Patent Publication Number: US-6701958-B2

Title: High performance fluid control valve

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a division of application Ser. No. 09/850,313, filed May 7, 2001 and now U.S. Pat. No. 6,536,472. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to fluid control valves and, more particularly, to fluid control valve structures which provide highly controllable flow characteristics and which limit sliding seal friction during valve plug travel. 
     BACKGROUND OF THE INVENTION 
     One type of prior art fluid control valve includes a valve body having inlet and outlet ports, a sleeve-like cage, a valve plug that is slidable within the cage and a bonnet assembly which retains the cage and the valve plug in the valve body. The inlet port communicates with the outlet port through apertures, or windows, in the cage. Fluid flow through the valve is determined by the position of the valve plug relative to the windows in the cage. An example of a prior art fluid control valve is disclosed in U.S. Pat. No. 3,776,278 issued Dec. 4, 1973 to Allen. 
     Prior art fluid control valves have provided satisfactory performance but have certain drawbacks. The flow characteristics may be difficult to control, particularly near the off position of the valve plug. In addition, the valve may generate undesirable noise under certain flow conditions. Furthermore, the seating surface of the valve plug may be subject to erosive wear over time, thereby degrading valve operation. Frictional forces encountered in changing the position of the valve plug may cause control systems to be unstable. Component tolerances and thermal expansion may produce an unsatisfactory fit between valve parts and may degrade performance. Conventional gate valves are limited in fluid flow capacity for a given orifice diameter. 
     Accordingly, there is a need for fluid control valve structures which overcome one or more of the above drawbacks. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, a fluid control valve is provided. The fluid control valve comprises a valve body having a fluid passageway, a cage mounted in the fluid passageway, and a valve plug assembly including a valve plug. The cage includes a cage bore having an axis. The cage defines one or more windows, a valve seat located below the windows and a sealing lip located above the windows. The valve plug is axially slidable in the cage bore. The valve plug has one or more pressure balancing passages between opposite ends thereof and a seating surface for engaging the valve seat. The valve plug assembly further comprises an elastically deformable sealing ring for engaging the sealing lip when the valve plug is in a closed position. 
     The deformable sealing ring may comprise an elastic metal. Preferably, the deformable sealing ring contacts the cage only in the closed position and near the closed position. The cage bore may have a larger diameter above the sealing lip than below the sealing lip. The valve plug assembly may further comprise an elastomer ring located below the deformable sealing ring. 
     According to another aspect of the invention, a fluid control valve is provided. The fluid control valve comprises a valve body having a fluid passageway, a cage mounted in the fluid passageway, and a valve plug assembly including a valve plug. The cage includes a cage bore having an axis. The cage defines one or more windows, a valve seat located below the windows and a flow control portion of the cage bore located between the valve seat and the windows. The flow control portion has an interior contour that varies in dimension as a function of distance from the valve seat. The valve plug is axially slidable in the cage bore between a closed position in engagement with the valve seat, a partially open position wherein fluid flow is determined by a spacing between the valve plug and the flow control portion of the cage bore, and a more open position wherein fluid flow is determined by the windows and by the spacing between the valve plug and the flow control portion. 
     In a first embodiment, the interior contour of the flow control portion has a diameter that is an exponential function of distance from the valve seat. In a second embodiment, the interior contour of the flow control portion has a diameter that is a linear function of distance from the valve seat. The interior contour of the flow control portion may be selected to provide a desired flow characteristic. 
     The valve plug may include a cylindrical section that defines a spacing between the valve plug and the flow control portion of the cage bore, and an annular expansion groove above the cylindrical section. The annular expansion groove may have a surface that slopes away from the cylindrical section at an angle of at least 30° with respect to the cage bore axis. 
     The valve plug may include a seating surface for engaging the valve seat and an extension below the seating surface. The extension may be shaped to provide initial throttling of the fluid, deflecting fluid flow away from the seating surface and thereby limiting erosive wear caused by high fluid velocity and entrained particles. The valve plug may further include a streamlined, curved contour below the extension for guiding the fluid smoothly into the windows when the valve is at or near the open position. This is further aided by streamlined entrance portions of the cage windows. 
     The valve plug may include one or more pressures balancing passages between opposite ends thereof. The cage bore may include a sealing lip located above the windows, and the valve plug assembly may include an elastically deformable sealing ring for engaging the sealing lip in the closed position. 
     The cage may be constructed to be axially deformable. The axially deformable cage compensates for machining tolerances and thermal expansion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, reference is made to the accompanying drawings, which are incorporated herein by reference and in which: 
     FIG. 1 is a cross-sectional view of a fluid control valve in accordance with a first embodiment of the invention, with the valve plug split along its axis, such that the left half of the valve plug is shown in the closed position and the right half of the valve plug is shown in the open position; 
     FIG. 2 is a cross-sectional view of a cage and a valve plug assembly in accordance with a second embodiment of the invention, shown in the open position; 
     FIG. 3 is a cross-sectional view of the cage and valve plug assembly of FIG. 2, shown in a partially open position; 
     FIG. 4 is a cross-sectional view of the cage and valve plug assembly of FIG. 2, shown in the closed position; 
     FIG. 5 is a cross-sectional top view of the cage of FIG. 2; 
     FIG. 6 is a cross-sectional side view of the cage of FIG. 2; 
     FIG. 7 is an enlarged, partial cross-sectional view of the sealing lip of the cage of FIG. 6; 
     FIG. 8 is an enlarged, partial cross-sectional view of the flow control portion and seating surface of the cage of FIG. 6; 
     FIG. 9 is a cross-sectional view of a cage and a valve plug assembly in accordance with a third embodiment of the invention, shown in the closed position; and 
     FIG. 10 is a cross-sectional view of a cage and a valve plug assembly in accordance with a fourth embodiment of the invention, shown in a partially open position. 
    
    
     DETAILED DESCRIPTION 
     A fluid control valve in accordance with a first embodiment of the invention is shown in FIG. 1. A cage and a valve plug assembly in accordance with a second embodiment of the invention are shown in FIGS. 2-8. A cage and a valve plug assembly in accordance with a third embodiment of the invention are shown in FIG. 9. A cage and a valve plug assembly in accordance with a fourth embodiment of the invention are shown in FIG.  10 . The cage and the valve plug assemblies shown in FIGS. 2-10 may be utilized in a fluid control valve of the type shown in FIG.  1 . Corresponding elements in FIGS. 1-10 have the same reference numerals. The differences between the embodiments are noted below. 
     A control valve  10 , as shown in FIG. 1, includes a valve body  12  having an inlet port  14  and an outlet port  16 , a cage  20 , a valve plug assembly  22  and a bonnet assembly  24 . A major component of valve plug assembly  22  is a valve plug  26 . 
     In the embodiment of FIGS. 2-8, cage  20  does not include a deformable section. In addition, the valve plug assembly  22  does not include an elastomer ring below the seating surface. In other respects, the embodiment of FIGS. 2-8 is similar to the embodiment of FIG.  1 . In the embodiment of FIG. 9, the cage  20  does not include a deformable section. In other respects, the embodiment of FIG. 9 is similar to the embodiment of FIG.  1 . Accordingly, the embodiments of FIGS. 1-9 may be described together, subject to the differences noted above. 
     The cage  20  is a sleeve-like structure having a generally cylindrical wall  30  and a cage bore  32  having an axis  34 . Cage bore  32  has a lower section  32   a  with a first diameter, a middle section  32   b  with a second diameter that is larger than the first diameter and an upper section  32   c  with a third diameter that is larger than the first and second diameters. In addition, cage bore  32  has a flow control portion  60  of variable diameter, as discussed below. Cage  20  defines a valve seat  40  and one or more apertures, or windows  42 . Windows  42  provide flow passages between cage bore  32  and the exterior of cage  20 . 
     A valve stem  44  attached to valve plug  26  extends through bonnet assembly  24  to an actuator (not shown). The valve plug assembly  22  is slidable along axis  34  within the middle section  32   b  of cage bore  32  between an open position, shown on the right of axis  34  in FIG. 1, an intermediate or partially open position (shown in FIG.  3 ), and a closed position, shown on the left of axis  34  in FIG.  1 . In the closed position, a seating surface  50  of valve plug  26  engages valve seat  40 , thereby blocking fluid flow through the control valve. In the open position, valve plug assembly  22  is moved along axis  34  to a position above windows  42  in cage  20 . In the open position, the inlet port  14  communicates with the outlet port  16  through cage bore  32  and windows  42 , aided by contour  82  on valve plug  26 . The valve plug assembly  22  may be positioned at any intermediate position between the open and closed positions to achieve a desired flow. The structure of the cage  20  and the valve plug assembly  22  determine the flow characteristic as a function of valve plug position as described below. 
     As illustrated, valve seat  40  is located below windows  42  in cage  20  and is spaced from windows  42 . As best shown in FIGS. 6 and 8, flow control portion  60  of cage bore  32  has an interior contour that is selected to provide a desired flow characteristic in low flow conditions. In particular, flow control portion  60  has a diameter that varies from smaller near valve seat  40  to larger near windows  42 . The flow control portion  60  may include all or a part of the cage bore  32  between valve seat  40  and windows  42 . In one embodiment, flow control portion  60  has a diameter that is an exponential function of distance from valve seat  40 . In another embodiment, the flow control portion  60  has a diameter that is a linear function of distance from valve seat  40 . In each case, the diameter increases with increasing distance from valve seat  40 . The effect of flow control portion  60  is a gradually increasing gap between a cylindrical section  90  (FIG. 3) of valve plug  26  and cage  20  as valve plug  26  is moved upwardly along axis  34 . This configuration permits precise control under low flow conditions in contrast to a rapid increase or decrease in flow when valve plug  26  moves past the lower edge of windows  42 . The shape of flow control portion  60  may be selected to provide a desired flow characteristic. In one embodiment, the diameter of flow control portion  60  varies from 100.5% to 105% of the diameter of middle section  32   b  of cage bore  32 . 
     When valve plug  26  is at or near the open position shown for example in FIG. 2, the flow characteristic is determined primarily by windows  42  in cage  20 . Windows  42  preferably are flared outwardly as shown in FIGS. 1-4. The gradually expanding windows minimize turbulence near the open position and therefore maximize flow capacity. This is further aided by guiding the fluid into the window with contour  82  of valve plug  26 . The entrance portions of the windows  42  may be curved, as shown at  62  in FIG. 5, to provide smooth fluid flow. 
     Windows  42  furthermore may have a gradually opening V-shaped lower edge  154 , as shown in FIG. 6, to aid the flow transition from flow control portion  60  to window  42 . In an alternative configuration, window  42  may have a straight lower edge. In general, the lower edges of windows  42  may be shaped to provide a desired flow characteristic. 
     Cage  20  may include a sealing lip  64  located above windows  42 . Sealing lip  64  is defined by a change in diameter of cage bore  32 . In particular, cage bore  32  has a diameter in a middle section  32   b  between windows  42  and sealing lip  64  that is slightly larger than the maximum diameter of valve plug  26 . Above sealing lip  64 , upper section  32   c  of cage bore  32  has a larger diameter, sufficient to provide clearance for a deformable sealing ring on valve plug assembly  22 , as described below. 
     Cage  20  may include an axially deformable section  70  (FIG.  1 ). The axially deformable section  70  compensates for machining tolerances and thermal expansion of cage  20  relative to valve body  12 . As a result, machining tolerances may be relaxed. By way of example, the axially deformable section  70  may be implemented by providing a wall section of cage  20  that is thinned and folded, similar to a bellows. 
     Valve body  12  is provided with a shoulder  72  that engages a corresponding shoulder  74  on cage  20 . Cage  20  is retained within valve body  12  by bonnet assembly  24 . When bonnet assembly  24  is installed on valve body  12 , cage  20  is axially deformed by the opposing forces exerted by shoulder  72  and bonnet assembly  24 . 
     As noted above, valve plug  26  is provided with seating surface  50  for engaging valve seat  40  in the closed position of valve plug  22 . Seating surface  50  and valve seat  40  may have matching angles of about 30° to ensure a fluid-tight seal. In addition, valve plug  26  may be provided with a groove for receiving an elastomer ring  80  located below seating surface  50 . Elastomer ring  80  engages lower section  32   a  of cage bore  32  below valve seat  40  and provides further sealing. Valve plug  26  preferably includes an extension  84  below seating surface  50  that is shaped to throttle fluid flow between itself and the lower section  32   a  of cage bore  32 . This results in a two step throttling process at low lift, where valve plug  26  is near the closed position. The first step is between extension  84  of valve plug  26  and lower section  32   a  of cage bore  32 . The second step is between cylindrical section  90  of valve plug  26  and flow control portion  60  of cage bore  32 . This two step process shifts the throttling away from seating surface  50 . Lower contour  82  of valve plug  26  may have a concave, curved shape that is symmetrical about axis  34  to guide fluid flow into windows  42  in the open or nearly open position of valve plug  26 . 
     Valve plug  26  is further provided with one or more pressure balancing passages  86  between upper and lower ends thereof. A fluid within the valve moves through passages  86  to a region  88  above valve plug  26 , thereby balancing the pressure on opposite ends of valve plug  26  and aiding in the deflection of sealing ring  100  against sealing lip  64 . 
     Valve plug  26  includes short cylindrical section  90  above seating surface  50 , followed by an annular expansion groove  92 . Cylindrical section  90  has a diameter that is slightly smaller than the diameter of cage bore  32  in middle section  32   b.  A surface  94  of expansion groove  92  slopes away from cylindrical section  90  at an angle of at least 30° and preferably about 45° with respect to cage bore axis  34 . The configuration of cylindrical section  90  followed by expansion groove  92  permits rapid jet expansion, maximum turbulence and low pressure recovery for reduced noise in low flow conditions. 
     Valve plug assembly  22  further includes an elastically deformable sealing ring  100  held on a shoulder  102  at the upper end of valve plug  26  by a threaded retainer  104 . Sealing ring  100 , which may be a metal such as a high nickel alloy, is selected for high tensile strength at high temperatures. Sealing ring  100  has an outside diameter that is larger than the maximum diameter of valve plug  26  but is smaller than the inside diameter of upper section  32   c  of cage bore  32  above sealing lip  64 . As a result, sealing ring  100  does not contact cage  20 , except at sealing lip  64 . The valve plug  26  may be provided with a groove for an elastomer ring  110  located below sealing ring  100 . Elastomer ring  110  may be utilized in applications involving temperatures below about 450° F. Elastomer ring  110  also has an outside diameter that is less than the inside diameter of upper section  32   c  of cage bore  32  above sealing lip  64 . 
     In operation, valve plug assembly  22  moves axially within cage bore  32  without seal friction until valve plug  22  is near the closed position. Before seating surface  50  engages valve seat  40 , sealing ring  100  engages sealing lip  64  of cage  20  and is slightly deformed as valve plug assembly  22  moves to the fully closed position. As shown in FIGS. 4 and 7, deformable sealing ring  100  contacts a surface of sealing lip  64  that is substantially perpendicular to the cage bore. In addition, elastomer ring  110  engages a beveled portion  112  (FIG. 7) of sealing lip  64  and is slightly deformed. Thus, sealing ring  100  and elastomer ring  110  provide a reliable seal between the region  88  above valve plug  22  and windows  42  when valve plug assembly  22  is in the closed position. In the open and partially-open positions of valve plug assembly  22 , sealing ring  100  and elastomer ring  110  do not contact cage  20 , and movement of valve plug  26  is substantially free of sliding seal friction. 
     A fourth embodiment of the valve plug is shown in FIG.  10 . Like elements in FIGS. 1-10 have the same reference numerals. A valve plug  126  is similar to valve plug  26  described above, except that the valve plug  126  does not include balancing passages or elastomer rings and does not include a deformable sealing ring at the upper end of valve plug  126 . The valve plug  126  relies for sealing on contact between seating surface  50  and valve seat  40 . Also, the cage  20  shown in FIG. 10 is not axially deformable. The embodiment of FIG. 10, with no elastomer rings, may be used in applications involving temperatures above about 450° F. 
     The valve structures have been described above in connection with the valve orientation of FIG.  1 . Thus, valve seat  40  is described as located “below” windows  42 , and sealing lip  64  is described as located “above” windows  42 . It will be understood that the control valve may have any desired orientation in use and that the relative positions of the valve elements will change. In addition, it will be understood that the valve features described herein may be utilized separately or in any combination to achieve high performance valve operation. 
     It should be understood that various changes and modifications of the embodiments shown in the drawings described in the specification may be made within the spirit and scope of the present invention. Accordingly, it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted in an illustrative and not in a limiting sense. The invention is limited only as defined in the following claims and the equivalents thereto.