Patent Publication Number: US-2011073789-A1

Title: Butterfly Valve Flow Control Device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims priority to U.S. Provisional Patent Application Ser. No. 61/104,312, filed Oct. 10, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     The present disclosure generally relates to a device to control the flow of a fluid through a butterfly valve. More specifically, the present disclosure relates to a flow control device that can be utilized with a butterfly valve to provide enhanced control of the flow characteristics of the butterfly valve. 
     Butterfly valves are in common usage for controlling the flow of various fluids, i.e. liquid or gas streams. Butterfly valves are used to throttle fluid flow and for on/off applications. A typical control valve assembly includes a body having a passage extending through it and a butterfly valve vane pivotally mounted within the body. The butterfly vane is characteristically in the form of a disk. 
     When fluid passes through a partially open butterfly valve, the fluid undergoes a significant pressure drop. One of the basic problems for butterfly valves is that the pressure drop tends to cause cavitation and consequent cavitation-induced damage in liquid service and noise in gas service. 
     In an attempt to solve these problems, it is proposed to use a diffuser with the butterfly valve. A diffuser is a perforated member that increases the restriction near the valve opening and breaks the fluid stream into multiple jets. This has a positive effect on the cavitation and noise problems. As shown in U.S. Pat. No. 3,960,177, diffusers can be integrally incorporated into the valve element. Although this configuration functions well, it is not possible to utilize the diffuser in any other valve since the diffuser is directly incorporated into the valve vane. In addition, this type of diffuser has little or no effect on the ability of the valve element to provide improved flow control near the fully opened valve position. 
     U.S. Pat. No. 7,264,221 illustrates a control valve assembly that includes a pair of cages attached to opposite sides of the butterfly valve body. Although the assembly shown in the &#39;221 patent provides advantages over a butterfly valve without the cages, a significant drawback with this type of valve assembly is that the combined valve housing with the cages cannot be inserted or slid between pipe sections, which makes the installation of the device in the field difficult. Further, the cage walls shown in the &#39;221 patent protrude into and block the flow of the fluid stream when the valve is in the wide open position. The use of this type of cage assembly reduces the maximum flow capacity of the valve by a significant amount. 
     Therefore, a need exists for a control device to be utilized with a butterfly valve that enhances the flow characteristics as the valve begins to open yet allows for increased flow capacity as compared to other types of control devices. 
     SUMMARY OF THE INVENTION 
     The present disclosure relates to a control device for use with a butterfly valve to enhance the flow characteristics of the butterfly valve. Preferably, the combination of the control device and butterfly valve can be assembled and slid between an inflow pipe and outflow pipe to enhance the flow characteristics of the butterfly valve. 
     The combined valve assembly of the present disclosure includes a control device that attaches to a downstream face surface of a butterfly valve. The control device includes an open flow passageway that receives the flow of fluid passing through the butterfly valve as the valve vane opens from a closed, sealed condition. 
     The flow control device includes a cylindrical inner wall that defines the cylindrical open flow passageway. The lower half of the inner wall includes a curved regress that extends into the open passage from a lower portion of the inner wall. The curved regress includes a series of flow control channels between a series of teeth. The teeth that define the curved regress each include a sloping inner surface that closely corresponds to the movement path of the sealing edge of the butterfly valve vane as the butterfly valve vane moves from a sealed position to an open position. 
     As the valve opens, the outer sealing edge of the vane moves along the curved face surface of each of the teeth to gradually expose the flow control channels formed in the control device. Additionally, as the valve vane rotates, the outer sealing edge gradually moves away from the curved inner surface of each of the teeth to allow further flow through the control device. 
     In an alternate embodiment, the flow control channels between each of the teeth can also include a sloped surface to restrict and limit the amount of fluid flowing through the control device. The configuration of each of the teeth and flow control channels formed in the control device can be selected to maximize the effect of the control device on the fluid flow through the valve assembly. 
     When the valve body and flow control device are combined to create the control valve assembly, the upstream end and the downstream end of the combined assembly provides a generally planar surface such that the combined assembly can be inserted between a pair of flow pipes. Specifically, the upstream and downstream face surfaces are generally planar to facilitate easy installation of the valve assembly between the inflow and outflow pipes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate the best mode presently contemplated of carrying out the invention. In the drawings: 
         FIG. 1  is an exploded view of a control valve assembly including a flow control device in accordance with the present disclosure; 
         FIG. 2  is an exploded section view taken along line  2 - 2  of  FIG. 1 ; 
         FIG. 3  is a section view of the assembled combination of the butterfly valve and the flow control device of the present disclosure; 
         FIG. 4  is an end view of the flow control device and butterfly valve taken along line  4 - 4  of  FIG. 3 ; 
         FIG. 5  is a section view of the butterfly valve and a second embodiment of the flow control device of the present disclosure; 
         FIG. 6  is an end view taken along line  6 - 6  of  FIG. 5 ; 
         FIG. 7  is a graph showing the control characteristics of a butterfly valve with the flow control device plotting the flow coefficient CV against the angle of valve opening; 
         FIG. 8  is a graph illustrating the coefficient of incipient cavitation Xfz for the butterfly valve including the flow control device versus a conventional butterfly valve; 
         FIG. 9  is a graph showing the dynamic torque for a butterfly valve alone and with the flow control device; 
         FIG. 10  is an exploded section view of an alternate embodiment of a flow control device that can be utilized with a butterfly valve; and 
         FIG. 11  is a section view of the butterfly valve and flow control device in an assembled condition. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates a control valve assembly  8  that includes a control system that modifies the control characteristics of a conventional butterfly valve  10  such that the butterfly valve  10 , with the control system installed, more closely approximates the flow characteristics of a globe valve. As shown in  FIGS. 1 and 2 , the butterfly valve  10  includes a valve body  12  that extends from a planar upstream face surface  14  to a downstream face surface  16  and is preferably formed from a metallic material, such as stainless steel. The valve body  12  defines an open passage  18  that allows fluid to flow through the valve body  12  from the upstream face surface  14  to the downstream face surface  16 . The open passage  18  is defined by a generally cylindrical inner wall  20 . 
     The butterfly valve  10  includes a valve disk  22  that is rotatably positioned within the open passage  18  by a pivot shaft  24 . The pivot shaft  24  defines a shaft axis about which the valve disk  22  is rotatable between the closed, sealing position of  FIG. 3  and the open position shown in  FIG. 1 . Preferably, the butterfly valve  10  could be either a triple offset butterfly valve or a standard butterfly valve while operating within the scope of the present disclosure. 
     Referring back to  FIG. 2 , the valve disk  22  includes an outer sealing edge  26  that provides a seal with the inner wall  20  when the butterfly valve  10  is in its closed, sealing position. 
     When the butterfly valve  10  is initially opened, the valve disk  22  rotates such that its first outer sealing edge  26  moves along a movement arc in the direction shown by arrows  28  in  FIG. 3 . As the valve disk  22  rotates away from the sealing position, liquid begins to flow around the outer circumference of the valve disk  22  between the valve disk  22  and the inner cylindrical wall  20 . 
     In  FIG. 7 , the dashed line  30  illustrates the flow coefficient Cv (gallons of water per minute at 1 psi pressure drop) for the butterfly valve  10  without any type of flow control device. The broken line  30  illustrates a rather rapid increase in flow relative to the angle of opening of the butterfly valve. 
       FIG. 8  illustrates the coefficient of incipient cavitation Xfz for a conventional butterfly valve  10  shown by dotted line  32 , against the angle of opening for the butterfly valve  10 . 
       FIG. 9 , in turn, illustrates the dynamic torque for the actuating device to overcome in order to open or close the valve against the flow of fluid. The dashed line  34  illustrates this dynamic torque as the butterfly valve  10  continues to open between a fully closed position and a fully open position. 
     Referring back to  FIGS. 1 and 2 , the control valve assembly  8  of the present disclosure includes a flow control device  36  that can be utilized with the butterfly valve  10 . The combination of the butterfly valve  10  and the flow control device  36  can be positioned between an inflow pipe  38  and an outflow pipe  40 . The inflow pipe  38  includes an attachment flange  42  defining a generally planar attachment surface  44 . The outflow pipe  40  also includes an attachment flange  46  that defines a generally planar attachment surface  48 . As can be seen in  FIG. 2 , the upstream face surface  14  of the valve body  12  contacts the attachment surface  44  while the planar downstream face surface  54  of the flow control device  36  contacts the attachment surface  48 . 
     Referring back to  FIG. 1 , the flow control device  36  is a generally cylindrical member formed from a metallic material, such as stainless steel. The flow control device  36  includes a generally cylindrical outer wall  50  extending between an upstream face surface  52  and a downstream face surface  54 . The control device  36  defines an open passage  56  that extends from the upstream face surface  52  to the downstream face surface  54 . 
     As shown in  FIG. 1 , the flow control device  36  includes a cylindrical inner wall  58  that extends uninterrupted over approximately the upper half of the generally cylindrical open passage  56 . The lower half of the inner wall  58  includes a curved regress  60  having a regress surface  61  that extends into the open passage  56  from the lower portion of the inner wall  58 . As shown in  FIG. 4 , the lower half of the inner wall  58  includes a series of flow control channels  62  that extend radially toward the inner wall  58  (shown by a dashed line) from the curved inner surface  64 . Each of the flow control channels  62  generally separates a pair of teeth  66  that each terminate at an inner end  63  that combine to define a curved inner surface  64 . 
     Referring now to  FIG. 3 , each of the teeth  66  includes a generally curved face surface  68  that forms part of the regress surface  61  ( FIG. 1 ). The curved face surface  68  of each of the teeth  66  is configured such that when the valve disk  22  rotates in the direction shown by arrow  28 , the lower outer sealing edge  26  will swing through the movement arc described by the dashed line  70 . As can be illustrated in  FIG. 3 , in one preferred embodiment the dashed line  70  indicating the path of the outer sealing edge  26  gradually separates from the regress surface formed by the curved face surface  68  of the individual teeth  66 . The degree of separation between the outer sealing edge  26  and the face surface  68  of the teeth  66  can be designed to determine the desired rate of fluid flow increase per given travel position of the valve disk  22 . Thus, as the valve disk  22  rotates, the outer sealing edge  26  exposes an increasing volume of each of the flow control channels  62  to increase the amount of flow through the control device  36 . Additionally, the increase in the separation between the outer sealing edge  26  and the face surface  68  of each of the teeth  66  allows for an increasing amount of fluid to flow between the valve disk and each of the teeth  66 . 
     Referring again to  FIG. 3 , the butterfly valve  10  and the flow control device  36  can be assembled as a combined unit and inserted between the inflow pipe  38  and the outflow pipe  40 . Specifically, an outer wall  71  of the butterfly valve  10  is received within a recess  72  formed in the flow control device  36  such that an attachment lip  74  of the control device extends into the open passage  18  of the butterfly valve  10 . A gasket  76  can be positioned between the downstream face surface  16  of the butterfly valve  10  and the upstream face surface  52  of the control device  36 . 
     Although the butterfly valve  10  and the flow control device  36  are shown as separate units that can be combined and inserted between the inflow pipe  38  and the outflow pipe  40 , it is contemplated that the flow control device  36  and the butterfly valve  10  could be integrated into a single cast component. 
     As illustrated in  FIG. 4 , the downstream face surface  54  of the control device  36  includes a series of openings  78  that each receive a connector for attaching the control device  36  to the butterfly valve body  12 . 
     As illustrated in  FIG. 3 , when the flow control device  36  is attached to the valve body  12 , the combined assembly is defined by the generally planar upstream face surface  14  of the valve body  12  and the generally planar downstream face surface  54  of a control device  36 . Thus, the combined control valve assembly  8 , including the valve body  12  and the control device  36 , can be slid between the attachment surface  44  of the inflow pipe  38  and the attachment surface  46  of the outflow pipe  40 . 
     Referring back to  FIG. 4 , the individual flow control channels  62  formed between the teeth  66  allow fluid to flow through the control device as the valve disk  22  opens along the dashed line  70  shown in  FIG. 3 . The size and shape of the flow control channels  62  determines the rate of fluid flow and affects the level of fluid velocity induced turbulence. One of the best ways to filter sound from the inside of the downstream pipe to the observed pipe exterior is by using the pipe wall as a barrier. The resultant sound absorption of the pipe wall is called the transmission loss TL. The transmission loss TL is most effective if it can be arranged such that the frequency at which the sound is produced occurs above the pipe&#39;s ring frequency Fr. The pipe&#39;s ring frequency Fr is equal to 5,000/3.14 D in Hz, where D is the interior pipe diameter in meters. The peak frequency Fp is determined by 0.2 Uvc/w, where Uvc is the jet velocity (assumed to be 333 m/second) and w is the width of the flow control channel  62  in meters. The additional transmission loss Δ TIfp due to higher frequencies is given by the equation: Δ TIfp=7.8+20 log (F p /F r ) in decibels (dB). 
     Based upon the above equations, it can be shown that for a flow control channel  62  with a width of 0.04 D, a sound reduction of 8 dB can be expected. This then makes the preferred width w of the flow control channels  62  less than 4% of the pipe diameter. 
     The flow control channels  62  may further be configured to meet certain manufacturing requirements. As an example, the bottom  80  of the flow control channels  62  may be rounded, as shown in  FIG. 6 , or squared, as shown in  FIG. 4 . 
     Referring back to  FIG. 6 , it also may be desirable to delay the onset of the exposure of the flow control channels  62  to fluid flow to a somewhat larger valve travel in order to achieve a more gradual opening characteristic. In the embodiment shown in  FIG. 6 , the flow control channels  62  between each of the teeth  66  includes a flow restricting wall  82  that extends upward into the flow control channels from the bottom edge  80 . As can be seen in  FIG. 5 , as the valve disk  22  rotates, the outer sealing edge  26  stays in close contact with the flow restricting wall  82  until the valve disk  22  rotates a larger degree of travel. The flow restricting wall  82  extends into the open passage  56  from the upstream face surface  52  to a peak  84 . The flow restricting wall  82  then extends away from the open passage  56  to the downstream face surface  54 . 
     Once the outer sealing edge  26  passes over the peak  84 , the individual flow control channels  62  between each of the fingers  66  are exposed to the flow of fluid. Thus, the curved flow restricting wall  82  that extends to the peak  84  further restricts the flow of fluid through the flow control device  36 . 
     In the embodiment shown in  FIG. 5 , the butterfly valve  10  is a triple eccentric butterfly valve. However, the butterfly valve could be a symmetrical butterfly valve, or a double eccentric butterfly valve while operating within the scope of the present disclosure. In either embodiment, the control device  36  enhances the operation of the butterfly valve, as will be described in detail below. 
       FIG. 10  illustrates an alternate embodiment of a flow control device  100  that can be used to retrofit a butterfly valve  102  mounted in place between an inflow pipe (not shown) and an outflow pipe  40 . When the butterfly valve  102  is mounted in place between the inflow and outflow pipes, minimal room exists to insert a flow control device  36 , such as is shown in  FIG. 1 . In such a situation, the flow control device  100  shown in  FIG. 10  can be utilized. 
     The flow control device  100  includes an attachment flange  104  that extends radially outward from an outer wall  106 . The outer wall  106  defines the open passage  56 . The flow control device  100  includes the same teeth  66  in the curved regress  60  as in the embodiment shown in  FIGS. 2 and 3 . However, the outer wall  106  is sized such that the outer wall  106  fits within the cylindrical inner surface  108  of the outflow pipe  40  and the cylindrical inner surface  110  of the outer wall  112  of the butterfly valve  102 . Thus, when the flow control device  100  is positioned between the butterfly valve  102  and the outflow pipe  40 , the only additional space requirement is the thickness of the attachment flange  104 . 
     In the embodiment shown in  FIG. 10 , a pair of connectors  114  pass through the attachment flange  46  of the outflow pipe  40  and through a series of openings  116  formed in the attachment flange  104 . The threaded ends of each of the connectors  114  are received within internally threaded attachment bores  118  formed in the outer wall  112  of the butterfly valve  102 . In the embodiment illustrated in  FIG. 10 , the attachment flange  104  has a thickness of between ¼ inch and ⅜ inch such that the connectors  114  previously used to secure the outflow pipe  40  to the butterfly valve  102  can be utilized when the flow control device  100  is inserted therebetween. 
     Although not shown in  FIG. 10 , a pair of resilient gaskets can be positioned on opposite sides of the attachment flange  104  of the flow control device  100  between the attachment flange  104  and the downstream face surface  120  of the butterfly valve  102  and the attachment surface  48  of the outflow pipe  40 . The pair of gaskets provides additional sealing between the flow control device  100  and both the butterfly valve  102  and the outflow pipe  40 . It is contemplated that the gaskets could be eliminated while operating within the scope of the present disclosure. 
     Referring now to  FIG. 11 , when the flow control device  100  is installed between the outflow pipe  40  and the butterfly valve  102 , the outer wall  106  extends into both the outflow pipe  40  and the butterfly valve  102 . The butterfly valve  102  and the outflow pipe  40  are separated by the thickness of the attachment flange  104 . Once the flow control device  100  is installed as shown in  FIG. 11 , the series of teeth  66  provide the flow characteristics as previously described. The embodiment shown in  FIGS. 10 and 11  allows the flow control device  100  to be retrofit into existing applications that already include an installed butterfly valve  102 . 
     Referring now to  FIG. 7 , thereshown is a graph illustrating the advantage of the flow control insert on the flow coefficient relative to the angle of valve opening. In the graph shown in  FIG. 7 , the shape of the solid line  86  represents the flow coefficient Cv against the angle of valve opening. The shape of the solid line  86  indicates a gradual increase in flow as the angle of valve opening increases. This gradual increase in flow is preferred for control purposes. Dashed line  30 , which indicates the flow characteristics for a butterfly valve without the flow control device, indicates a substantially faster rate of flow increase for lower angles of opening of the butterfly valve. Thus, the flow control device  36  shown in the drawing Figures has the advantage of providing a gradual increase in flow relative to a butterfly valve without the flow control device, which is much preferred for pressure or flow control purposes. 
     Another drawback of conventional butterfly valves is their high tendency to cavitate at relatively low-pressure drops. Cavitations cause damage and noise in a piping system including a butterfly valve. In the graph of  FIG. 8 , the flow control device provides a higher coefficient of incipient cavitation, Xfz, which is shown by the solid line  88  in  FIG. 8 . The coefficient of incipient cavitation, Xfz, is an industrial standardized term that is defined as the pressure ratio at which there is an audible indication of beginning cavitation (vaporizing of water). In a conventional butterfly valve without the flow control device, the coefficient of incipient cavitation is reduced, as indicated by dashed line  32  allowing for a more then 50% increase in pressure drop without incurring cavitation. 
       FIG. 9  illustrates yet another advantage of the flow control device utilized with the butterfly valve in accordance with the present disclosure. As shown by solid line  90 , the dynamic torque that the actuating device must overcome to open the butterfly valve is decreased as compared to the butterfly valve without the flow control device, which is shown by dashed line  34 . Thus, the use of the flow control device reduces the dynamic torque as compared to a butterfly valve not including the flow control device. The reduction in dynamic torque offers substantial economic advantages by allowing the use of much smaller actuating devices. 
     The drawings and the above description depict the currently preferred embodiment of the present disclosure. However, without departing from the scope of the disclosure, numerous modifications can be made without departing from the intent of the invention. As an example, the control element could be an integral part of means to retain a sealing element within the valve housing. Furthermore, the control element could be fastened by welding to the valve housing or could be an integral cast portion of the valve housing.