Abstract:
An assembly for actuating a valve that is in a differential screw assembly when the valve is in a portion of its stroke that experiences high resistance. The actuating assembly is selectively changeable into a direct drive configuration when the valve is in a lower resistance portion of its stroke. A sliding sleeve moves axially within the actuating assembly and has a profile that is strategically dimensioned to change the actuating assembly configuration.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates in general to a valve actuator. More specifically, this invention relates to a valve actuator having a varying applied torque. 
         [0003]    2. Description of Related Art 
         [0004]    A variety of equipment or tools used in oil field drilling and production have threaded members that rotate relative to each other while under a load. For example, gate valves are often used for oil and gas production control equipment. A gate valve has a body with a cavity. A flow passage intersects the cavity. A gate is moved between open and closed positions relative to the flow passages. The gate valve has to be able to move from a closed position to an open position while under the pressure of the flowline, which may be quite high. The gate is moved by a stem, which may be either a rising stem or non-rising stem. A rising stem moves axially as the nut rotates. With a non-rising type, the stem remains axially stationary while being rotated. The stem is threaded in both types and engages a threaded nut or a drive bushing. The flowline pressure forces the gate tightly against the seat. Frictional forces at this interface must be overcome in order to move the gate from the closed to the open position and vice versa. 
       SUMMARY OF THE INVENTION 
       [0005]    Disclosed herein is an apparatus for actuating a valve, where resistance to actuating the valve is concentrated in a portion of the valve stroke. In an example embodiment, the valve actuator includes an annular actuator nut that is threaded on an outer surface. The nut includes threads on an inner surface that are oriented in the same direction to the threads on the outer surface. Moreover, the threads on the inner surface have a greater pitch than those on the outer surface. Also included is a latching sleeve that encircles a portion of the actuator nut and can move along an axis of the valve actuator. The apparatus also has a linkage attached to the actuator nut and that includes threads engaging threads on an outer surface of the latching sleeve. A profile is on an inner surface of the latching sleeve, where a portion defines an engaged portion and another portion defines a disengaged portion for the lever. A lever is included that is slidable within the profile. The apparatus has a collar threaded to the outer surface of the actuator nut that is rotatable with respect to the actuator nut when the lever is in the engaged portion of the profile and rotates with the actuator nut when the lever is in the disengaged portion of the profile. A valve stem is assembled by the threads on the inner surface of the actuator nut. In an alternative embodiment, the linkage has an annular elevator nut with threads on an inner surface engaging the threads on the outer surface of the latching sleeve. Optionally, a tubular housing telescopingly mounts over a portion of the elevator nut and end wall attached to the actuator nut. A key may be optionally attached to an inner surface of the housing, wherein in an example the key protrudes into an axial slot on an outer surface of the elevator nut, so that the elevator nut and housing are rotatingly coupled and axially slideable to one another. By rotating the actuator nut, the latching sleeve and the profile are axially moved across the lever. Alternatively, a ledge is provided that projects radially outward from an outer surface of the collar, pockets may be formed in the ledge for engaging the levers. An inner sleeve may be set in an annular space between the actuator nut and the latching sleeve. Yet further optionally is a lip radially projecting outward from an outer surface of the inner sleeve. A pivot pin can be included on the lip on which the lever is coupled. In an alternate embodiment, when the lever is in the engaged portion of the profile a torque input to the actuator nut generates a force on the valve stem at a force to torque ratio that is greater than a force to torque ratio when the lever is in the disengaged portion of the profile. In another alternate embodiment, when the lever is in the disengaged portion of the profile, each revolution of the actuator nut moves the valve stem an incremental distance at a revolution to displacement ratio that is greater than a revolution to displacement ratio when the lever is in the engaged portion of the profile. Optionally included is a transition portion in the profile between the engaged and disengaged portions, so that as the latching sleeve axially moves with respect to the collar, the collar selectively changes between engaged and disengaged configurations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a side sectional view of an embodiment of valve actuator and valve in a closed position in accordance with the present disclosure. 
           [0007]      FIG. 2  is a sectional view of the valve actuator of  FIG. 1  taken along lines  2 - 2 . 
           [0008]      FIG. 3  is side sectional view of the valve actuator and valve of  FIG. 1  with the valve in a partially open/closed position. 
           [0009]      FIG. 4  is side sectional view of the valve actuator and valve of  FIG. 1  with the valve in an open position. 
           [0010]      FIG. 5  is a sectional view of the valve actuator of  FIG. 4  taken along lines  5 - 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    The apparatus and method of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. This subject of the present disclosure may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. For the convenience in referring to the accompanying figures, directional terms are used for reference and illustration only. For example, the directional terms such as “upper”, “lower”, “above”, “below”, and the like are being used to illustrate a relational location. 
         [0012]    It is to be understood that the subject of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the subject disclosure and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the subject disclosure is therefore to be limited only by the scope of the appended claims. 
         [0013]    An embodiment of a valve actuator assembly  20  coupled to a valve  22  is shown in a side sectional view in  FIG. 1 . The valve actuator assembly  20  is made up of a cylindrical housing  24  that is closed on an upper end and open on a lower end. Shown disposed on the closed end of the housing  24 A is a hand wheel  26  that includes a round outer handle and spokes that project radially inward from the handle. The spokes converge to an outer periphery of an actuator nut  28  shown generally coaxial with an axis A X  of the valve actuator assembly  20 . The actuator nut  28  is a tubular member having threads  30 ,  32  formed on its outer and inner surfaces. The threads  30  on the outer surface run in a direction opposite than the threads  32  on the inner surface. An annular collar  34  circumscribes a portion of the actuator nut  28  and includes a radial ledge  35  shown protruding outward from the outer surface of the collar  34 . The inner circumference of the collar  34  has threads  36  that engage the threads  30  on the outer surface of the actuator nut  28 . 
         [0014]    Threadingly inserted within the actuator nut  28  is an elongated cylindrical upper stem  38 , that in the embodiment of  FIG. 1  is shown having an upper end disposed proximate the upper end of the collar  34 . An opening on the lower end of the upper stem  38  is shown receiving and upper end of a valve stem  39 , that as will be described in more detail below, couples with components of the valve  22 . A lower end of the upper stem  38  and the valve stem  39  are shown circumscribed by a bore  42  that is coaxial with the axis A X  and formed through a flange mount  44  on the lower end of the valve actuator assembly  20 . The outer circumference of the flange mount  44  increases at its lower end to provide for mounting surface for the insertion of bolts (not shown) to assemble flange mount  44  on to the bonnet. 
         [0015]    An annular inner sleeve  46  projects upward from the flange mount  44  and into the space between the actuator housing  24  and actuator nut  28 . The upper end of the inner sleeve  46  terminates at a location just above the upper end of the collar  34 . A radial lip  48  projects radially outward from the outer surface of the inner sleeve  46  at an elevation between the radial band  35  and lower end of the collar  34 . Upper and lower bearing assemblies  50 ,  51  are shown in the annular space between the inner sleeve  46  and collar  34  and on the respective upper and lower surfaces of the radial band  35 . The lower bearing assembly  51  is set within a recess formed on the inner surface of the inner sleeve  46 . A locknut  52  which is shown threadingly engaged on an upper end of the collar  34 , is provided with an outer radial flange on its upper end for retaining the bearing assemblies  50  between the locknut  52  and recess in the inner circumference of the inner sleeve  46 . The presence of the bearing assemblies  50 ,  51  allows relative rotation between the collar  34  and inner sleeve  46 . 
         [0016]    Still referring to the embodiment of  FIG. 1 , a cylindrical pivot pin  54  projects axially from an upper surface of the radial lip  48 . Mounted on the pin  54 , and oriented transverse to the axis A X , is a lever  56  that is rotatable about the pivot pin  54  and as will be described in more detail below, selectively locks the collar  34  so it remains static with rotation of the actuator nut  28 . An aperture  57  is provided through a side wall of the inner sleeve  46  through which the lever  56  extends and into selective contact with the radial band  35 . The end of the lever  56  opposite where it contacts the radial band  35  is shown set within a slot  58  in the inner circumference of a latching sleeve  59 . The latching sleeve  59  of  FIG. 1  is an annular member that circumscribes an upper portion of the inner sleeve  46  and a portion of the actuator nut  28 . The slot  58  includes a disengaged portion  60  that makes up the upper portion of the slot  58 , and an engaged portion  61  that makes up the lower portion of the slot  58 . A transition  62  is included within the slot  58  that connects the disengaged and engaged portions  60 ,  61 . The transition  62  includes curved portions and is formed along a path oblique to the axis A X . The disengaged and engaged portions  60 ,  61  each are substantially parallel with the axis A X , but are offset from one another by an angle with respect to the axis A X . 
         [0017]    Also shown in  FIG. 1  are threads  64  formed on a lower end and outer surface of the latching sleeve  59 . The threads  64  extend along a portion up to a transition  66  wherein the outer radius of the latching sleeve  59  decreases at the transition  66 . The threads  64  contact threads  68  formed on an inner circumference of an annular elevator nut  69 . The elevator nut  69  is provided in the annular space between the housing  24  and latching sleeve  59 . A key  70  is shown mounted into the inner surface of the housing  24  that projects radially inward into a slot  71  extending axially on the outer surface of the elevator nut  69 . The key  70  and slot  71  couples the housing  24  and elevator nut  69  so rotation of one of the elevator nut  69  or housing  24  can correspondingly rotate the other member. Bearings  72  are provided to allow rotation of the elevator nut  69  with respect to the inner sleeve  46  and axially lock elevator nut  69  in one elevation. At the inner circumference of the latching sleeve  59  and proximate its lower end, a key  76  is mounted that projects radially inward to a slot  78  shown axially extending along the outer surface of the inner sleeve  46 . The latching sleeve  59  is thus limited to axial movement with respect to the inner sleeve  46  as the key  76  and slot  78  prevent relative rotation between the latching sleeve  59  and inner sleeve  46 . 
         [0018]    Still referring to  FIG. 1 , the valve  22  includes a gate  80  with an opening  82  shown slidably disposed within a valve body  84 . A passage  86  is in the body  84  and oriented transverse to the elongate side of the gate  80 . As shown, the solid portion of the gate  80  is blocking the passage  86  thereby putting the valve  22  in a closed configuration. A balanced stem  87  is attached on a side of the gate  80  opposite to the valve stem  39 . In an example embodiment, the balanced stem  87  is the same as that of the valve as stem  39 . The balanced stem  81  can offset the force exerted by valve stem  39 , and may bottom out at a valve body cavity or on an insert (not shown) attached to a lower portion of the valve body  84 . 
         [0019]    Referring now to  FIG. 2 , shown is a sectional view of the valve actuator assembly  20  taken along lines  2 - 2  that illustrates engagement between the lever  56  and collar  34 . Further provided in the embodiment of  FIG. 2  are pockets  88  that are formed within the radial band  35  of the collar  34 . An end of each of the levers  56  contacts the radial band  35  within the pockets  88 . An opposing end of each lever  56  contacts the latching sleeve  59  within the space formed by the engaged portion  61  of the slot  58 . The simultaneous contact by the opposing ends of the levers  56  within the pockets  88  and engaged portions  61  couples the collar  34  to the inner sleeve  46 . So by rotating the hand wheel  26  about the axis A X , the housing  24  and elevator nut  69  rotate with the actuator nut  28 . 
         [0020]    As indicated above, threads  32 ,  40  are same in direction with threads  30 ,  36 . Thus, the rotational direction of the hand wheel  26  that downwardly urges the upper stem  40  also generates a reactive force that is directed upward against the actuator nut  28  and downward on the collar  34 . By setting the pitch of the threads  32 ,  40  greater than the threads  30 ,  36 , the upper stem  38  moves downward within the bore  42 , but at an increment per revolution of the hand wheel  26  reduced by the pitch of the threads  30 ,  36 . The differential thread pitch also results in a greater output force exerted onto the upper stem  38 , with the same input torque provided at the hand wheel  26 , than if the collar  34  were not included. For the purposes of discussion herein, this is referred to as a differential screw configuration. As noted above, when the valve  22  is in the closed position of  FIG. 1 , the actuation force for opening the valve is greater in the initial stages and reduces as the valve becomes opened. 
         [0021]    Referring now to  FIG. 3 , an example embodiment of the valve actuator assembly  20  is shown combined with the valve  22  wherein the upper stem  38  has moved downward within the bore  42  with respect to its position from  FIG. 1 . Correspondingly, the gate  80  is moved within the valve body  84  so the opening  82  within the gate  80  is partially registered with the passage  86 . The force required for repositioning the gate  80  from its position in  FIG. 1  to the partially opened position in  FIG. 3  is greater than the force to fully open the valve  22 . Thus to obtain a mechanical advantage for this stage of the actuation of the valve  22 , the actuator assembly  20  is in a differential screw configuration. The device described herein provides an advantage of seamlessly converting from the differential screw configuration into a direct drive configuration. When changing between configurations, the lever  56  is within the transition slot  62  and beginning to disengage from the collar  34 . So that additional rotation of the hand wheel  26  will not experience the differential pitch figuration of  FIG. 1 , but instead the collar  34  decouples from the latching sleeve  59  and no longer rotates with respect to the actuator nut  28 , but instead rotates with the actuator nut  28 . When in the direct drive configuration, the upper stem  38  is urged axially at an incremental distance with each rotation of the hand wheel  26  substantially equal to the pitch of the threads  32 ,  40 . 
         [0022]    As illustrated in the side sectional view of  FIG. 4 , further rotation of the hand wheel  26  can be used to downwardly drive the upper stem  38  and lower stem  39  until the gate  80  is moved within the valve body  84  to register the opening  82  with the passage  86 . In this configuration, the valve  22  is in an open position so that fluid may flow through the valve body  84 . In the embodiments of  FIGS. 3 and 4 , the housing  24  is shown having moved upwards relative to the elevator nut from the interaction between the actuator nut  28  and collar  34 . The key  70  and slot  71  coupling between the housing  24  and elevator nut  69  allows the relative vertical motion between these two members. Further, it should be pointed out that the threaded connection between the latching sleeve  59  and elevator nut  69  reciprocate the latching sleeve  59  within the elevator nut  69 ; in a direction depending on the rotational direction of the hand wheel  26 . Reciprocating the latching sleeve  59  in turn axially moves the slot  58  relative to the lever  56 . When the slot  58  is moved so that the lever  56  engages the disengaged portion  60 , the lever  56  pivots from its contact with the radial band  35  in the pocket  88  to decouple the collar  34  and latching sleeve  59 . When the collar  34  and latching sleeve  59  are decoupled, the valve actuator assembly  20  is in the direct drive mode. Rotating the hand wheel  26  in a direction opposite from that to change the valve actuator assembly  20  from its configuration of  FIG. 1  to its configuration of  FIG. 4  can then turn the valve  20  to its closed position of  FIG. 1 . 
         [0023]    In an embodiment, strategically positioning the component parts of the valve actuator assembly  20  create the differential screw configuration, and thus the mechanical advantage, to occur when the valve  22  is proximate its closed position. Another advantage of the device disclosed herein is that when the valve  22  is in positions that do not require an increased force for actuation, the valve actuation assembly  20  converts into the direct drive configuration of  FIG. 4 ; When in direct drive, a greater incremental movement distance of the upper stem  38  is realized with each rotation of the hand wheel  26  over that of the differential screw configuration. The device described herein then increases the speed of opening or closing the valve  22  over that of an assembly that employs a differential pitch throughout the entire opening and closing sequence and reduces the number of turns to achieve the same travel distance. 
         [0024]      FIG. 5  is a side sectional view of the embodiment of the valve actuator assembly  20  of  FIG. 4  and taken along lines  5 - 5 . In this embodiment, the latching sleeve  56  has moved downward with respect to the lever  56  so that the lever  56  has been moved from the engaged portion  61  to the disengaged portion  60 . As previously noted, the disengaged and engaged portions  60 ,  61  are angularly offset from one another thereby pivoting the lever  56  in and out of contact with the pockets  88 . Moving the levers  56  out of the pockets  88  thereby decouples the collar  34  from the inner sleeve  46  and allowing free rotation of the collar  34  with the actuator nut  28 . 
         [0025]    One example of use, the valve actuator  20  is coupled with a valve  22  where the valve can be exposed within a well control device such as a production tree or one controlling the flow of fluids used for fracturing within a wellbore. Referring back to  FIG. 1 , when the valve  22  is in the closed position and the opening  82  is unregistered with the passage  86 , a pressure gradient exists across the gate  80  inducing a force to resist movement of the gate  80  within the valve body  84 . The resistive forces at the beginning of the stroke that opens the valve  22  exceed those present at the end of the opening stroke. The strategic positioning of the components of the valve actuator assembly  20  form a differential screw configuration at the beginning of the opening stroke. The different pitch of threads  32 ,  40  and threads  30 ,  36 , limit the axial movement of the gate  80  to the difference of these pitch values for each rotation of the hand wheel  26 . However, this in turn produces a mechanical advantage that the hand wheel  26  can move the gate  80  with an applied force or torque less than that which would be necessary if the differential screw configuration was not in place. Continued rotation of the hand wheel over time axially moves the latching sleeve  59  downward to register the lever  56  and the transition portion  62  of the slot  58 . Further movement moves the lever  56  into the disengaged portion  60  thereby decoupling the collar  34  and latching sleeve  59  so that direct drive between the hand wheel  26  and upper stem  38  is realized. Although the mechanical torque advantage is removed at this point, the resistant forces within the valve  22  are not present so that less torque on the hand wheel  26  is required to actuate the gate  80  within the valve  22 . When in the reduced torque advantage configuration, the speed of movement of the gate  80  is increased over that of the differential configuration of  FIG. 1 . Thus, the assembly disclosed herein provides the double advantage of an increased torque output when needed, that automatically switches to a faster direct drive configuration when less torque is required. 
         [0026]    While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention. For example, a motor could be mounted onto the actuator nut  28  for driving the valve actuator assembly  20 .