Abstract:
A flow control system includes a pilot driven valve having a pilot assembly and a main valve assembly; a displacement measurement component coupled to the main valve assembly indicating displacement of the main valve assembly; and a proportional solenoid responsive to a signal from the displacement measurement component that displaces the pilot assembly in proportion to the changes in displacement of the main valve assembly. The valve is controlled by sensing a displacement of the main valve assembly; and modulating the proportional solenoid in response to the displacement of the main valve assembly.

Description:
TECHNICAL FIELD 
       [0001]    The subject matter disclosed herein generally relates to control valves. More specifically the subject matter relates to process fluid actuated pilot operated control valves. 
       BACKGROUND 
       [0002]    Many industrial processes require the control of the flow of fluids through conduits. In some cases it is desirable to keep a process variable (e.g. pressure, flow, etc.) within an operating range. However, the flow of fluids through a conduit may be subject to disturbances that affect the process variables. To reduce the effect of disturbances, sensors and transmitters collect information about the process variable and its relationship to a set point. A controller may then determine what changes have to be implemented to get the process variable to the desired value. To effect the changes requires a control element such as a control valve. The control valve regulates the flowing fluid (e.g. gas, steam, water, etc.) to correct the changes resulting from the load disturbances. 
         [0003]    There are a wide variety of control valves that are in commercial use. These include ball valves; gate valves; check valves; and butterfly valves, among others. Some control valves may include hydraulic actuators (e.g. pilots). These valves respond to changes of pressure or flow to open or close the valve in response to those changes. In some pilot driven control valves the fluid pressure is used to open and close the valve. Other control valves may be responsive to signals generated by independent devices such as flow meters or temperature transmitters. 
         [0004]    Some control valves make use of a pilot or pressure amplifier to improve the sensitivity of the control valve to pressure variations. Pilot driven control valves include a pilot valve, a main valve, a pressure conduit, a dome, a piston and a seat. Pressure from the upstream side is provided to the dome often by a small pitot tube. The upstream pressure tries to push the piston open but it is opposed by that same pressure because the pressure is routed around to the dome above the piston. The area of the piston exposed to pressure is larger in the dome than it is on the upstream side; the result is a net sealing force. The pressure from the pitot tube to the dome is routed through the actual control pilot valve. There are many designs but the control pilot is essentially a conventional pressure reducing valve with a stem and a plug that control pressure to the main valve dome. When the pilot valve reaches a set pressure it opens and releases the pressure from the dome. The piston is then free to open and the main valve exhausts the system fluid. In some cases the control pilot opens either to the main valve exhaust pipe or to atmosphere. 
         [0005]    The stem of the control valve usually include a packing box (e.g. packing around the valve stem) to prevent leakage of fluids. However, packing box leakage is a common problem and is a large contributor to fugitive emissions in process applications. Several factors exacerbate the problem. For instance, the concentration of hydrogen sulfide in hydrocarbons in some processes is increasing significantly with the shift of production to more challenging oil and gas fields. These compounds negatively impact the performance of the packing box and consequently affect the performance of the control valve. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    In accordance with one exemplary non-limiting embodiment, the invention relates to a valve having a housing with an upstream port and a downstream port. The valve includes a pilot assembly coupled to the upstream port and a plunger adapted to engage and displace the pilot assembly. A proportional solenoid electromagnetically coupled to the plunger. The valve also includes a main valve fluidly coupled to the pilot assembly having a main valve plug and a piston coupled to the main valve plug. The valve is also provided with a displacement measurement component coupled to the piston that measures displacement of the piston. 
         [0007]    In some embodiments the displacement measurement component may include a position indicia component and a sensor to detect changes in position indicia component. 
         [0008]    In some embodiments, the valve may include an electronic valve controller coupled to the proportional solenoid. 
         [0009]    In another embodiment, a flow control system includes a pilot driven valve having a pilot assembly and a main valve assembly. A displacement measurement component is coupled to the main valve assembly indicating displacement of the main valve assembly. The flow control system includes a proportional solenoid responsive to a signal from the displacement measurement component that displaces the pilot assembly in proportion to the changes in displacement of the main valve assembly. 
         [0010]    In another embodiment, a method of controlling a valve having a pilot assembly, a main valve assembly and a proportional solenoid coupled to the pilot assembly, the method includes sensing a displacement of the main valve assembly and modulating the proportional solenoid in response to the displacement of the main valve assembly. 
         [0011]    Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of certain aspects of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a cross sectional view of an embodiment of a process fluid actuated pilot operated control valve. 
           [0013]      FIG. 2  is a cross sectional view of the main valve assembly and the pilot valve assembly of the process fluid actuated pilot operated control valve according to an embodiment. 
           [0014]      FIG. 3  is a schematic of an embodiment of a control valve system showing the sensor and control elements. 
           [0015]      FIG. 4  is a flow chart illustrating an exemplary method implemented by a process fluid actuated pilot operated control valve. 
           [0016]      FIG. 5  is a flowchart illustrating a second exemplary method implemented by process fluid actuated pilot operated control valve. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Illustrated in  FIG. 1  is an embodiment of a control valve  11 . The control valve  11  includes a housing assembly  13 , a main valve assembly  15 , and a pilot assembly  17 . The control valve  11  also includes a proportional solenoid  18  electromagnetically coupled to the pilot assembly  17  and a position indicator assembly  19  coupled to the main valve assembly  15 . 
         [0018]    The housing assembly  13  may include a main housing body  21 , an inlet port  23 , and an outlet port  25 . The housing assembly may also include an upper casing  27 , and a lower casing  29 . 
         [0019]    As illustrated in  FIG. 1 , the solenoid assembly  18  may include a proportional solenoid  30  having a plunger  31  that acts as an armature and a coil  32  disposed in the upper casing  27  of the housing assembly  13 . The solenoid assembly  18  may also include a plunger spring  33  that biases the plunger  31  in an upward direction. 
         [0020]    The position indicator assembly  19  includes a rod  35 , a position indicator  36 , (e.g. a magnet) disposed within a nonmagnetic pressure boundary  37 . 
         [0021]    Illustrated in  FIG. 2  are the components of the main valve assembly  15  and the pilot assembly  17  of an embodiment of the control valve  11 . The main valve assembly  15  is disposed within the housing assembly  13 . The main valve assembly  15  may include a main valve plug  45  that engages a main valve seat  46 . The main valve plug  45  is coupled to main valve stem  47  which in turn may be coupled to a piston  48 . The main valve plug  45  is biased in a downward position by main valve spring  49  that is held in place by main valve spring retainer  50 . The piston  48  may be coupled to a dashpot  51  which may dampen the motion of the piston  48 . 
         [0022]    The pilot assembly  17  includes a pilot stem  53  coupled to a pilot plug  54 . The pilot stem  53  and the pilot plug  54  are disposed in a pilot valve housing  55  which may be integrally formed with main valve spring retainer  39 . A pilot spring retainer  56  may be formed in the pilot valve housing  55 . Pilot spring  58  may be disposed inside the pilot spring retainer  56  and coupled to the pilot plug  54 , The pilot spring  58  biases the pilot plug in an upward direction. The pilot spring retainer  56  may include a pilot seat  50  that is engaged by the pilot plug  54  when in the closed position. 
         [0023]    The housing assembly  13 , the main valve assembly  15  and the pilot assembly  17  define a first chamber  59 , a second chamber  60 , a third chamber  61  and a fourth chamber  62 . The housing assembly  13  may also include a fluid conduit  63  connecting the second chamber  60  with the fourth chamber  62 . 
         [0024]    Illustrated in  FIG. 3  is a valve control system  71 . The valve control system  71  includes a position sensor  73  that detects displacement of the position indicator  36 . Examples of position sensor  73  may include a Hall effect sensor or a magnetorestrictive sensor, among others. The position sensor  73  and the position indicator  36  serve as a displacement measurement component that measures displacement of the main valve assembly  15 . 
         [0025]    The valve control system  71  includes a valve controller  75  that receives signals from the position sensor  73  and may receive signals from a process controller  77  that controls processes in a larger system. Based on those signals, the valve controller  75  modulates proportional solenoid  18  based upon the displacement of the position indicator  36 . The valve control system  71  may be separate or integral with the controller  79 . 
         [0026]    The valve control system  71  may include an electrical supply  79  that powers the valve controller  75 , the position sensor  73 , and the proportional solenoid  18 . The use of position indicator  36  and position sensor  73  may be accomplished without the need for a separate power supply as in the case of linear variable differential transformer (LVDT). Simplified wiring will result in the use of a two-wire rather than four-wire hookup. 
         [0027]      FIG. 1  illustrates the control valve  11  in the closed position. Fluid from the inlet port  23  is prevented from flowing to and through outlet port  25  by main valve plug  45 . Main valve plug  45  is tightly seated against main valve seat  33  by the compression force exerted by main valve spring  49  and the differential fluid pressure acting on the main valve plug  45 . In the closed position, pilot plug  54  is tightly seated against the pilot seat  57  by the force applied by pilot spring  58 . 
         [0028]    When control valve  11  is actuated, coil  32  is energized, forcing plunger  31  to be displaced downwardly. The displacement of plunger  31  causes the displacement of pilot stem  53  and pilot plug  54 . The force applied by plunger  31  overcomes the force applied by pilot spring  58 . This movement unseats pilot plug  54  from pilot seat  57  thereby allowing fluid to enter third chamber  61 . Fluid from the inlet port  23  flows through the third chamber  61  through the fluid conduit  63  and into the fourth chamber  62 . The increased pressure in the fourth chamber  62  displaces the piston  48  which in turn unseats the main valve plug  45  from the main valve seat  46 . The displacement of main valve plug  45  allows flow from first chamber  59  to the second chamber  60 . 
         [0029]    The displacement of the piston  48  causes the displacement of the position indicator  36 . The displacement of the position indicator  36  is detected by the position sensor  73  which may provide a signal to the process controller  77  and/or valve controller  75 . This position feedback enables the valve controller  75  to control the flow through the control valve  11  through the modulation of the solenoid assembly  18 . 
         [0030]      FIG. 4  is a flowchart illustrating a method of controlling a control valve  11  (method  91 ). A determination is made as to whether the main valve assembly  15  needs to be displaced (method element  93 ). If the main valve assembly  15  needs to be displaced the required displacement of the pilot assembly  17  is calculated (method element  95 ). Current is applied to the solenoid assembly  18  (method element  97 ), leading to the displacement of the main valve assembly  15  (method element  101 ). After setting the position of the main valve assembly  15 , the position of the main valve assembly  15  is measured periodically (method element  103 ). The system then determines whether the position of the main valve assembly  15  has changed as a result of any disturbance (method element  105 ). If the position of the main valve assembly  15  has changed the process is repeated by initially calculating the required displacement of the pilot assembly. 
         [0031]      FIG. 5  illustrates a method  111  that may be implemented by valve controller  75 . The valve controller  75  may receive a signal from the position sensor  73  that is proportional to the position of the main valve assembly (method element  115 ). The valve controller  75  may then make a determination as to whether the main valve assembly is in the correct position (method element  117 ). If the main valve assembly  15  is not in the correct position, the valve controller  75  may then make a determination of the required displacement of the pilot assembly  17  to compensate for the position error (method element  119 ). Based on the required displacement of the pilot assembly  17 , the valve controller  75  may then determine the current to be provided to the solenoid coils  32  to displace the pilot assembly  17  by the required displacement (method element  121 ). The valve controller  75  may then provide the appropriate current to the solenoid coils  32  to effect the required displacement of the pilot assembly  17 . It should be noted that although in the embodiment described in this example the valve controller  75  may be a standalone component, it would be apparent to one of ordinary skill in the art to include the valve controller  75  as a component of a larger system such as process controller  77 . 
         [0032]    As one of ordinary skill in the art will appreciate, the many varying features and configurations described above in relation to the several exemplary embodiments may be further selectively applied to form the other possible embodiments of the present invention. For the sake of brevity and taking into account the abilities of one of ordinary skill in the art, all of the possible iterations is not provided or discussed in detail, though all combinations and possible embodiments embraced by the several claims below or otherwise are intended to be part of the instant application. In addition, from the above description of several exemplary embodiments of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are also intended to be covered by the appended claims. Further, it should be apparent that the foregoing relates only to the described embodiments of the present application and that numerous changes and modifications may be made herein without departing from the spirit and scope of the application as defined by the following claims and the equivalents thereof.