Abstract:
Butterfly valves comprise a valve seat comprising a generally S-shaped cross-section and a valve seat retainer configured with appropriately shaped cooperating surfaces. Fluid control systems comprising such a butterfly valve are also disclosed.

Description:
PRIORITY CLAIM 
     This is a national phase entry under 35 U.S.C. §371 of International Patent Application PCT/US2008/068429, filed Jun. 26, 2008, published in English as International Patent Publication WO 2009/157940 A1 on Dec. 30, 2009, the entire disclosure of which is hereby incorporated herein by this reference. 
     TECHNICAL FIELD 
     The present invention relates generally to butterfly valves, and, more particularly, to an annular valve seat and valve seat assembly. 
     BACKGROUND 
     Butterfly valves, in general, are well known and widely employed due to their simplicity of construction and relatively inexpensive cost, as compared to more complicated and detailed plug and ball valves. A typical butterfly valve generally comprises a disc mounted for rotation between the open position, in which the disc lies substantially parallel to the axis of the fluid flow channel through the valve, and the closed position, in which the disc lies perpendicularly to this axis. The disc is mounted for rotation on a valve stem or shaft, which is attached to the disc on one side. The disc cooperates with an annular flexible seat circumscribing the fluid flow channel for the purpose of effecting a resilient seal against the disc to shut off fluid flow through the channel. The annular flexible seat is conventionally held in position by being clamped in a recess formed between complementary surfaces of a portion of the valve body and a valve seat retainer. 
     The need for a certain degree of resilience and, thus, displaceability of the valve seat necessitates the use of an elastomeric material. If thermal or fluid pressure stresses cause distortions to the valve seat that could inhibit complete sealing, the elastomeric material is capable of distorting, so as to deform into the shape of the peripheral surface of the disc and establish a seal. However, materials of this type have a tendency to creep or migrate when subjected to high pressure, particularly when the pressure is applied to the seat on one side of the disc without a corresponding supporting pressure on the other side of the disc. Some conventional valve seats incorporate a reinforcing member in the seat in order to control this migration or creep without sacrificing the necessary resilience of the elastomeric material. The reinforcement is conventionally an annular ring or band of rigid material embedded within the seat as the seat is molded. An example of such a valve seat is disclosed in U.S. Pat. No. 3,940,108, to Edwards. 
     Other valve seats made of an elastomeric material have been provided that are configured to control migration or creep by configuring the seat to increase sealing pressure as a result of the pressure applied to the seat on one side. For example, U.S. Pat. No. 4,331,319 to Summers et al. discloses a valve seat having a U-shaped cross-section which provides surfaces to enhance the sealing effectiveness of the valve as a result of line pressure, regardless of the direction of application. However, the U-shaped valve seat requires a special groove formed into the valve body in order to compensate for the specific U-shaped configuration. This groove requires additional machining to the valve body and may further introduce additional stresses on the body while requiring a thicker overall body. In addition, although the U-shaped valve seat provides for some flexibility and resiliency in the radial direction, that flexibility may be limited, causing the valve seat to wear substantially during use as the seat rubs against the disc during opening and closing cycles. 
     DISCLOSURE OF INVENTION 
     Various embodiments of the present invention are directed toward a valve seat and valve seat retainer for a butterfly valve in which the valve body may include a flat face or surface for receiving the valve seat and valve seat retainer. Furthermore, embodiments of valve seats of the present invention may be configured to provide increased resiliency and flexibility in the radial direction to reduce wear on the valve seat, while providing enhanced sealing effectiveness as a result of line pressure from either direction. 
     One embodiment of the present invention includes a butterfly valve seat. The valve seat may include an annular ring comprising a substantially S-shaped cross-section. The annular ring may include a plastic material. In another embodiment, the annular ring may include a first concave region and a second concave region. The first and second concave regions may be configured to open in opposing directions. 
     Other embodiments of the present invention include a butterfly valve seat retainer. The valve seat retainer may include an annular ring. The annular ring may include a first channel proximate the radially inward edge of the annular ring. A second channel may be positioned between the first channel and the radially inward edge of the annular ring. The depth of the first and second channels may have a depth sufficient to entirely receive a valve seat therein. A first protrusion may separate the first channel from the second channel. The height of the first protrusion may be less than the depth of the first and second channels. The second channel may be bound by a second protrusion, the height of the second protrusion being less than the height of the first protrusion. Furthermore, the radially inward edge of the second protrusion may form a portion of the radially inward edge of the annular ring. 
     Another embodiment of the present invention includes a butterfly valve. The butterfly valve may include a valve body that further includes a substantially circular flow channel. The valve body may also include a substantially flat surface extending radially outward from the flow channel. A disc may be rotatably mounted within the flow channel of the valve body and configured to rotate between a fully open position and a fully closed position. A valve seat comprising a plastic annular ring may include a cross-section of the valve seat having a substantially “S” shape. The valve seat may be positioned adjacent the substantially flat surface such that a radially inward portion of the valve seat contacts a circumferential sealing edge of the disc when the disc is in the fully closed position. A valve seat retainer may be positioned adjacent the substantially flat surface and may include an annular ring having at least one channel configured to receive the valve seat therein. 
     In yet another embodiment of the present invention, a fluid control system may include a butterfly valve comprising a valve body having a substantially circular flow channel and a substantially flat surface extending radially outward from the flow channel. A disc may be rotatably mounted within the flow channel of the valve body and may be configured to rotate between a fully open position and a fully closed position. A valve seat that includes a plastic annular ring comprising a cross-section having a substantially “S” shape may be positioned adjacent the substantially flat surface such that a radially inward portion of the valve seat contacts a radially outer surface of the disc when the disc is in the fully closed position. A valve seat retainer may be positioned adjacent the substantially flat surface and may include an annular ring comprising at least one channel configured to receive the valve seat therein. An actuator may be operably coupled to the disc and configured to rotate the disc. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a perspective view of a butterfly valve according to an embodiment of the present invention; 
         FIG. 2  illustrates a top sectional view of an embodiment of the butterfly valve of  FIG. 1  through line  2 - 2 ; 
         FIG. 3  shows a magnified partial section view of a valve seat and a valve seat retainer according to a particular embodiment of the invention; 
         FIG. 4  illustrates the pressures on the valve seat of  FIG. 3  with a fluid flow in which the shaft is downstream; 
         FIG. 5  illustrates the pressures on the valve seat of  FIG. 3  with a fluid flow in which the shaft is upstream; 
         FIG. 6  is a system diagram of a fluid control system according to one embodiment of the present invention comprising a butterfly valve. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The illustrations presented herein are, in some instances, not actual views of any particular butterfly valve, valve seat, or seat retainer, but are merely idealized representations which are employed to describe the present invention. Additionally, elements common between figures may retain the same numerical designation. 
       FIG. 1  shows a perspective view of a butterfly valve  100  according to one embodiment of the present invention and  FIG. 2  shows a cross-sectional top view through line  2 - 2  of  FIG. 1 . The butterfly valve  100  comprises a valve body  110  defining a flow channel  120  of substantially circular cross-section, a disc  130  mounted for rotation within the flow channel  120 , a shaft  140  coupled to the disc  130  as is generally known in the art for rotating the disc  130 , an annular valve seat  150 , and a valve seat retainer  160 . 
     The valve body  110  comprises a substantially circular opening defining the flow channel  120  configured to allow a fluid to flow therethrough. The valve body  110  may further comprise a substantially flat surface  170  ( FIG. 3 ) extending radially outward from the flow channel  120 . The disc  130  is rotatably mounted within the flow channel  120  of the valve body  110  and configured to rotate between a fully open position (when the disc  130  is positioned substantially parallel to the flow channel axis) and a fully closed position (when the disc  130  is positioned substantially perpendicular to the flow channel axis so that no fluid passes therethrough). Disc  130  may comprise a circumferential sealing edge  180 , which is inclined with respect to the flow channel axis. The shaft  140  is coupled to the disc  130  and may extend outside of the valve body  110  so that rotation of the disc  130  may be controlled from outside the valve body  110 , as is generally known in the art. 
       FIG. 3  is a magnified partial section view of a valve seat  150  and a valve seat retainer  160  showing the cooperation between the valve body  110 , the valve seat  150 , the valve seat retainer  160  and the disc  130 . The valve seat  150  may be positioned adjacent the substantially flat surface  170  of the valve body  110 . The valve seat  150  may comprise an annular ring circumscribing the flow channel  120 . The valve seat  150  may comprise a substantially S-shaped cross-section comprising a first concave region  190  and second concave region  200  configured to open in opposing directions. The valve seat  150  may comprise a plastic material, such as, by way of example and not limitation, an ultra high molecular weight polyethylene material. The S-shaped configuration provides improved compliance in the radial direction, allowing the valve seat  150  to conform and seal more effectively against the disc  130 , as will be discussed in further detail below. Furthermore, this “S” shape may be capable of providing a relatively shorter valve seat, taken in the axial direction. 
       FIG. 3  shows the valve seat  150  in its totally undeflected position, i.e., in the position which it would occupy if the disc  130  was rotated into the open position, out of contact with the valve seat  150 . The first concave region  190 , comprising the radially outermost portion of the valve seat  150 , may include a first leg  210 , a first support segment  220 , and a center leg  230 . The first support segment  220  may extend radially inward from the first leg  210  and substantially perpendicular thereto. The center leg  230  may extend from the first support segment  220  in the same direction as the first leg  210  and substantially parallel thereto, the center leg  230  also being substantially perpendicular to the first support segment  220 . 
     The second concave region  200 , comprising the radially innermost portion of the valve seat  150 , may comprise the center leg  230 , a second support segment  240 , and a second leg  250 . The second support segment  240  may extend radially inward from the center leg  230  and substantially perpendicular thereto, the second support segment  240  extending substantially parallel to the first support segment  220 . The second leg  250  may extend from the second support segment  240  in the same direction as the center leg  230  and substantially parallel thereto, the second leg  250  being substantially perpendicular to the second support segment  240 . 
     The second leg  250  further comprises a sealing tab  260  extending radially inward and configured to contact the circumferential sealing edge  180  of the disc  130  when the disc  130  is in the closed position. The inside diameter of the valve seat  150 , when unstressed, may be slightly smaller than the diameter of the disc  130 . This dimensional relationship may ensure an interference fit, designated as the sealing point  270 , between the sealing tab  260  and the circumferential sealing edge  180 . The increased compliancy and spring effect in the radial direction provided by the S-shaped valve seat  150  coupled with the interference fit at the sealing point  270  enhance the sealing effectiveness of the valve seat  150 , even at low line pressures. Furthermore, the sealing tab  260  may comprise an incline at the radially innermost edge. In some embodiments, the angle of the radially innermost edge below the sealing point  270  may be nearly parallel to circumferential sealing edge  180  of the disc  130 . With an incline on the sealing tab  260 , as the valve seat  150  wears, the surface area of the sealing point  270  in contact with the circumferential sealing edge  180  will increase, and the valve seat  150  will continue to seal. In addition, as discussed above, the “S” shape of the valve seat  150  may provide the seal with increased resiliency and compliance in the radial direction. Such an increased flexibility in the radial direction may allow more radial movement to compensate for wear of the valve seat  150 , dimensional tolerances between the parts, and also for thermal expansion and contraction caused by different operating temperatures. Furthermore, the increased flexibility may create less friction forces between the disc  130  and the valve seat  150 , and may, therefore, reduce wear of the valve seat  150 . 
     The valve seat retainer  160  is positioned over the valve seat  150  and may include an annular ring configured to retain the valve seat  150  in position. The valve seat retainer  160  includes a flat surface configured to mate with the substantially flat surface  170  when the valve is assembled. The valve seat retainer  160  may include a first recess or channel  280  formed proximate a radially inward edge  290 , and a second recess or channel  300  formed between the first channel  280  and the radially inward edge  290 . The first channel  280  may be configured to substantially receive the first concave region  190  of the valve seat  150 . Similarly, the second channel  300  may be configured to substantially receive at least a portion of the second leg  250  of the valve seat  150 . The depths of the first channel  280  and the second channel  300  are configured to sufficiently receive the valve seat  150 , such that portions of the valve seat  150  may lie adjacent the substantially flat surface  170  of the valve body  110 . In some embodiments, the first channel  280  and the second channel  300  may have substantially similar depths. This may allow for a valve body  110  that does not require any substantial groove to receive a portion of the valve seat  150 , which groove may generally require a thicker body. In addition, the lack of a groove in the valve body  110  may provide a body which is more structurally sound. 
     Located between the first channel  280  and the second channel  300  is a first retaining tooth or protrusion  310 . The first protrusion  310  may be positioned and configured to extend at least partially into a portion of the second concave region  200  of the valve seat  150 . The length or height of the first protrusion  310  may be less than the depths of the first channel  280  and the second channel  300  to allow adequate space for the second support segment  240  between the first protrusion  310  and the substantially flat surface  170  of the valve body  110 . A second retaining tooth or protrusion  320  may be positioned adjacent the radially inward edge  290 . The second protrusion  320  may form a radially inward boundary of the second channel  300  and may be configured to circumscribe an outer surface of the radially inward edge of the second leg  250  of the valve seat  150 . The valve seat retainer  160  may comprise any suitable metal material. 
     The first and second protrusions  310 ,  320 , respectively, may further provide retention features to help retain the valve seat  150  in the valve seat retainer  160 . These retention features may also limit the movement of the valve seat  150  and prevent excessive deflection which, in turn, may lead to plastic yielding. For example, the second protrusion  320  may retain the second leg  250 , extending into the second channel  300 , from excessively deflecting. Without such features, pressure differentials across a partially closed valve may deflect the valve seat  150  downstream and radially inward, or the seat may catch onto the disc  130  when it is rotating and be pulled out of the valve seat retainer  160 . When the disc is distorted or pulled out of the valve seat retainer  160 , closing the disc  130  may bend the valve seat  150  backwards or even invert it, causing damage to the valve seat  150  and severe leakage. 
     In some embodiments, the valve seat  150  may be press-fit into the valve seat retainer  160 . An interference fit may be provided between that radially outermost edge of the first leg  210  and the relative mating surface of the valve seat retainer  160 , depicted as surface  350 . Such an interference fit may positively align the valve seat  150  to the valve seat retainer  160 . With the valve seat  150  positioned and fit into the valve seat retainer  160 , the valve seat retainer  160  may be positioned adjacent to the substantially flat surface  170  of the valve body  110 . Before the valve seat  150  and valve seat retainer  160  are secured in position, the valve seat retainer  160  may be allowed to float or move to center itself as a unit around the disc  130  rotated to its closed position. After the valve seat  150  and valve seat retainer  160  are positively aligned with the disc  130 , the valve seat retainer  160  may be secured in place adjacent the substantially flat surface  170 . 
     When the valve seat  150  and valve seat retainer  160  are secured in place, the first leg  210  of the valve seat  150  may be clamped or compressed between the substantially flat surface  170  and the first channel  280  of the valve seat retainer  160  to further secure the valve seat  150  in place. The compressed first leg  210  may also create a seal between the valve seat retainer  160  and valve body  110  to prevent fluid from leaking around the outside of the valve seat  150 . The first leg  210 , therefore, may comprise a length which is greater than the depth of the first channel  280  to create the interference fit. 
     In addition to providing the valve seat  150  with increase resilience and compliance in the radial direction, the “S” shape of the valve seat  150  may also improve the bi-directional pressure assisted sealing characteristics. Conventionally, when closed and pressurized, inline fluid pressure is applied to both the valve seat and the disc. In embodiments of the present invention, this inline pressure enhances the sealing effectiveness, regardless of whether the valve is pressurized from flow with the shaft  140  upstream or downstream.  FIG. 4  illustrates the pressures on the valve seat  150  according to one embodiment with a fluid flow in which the shaft  140  is downstream. In other words, the fluid flow is from top to bottom of the valve, as the valve is oriented in  FIG. 4 . With increased pressure applied from a flow with the shaft  140  downstream, the disc  130  axially deflects in the downstream direction. The “S” shape of the valve seat  150  is such that unbalanced areas exposed to the pressure result in a sealing stress which increases proportionally to the pressure differential. More specifically, when pressure is applied to the valve seat  150  with the shaft  140  downstream, pressure may be applied on the valve seat  150  in the directions of the arrows as a result of fluid flow in the spaces between the valve seat  150  and the valve seat retainer  160 . The surface area of the radially outward surface  330  of the second leg  250  may be larger than the combined surface area of the radially inward surface  340  of the second leg  250  and the exposed surface of the sealing tab  260 . The valve seat  150  may, therefore, be deflected both downstream and radially inward into the circumferential sealing edge  180  of the disc  130  to a degree greater than the above-mentioned deflection of the disc  130 . This deflection of the valve seat  150  may enhance the sealing effectiveness of the valve. 
       FIG. 5  illustrates the pressures on the valve seat  150  according to one embodiment with a fluid flow in which the shaft  140  is upstream from the fluid flow. In other words, the fluid flow is from bottom to top of the valve, as the valve is oriented in  FIG. 5 . With increased pressure applied to the shaft side of the valve, a two-fold stress-versus-deflection phenomenon may occur in the valve seat  150 . The disc  130  may displace axially in the downstream direction. The axial displacement of the disc  130  may increase the elastic internal stresses in the valve seat  150  by virtue of a compression on the valve seat  150  between the circumferential sealing edge  180  and the surface  350  at the radially outer most edge the valve seat retainer  160 . Furthermore, when pressure is applied to the valve seat  150  with the shaft  140  upstream, pressure may be applied to the radially outer surface of the center leg  230 , the upstream surface of the second support segment  240 , and the exposed surface of the sealing tab  260  in the direction of the arrows as a result of fluid flow in the spaces between the valve seat  150  and the valve body  110 . The surface area of the radially outer surface of the second support segment  240  may be larger than the surface area of the exposed surface of the sealing tab  260 , resulting in a net force pushing the valve seat  150  both downstream and into the disc  130 . These forces tend to increase proportionally with the fluid pressure. Additionally, the deflection of the valve seat  150  downstream, combined with the pressures on the second concave region  200 , may cause the second concave region  200  to bend around the first protrusion  310  of the valve seat retainer  160 , creating essentially compressive stresses on the downstream surface of the second support segment  240  and tensile stresses on the upstream surface of the second support segment  240 . These stresses tend to increase proportionately with disc deflection. These actions may enhance the sealing effectiveness of the valve. 
       FIG. 6  is a system diagram of a fluid control system according to one embodiment of the present invention comprising a butterfly valve  100 . The butterfly valve may include a butterfly valve  100  of the present invention as previously described. More particularly, the butterfly valve  100  may include a valve body and a disc rotatably secured within the valve body. A valve seat may be coupled to the valve body with a valve seat retainer. The valve seat  150  and the valve seat retainer  160  may be configured according to an embodiment, as described above. An actuator  360  may be controllably coupled to the shaft  140  and configured to control the rotation of the disc  130 . The actuator  360  may comprise any conventional actuator known in the art. By way of example and not limitation, the actuator  360  may comprise a Valtek-brand actuator, available from Flowserve Company of Irving, Tex. A positioner  370  may be operably coupled to the actuator  360 . The positioner  370  may comprise any conventional positioner  370  as is known in the art. By way of example and not limitation, the positioner  370  may comprise a Valtek-brand positioner, available from Flowserve Company of Irving, Tex. 
     While certain embodiments have been described and shown in the accompanying drawings, such embodiments are merely illustrative and not restrictive of the scope of the invention, and this invention is not limited to the specific constructions and arrangements shown and described, since various other additions and modifications to, and deletions from, the described embodiments will be apparent to one of ordinary skill in the art. Thus, the scope of the invention is only limited by the literal language, and equivalents, of the claims which follow.