Abstract:
A valve assembly having a housing including a first and second port. A closure element is disposed within the housing and is selectively moveable between an open position wherein the first port is in fluid communication with the second port and a closed position wherein fluid communication between the first and second ports is blocked and/or controlled. A first magnet assembly is coupled to the closure element for actuating the closure element between the open and closed positions whereby the fluid communication is blocked and/or controlled. A second magnet assembly is magnetically coupled to the first magnet assembly for imparting movement to the first to provide fluid communication blocking and/or controlling. The drive mechanism is adapted to actuate the second magnetic assembly and is alternatively operable through a first and/or a second drive input. The first drive input is unable to drive the second drive input.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a sealed fluid valve utilizing a magnetically coupled piloted valve providing a hermetically sealed control valve with improved flow control elements. 
         [0002]    Conventional valves have an inlet port and outlet port which are separated by a valve closure element which controls the flow of fluid from the inlet to the outlet. The valve typically has a mechanical movement which moves the closure element from a closed position to an open position. In some prior designs a valve housing is provided having an opening to allow a screw type mechanism to move the closure element from the open to the closed positions and vice versa. Screw mechanisms in these types of valve arrangements would pass through the outer housing of the valve and include a hand wheel or other device to turn the screw mechanism to move the valve between open and closed positions. Such screw mechanisms also include a packing material to provide a dynamic seal between the screw shaft, which is connected directly to the closure element, and the outer housing to prevent leakage of fluid from the valve. However, a problem with this prior design is that it requires constant maintenance of the packing to prevent fluid leakage. Such valves are frequently unacceptable due to fluid leakage to the environment, requiring the use of hermetically sealed designs. 
         [0003]    An alternative contemporary design uses a solenoid valve to control the fluid flow. The solenoid valve involves the use of a magnetic movable core which is mechanically linked to the valve closure element. The movable core is typically housed in a cylinder or other housing adjacent to the closure element. An electromagnetic field is produced by an electric coil to control the movement of the movable core to move the closure element between open and close positions. Typically, the magnetic coil is energized to move the core to in turn move the closure element to an open position to allow fluid to flow from either the inlet to the outlet or from the outlet to the inlet port. However, the problem with the solenoid valves currently in use is that if a large valve is needed for a particular application, the amount of energy required to move the movable core and closure element is very great. In addition, once the valve is opened, the magnetic coil must be maintained in an energized state to hold the movable core in an open position. If the movable core is extremely heavy or large, the magnetic coil must be fully energized from the initial stages to the final open stage. This type of solenoid valve consumes a large amount of energy and is not efficient. 
         [0004]    Thus, it is desirable to provide a valve assembly which overcomes the shortcomings found in the art of valves as set forth above while also providing improved structural and operating features. 
       SUMMARY OF THE INVENTION  
       [0005]    One aspect of the present invention includes a valve assembly having a housing, a first magnet assembly, a second magnet assembly and a drive mechanism. The housing includes a first port and a second port. The closure element is disposed within the housing and is selectively moveable between an open position wherein the first port is in fluid communication with the second port and a closed position wherein fluid communication between the first and second ports is at least one of blocked and controlled. The first magnet assembly is coupled to the closure element, for actuating the closure element between the open position and the closed position whereby the fluid communication is at least one of blocked and controlled. The second magnet assembly is magnetically coupled to the first magnet assembly for imparting movement to the first magnetic assembly to provide at least one of the fluid communication blocking and controlling. The drive mechanism is adapted to actuate the second magnetic assembly. Also, the drive mechanism is alternatively operable through at least one of a first drive input and a second drive input, wherein the first drive input is unable to drive the second drive input. 
         [0006]    Additionally, the movement imparted to the first magnet assembly could be either rotational or axial movement, depending on the design. Further, the first and second magnet assemblies could be separated by a barrier, preventing fluid communication past the first and/or second magnet assemblies. Further still, the drive mechanism could include a gear assembly continuously engaged from said second magnet assembly to the first and/or second drive inputs. Also, the closure element could include a pilot valve. 
         [0007]    Additionally, the valve closure element could include a stem and a first valve disc. The stem could be coupled to the first magnet assembly and the first valve disc. Also, the first valve disc could be contained within the housing and adapted to fully block fluid communication between said first and second ports. Further, the stem could be threadedly engaged to the first magnet assembly. Further still, the valve closure element could include a second valve disc and a disc fluid passage through the first valve disc in fluid communication with said first and second ports. The second valve disc could be contained within the first valve disc. Also, the second valve disc could be moveable between a first position blocking the one disc fluid passage and a second position allowing fluid communication through the disc fluid passage. 
         [0008]    Another aspect of the present invention involves a valve assembly including a housing having a first port and a second port. A valve closure element is disposed within the housing, and the closure element includes a stem and first disc. The first disc is coupled to the stem and selectively moveable between a first position and a second position. The first position places the first port in fluid communication with the second port. The second position blocks and/or restricts fluid communication between the first and second ports. A first magnet assembly is threadedly engaged to the stem for actuating the head cylinder between the first and second positions. A second magnet assembly magnetically is coupled to the first magnet assembly for actuating the first magnetic assembly thereby providing the actuation of the head cylinder. Also, a drive mechanism is provided for actuating the second magnetic assembly thereby actuating the first magnetic assembly. 
         [0009]    It is desirable to provide a valve that does not require packing and eliminates maintenance and other troubles associated with leakage of external dynamic seals in a valve assembly. It is further desirable to provide a valve having a completely hermetically sealed outer housing that does not have any through openings to reduce or prevent leakage to the outer environment of fluid flowing through the valve. It is further desirable to provide a valve which uses a pilot disc which reduces the actuating forces required to open, close and/or adjust the valve opening. And it is desirable to provide a valve which provides exquisite command of the valve closure element so that fluid flow is more precisely controlled thereby reducing and/or preventing damage to the valve seat upon closure. 
         [0010]    These and other objective, features, and advantages of this invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a cross-sectional view of a valve assembly in accordance with an embodiment of the present invention. 
           [0012]      FIG. 2  is an enlarged cross-sectional view of portions of the valve housing, disc collar and inner disc assemblies of  FIG. 1 . 
           [0013]      FIG. 3  is an enlarged cross-sectional view of the magnet housing assembly of  FIG. 1 . 
           [0014]      FIG. 4   a  is an enlarged perspective view of the magnet assemblies of  FIG. 1 . 
           [0015]      FIG. 4   b  is a front view of the magnet assemblies of  FIG. 4   a.    
           [0016]      FIG. 4   c  is a cross-sectional view of the magnet assemblies of  FIG. 4   b  at A-A. 
           [0017]      FIG. 5  is a cross-sectional view of a valve assembly in accordance with an alternative embodiment of the present invention. 
           [0018]      FIG. 6   a  is an enlarged perspective view of the magnet assemblies of  FIG. 5 . 
           [0019]      FIG. 6   b  is a front view of the magnet assemblies of  FIG. 6   a.    
           [0020]      FIG. 6   c  is a cross-sectional view of the magnet assemblies of  FIG. 6   b  A-A. 
           [0021]      FIG. 7  is an enlarged cross-sectional view of the gear assembly of  FIG. 5 . 
           [0022]      FIG. 8  is an alternative enlarged cross-sectional view of a gear box with an extension housing and encoder assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    This invention pertains to a valve assembly that offers exquisite control of the valve disc position, selectively by either manual or motor drive input, while providing a hermetically sealed design. 
         [0024]    With reference to the drawings,  FIG. 1  shows a piloted globe valve assembly  10 . The outer elements of the valve assembly  10  preferably include a valve housing  100 , a valve disc collar  200 , a bonnet  300 , a magnet housing  400  and a gear box  500 . It is desirable that the outer elements  100 ,  200 ,  300 ,  400 ,  500  be secured in such a way as to hermetically seal the overall assembly  10  and prevent either external leakage or internal contamination. As shown, some of the outer elements are provided with coupling flanges  105 ,  205 ,  305 ,  405  or surfaces  207 ,  507  for securing and sealing adjacent outer elements, using conventional fasteners and seals. Also, some of the outer elements are joined through mating threads  303 ,  403 . 
         [0025]    It should be understood that some or all of the outer elements  100 ,  200 ,  300 ,  400 ,  500  could be integrally formed or formed into a single continuous element. For example, the embodiment shown in  FIG. 5  illustrates a valve assembly  11  formed with fewer outer elements. Alternatively, the outer elements in any embodiment could be formed by more parts than that shown. Also, additional or redundant sealing elements can be employed, such as a bellows or flexible membrane. For example, the canopy ring  330  shown in  FIG. 5  ensures a hermetic seal between valve housing  101  and magnet housing  401 . 
         [0026]    Referring to  FIGS. 1 and 2 , the valve assembly  10  preferably includes a valve housing  100  that has a first port  110  and second port  115 . The housing  100  contains a main closure element or disc  130 , which is shown in more detail in  FIG. 2 . The main disc  130  controls the flow of fluid communicating between the first  110  and second  115  ports. Preferably, the main disc  130  is moveable between a closed position, shown in  FIG. 1  and at least one open position (not shown). The open position can vary to regulate or control the flow of fluid. In the closed position, a portion  132  of the main disc head  131  engages a disc seat  120  in order to block fluid flow. The disc seat  120  rests in a seat ring  125  positioned in the interior wall of housing  100 . Additional elements can be provided at the contact points between the main disc  150  and the disc seat  120  in order to control or prevent leakage across the seal, as is known to those of ordinary skill in the art. Preferably, the main disc  130  is made of a material that is harder than or equal in hardness to the disc seat  120 . In low pressure/temperature applications the materials can be base metals, such as bronze or grade 316 stainless steel (316SS), or softer non-metallic materials, such as Teflon, polyimide or rubber. However, the design is not limited to any specific materials, but rather certain materials properties are preferred based on application parameters, such as what types of fluids, pressures and temperatures are involved and how tight a seal is desired. 
         [0027]    Main Disc  130  preferably includes a base  139  and a stem  135 . The diameter of the main disc stem  135 , while preferably narrower than either the main disc head  131  or the main disc  139 , could be designed with a smaller or larger diameter than that shown. By reducing the diameter of a portion of the main disc  130 , such as a central stem  135 , the weight and mass of the main disc  130  is also reduced, making it easier to move. However, it is understood that the main disc  130  is not required to have narrower stem  135 . Additionally, main disc  130  also preferably includes a cavity  137  in at least an upper portion of disc base  139 . It should be understood that the terms “upper” and/or “lower” used herein refer to the orientation(s) shown in referenced drawings. Further, the main disc  130  has an inner bore  140  that traverses the axial length of the main disc  130  from the lower surface of the main disc head  131  to the cavity  137 . The inner bore  140  also preferably includes a narrower portion or head nozzle  141  inside at least a lower portion of the main disc head  131 . 
         [0028]    Contained within the main disc bore  140  and head nozzle  141  preferably is sleeve  150 . The sleeve  150  is a hollow element that contains and guides a secondary closure element or pilot disc  160 , and extends through nozzle  141 . The use of a piloted disc design reduces the required actuator forces necessary to move main disc  130  from a closed position to open the valve  10 . Sleeve  150  provides an inner lining to the lower portion of bore  140  and the nozzle  141 . Also, a portion of sleeve  150  engages the pilot disc  160  in much the same way as the disc seat  120  engages the main disc head  131 . Thus, when pilot disc  160  is in a lowermost position, it should provide a sealed engagement with sleeve  150 . The sleeve  150  should be made of a material that is appropriate to the environment of the overall valve, and should be particularly suited to guide the pilot disc without being galled. Examples of preferred materials are 316SS, Nitronic 60® (AK Steel Corp., Middletown, Ohio), bronze or even polymer materials, such as Teflon® (Du Pont, Wilmington, Del.). However, other considerations such as cost, performance and/or the interaction or relationship with other parts in the assembly could also be considered when selecting materials. Additionally, sleeve  150  should have one or more openings  152 , which align and are in fluid communication with one or more fluid passages  145  in the main disc stem  135 . The fluid passages  145  are in fluid communication with valve chamber  117 , which is preferably in open fluid communication with outlet port  115 . 
         [0029]    Pilot disc  160  is adapted to move axially within sleeve  150  between a first position (shown in  FIGS. 1 and 2 ) wherein fluid flow is interrupted between inlet port  110  and fluid passages  145 , and a second position (not shown) wherein fluid flow is established between inlet port  110  and fluid passages  145 . Pilot disc  160  is preferably actuated via a pilot disc stem  170  that is in turn axially actuated by a drive mechanism, as discussed in more detail below. The initial axial displacement of stem  170  causes pilot disc  160  to move from its first position toward a second position above opening(s)  152 , thus establishing a fluid connection between head nozzle  141  and fluid passage(s)  145 . Additional axial displacement of stem  170  preferably results in the movement of main disc  130  from the closed position to an open position providing direct fluid communication between inlet port  110  and outlet port  115 . 
         [0030]    A pilot disc pin  165  preferably couples pilot disc  160  to stem  170 . Preferably, a biasing element  162  exerts axial pressure on pilot disc  130  relative to the stem  170  in order to maintain engagement between those elements  130 ,  170  and the pilot disc pin  165  that holds them together.  FIGS. 1 and 2 , show biasing element  162  in the form of a coil spring mounted in a recess  172  in the lowermost portion of stem  170 . The spring  162  also applies pressure to a top portion of the pilot disc  160 . It should be understood in the art, that other more or less elaborate means of biasing could be used in place of the configuration shown. Also, alternatively no biasing element need be provided between the pilot disc  160  and the stem  170 . 
         [0031]    In contrast to the configuration of the pilot disc pin  165 , main disc pin  155  preferably couples main disc  130  to stem  170  without a biasing element applying pressure there between. In fact, stem  170  preferably includes a pin passage  175  that has a larger diameter than the diameter of main disc pin  155 . Thus, upward axial movement of stem  170  from the position shown in  FIG. 2  will not immediately engage stem  170  with main disc pin  155 . This configuration enables pilot disc  160  to actuate prior to main disc  130 . In this way, upon positive contact between the lower side of stem passage  175  with main disc pin  155 , main disc  130  is moved in unison with stem  170 , thus causing main disc  170  to move to an open position. Once moved to an open position, main disc  130  can be once again moved to a closed position after stem  170  moves downward causing main disc pin  155  to make positive contact with the upper side of stem passage  175 . 
         [0032]    The main disc base  139  acts like a piston guided within the lower portion  210  of collar  200 . The collar  200  encloses portions of the stem  170  as well as the stem guide  350 . As mentioned above, it should be understood that collar  200  could alternatively be integrally formed with either the valve housing  100  or the bonnet  300 . 
         [0033]    As further shown in  FIG. 1 , bonnet  300  is mounted and secured to the top of collar  200 . The bonnet  300  is also preferably provided with stem guide mating threads  302  on its lower end that mate with outer threads  352  on the stem guide  350 . Also, the bonnet  300  is provided with magnet housing mating threads  308 , which are preferably adapted to mate with outer threads  408  on the magnet housing  400 . It should be understood that bonnet  300  and stem guide  350  could be integrally formed. Providing separate bonnet  300  and stem guide  350  elements allows the use of different materials, such as materials better suited as a guide surface versus corrosion resistant materials. As with virtually all materials of the present valve assembly, the intended application (i.e., working environment and fluid being handled) can greatly influence the choice of materials. 
         [0034]    The stem guide  350  is preferably an annular member that includes an inner stem passage  355 . The stem passage  355  allows the pilot stem  170  to move up and down (back and forth) within, when the valve is being moved between the closed and open positions. It is desirable that at least a portion of the stem passage  355  have a non-circular cross-section (shown as the lower portion of stem passage  355 ) that matches the slightly smaller non-circular cross-section of portion  171  of the pilot stem  170 . As discussed further below, the non-circular mating configuration between the pilot stem  170  and the stem passage  355  should allow axial movement, but prevent the pilot stem from rotating relative to the assembly.  FIGS. 1 and 2  show a hexagonal lower portion of the stem passage  355  that guides the central stem position  171  that comprises a similar hexagonal cross-section. Additionally, the stem passage  355  is preferably provided with a stem seal  358  to prevent communication of fluids through the passage  355 . It should be understood that additional sealing elements can be provided throughout the assembly to ensure or improve the hermetic sealing of the valve assembly  10 . Although stem seal  358  is a dynamic seal, it is desirable to avoid dynamic seals especially that penetrate the outer housing elements, to further ensure a hermetic seal. It will be recognized that such a design eliminates or greatly minimizes any possibility of leakage, and also greatly reduces the amount of maintenance normally required in such environments. Further, debris magnets  359  are also preferably included within the stem passage  355  to trap the migration of dust or the like within the assembly. Once assembled as shown in  FIG. 1 , the upper end of the stem guide  350  acts as a retainer for the lower side of the inner portions of the magnet assembly  410 . 
         [0035]    The magnet housing  400  preferably contains the primary magnetic coupling components of the assembly. The magnet assembly  410  that is contained within the magnet housing  400 , shown in  FIG. 3 , includes an inner set of plunger magnets  430  and an outer set of actuator magnets  450 . These concentrically configured sets of magnets  430 ,  450  translate the actuating forces from the actuator stem  470  to the pilot stem  170 . The sets of magnets  430 ,  450  are preferably separated by a tube or sleeve  440  that further ensures a hermit seal on the overall assembly. 
         [0036]    Located adjacent to bonnet  300 , the magnet housing  400  preferably encloses the threaded end  178  of pilot stem  170  that is opposite the end secured to the pilot disc  160 . As shown in  FIG. 3 , the pilot stem threading  178  is slidingly engaged with the inner guide threads  425  of the pilot stem coupling  420 . In this way, since the pilot stem  170  is prevented from rotating by the non-circular portions of the stem passage  355 , rotation of the pilot stem coupling  420  translates into axial displacement of the pilot stem  170 . 
         [0037]    The pilot stem coupling  420  forms the innermost part of the magnet assembly  410  and supports the inner set of plunger magnets  430 , which are secured thereto. The plunger magnets  430  could be secured to the pilot stem coupling  420  in various known ways, such as the use of bonding agents, mating keys/slots or other fastening techniques. Similarly, the actuator magnet retainer  460  forms the outermost part of the magnet assembly  410  and supports the outer set of actuator magnets  450 , which are secured thereto.  FIG. 3  more clearly shows thrust bearings  415  used on the actuator side of the assembly to compensate for axial forces on both the inner  430  and outer  450  sets of magnets. As shown in  FIG. 1 , such thrust bearings are also preferably used on the opposite side of the magnet assembly  410 . 
         [0038]    As shown in  FIGS. 4   a,    4   b  and  4   c,  each of the sets of magnets  430 ,  450  comprise bar-shaped permanent magnets  431 ,  451  sandwiched between permeable iron bars  432 ,  452 , configured in an annular arrangement. Alignment of the magnetic flux fields of the inner  430  and outer  450  cells creates a strong attractive force that resists relative rotation between those sets of magnets  430 ,  450 . Thus, once the cells  430 ,  450  are aligned by the magnetic forces, they define a stable “null” position. Relative rotational movement between magnets  430 ,  450  results in an opposing force biasing the magnets to return to a null position. Thus, rotational movement of the outer cells  450  encourages similar rotational movement of the inner cells  430 . Also, the opposing force increases as the cells  430 ,  450  move from the null position, until they reach alignment with an adjacent cell. However, the magnet assembly  410  should be designed with sufficiently strong magnetic forces to avoid rotational displacement that reaches or goes beyond direct alignment with the adjacent cells. In fact, in a preferred embodiment, the magnet assembly  410  is designed to resist 10 times the maximum loads predicted or required by guidelines or specifications, before slipping. 
         [0039]    As shown in  FIG. 1 , the gear box  500  transfers the actuating forces to the actuator stem  470 . The gear box is preferably provided with both a motor input drive  560  and a manual input drive  570 . The input drives  560 ,  570  independently turn a worm gear  550 , which in turn rotates a combination rotary gear  540 . The combination rotary gear preferably includes a portion that couples to the worm gears  550  and a portion that couples to a bevel gear  530 . It is the bevel gear  530  that rotates around the axis of the actuator stem  470 . Also, bevel gear  530  transfers rotational movement to bevel gear carrier  520 , which is in turn secured to the actuator stem  470 . Preferably, the combination rotary gear  540  can not back-drive the worm gears  550 . Thus, once the input drives  560 ,  570  stop, the discs  130 ,  160  are retained in a fixed position. In this way, failure of the motor or manual input stops the valve opening, results in a “fail-as-is” design. Also, neither of the input drives  560 ,  570  can drive the other. It should be understood that various drive input mechanisms can be used in combination with the gear box  500  of the present invention. For example, electric, air and/or hydraulic motors could be used. 
         [0040]      FIG. 5  shows an alternative embodiment valve assembly  11  that uses a magnetic coupling that transfers axis forces, rather than the rotational version discussed above. Also, the embodiment shown in  FIG. 5 , integrally forms some of the outer elements, thus reducing the number of parts that form the outer housing for the overall assembly. The valve housing  600  combines elements of the previously discussed valve housing  100  and disc collar  200 . Also, the magnet housing  700  combines elements of the previously discussed disc collar  200 , bonnet  300 , stem guide  350  and magnet housing  400 . Further, the valve assembly  11  uses a flexible bellows or canopy ring  690  that seals together the outer elements  600 ,  700 . As mentioned above, it should be understood that alternative seals and couplings could be employed as are known in the art. 
         [0041]    The valve housing  600  includes inlet  610  and outlet  615  ports. The main disc  630  has a more continuous cylindrical design than that used for disc  130 . Also, main disc  630  and pilot disc  660  share a common disc pin  655 . A larger pin passage is preferably provided in main disc  630  than that provided in pilot disc  660 . In this way, the pilot disc  660  will respond to the axial movements of disc stem  670  before main disc  630  will respond. 
         [0042]    Valve assembly  11  actuates axial movement of the disc stem  670  through plunger  710 , in contrast to the rotational movement of the previous embodiment. The rotational movement design can produce higher actuating forces for comparably sized magnet assemblies. However, the axial movement design is well suited for low-pressure on-off valves. In valve assembly  11 , plunger  710  is secured at its base  712  to the disc stem  670 , while secured at its other end to plunger cap  718 . The disc stem  670  is preferably threadedly engaged with plunger base  712 . The stepped profile of the plunger  710  together with the plunger cap  718  axially secures the plunger magnets  730  to the plunger  710 . As in the previously discussed embodiment, the plunger magnets  730  and the actuator magnets  750  are separated by a tube or bonnet sleeve  740 . Also, the outer magnet cells  750  are held together by a retainer  760 . The actuator magnet retainer is secured to and transfers axial movement from actuator stem  770  to the actuator magnets  750  and thus the overall magnet assembly. 
         [0043]      FIGS. 6   a,    6   b  and  6   c  show portions of the magnetic assembly of  FIG. 5 . Both the plunger magnets  730  and the actuator magnets  750  comprise annular permanent magnets  731 ,  751  sandwiched between annular permeable iron magnets  732 ,  752  configured in an axial arrangement. Alignment of the magnetic flux fields of the inner  730  and outer  750  cells creates a strong attractive force that resists relative axial displacement between those sets of magnets  730 ,  750 . Thus, similar to the previous embodiment, once the cells  730 ,  750  are aligned by the magnetic forces, they define a stable “null” position. Relative axial movement between magnets  730 ,  750  results in an opposing force biasing the magnets to return to a null position. Thus, axial movement of the outer cells  750  encourages similar axial movement of the inner cells  730 . 
         [0044]      FIG. 7  shows additional details of gear box  800 , which axially actuates the stem  770 . Similar to gear box  500 , gear box  800  is preferably provided with a motor input drive  860 , a manual input drive  870  and internal bearings  835 . The input drives  860 ,  870  independently turn a worm gear  850 , which in turn rotates a combination rotary gear  840 . The combination rotary gear  840  preferably includes a worm gear portion  844  that couples to the worm gears  850  and a beveled portion  842  that couples to a bevel gear  830 . Bevel gears  830  are mounted on gear pins  825  and carrier  820 . Rotation of the combination rotary gear  840  preferably not only causes rotation of the beveled gears  830  but also causes them to act as planetary gears that orbit the axis of the stem  770 , along with the pins  825  and carrier  820 . The carrier  820  is threadedly engaged with stem  770 , such that rotation of carrier  820  axially displaces the actuator stem  770 . The gear box  800  has a similar “fail-as-is” design to that of gear box  500 . 
         [0045]    As a further alternative embodiment, position indicators or position feedback systems, as shown in  FIG. 8 , can be employed for tracking the position of one or more stems  170 ,  470 ,  670 ,  770 . A shaft position encoder (SPE)  910  is a device that transmits an analog voltage that is proportional to the stem&#39;s position. The SPE  910  can be a commercial-off-the-shelf unit or one customized to suit a particular valve application. Preferably, optical encoders could be used to accurately measure shaft position. Also, optical encoders avoid internal parts that will wear over time. Thus, as shown in  FIG. 8  an extension housing  900  can be secured to the gear box  800 , in order to contain and protect the SPE&#39;s  910 , as well as programmable control systems  930  and other supporting structure  920 . An SPE  910  located at the top of the actuator could also be used in conjunction with another SPE (not shown) located on the other side of the gear assembly, toward the main disc  130 . Such SPE&#39;s  910  can be used to track axial or rotational displacement, based on the valve design employed and which portion of the assembly is being tracked. 
         [0046]    One benefit to using position encoders it that operation of the valve assembly  10 ,  11  can be preprogrammed and closely controlled and/or maintained by computer. Additionally, a computer can easily translate the analog signal transmitted by an encoder into a user friendly display, which provides a precise position indicator. Also, the signal information can be stored or analyzed for diagnostic purposes. Further, the computer could also be used to control the motorized input drive  560 ,  860 , which would provide the ability to pulse the main  130  or pilot  160  discs to seat and/or precisely stop, as desired. Such automation can prevent damage to the valve and particularly the main  130  and/or pilot  160  discs. Also, by further monitoring of the motorized input device  560 ,  860  un-safe torque or current levels can be further indicated through either a visual or audio alarm. 
         [0047]    While various embodiments of the present invention are specifically illustrated and/or described herein, it is to be understood that the invention is not limited to those precise embodiments and that various other changes and modifications may be affected herein by one skilled in the art without departing from the scope or spirit of the invention, and that it is intended to claim all such changes and modifications that fall within the scope of the invention.