Abstract:
A flow control valve and method for controlling fluid flow includes a valve housing defining a valve chamber. A port member mounted within the valve chamber receives a reciprocally movable piston/spool assembly. The assembly is engageable with a valve seat for blocking fluid flow through the chamber. The assembly includes a piston body defining an annular recess for receiving an annular seal and a compression bonnet received by the piston body which is operatively engageable with the annular seal. When the assembly is not engaging its associated valve seat, the seal is relaxed and thus reciprocal movement between the assembly and the port member is not substantially hindered or resisted.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/443,794, filed Feb. 17, 2011, the entirety of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to fluid flow control and, in particular, to an improved flow control valve assembly. 
       BACKGROUND 
       [0003]    Control valves of the type to which this invention pertains are used to control or throttle high pressure fluid flows such as applications that involve steam flow. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention provides a new and improved control valve assembly for controlling or throttling the flow of fluid such as steam. 
         [0005]    According to one preferred embodiment of the invention, a flow control valve is provided that includes a valve housing that defines a valving chamber. A port member mounted within the valving chamber receives a reciprocally movable piston/spool assembly. The relative position of the piston/spool assembly within the port member determines the flow rate of fluid through the valving chamber. An actuator is used to move the piston/spool assembly within the port member. The piston/spool assembly is engageable with a valve seat which, when engaged, blocks fluid flow through the valving chamber. An actuating member is operatively connected to the piston/spool assembly and can move the assembly in opening and closing directions within the port member. 
         [0006]    According to the invention, the piston/spool assembly includes a piston body that defines a seal recess for receiving an annular seal. The seal sealingly engages an inside surface of the port member and inhibits fluid flow between the piston/spool assembly and the inside surface of the port member. The assembly also includes a bonnet that is received by the piston body and is engageable with the annular seal. The seal, the bonnet and the actuating member are arranged such that when the actuating member moves the piston/spool assembly into sealing contact with the valve seat, forces are exerted on the annular seal by the bonnet which cause increased sealing engagement between the inside surface of the port member and the annular seal. 
         [0007]    In the exemplary embodiment, the bonnet applies compression forces to the seal which, in turn, causes the seal to expand in the radial direction, thus increasing its sealing engagement with the inside surface of the port member. 
         [0008]    According to a further feature of this embodiment, the actuating member abutably engages the bonnet and is attached to the associated piston body with a connection that allows relative movement between the actuating member and the piston body. With this preferred embodiment, when the actuating member moves the piston/spool assembly into sealing contact with the valve seat, the bonnet, by virtue of the lost motion connection (between the actuating member and the piston body) moves relative to the piston body a slight amount, thus applying forces to the seal that is captured between the bonnet and the piston body. These forces cause at least a portion of the annular seal to expand in the radial direction, thus increasing the sealing contact between the annular seal and the inside surface of the port member. 
         [0009]    With the disclosed embodiment, the annular seal engages the inside surface of the port member with increased engagement force only when the piston/spool assembly is moved to a position where it sealingly engages the associated valve seat. When the actuating member moves the piston/spool assembly away from the valve seat, the compression forces applied by the bonnet are released, thereby relaxing the seal and reducing the friction between the seal and the inside surface of the port member. As a result, reciprocal movement of the piston/spool assembly within the port member is not resisted by a substantial frictional force that would be present if the seal were permanently preloaded to exert the substantial sealing engagement that is present when the piston/spool assembly is moved to its valve seat engaging position. 
         [0010]    According to a further feature of the invention, a gap is preferably maintained between the bonnet and the piston body. The gap, in cooperation with pressure balancing passages equalizes fluid pressures on the piston/spool assembly. 
         [0011]    The preferred method of controlling the flow rate of high pressure fluid in a control valve, includes the steps of providing a valve housing that defines a valving chamber, providing a port member within the valving chamber that receives a reciprocally movable piston/spool assembly. In addition, the method provides a valve seat engageable by the piston/spool assembly for blocking flow through the valving chamber. Enhanced sealing between the piston/spool assembly and an inside surface of the port member is provided by moving the overall assembly within the port member with an actuating member. The actuating member is allowed to move relative to a portion of the piston/spool assembly in order to allow another portion of the piston/spool assembly to move relative to the first portion thereby applying forces to the seal. This causes the seal to expand radially and to increase its sealing engagement with the inside surface of the port member. 
         [0012]    With the disclosed invention, sealing between a piston/spool assembly and its associated port member are substantially increased when the piston/spool assembly engages its associated valve seat. When the piston/spool assembly is in a position other than its valve seat engaging position, the seal is relaxed. With the seal relaxed, friction between the seal and port member is reduced. Consequently, the relative movement between the piston/spool assembly and the port member is not substantially resisted by the engagement of the seal with the port member. Thus, the control of the fluid flow rate through the valving chamber is substantially improved. 
         [0013]    Additional features of the invention will become apparent and a fuller understanding obtained by reading the following detailed description made in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a fragmentary sectional view of a prior art valve assembly; 
           [0015]      FIG. 1A  illustrates an overall view of the type of valve to which this invention pertains; 
           [0016]      FIG. 2  is a fragmentary sectional view of a valve assembly constructed in accordance with a preferred embodiment of the invention; 
           [0017]      FIG. 3  is a side devotional view of a piston assembly and associated sleeve constructed in accordance with a preferred embodiment of the invention; 
           [0018]      FIG. 4  is a sectional view of the assembly shown in  FIG. 3 , as seen from the plane indicated by the line  4 - 4  in  FIG. 3 ; and 
           [0019]      FIG. 5  is an exploded view of the assembly shown in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  illustrates, in sectional view, a portion of a prior art valve assembly  10 . The valve assembly is termed a balance seal or flow control valve which is used, for example, in the steam industry to control or throttle steam flow.  FIG. 1A  illustrates an overall view of the type of valve shown in  FIG. 1  and that this invention pertains to. 
         [0021]    The valve assembly  10  includes a valve housing  12 , which includes a flow passage  20  having an inlet end  20   a  and an outlet end  20   b.  In the illustrated construction, the inlet and outlet ends  20 ,  20   b  define respective bolt flanges  22   a,    22   b  to which suitable piping (not shown) is fastened in a known way. 
         [0022]    The flow of fluid (i.e., steam) from the inlet  20   a  to the outlet  20   b  is controlled by a valving assembly indicated generally by the reference character  30 . The valving assembly  30  includes a ported sleeve  32  that is fixed within a valve chamber  20   c  also defined by the valve housing  12 . In the illustrated construction, the sleeve  32  may be captured within the valve body between a step  40  and a cylindrical spacer  42 . A valve cap  50  exerts a clamping force on the sleeve  32 . The valve cap  50  is secured by a plurality of studs  54  that extend upwardly from the valve housing  12 , extend through bores  56  in the cap  50  and receive suitable nuts  58  which retain the cap in position and apply a clamping force to the cylindrical spacer  42 . 
         [0023]    A flow control piston or spool  60  is reciprocally movable within the sleeve  32  and when it is moved upwardly, (as viewed in  FIG. 1 ), it uncovers one or more ports  32   a  defined by the sleeve  32 . The more ports  32   a  that are uncovered, the greater the fluid flow between the inlet  20   a  and the outlet  20   b.  The piston/spool  60  is reciprocally movable by an operating stem  66  is which operatively attached to an actuator, one of which is shown in Appendix 1. The actuator is conventional and does not form part of the present invention. 
         [0024]      FIG. 2  illustrates a valve assembly  10 ′ constructed in accordance with a preferred embodiment of the invention. The valve assembly  10 ′ constitutes a substantial improvement over the valve assembly  10  shown in  FIG. 1 . To facilitate the explanation, components in  FIG. 2  that are the same or perform similar functions as components in  FIG. 1  will be given the same reference character followed by an apostrophe. 
         [0025]    The valve assembly  10 ′ includes a valve housing  12 ′ that defines a flow passage  20 ′ having an inlet end  20   a ′, an outlet end  20   b ′ and a valve chamber  20   c ′. A valving assembly  30 ′ constructed in accordance with a preferred embodiment of the invention in located in the valve chamber  20   c ′ and controls the flow of fluid i.e. steam, from the inlet  20   a ′ to the outlet  20   b ′. The valving assembly  30 ′ includes a ported sleeve  32 ′ that is clamped between the seat or step  40 ′ and the annular spacer  42 ′. 
         [0026]    The valving assembly  30 ′ includes a piston/spool assembly  60 ′ constructed according to a preferred embodiment of the invention. The piston/spool assembly  60 ′ is reciprocally movable within the port sleeve  32 ′ and controls or throttles fluid flow between the inlet  20   a ′ and outlet  20   b ′. It should be apparent that the more ports  32   a ′ that are exposed as the piston/spool assembly  60 ′ is raised (as viewed in  FIG. 2 ), the greater the flow of fluid, i.e., steam through the valve housing  12 ′. Referring also to  FIGS. 4 and 5 , when the piston/spool assembly  60 ′ is moved to its lowermost position (as viewed in  FIG. 2 ), the lower annular edge  61  of the piston/spool assembly  60 ′ contacts and sealingly engages an angled seat surface  40   a  defined by the seat  40 ′ (shown best in  FIG. 5 ). In this position, the piston/spool assembly  60 ′ blocks flow through the passage  20 . 
         [0027]    The piston assembly  60 ′ includes a piston body  76  having an upper, reduced diameter section  76   a  which defines an open-ended groove for receiving an annular seal  78 . A compression bonnet  80  is at least partially received by the reduced diameter section  76   a  of the piston body  76  and includes a downwardly depending (as viewed in  FIG. 4 ) axial flange  80   a.  The lower edge of the axial flange  80   a  abuts the upper (as viewed in  FIG. 4 ) radial face of the annular seal  78  and can exert compression forces on the seal when the bottom edge  61  of the piston body  76  is moved into sealing contact with the sealing surface  40   a  of the seat  40 ″. 
         [0028]    Referring to  FIGS. 3-5 , the piston/spool assembly  60 ′ includes a central bore  70  which slidably receives a reduced diameter portion  66   a ′ of the operating stem  66 ′. The reduced diameter portion  66   a ′ defines a step  72 , the function of which will be described 
         [0029]    When the piston body  76  is in contact with seat  40 ′ and the stem  66 ′ continues to be urged downwardly by its associated actuator, the step  72  applies a downward directed force to the top of the compression bonnet  80  and urges it downwardly. This downward force causes the axial rim  80   a  of the bonnet  80  to exert a compression force on the annular seal  78  and may reduce its axial dimension (depending on the material composition of the seal  78 ). The compression of the seal  78  in the axial direction causes the seal to expand radially and thus create a tight sealing engagement between the upper part  80   a  of the piston body  76  and the inside surface of the sleeve  32 ′, thus inhibiting leakage between the piston body  76  and the sleeve  32 . 
         [0030]    In the preferred embodiment, the piston body  76  includes pressure-balancing bores  88  and the compression bonnet  80  includes arcuate slots  80   b  for equalizing fluid pressure above and below the piston assembly  60 ′ when the piston body  76  is in sealing contact with the associated seat  40 ′. In this position, fluid flow from the inlet  20   a ′ to the outlet  20   b ′ is blocked. Absent the balancing bores  88  and openings  80   b  in the bonnet  80 , full inlet pressure would urge the piston body  76  upwardly, which would tend to move the piston assembly  60 ′ toward an open position. The communication of inlet fluid pressure to the top surface of the bonnet/ 80  (as viewed in  FIG. 4 ) balances the force on the piston assembly  60 ′. 
         [0031]    With the disclosed construction, sealing engagement of the piston body  76  to the sleeve  32 ′ is substantially enhanced without detrimentally affecting the ability of the piston assembly  60 ′ to be reciprocally moved within the sleeve  32 ′ by the associated actuator. Downward movement of the stem  66 ′ (by an associated actuator) causes compression of the annular seal  78  once the bottom edge or skirt  61  of the piston body sealingly contacts the associated seat  40 ′. As discussed above, compression of the annular seal  78  causes radial expansion, thus causing a tight engagement between the seal  78  and the inside surface of the ported sleeve  32 ′. However, when the piston body  76  moves off the seat  40 ′, as the stem  66 ′ is raised upwardly, the upward movement of the bonnet  80 ′ (which depending on the material from which the seal  78  is made may be very slight) relaxes the seal  78 , thus decreasing the force necessary to reciprocally slide the piston assembly  60 ′ within the sleeve  32 ′ to achieve a desired flow rate. With the disclosed invention, when the piston body  76  is off its seat  40 ′, the piston assembly  60 ′ can be moved by the actuator relatively easily in order to control the flow rate through the valve. In normal operation, the actuator may continually move or dither the piston assembly  60 ′ within the sleeve in order to achieve a desired flow rate. In the prior art, the piston seal was fully loaded at all times, thus requiring significant actuator force to reciprocally move the piston within the sleeve even when the piston disengaged the associated seat. 
         [0032]    It should be noted here, that the connection of the stem  66 ′ with the compression bonnet  80 ′ and piston body  76 ′ resembles a lost motion connection. In particular, the narrow diameter portion  66   a ′ of the stem  66 ′ can move relative to the piston body  76  a predetermined amount in order to relax and compress the seal  78 . The distal end  66   b  of the stem  66 ′ is threaded and receives a nut  90  by which an initial pre-load is preferably applied to the seal  78  by the compression bonnet  80 , to initially compress the seal  78  a minimal amount. When the stem moves downwardly from its relaxed position to its full force applying position shown in  FIG. 4 , the compression bonnet  80  preferably moves downwardly a slight amount thus slightly reducing the gap “G” between the underside of the bonnet  80  and the top of the piston body  76  to compress the seal  78  and effect the substantial sealing engagement between the seal  78 , the inside surface of the ported sleeve  32 ′ and the upper portion  76   a  of the piston body  76 . It is should be noted here that the compressibility of the seal will determine the extent of movement of the compression bonnet  80  with respect to the piston body  76 . Accordingly, the amount that the gap “G” is reduced when the compression bonnet  80  is in the force applying position shown in  FIG. 4 , will be dependent on the compressibility of the seal material. In the preferred embodiment, however, it is preferred that the material for the seal and the gap “G” is chosen such that there is always some gap between the compression bonnet  80  and the piston body  70  when the seal  78  is fully compressed. 
         [0033]    As seen best in  FIG. 5 , a cotter pin  92  is used to lock the relative rotated position of the preload adjustment nut  90  on the threaded end  66   b  of the stem  66 ′. 
         [0034]    In the preferred embodiment, a gap G was maintained between the underside of the compression bonnet  80  and the top of the piston body  76 . Depending on the material composition of the seal  78 , the gap may change slightly or substantially. In any event, in the preferred embodiment, a gap G preferably always exists even when the piston body  76  is in tight sealing engagement with the seat  40   a.  By maintaining a gap G throughout valve operation, the full downward force applied by the stem  66 ′ is always applied to the seal, rather than directly to the piston body  76 . With this preferred construction, fluid communication between the pressure balancing bores  88  and the arcuate slots  80   a  is maintained even if the slots are not aligned with the bores  80   a.  In addition, any wear that occurs in the seal  78  is taken up by slight reductions in the gap G without reducing the forces applied to the seal when the piston body  76  is seated against the seat  40 ′. 
         [0035]    Although the invention has been described with a certain degree of particularity, it should be understood that those skilled in the art can make various changes to it without departing from the spirit or scope of the invention as hereinafter claimed.