pivotally connected to the end of the lever upstream of the lever pivoting point to thereby form a lever-type detecting mechanism. It is also possible, however, to pivotally connect the other end of lever (i.e. the end on the downstream side of the lever pivoting point) with the pilot valve stem. With the latter arrangement, the pilot valve should have such a structure so that its pressurized chamber, which connects with the fluid pipe, is located under the valve core, and the release chamber  61 , which is open to the atmosphere, is located above the valve core. The lever-type detecting mechanism can be protected by providing a shield  71 . 
     The present fluid-controlled valve, when in a normal working state for controlling the fluid, operates the same way as that of Embodiment 1. That is, the electromagnetic switch  29  is controlled by operating the electric controller  32 , and the opening, closing and degree of openness of the main valve  1  is controlled by the pilot valve  56  and the hydraulic cylinder  6  so as to control the flow of the fluid. 
     The operation of the lever-type detecting mechanism will be described below. When, upon cleaning the fluid pipe with a pipeline pig, the pipeline pig  19  comes to the push rod  68 , as shown in  FIG. 12 , the pipeline pig  19  pushes the push rod  68  upward, causing the lever  66  to pivot and the push rod  69  to descend. Due to the rotation of the lever  66 , the pilot valve stem  70  and hence the pilot valve core  59  move upward. As a result, the upper chamber  9  of the hydraulic cylinder  6  is open to the atmosphere via the release chamber  61  to discharge the fluid in the upper chamber, and the pressurized fluid in the fluid pipe enters the lower chamber  10  of the hydraulic cylinder via the valve cavity of the main valve  1  and the two-way control valve  55 . Piston  7  thereby ascends and lifts the main valve core via the piston rod  8  and the main valve stem  5  to open the main valve so that the pipeline pig can pass through. 
     When the pipeline pig  19  comes to the push rod  69 , as shown in  FIG. 11 , the pipeline pig  19  pushes the push rod  69  upward, causing the lever  66  to pivot and the push rod  68  to descend. Due to the rotation of the lever  66 , the pilot valve stem  70  and hence the pilot valve core  59  descend and return to the original position. The upper chamber  9  of the hydraulic cylinder  6  is connected with the fluid pipe  3  via the pressurized chamber  60 , through which the pressurized fluid enters the upper chamber. Fluid in the lower chamber  10  of the hydraulic cylinder flows into the valve cavity of the main valve via the two-way control valve  55 . The flow rate at which the fluid in the lower chamber  10  of the hydraulic cylinder flows into the valve cavity of the main valve is adjusted by the two-way control valve  55 , so that the descending speed of the piston  7  and hence the main valve core is controlled to ensure that the pipeline pig passes through the main valve smoothly. After the pipeline pig has passed through the main valve, the piston  7  and hence the main valve core descend and return to the original position, and the fluid-controlled valve returns to the normal working state. 
     As an alternative, the push rod  68  pivotally connected to the lever  66  can be omitted, and the end of the pilot valve stem  70  of the pilot valve  56 , which is pivotally connected to the lever, may extend into the fluid pipe  3  by an appropriate depth. 
     As another alternative, the push rod  68  pivotally connected to the lever  66  can extend into fluid pipe  3  by an appropriate depth on the downstream side of the main valve  1 . In this case, the operation of the fluid-controlled valve is similar to that shown in FIG.  10 . 
     As still another alternative, a two-way control valve having a time delay function is used as the two-way control valve  55  (See China Patent No. 87103004.7 granted to the inventor, filed in 1987), and the pipeline pig passes through the main valve during the time delay caused by the two-way control valve. 
     Furthermore, the lower chamber  10  of the hydraulic cylinder can also be connected with the fluid pipe  3  through a pipeline, and the two-way control valve is provided in the pipeline. 
     Embodiment 8 
       FIG. 13  illustrates the eighth embodiment of the fluid-controlled valve for pipeline pig of the invention. As shown in  FIG. 13 , the general arrangement of this embodiment is substantially the same as that of Embodiment 7, except as described below. 
     The hydraulic cylinder  6  is secured to the valve body  2  of the main valve  1  transversely by means of a support. The lower chamber  10  of the hydraulic cylinder is connected with the valve cavity of the main valve  1  through a pipeline  72 , in which a two-way control valve can be provided. The piston rod  8  and the main valve stem  5  are perpendicular to each other, and the piston rod  8  of the hydraulic cylinder has a rack  52  formed on its end which extends beyond the hydraulic cylinder. 
     A gear  53 , which meshes with the rack  52 , is fixedly mounted on the main valve stem  5  of the main valve  1  so that the main valve stem  5  rotates as the piston rod  8  reciprocates. The main valve stem is secured to the main valve core. Correspondingly, a valve with a rotating valve core, e.g. a ball valve, is used as the main valve. 
     As an alternative, axial sliding grooves  54  may be formed on the main valve stem  5  such that the main valve stem has a structure similar to that of a spline shaft, and a gear  53  is mounted slidingly on the main valve stem. The lower end of the main valve stem is rotatably connected with the main valve core, and the main valve stem and the valve cover  4  are connected with each other and form a screw pair. Thus, when the piston rod  8  of the hydraulic cylinder reciprocates, the main valve stem moves up and down while rotating, thereby driving the main valve core to move reciprocally up and down. Therefore, the main valve can be gate valve, a sluice valve, a plunger valve, etc. 
     The operation of the fluid-controlled valve of this embodiment is substantially the same as that of Embodiment 7.