Abstract:
A control element for a rotary control valve is attached to a rotating shaft by at least one ear. The control element includes at least two surfaces, the first surface being generally sealable with a flow ring. The second surface is generally recessed from the first surface to facilitate fluid flowing through the valve across the first surface to prevent scaling or buildup of foreign material on that surface.

Description:
TECHNICAL FIELD  
         [0001]    The present anti-scaling control element relates generally to rotary control valves, and more particularly to a ball valve that inhibits scale formation.  
         BACKGROUND  
         [0002]    Ball valves are commonly used to control the flow of a fluid in a pipe. These valves are particularly advantageous for controlling the flow of erosive slurries, such as those found in the mining industry. Unlike butterfly valves and eccentric plug valves, ball valves allow a fluid flow path that is substantially parallel to the flow in the pipe. Parallel flow reduces impingement erosion of valve components and downstream pipe.  
           [0003]    Typical ball valves include a generally hemispherical or ball-shaped control element that is movable between open and closed positions. In the closed position, a curved surface of the control element engages a sealing surface to prevent or regulate fluid flow through the valve body. In the open position, fluid may primarily flow past an inner sealing surface of the control element and through the flow ring. Internal features of the valve or control element, however, may reduce flow velocity through some regions of the valve. For example, one region of low velocity flow in many ball valves is located between the outside surface of the ball and the flow ring when the valve is in an open position.  
           [0004]    Some erosive slurries may form scale on the valve components in regions of reduced velocity flow or stagnation. Scale can eventually inhibit operation of the valve, which may cause expensive and time-consuming maintenance or even dangerous working conditions for personnel. In some cases, slurries may form an extremely hard scale that may cause unusually extensive downtime or even require valve replacement. Many thousands of dollars may be lost if a process is halted to maintain or replace a non-operational valve.  
           [0005]    A ball valve that does not create regions of low velocity flow that are likely to promote scale formation is, therefore, desirable.  
         SUMMARY  
         [0006]    In accordance with one embodiment of the present control element, a rotary control valve is attached to a rotating shaft by at least one ear. The control element includes first and second surfaces, the first surface being generally sealable with a flow ring. The second surface is generally recessed from the first surface to facilitate fluid flowing through the valve across the first surface to prevent scaling or buildup of foreign material on the second surface.  
           [0007]    In another embodiment of the present control element, a rotary control valve has a valve body and a control element that rotates within the valve body to control fluid flow through the valve body. The control element has a surface area that seats with a flow ring of the valve body to prevent fluid from flowing through the valve body. The control element also has a second surface that is generally recessed in relation to the first surface to create a secondary flow path through the valve body and across the first surface when the valve is in an open position to prevent scale or material build up along the first surface. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The features of this present control element which are believed to be novel and are set forth with particularity in the appended claims. The present control element may be best understood by reference to the following description taken in conjunction with the accompanying drawings in which like reference numerals identify like elements in the several figures and in which:  
         [0009]    [0009]FIG. 1 is a cross-sectional view of a fluid control valve according to the prior art.  
         [0010]    [0010]FIG. 2 is a cross-sectional view of a fluid control valve according to one embodiment of the present control element.  
         [0011]    [0011]FIG. 3 is a plan, partial sectional view of a control element of a fluid control valve according to one embodiment of the present control element.  
         [0012]    [0012]FIG. 4 is an elevation sectional view of a control element of a fluid control valve according to one embodiment of the present control element.  
         [0013]    [0013]FIG. 5 is an elevation sectional view of a control element of a fluid control valve according to one embodiment of the present invention.  
         [0014]    [0014]FIG. 6 is a plan, partial sectional view of a control element of a fluid control valve according to another embodiment of the present control element. 
     
    
     DETAILED DESCRIPTION  
       [0015]    Although the making and using of various embodiments of the present control element are discussed in detail below, it should be appreciated that the present control element provides many applicable inventive concepts that may be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the control element and do not delimit the scope of the control element.  
         [0016]    Referring now to FIG. 1, a fluid control valve  10  according to the prior art is depicted. A valve body  12  houses a control element  14 , which may be rotated about the axis of a control shaft  16 . A front surface  18  of the control element  14  is in frictional or close engagement with an annular seating surface  20 , which may be formed, using a flow ring  22 . When the fluid control valve  10  is in an open position, fluid may flow in the direction indicated by arrow  24  from an upstream orifice  26  through the flow ring  22  and into a downstream orifice  28 . Low velocity flow or stagnation, however, may occur in a region  30 . Consequently, scale  32  is likely to form on the front surface  18  of the control element  14  that is located in region  30  when the control element  14  is in an open position. Scale  32  may interfere with movement of the front surface  18  of the control element  14  across the annular seating surface  20  of the flow ring  22  and render the fluid control valve  10  inoperable. An inoperable fluid control valve  10  may require a process to be stopped while the fluid control valve  10  is serviced or replaced. Stopping a process for unscheduled maintenance could cause great economic loss. In some cases, an inoperable fluid control valve  10  may cause a dangerous or even life-threatening process condition.  
         [0017]    The present control element reduces or eliminates scaling caused by low velocity flow or stagnation. Turning now to one embodiment of the present control element depicted in FIG. 2, a fluid control valve  50  has a valve body  52  that houses a control element  54 . The control element  54  may be rotated about the axis of a control shaft  56 . A face  58 A of the control element  54  has a control element seating surface  60  and a recessed surface  62 . When the fluid control valve  50  is in the closed position, the control element seating surface  60  is in frictional or close engagement with an annular seating surface  64  of a flow ring  66 , which may substantially reduce or stop fluid flow through the fluid control valve  50 . When the fluid control valve  50  is in an open position, fluid may flow along the primary flow path  68 , which generally flows from an upstream orifice  70  though the flow ring  66  and into a downstream orifice  72 . Additionally, when the fluid control valve  50  is in an open position, fluid may also flow across the face  58 A of the control element  54  through a secondary flow path  74 .  
         [0018]    Fluid flow across the face  58 A of the control element  54  may reduce or eliminate regions of low velocity flow or stagnation, which promote scale formation. Fluid flow through the secondary flow path  74  effectively prevents or reduces scale formation on the control element seating surface  60  and recessed surface  62 . The fluid control valve  50 , therefore, has an increased time between service as compared to prior valves. Reducing scheduled or necessary service times increases process efficiency and ultimately conserves operating costs. The fluid control valve  50  is also less likely to bind or seize because of scale formation on the face  58 A. Fluid control valve  50  is consequently safer and more reliable than prior valves.  
         [0019]    Turning now to FIGS. 3-6, the control element  54  according to one embodiment of the present control element is depicted. The control element  54  may be made from heat-treated steel, ceramic, polymer, and the like. The control element  54  may also be made from other materials that will be apparent to those having ordinary skill in the art. The control element  54  may be cast, machined from a single piece of material or fabricated from multiple materials.  
         [0020]    As depicted in FIG. 4, the face  58 A, for example, may be fabricated separately and attached to the control element  54  by welds, screws, press-fitting, adhesives and the like. The face  58 A may be removable from the control element  54  to facilitate maintenance or replacement of a worn or damaged fluid control valve  50 . One or more screws (not shown) through the control element  54  may attach the face  58 A to the control element  54 . Ears  76  interface with the control shaft  56  through aperture  78  to move the control element  54  between open and closed positions when the control shaft  56  (depicted in FIG. 2) is rotated about its axis.  
         [0021]    The face  58 A may be made from different materials than the control element  54  or the flow ring  66  according to a particular process or application. For example, the control element  54  may be heat-treated steel and the face  58 A may be a polymer to better withstand a corrosive environment, ease operation of the fluid control valve  50 , or provide a particular sealing interface with the annular seating surface  64  of the flow ring  66 .  
         [0022]    The interface between the control element seating surface  60  and the annular seating surface  64  of the flow ring  66  (depicted in FIG. 2) may vary depending on the requirements of a particular process application. If the fluid flowing through the fluid control valve  50  contains extremely corrosive or erosive fluids including strongly adhering scale, a loose tolerance between the control element seating surface  60  and the annular seating surface  64  may be desired. If a particular application requires that fluid flow be completely stopped tighter tolerances between the control element seating surface  60  and the annular seating surface  64  may be specified.  
         [0023]    Recessed surface  62  allows fluid to flow over the face  58 A of the control element  54  when the control element  54  is rotated into an open position. The shape of the recessed surface  62  may be varied according to a particular process or application. Although depicted as circular, the recessed surface  62  may be oval-shaped or even a channel cut through the face  58 A of the control element  54 . The recessed surface  62  may be tangential to the control element seating surface  60  or generally within a single plane. Additionally, the recessed surface  62  may be concentric to or offset from the centerline of the valve body  52 . Other shapes for the recessed surface  62  will be apparent to those having ordinary skill in the art of fluid dynamics.  
         [0024]    The recessed surface  62  allows adequate flow velocity to prevent or reduce scaling between a control range of about 5 degrees to about 85 degrees of rotation of the control element  54 . If the recessed surface  62  is too deep, adverse flow conditions may result in the primary flow path  68 . If the recessed surface  62  is too shallow, inadequate flow velocity along the secondary flow path  74  may be conducive to scale formation. Ideal dimensions of the recessed surface  62  may be determined according to desired operating characteristics for a particular process or application.  
         [0025]    For example, the seating surface  60  of the control element  54  may have a spherical radius of generally 3.000-(0.001 to 0.003) inches from a point on the axis of the control shaft  56  that intersects the centerline of the face  58 . Referring to FIG. 2, to ensure that the control element  54  may be operated within the annular seating surface  64 , which has a nominal spherical radius of 3 inches, the dimensional tolerance is biased towards the minimum diameter. The recessed surface  62  may have a spherical radius of 2.81 inches from the point on the axis of the control shaft  56  that intersects the centerline of the face  58 A. The seating surface  60  begins 1.75 inches from a plane through the axis of the control shaft  56  and perpendicular to the centerline of the face  58 A and ends 2.37 inches from the plane.  
         [0026]    As depicted in FIG. 5, the recessed surface  63  may also be generally flat and generally parallel to the plane defined by the axis of the control shaft  56  and perpendicular to the centerline of the face  58 B. The generally planar recessed surface  63  allows fluid to flow along a path that is substantially parallel to the flow in the pipe, thereby reducing impingement erosion of the valve components and the downstream pipe (not shown). The recessed surface  63  preferably allows fluid flow along the secondary flow path  74  with as little as about 5 degrees of rotation of the control element  54 . The amount of rotation that will open the secondary flow path  74  is a function of the diameter or width of the recessed surface  63 . The diameter or width of the recessed surface  63  also determines the area of the control element seating surface  60  that will interface the annular seating surface  64  of the flow ring  66 . Consequently, the diameter or width of the recessed surface  63  may be varied according to the desired sealing and operating characteristics of the fluid control valve  50 .  
         [0027]    Another embodiment of the present control element  54  provides advantages when exposed to strongly adhering scale. As previously described, the interface between the control element seating surface  80  and the annular seating surface  64  of the flow ring  66  (depicted in FIG. 2) may vary depending on the requirements of a particular process application. If the fluid flowing through the fluid control valve  50  contains strongly adhering scale, a loose tolerance between the control element seating surface  80  and the annular seating surface  64  may be desired. Conversely, the embodiment depicted in FIG. 6 uses two recessed surfaces  82  and  84  placed on both sides of the seating surface  80  to create a flow path that inhibits flow stagnation and scale build up on valve component surfaces  64 ,  82 ,  84 . This embodiment provides tighter tolerances between the control element seating surface  80  and the annular seating surface  64  in the presence of strongly adhering scale. The seating surface  80  of the control element  54  may have a spherical radius of approximately 3.000-(0.001 to 0.003) inches from a point on the axis of the control shaft  56  that intersects the centerline of the face  58 C (as defined in FIG. 2). Additionally, the recessed surfaces  82  and  84  may have a spherical radius of 2.81 inches from the point on the axis of the control shaft  56  that intersects the centerline of the face  58 C (as defined in FIG. 2).  
         [0028]    Although this present control element has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the present control element, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.