Abstract:
A pressurized sealing arrangement suited for providing a seal between a valve stem and a valve body is disclosed. The sealing arrangement includes a piston that is restrained in and statically sealed to the valve body and which surrounds the valve stem. Contained within the piston is an annular seal packing that includes two sealing elements spaced apart by a spacer element. The piston includes a face acted upon by a process fluid flowing through the valve body in such a manner that the piston exerts pressure upon a lubricant cavity. The lubricant cavity is in fluid communication with the seal packing such that lubricant contained therein forms a lubricant ring around the stem. Lubricant is also thereby supplied to sealing elements of the packing seal. To prevent contamination of the seal packing, a removable cover is provided that encloses the piston and seal packing.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of U.S. application Ser. No. 10/340,017 filed on Jan. 10, 2003. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to seals and sealing, and more particularly to pressurized seals for sealing a reciprocating stem or shaft. The present invention finds particular utility in regulating values in which leakage of the process fluid being regulated is to be minimized.  
         BACKGROUND OF THE INVENTION  
         [0003]    Flow regulating valves are devices that can be adjusted to restrict or increase the flow of a fluid through a conduit. Such valves are generally well known in the art and have many practical applications. For example, in the commercial natural gas production industry, flow-regulating valves are commonly used to vary the flow of natural gas through a network of gas collection pipes. The network of collection pipes often will connect and branch together tens to hundreds of natural gas ground wells in a localized geographic region. The individual wells will feed natural gas through the network of gas collection pipes to a common output location. Often, the desired natural gas output is less than the maximum production capacity of the several wells combined. Such demands can change due to cyclical seasonal trends and for other economic reasons. This creates a need for regulating and monitoring natural gas production from each well to control the supply.  
           [0004]    To regulate the production output of each individual well, the branch collection pipe for each individual well typically includes a flow-regulating valve and a gas flow sensor arranged in fluid series. The gas flow sensor indicates the amount of natural gas that flows through the collection pipe. The regulating control valve provides a variable degree of opening that forms a restriction orifice in the collection pipe and thereby sets the natural gas flow rate in the collection pipe.  
           [0005]    To adjust the restriction orifice within the collection pipe, the flow-regulating valve is typically a movable/positionable type of valve such as a linearly translatable valve. A valve of this design generally includes a valve body through which a flow passage is disposed. Other components include a plug member located within the flow passage and an elongated valve stem attached to the plug member and that passes through a valve bonnet. The plug member can be linearly translated toward or away from a valve seat within the flow passage between a fully opened position and a fully closed position, and intermediate positions therebetween. The plug member blocks all flow when in the fully closed position and allows for maximum flow when in the fully opened position.  
           [0006]    To linearly translate the plug member towards and away from the valve seat, the valve stem can be connected to an actuator typically located adjacent the valve bonnet and which imparts linear translation motion to the valve stem. Accordingly, the valve stem will have to move with respect to the valve housing that it passes into. To prevent the unnecessary loss of process fluids passing through the valve, it is desirable that the intersection between the reciprocating valve stem and the valve bonnet into which the stem passes is well sealed. This is especially desirable where the process fluid is a flammable natural fluid that can potentially produce an explosion or some other poisonous or environmentally harmful process fluid.  
           [0007]    One device and sealing method that has been proposed for sealing a linearly moving valve stem is a pressurized seal arrangement of the type taught in, for example, U.S. Pat. No. 6,161,835 to Donald Arbuckle. In pressurized seal arrangements of the type disclosed in Arbuckle, pressure from the process fluid is used to create a dynamic seal preventing leakage from valve stem and pressurizing piston intersection. Specifically, the device uses an intermediary fluid or lubricant onto which the pressure of the flowing process fluid can be imparted. The pressurized intermediary fluid is thereby forced toward the stem thus creating a fluid seal around the stem that prevents leakage of the process fluid to the environment. Additional sealing may be provided by the inclusion of other sealing elements surrounding the stem that are lubricated by the pressurized intermediary fluid. Improvements to this prior art design are presented herein.  
         BRIEF SUMMARY OF THE INVENTION  
         [0008]    The present invention is directed toward a novel pressurized seal arrangement for a stem that is simple to assemble and that is easy to service. The pressurized seal arrangement can be implemented in, for example, a well-head regulating valve attached to a collection pipe through which process fluids, such as natural gas, may pass. The regulating valve may have a valve housing that defines a flow passage therethrough. An elongated stem extends from a valve plug member located along the flow passage through the valve housing to an actuator that can impart a translating motion to the valve stem. Linear translation of the plug member toward and away from a valve seat formed in the flow passage results in blocking or permitting flow through the valve.  
           [0009]    To provide the pressurized seal between the valve bonnet and the valve stem, the stem extends through and is surrounded by an annular piston. The piston and the bonnet in turn are restrained and statically sealed to the valve body so as to prevent leakage of the process fluid. The piston separates the process fluids in the flow passage from a lubricant cavity located between the piston and the bonnet. The piston also includes a sleeve portion that surrounds and extends axially along the stem and that is received in the bonnet. Attached to an outside surface of the bonnet can be the actuator.  
           [0010]    Contained within the sleeve portion is a seal packing that fits around valve stem. The seal packing includes two sealing elements, such as pressure and spring actuated cup seals, that are axially spaced apart by the spacer element. The seal packing can also include seal retaining washers located between the sealing elements and the spacer element and a PTFE guide bushing. To axially retain the seal packing in the sleeve portion, a snap ring snaps into a groove formed in the sleeve. Also included may be a retaining washer between the PTFE guide bushing and the snap ring. The spacer element includes ports that are in fluid communication with lubricant stored in the lubricant cavity. Because the lubricant cavity is pressurized by the process fluid impinging on the piston, pressurized lubricant forms a ring that acts as a fluid seal around the valve stem between the first and second sealing elements. The lubricant also lubricates the seal elements to facilitate their dynamic sealing effect.  
           [0011]    In another aspect of the present invention, to check the level of the lubricant in the sealant cavity, the sleeve can be received in the bonnet such that the sleeve end is flush with the top surface of the bonnet. Leakage of lubricant from the sealant cavity will cause axial motion of the piston with respect to the bonnet such that the end of the piston sleeve will rise above the top surface of the bonnet. To prevent dust or other containments from affecting the seal packing, a cover can be placed adjacent the top surface of the bonnet enclosing the seal packing.  
           [0012]    An advantage of the present invention is that a pressurized seal is created between a valve bonnet and a linearly translating stem passing through the valve housing such that process gases flowing through a valve body are sealed therein. Another advantage is that the pressurized seal is arranged in such a manner that simplifies its construction and maintenance. These and other advantages, as well as additional features, will become apparent from the description of the invention provided herein.  
           [0013]    The present invention will be described in association with a valve application although it will be appreciated that the claimed invention of certain claims may have other applications.  
           [0014]    Other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a schematic plan view of a wellhead system incorporating the electrically actuated valve according to a preferred embodiment of the present invention.  
         [0016]    [0016]FIG. 2 is an isometric view of the electrically actuated valve shown in FIG. 1.  
         [0017]    FIGS.  3 - 4  are cross sections of the electrically actuated valve shown in FIG. 2 with the cross sectional views being shown from the front and the side.  
         [0018]    [0018]FIGS. 5 and 6 are cross sections of the electrical actuator portion of FIG. 3.  
         [0019]    [0019]FIG. 7 is a cross section of the electrical actuator shown in the previous FIGURES as viewed from the top.  
         [0020]    [0020]FIG. 8 is an enlarged cross section of the valve portion of the electrically actuated valve shown in FIG. 4.  
         [0021]    [0021]FIG. 9 is an enlarged cross section of FIG. 8 illustrating a sealing arrangement for the valve.  
         [0022]    [0022]FIG. 10 is an exploded assembly view of the sealing arrangement shown in FIG. 9.  
         [0023]    [0023]FIG. 11 is an isometric view of the guts of the electrical actuator shown in previous figures.  
         [0024]    [0024]FIG. 12 is a side view of the guts of the electrical actuator shown in previous figures.  
         [0025]    FIGS.  13 - 14  are frontal and back views of the guts of the electrical actuator shown in previous figures.  
         [0026]    [0026]FIGS. 15 and 17 are front and rear end views of the brake mechanism used in the electrical actuator shown in previous figures.  
         [0027]    [0027]FIG. 16 is an isometric view of the brake housing.  
         [0028]    [0028]FIGS. 18 a  and  18   b  are cross sections of the brake mechanism shown in FIGS.  15 - 17 , illustrated in the on and off positions, respectively.  
         [0029]    [0029]FIG. 19 is an exploded assembly view of the brake mechanism shown in FIGS.  15 - 18 .  
         [0030]    [0030]FIG. 20 is the same view as FIG. 3, except that the spring is reversed to bias the valve toward an open position.  
         [0031]    [0031]FIG. 21 is a cross section of a drop in clutch gear which may be used in the electrical actuator, being substituted for one of the gears.  
         [0032]    [0032]FIG. 22 is a schematic view of a commonly employed control system for a well head valve.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]    An electrical actuator  10  that is particularly suited for a well-head valve  12  is shown throughout the figures in accordance with a preferred embodiment of the present invention. FIG. 1 illustrates a natural gas well production system  14  which is an exemplary application and operational environment for the electrical actuator  10 . As shown in FIG. 1, the well-head valve  12  regulates the production output of a natural gas production well  16  through a collection pipe  18 . The well head valve  12  is mounted in the collection pipe  18  in fluid series with a gas flow sensor  20 . The degree of opening of the well head valve  12  and the natural gas pressure of the well  16  (which typically ranges between about 10-900 psi or even higher for most production wells) determine the natural gas flow rate through the collection pipe  18 . The gas flow sensor  20  measures the amount of natural gas that flows through the pipe  18 . The gas flow sensor  20  provides electrical feedback representative of the sensed flow rate to an electronic controller  22  for closed loop control over the electrical actuator  10  and well-head valve  12 .  
         [0034]    Since the well  16  may be located remote from a commercially available electrical power supply, the system  14  is shown to include a local electrical power supply which typically comprises a small solar panel  24  and battery  26 . The solar panel  24  generates a small electrical power supply and the battery  26  stores the electrical power supply. Advantageously, the electrical actuator  10  can replace pneumatic actuation systems without needing any additional power or electrical generation, using only the existing local electrical power supply if desired. As such, additional cost need not be wasted on electrical generation, and the present invention may be employed as a retrofit device to replace pneumatic actuating systems at existing well-head valves. However, it should be noted that in some instances that some additional expansion of the electrical generation or storage capabilities may be desirable.  
         [0035]    In FIG. 1, two separate controllers  22 ,  82  are indicated, but these may be integrated if desired into a single controller assembly. To provide for both retrofit and new systems, typically two separate controllers  22 ,  82  will be used.  
         [0036]    The well-head valve  12  may be a linearly translatable valve, a rotary valve or other movable/positionable valve. Referring to FIGS. 24 and 8, the illustrated well-head valve  12  is shown as the linear type comprising a valve housing  28  and linearly translatable valve member  20 . The valve housing  28  includes a valve body  41  defining a flow passage  32 . The flow passage  32  extends between and through a pair mounting flanges  34  on ends of the valve body  41 . The mounting flanges  34  are adapted to mount the wellhead valve  12  on a collection pipe  18 . The valve member  20  may include separate components including a plug member  36  and an elongate valve stem  38  extending from the plug member  38 , as is shown. The valve stem  38  extends through the valve housing  20  and is acted upon by the electrical actuator  10 . The valve stem  38  transmits the selective positioning force from the electrical actuator  10  to the plug member  36 . The plug member  36  is situated in cage  42  along the flow passage  32  to provide a restriction orifice that regulates flow through the valve. The plug member  36  is linearly translatable toward and away from a valve seat  40  between fully closed and fully open positions, and intermediate positions therebetween. The plug member  36  blocks all flow when in the fully closed position and allows for maximum flow when in the fully open position.  
         [0037]    To provide for installation of the movable valve member  20 , the valve housing  38  may be composed of multiple pieces including the valve body  41 , a metering cage  42  which radially restrains and guides movement of the valve plug member  36  and a bonnet  44  which radially restrains and provides for a seal arrangement  46 . The seal arrangement  46  provides a static seal and dynamic seal that prevents leakage of natural gas from the valve  12 . One suitable seal arrangement for preventing natural gas leakage in the valve is illustrated in U.S. Pat. No. 6,161,835 to Don Arbuckle, the entire disclosure of which is incorporated by reference.  
         [0038]    However, the disclosed embodiment includes a more advantageous and novel seal arrangement  46  that is less complicated, less expensive and more reliable. Referring to FIGS.  9 - 10 , the sealing arrangement  46  includes a pressuring annular piston  47  extending through and surrounding the valve stem  38 . One face of the piston  47  is acted upon by process fluid contained in the valve flow passage  32  to pressurize seal lubricant fluid that is contained in a sealant cavity  48 . The piston  47  includes a sleeve portion  49  that contains a seal packing. The outer periphery of the piston  47  carries an o-ring seal  50  for preventing communication between process fluid and lubricant. Not much, if any, piston movement is anticipated where the o-ring seal  50  is located, and therefore this may be considered a static seal for all practical purposes. Another static o-ring seal  51  is located between the valve body  41  and the bonnet  44  for preventing leakage from the sealant cavity  48 . Thus, the two o-ring seals  50 ,  51  are arranged in series and provide redundant backup to ensure process fluid does not leak through the sealant cavity.  
         [0039]    The seal packing contained in the piston sleeve portion  49  includes a pair of dynamic pressure and spring urged cup seals  52  arranged in fluidic series, a spacer element  53 , a pair of seal retainer washers  54 , a PTFE guide bushing  55 , a snap ring  56  and a retaining washer  57 . The snap ring  56  snaps into a groove in the piston sleeve portion  49  to axially retain the seal packing in place. The PTFE guide bushing  55  is tightly fit around the valve stem  38  to provide for low friction sliding movement of the valve member  30 . The spacer element  53  axially spaces the cup seals  52  with the seal retainer washers  54  providing for balance and retention of the seals  52 . Ports  58  extend through the spacer element  53  such that a pressurized cylindrical ring of lubricant surrounds the valve stem  38  between the seals  52  such that the lubricant acts upon each of the dynamic seals  52 .  
         [0040]    A cover  59  is provided that encloses the packing and piston to prevent dust and other external contaminants from damaging the sealing arrangement  46 . The cover  59  can be removed to manually check the level of lubricant which is indicative of how well the seals  50 ,  51 ,  52  are working. Specifically, the end of the piston sleeve portion acts as an sealant level indicator  61 . When the sleeve end or indicator  61  is flush or coplanar with the top surface of the bonnet  44 , the proper amount of sealant lubricant is contained in the sealant cavity  48 . If the indicator is raised above the top surface by virtue of axial piston movement, that is indicative that sealant has leaked out. A partitioned scale may be provided along the outer surface of the piston sleeve portion  49  to provide a numerical indication of lubricant level if desired. Several advantages are provided with this seal arrangement  46 , including easier manufacture and assembly, prevention of contaminants from reaching the sealing arrangement and an integral mechanism to indicate the seal lubricant level.  
         [0041]    The wellhead valve  12  may include a spring  60  for biasing the movable valve member  30  to either the open position or the closed position. As shown in FIGS. 3 and 8, the spring  60  is shown as a steel coil spring that is arranged to bias the valve member  30  to the closed position. A spring housing  62  mounts between the electrical actuator  10  and the valve body  41  to house and support the spring  60 . The spring  60  is supported by one end of the spring housing  62  and upon a spring seat plate  64  that is supported by an actuator stem  66 . One end of the actuator stem  66  engages the valve stem  38 , while the other end has a drive rack  68 .  
         [0042]    Referring to FIGS. 3 and 11- 13 , the drive rack  68  provides a sleeve member  67  that is slid onto the actuator stem  66  such drive rack  68  can rotate relative to the actuator stem  66 . A thrust bearing  70  better ensures free rotation of the drive rack  68  particularly since it is held axially in position by a wave spring  71 . The sleeve member  67  is axially constrained between a pair of nuts  69  mounted on the actuator stem  66  and the wave spring  71  that biases the sleeve member  67  and drive rack  68  to a fixed position on the actuator stem  66 . This arrangement allows for free rotation of the drive rack such that forces from the spring  60  do not cause the drive rack  68  to twist, thereby preventing premature wear, but it also holds the drive rack in a fixed axial position on the actuator stem. The wave spring  71  also compresses lightly when the valve member  30  contacts the seat, thereby reducing the resulting impact load on the gears. Another alternative to a rack and pinion mechanism for converting rotational energy to linear motion is a ball screw mechanism, and that and other conversion mechanisms may be used as an alternative.  
         [0043]    It should be noted that the spring housing  62  and spring  60  are shown in FIG. 8 to be part of the wellhead valve  12 . However, the spring housing  62  and spring  60  may alternatively be considered to be part of the electrical actuator and/or can be integrated into components of the electrical actuator or the valve. In either event, the spring  60  applies a biasing force to the electrically actuated valve which effectively acts both upon the valve plug member  36  and the gear reduction train  76 , either directly or indirectly.  
         [0044]    The disclosed embodiment also provides a support structure  65  on the actuator stem  66  that provides a feature for reversing the actuation force of the spring  60  is also reversible. As shown in FIG. 20, the spring  60  may engage the other end of the spring housing  62  with the spring seating plate  64  supported by the alternative support structure  65 , such that the spring as compressed between the spring seating plate  64  and the spring housing  62  biases the valve toward the open position. Thus, the spring is reversible such that the electrically actuated wellhead valve can be configured to bias the well-head valve either open or closed.  
         [0045]    Referring to FIGS.  2 - 7 , the electrical actuator  10  comprises an actuator housing  72  (comprised of several aluminum shells fastened together preferably in a leak proof manner) that generally contains and supports a stepper motor  74 , a gear reduction train  76 , a brake mechanism  78 , a manual override mechanism  80  and a motor driver generically indicated as a motor controller  82 . The actuator housing  72  mounts onto the spring housing  62 . The stepper motor  74  is a non-incendive type motor that prevents spark formation when the electrical actuator is used around natural gas or other flammable fluids and thereby further reduces the potential for a hazardous situation should there be gas leakage. Other potential appropriate spark free types of motors include a brushless DC motor, and a spark-free AC motor.  
         [0046]    In an embodiment of the present invention pertaining to wellhead valve applications, the controller  82  selectively energizes the motor  74 . The electrical motor  74  can be operated by the controller  82  in a hold mode for holding the current position of the wellhead valve  12  and in an actuation mode for driving the wellhead valve  12 . The electrical motor consumes between 1 and 3 watts in the hold mode (to provide a force that holds a current valve position with the brake off) and between 4 and 12 watts in the actuation mode. This very low power consumption makes the electrical actuator  10  capable of operating solely off an existing electrical power supply provided by a solar panel  24  and battery  26  (which local power source may have been originally intended for regulating electro-pneumatic wellhead valves).  
         [0047]    Referring to FIGS.  11 - 14 , the stepper motor  74  includes a motor housing or stator  84  mounted in fixed relation relative to the actuator housing  72  and a rotor comprising an output shaft  86 . The output shaft  86  rotates relative to the stator  84 . The output shaft  86  integrally provides a pinion gear  88  thereon (either by machining the output shaft or mounting a separate gear cog mounted thereto) which provides an input for the gear reduction train  76 . The gear reduction train  76  comprises a plurality of individual reduction gears  90   a - d  that each comprise a larger upstream gear cog  92   a - d  and smaller downstream gear cog  94   a - d  (i.e. a “pinion” gear) that are mounted on a common gear shaft  96   a - d.    
         [0048]    The gear shafts  96   a - d  are rotatably mounted or supported for rotation by the actuator housing  72  in parallel relationship. The pinion gear  88  on the output shaft  86  is meshed with the larger cog  92   a  of the first reduction gear  90  such that the force is amplified from the motor output shaft  86  to the first gear shaft  96   a . The other gears in the gear reduction train are similarly arranged with the smaller gear cogs  94   a - 94   c  driving the larger gear cogs  92   b - 92   d , respectively. As the motor rotates, the electrical actuation force provided by the motor  74  is applied and amplified across the gear reduction train  76  from the motor output shaft  86  to the rotary output, which is then applied by the last smaller pinion gear cog  94   d . The smaller gear cog  94   d  is meshed with the drive rack  68  to drive the drive rack  68  and thereby convert rotational energy into linear translation energy. A spring biased cam element  73  supported by the actuator housing  72  keeps the racked biased against the pinion gear cog  94   d  in meshed relation (this may be used as a torque limiting device to prevent damage in the event of error or an overtorquing situation). Another alternative to a rack and pinion mechanism for converting rotational energy to linear motion is a ball screw mechanism, and that and other conversion mechanisms may be used as an alternative.  
         [0049]    In order to be sufficient for driving the wellhead valve  12  in wellhead valve systems  14 , the gear train preferably has a gear reduction ratio of at least 100:1 and more preferably of at least 400:1. With such a substantial gear reduction ratio, a small motor force (e.g. consuming 4-12 watts for driving the valve with current motor technology that is readily available) is amplified by the gear reduction train to provide sufficient actuation force for driving and positioning the valve  12  against spring forces and/or fluid forces, which can be very substantial in view of the fact that well pressures can vary in a range of about 10-900 psi. Obviously, the speed of the actuation will be decreased substantially with the slew time of the valve  12  between fully open and closed positions taking about 1-5 minutes. It has been realized that a slow slew time is acceptable and does not appreciable affect well production control (particularly since production often occurs 24 hours a day with demanded changes in well output occurring on a relatively infrequent basis). This is also particularly true when considering the significant advantages associated with reducing and in fact eliminating for all practical purposes all fugitive gas emissions using the local power source typically provided at wellhead valve sites.  
         [0050]    Referring to FIGS.  15 - 19 , the brake mechanism  78  acts at least partially through the gear reduction train  76  and as shown in the disclosed embodiment, directly on the output shaft  86  of the motor  74 . The brake mechanism  78  may act on the motor pinion  88  to retard the forces of the return spring and/or fluid pressure forces transmitted through the gear train such that only a fraction of the force is transmitted to the motor shaft  86  of the motor  74 . Thus the brake mechanism  78  may be used to greatly reduce the amount of holding force needed by the motor to hold a current position of the valve, or to completely eliminate a holding force to maintain a current valve position.  
         [0051]    The brake mechanism  78  includes a pair of brake calipers  110  and a rotor  112 . The calipers  110  include slots  114  on their outer peripheries that receive stationary support pins  116  which are supported and mounted into, by and extend from the actuator housing  72 . The pins  116  hold the calipers  110  stationary and prevent rotation of the calipers  110 . The outer caliper  110  is also axially abutted up against and supported by the actuator housing  72 . The rotor  112  includes a sleeve portion  118  that is splined to the output shaft  86 , and a plate portion  120  sandwiched axially between the brake calipers  110 . The calipers  110  include radially inward projecting circular ribs  122  that frictionally engage the rotor plate portion  120  when the brake is engaged in the on position. The ribs  122  are relatively thin radially to provide a substantially constant diameter ring that engages the rotor  112  to provide a more consistent braking force (e.g. thereby avoiding slippage at a smaller diameter that could occur with a radially wider brake pad caliper). A braking spring  124  applies an axial force to frictionally engage the calipers  110  against opposing sides of the rotor  112 .  
         [0052]    Although the brake mechanism  78  may be permanently positioned in the on position and therefore designed solely as a dynamic brake, preferably the brake mechanism also includes an actuator device  126  for manually engaging and disengaging the brake between on and off positions as shown in FIGS. 18 a  and  18   b . The brake may have different levels of engagement as well to provide different levels of braking force. In the disclosed embodiment, the actuator device  126  includes a sleeve shaped support housing  128  that threads into or otherwise mounts into the actuator housing  72 . The actuator device  126  also includes shank shaped selector switch member  130  that is slidably inserted into the support housing  128  for rotation and linear movement relative to the support housing  128 .  
         [0053]    The linear and rotational movement of the switch member  130  relative to the support housing  128  is constrained with a pin  132  and slot  134  mechanism. The pin  132  is securely mounted to switch member  130  and extends radially outward therefrom into the slot  134 , which is defined by the support housing  128 . The slot  134  includes first and second axially extending legs  138 ,  140  that correspond to the on and off positions, respectively, and a radially extending intermediate section  142  separating the legs  138 ,  140 . The first leg  138  is longer than the second leg  140  to provide for on and off positions. An outer spring  144  is supported by a washer  146  that is held stationary in a fixed position by the actuator housing  72 . The outer spring  144  axially biases the switch member  130  toward the support housing  128  such that the pin  132  is restrained and urged toward the terminating end of leg when the pin  132  is positioned in either of the legs  138 ,  140 .  
         [0054]    The switch member  130  includes an actuating stem portion  148  that extends through a central hole in the support housing  128 . The stem portion  148  includes a manually crankable head portion exposed on the outside of the actuator housing  72 . The crankable head portion is shown as including a screwdriver slot  150  or other structure that is adapted to be rotated by a tool or crank mechanism. As shown in FIGS. 18 a ,  18   b , the switch member  130  can be manually pushed inward against the action of the outer return spring  144  and manually rotated between on and off positions (as indicated on the outside of the support housing as shown in FIG. 15).  
         [0055]    The selector switch member  130  carries the brake spring  124  that is adapted to apply the axial braking force to the brake calipers  110 . The brake spring  124  is supported at one end by a spring seat  152  and axially urges a brake applicator plate  154  away from the selector switch member  130 . The spring seat  152  includes a threaded stem  156  that threads and locks into a threaded opening  158  in the selector switch member  130 , via a self-locking thread such that the position of the spring seat  152  is fixed relative to the selector switch member  130 . How far the spring seat  152  is screwed into the selector switch member  130  generally determines and is used during assembly to gauge and set the braking force that is applied in the on position for the brake mechanism  78 . The brake applicator plate  154  is axially movable relative to the spring seat  152 . A shoulder bolt  160  extends through the brake applicator plate  154  and is mounted into the spring seat  152 . The shoulder bolt  160  supports and guides axial sliding movement of the applicator plate  154 .  
         [0056]    When the brake mechanism  78  is in the on position as shown in FIG. 18 a , the braking spring  124  urges the applicator plate  154  against the inner brake caliper  110  such that the spring compresses the brake calipers  110  against the rotor  112 . When the brake mechanism  78  is in the off position as shown in FIG. 18 b , the braking spring  124  urges the applicator plate  154  against the head of the shoulder bolt  160  which acts as a stop to prevent the spring from acting upon the calipers  110 .  
         [0057]    Also provided in the electrical actuator  10  is the manual override mechanism  80  which includes a crankable input shaft  162  that includes a head with a rectangular structure  164  that can be engaged and rotated by a manual crank or tool. The input shaft  162  is journalled in the actuator housing  72 . The input shaft  162  acts through a torque limiting clutch  166  (or other torque limiting device, e.g. a shear pin) upon one of the gear shafts  90   d  such that rotation of the input shaft  162  is operable to linearly the valve member  30  manually. The torque limiting clutch  166  prevents manual overtorquing of the apparatus and thereby prevents damage to the drive rack  68  and the drive pinion  94   d  that could otherwise occur with manual overtorquing. The torque limiting clutch  166  may include an input plate coupled to the input shaft  162  that frictionally engages an output plate coupled to the gear shaft  90   d . At a predetermined force or torque, the plates of the clutch  166  slip relative to each other to prevent overdriving of the valve. The clutch  166  is set such that the predetermined torque at which slippage occurs is small enough to prevent damage to the wellhead valve  12  from manual overtorquing but large enough to be sufficient to overcome all braking and biasing forces acting on the valve such as those caused by the brake mechanism  78  and the valve biasing spring  60 , whereby the manual override mechanism  80  is manually operable to drive the valve member  30  to a selected position between fully open and fully closed positions, even with the brake mechanism  78  engaged in the on position. The head of the input shaft  162  has a pointer  172  and the actuator housing  72  has a scale  174  that indicate the degree of opening of the valve  12 . The pointer  172  and scale  174  are used to indicate the position of the valve visually and for maintenance personnel when adjusting the valve manually.  
         [0058]    A significant feature of the disclosed embodiment is that the electrical actuator  10  is configurable between three different possible modes of operation. Configuration is accomplished by having a biasing force of the spring  60  that is manually reversible and a brake mechanism  78  that also has on and off positions such that the spring  60  can drive the gear reduction train  76  and valve member  30 , or the brake mechanism  78  can be used to hold valve position, when there is electrical power loss. The electrical actuator  10  thus has three different configurable operational modes upon power loss to the electrical motor  74 , including a fail-open mode wherein the spring is arranged to urge the gear reduction train  76  and valve member  30  toward the fully open position upon power loss  60  with the brake mechanism  78  in the off position, a fail-close mode wherein the spring  60  is arranged to urge the gear reduction train  76  and valve member  30  toward the fully closed position upon power loss with the brake mechanism  78  in the off position, and a fail-fix mode wherein the brake mechanism  78  is in the on position and holds the current position of the gear reduction train  76  and the valve member  30 .  
         [0059]    Multiple position sensing devices are employed in the disclosed embodiment. First, the motor controller  82  integrally incorporates an analog position sensor  176  that derives position of the rotary output from motor position control signals sent to the electrical stepper motor  74 . The analog position sensor is a form of an accumulator or counter that adds numbers and subtracts numbers from a count as the stepper motor  74  is driven to electronically derive position of the valve  12 . The changes in valve position are linearly proportional to the changes in the count of the analog position sensor  176 . The disclosed embodiment also includes a redundant position sensor electrically wired and providing feedback to the motor controller  82 , which is shown in the form of a potentiometer  178 . The potentiometer  178  is positioned by a cam that is acted upon by an eccentric surface on an extended portion of the last gear shaft  96 . The potentiometer  178  provides redundant feedback that is used to check the accuracy of the analog position sensor  176  which could have error should there be a loss of electrical power or slippage in the stepper motor  74 . Finally, the disclosed embodiment may also include limit switches  184  that are mounted proximate the last gear shaft  96   d  at set points representing the end of travel for the wellhead valve  12  also defined as the fully open and fully closed positions. The extended output gear shaft  96   d  includes cam eccentrics which trigger the limit switches  184  at the set points. The limit switches  184  are electrically wired to a customer interface to provide indication of when the valve is at a set point. This provides independent feedback to check accuracy of operation. Alternatively, the limit switch signals can be used to shut off power to the motor  74  to ensure that the controller  82  does not signal the motor to drive the valve past either of the fully open or closed positions. The limit switches  184  are also adjustable and manually rotatable relative to the output shaft  96   d  such that if an end user wishes to define a different end of travel range, the end user can manually configure and define the end of travel range as he deems fit.  
         [0060]    Referring to FIG. 1, the system  14  may also include a wireless transceiver  186  powered by the local power source that is in electrical communication with one or both of the controllers  22 ,  82 . It should be noted that the first controller  22  is provided at a wellhead valve site typically external to the electrical actuator  10  to provide system level control. The motor controller  82  is more of a motor driver to facilitate control over the driving of the electrical actuator  10  and positioning of the wellhead valve  12 . In any event, the wireless transceiver  186  can receive remote control input and demand signals wirelessly from a remotely positioned transceiver  188 , such that either or both of the controllers  22 ,  82  can be remotely controlled to adjust position of he wellhead valve  12  wirelessly. The transceiver  186  can also transmit feedback to a remote location and thereby inform maintenance personnel about the operating parameters at the well head site (e.g. flow rate, valve position, power levels, malfunctions, ect.).  
         [0061]    Another alternative aspect of an embodiment may be the incorporation of a sleep mode for the electrical actuator  10  in which it consumes virtually no electrical power and powers itself down automatically when the valve  12  is correctly positioned. According to this mode, the brake mechanism  78  is normally in the on position and therefore acting as dynamic brake arranged to provide resistance to movement of the valve  12 . Since the brake mechanism  78  when on provides sufficient force to prevent backdriving of the gear train upon power loss, the brake mechanism  78  is operable to hold a current position for the wellhead valve  12 . The electrical motor  74  provides sufficient force and torque to cause the brake to slip and thereby overpower the brake to move the wellhead valve  12  when desired. The sleep mode further provides for energy efficiency and lowers power consumption when electrical power in these remote locations is scarce.  
         [0062]    Another feature shown in FIG. 21 is an alternative drop in clutch reduction gear  190   b  that can replace reduction gear  90   b . The clutch reduction gear  190   b  is particularly useful and can be used for the actuator when configured for fail-open mode, in which the spring  60  is arranged to bias the valve open as shown in FIG. 20. The clutch reduction gear  190   b  similarly includes a larger gear cog  192   b  and smaller pinion gear cog  194   b  on a gear shaft  196   b . As shown, the larger gear cog  192   b  is slidably mounted with a sleeve bushing  191 . A pair of spring washers  193 , supported by axially fixed bearing support members  195  (which are supported by the actuator housing) urge a pair of support plates  197  and frictional engaging discs  198 , with the larger gear cog  192   b  therebetween, together against the pinion gear  194   b . The support plates  197  are splined or keyed to the shaft  196   b  such that the compression applied by the spring washers  193  is operable to lock the larger gear cog  192   b  to the shaft  196   b  below a predetermined torque and allow rotational slippage of the larger gear cog  192   b  above the predetermined torque. The advantage of the clutch mechanism incorporated into the reduction gear  190   b  is that slippage at a predetermined torque occurs. When using a stepper motor  74 , slippage can occur within the stepper motor at high loads. By setting slippage in the clutch reduction gear at a lower load (accounting for gear amplification), this better ensures that slippage in the stepper motor  74  does not occur which could otherwise allow the spring to move the valve to an undesired position.  
         [0063]    Finally, although the present invention is shown for use in controlling or regulating natural gas at a well head, the present invention may have other applications. For example, the actuator  10  may be used with a valve for regulating the flow of other types of process fluid, including other types of gases and liquids.  
         [0064]    All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.  
         [0065]    The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.  
         [0066]    Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.