Patent Document

FIELD OF THE INVENTION 
     The present invention relates to balanced plug valves, and more particularly to balanced plug valves having contoured valve walls, the contour shape being alterable to result in desired flow characteristics. 
     BACKGROUND OF THE INVENTION 
     Control systems and manual applications utilize various types of valves to turn fluid flows on and off, and also to modulate the rate of fluid flow through the valve. Fluid flow through a valve results from pressure differentials between upstream sources and downstream destinations. Fluid flow is a function of pressure differentials and conduit resistance. Control is generally achieved by varying the resistance to flow by varying the available flow area between zero and a maximum. A valve is the conventional method of varying area. 
     Sliding gate valves present one method of varying flow area. However, in such a valve, the differential pressure from the upstream side to the downstream side multiplied by the area of the obstruction separating each side results in a substantial number. This number represents a load on the guides supporting the gate. This load increases friction in a manner proportional to the area and pressure drop. With increased friction, the amount of force required to move the gate increases, thus requiring more powerful actuators. With greater actuator force requirements, costs escalate. Further, control system deadband becomes larger, which negatively affects system stability. 
     Plug type valves are an additional method of varying flow area. These valves reduce the flow area by forcing a plug into a hole. When the plug is lowered from the upstream side, typically the result is that the plug slams shut against a valve seat due to upstream pressure and inertia forces pushing the plug toward the hole. This slamming causes hammering which creates noise and valve damage. Forcing a plug into a hole from the downstream side can also reduce the flow area. In such a scenario, the obstruction pushes against a substantial opposing force, the force being proportional to hole size and pressure drop between the upstream and downstream sides. With increased opposing forces, the amount of force required to move the plug increases, thus requiring more powerful actuators. Again, with greater actuator force requirements, costs escalate. 
     In both the gate valve and plug valve instances, the difference in upstream and downstream pressures is the root of their shortcomings. To overcome these shortcomings, balancing of fluid forces is required. 
     One known arrangement utilizes two circular seats where the pressure forces cancel. These valves are relatively larger and more expensive than the standard gate and plug valves. Further, it is often difficult to ensure proper mechanical closure of both seats. 
     A second known arrangement utilizes one circular seat with a balancing chamber connected to the upstream pressure with a movable piston tied to a valve stem. These valves are complex, and again more expensive to manufacture. 
     As an alternative to the aforementioned larger and more costly balanced valves, it is known to create a balanced valve where the flow passes through a balanced plug that is typically in the shape of a cylinder. The cylindrical or other closed perimeter shaped plug that allows fluid to pass through is known as a balanced plug and is a key element in forming a balanced plug valve. The cylinder method successfully eliminates the friction and back pressure forces, thus forming a balanced valve. However, the known cylinder type balanced valves have their own shortcomings. These include the fact that they have poor capability for flow modulation or for tight shut-offs. 
     In view of the foregoing limitations and shortcomings of the above noted devices, as well as other disadvantages not specifically mentioned, there exists in the art a need for a balanced plug valve with the ability to predictably modulate flow and also provide for tight shut-off of flow. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a balanced plug valve. The valve has a valve body with at least an input port and an output port. Typically, there is a valve bonnet having a side facing an interior of the valve body. The bonnet is removably attached to the valve body at a bonnet aperture. A valve stem is slidably mounted through the bonnet or the valve wall. The valve stem is connected at a first end to an actuator at a location exterior to said valve body. The valve stem has a second end located within the interior of the valve body. A balanced plug is mounted on the interior valve stem end. At least one wall has a contour shape located on the interior. The wall is tightly sealable with the balanced plug at a closed balanced plug position. The wall is dimensioned to form a variable gap with the balanced plug, through which fluid flows, as the balanced plug is displaced. The contour shape, which determines the flow area, influences the fluid flow rate relative to a plug position or displacement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The aforementioned objects and advantages, and other features and aspects of the present invention, will become better understood with regard to the following description and accompanying drawings, wherein: 
     FIG. 1 is a cross-section of a two-way balanced plug valve having contoured walls in accordance with one embodiment of the present invention. 
     FIGS. 2-5 are cross-section of alternate embodiments of the valve of FIG. 1 having differing contoured wall structures with the contoured walls outside the movable plug. 
     FIGS. 6 is a cross-section of a two-way balanced plug valve of a stem out closed configuration utilizing contoured walls pursuant to an embodiment of the present invention with the contoured walls inside the movable plug. 
     FIG. 7 is a cross-section of a two-way balanced plug valve having a stem down closed configuration utilizing contoured walls pursuant to an embodiment of the present invention with the contoured walls outside the movable plug. 
     FIG. 8 is a cross-sectional schematic of a similar valve to that of FIG. 7, but with the contoured walls internal to the moveable plug. 
     FIG. 9 is a cross-sectional schematic of a three-way balanced mixing valve utilizing contoured walls pursuant to an embodiment of the present invention. 
     FIG. 10 is a cross-sectional schematic of a three-way balanced diverting valve utilizing contoured walls pursuant to an embodiment of the present invention. 
     FIG. 11 is a graph plotting the Flow Coefficient vs. the Percentage Stroke of a 2-inch balanced plug valve with contoured wall pursuant to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring now in detail to the drawings wherein like parts are designated by like reference numerals throughout, there are illustrated in FIGS. 1-10 multiple embodiments of the present invention. 
     A cross-sectional schematic of a two-way balanced stem out closed external contoured plug valve  10  is shown in FIG.  1 . Contoured plug valve  10  has a valve body  12 . Removably secured in an aperture of valve body  12  is a bonnet  14 . Valve packing  16  exists on an exterior side of bonnet  14 , and is removably mounted in place via mounting nut  18 . Slidably mounted within packing  16  and through bonnet  14  is a valve stem  20 . Valve stem  20  slides in two directions generally along axis A, to operate the valve. Axis A may be angled with respect to the inlets and outlets for flow efficiency. An actuator (not shown) drives the valve stem  20 . Other embodiments may include elements such as knobs, wheels, etc. to drive valve stem  20 . At a valve stem end  22  internal to the valve  10 , a balanced plug  24  is attached to valve stem  20 . Note that the attachment of plug  24  to valve stem  20  may include some play to allow the plug  24  to self-align. 
     Balanced plug  24  is generally cylindrical in shape, but can be of other closed perimeter shapes. Valve stem  20  is mounted to plug  24  at a center hub  26 . Supporting center hub  26  are multiple spokes  28  extending to a perimeter wall  30  of plug  24 . Plug  24  is prevented from moving in directions other than generally along axis A by a guide  32  extending from valve body  12 . The guide  32  may be integral with valve body  12 . The edges  34 ,  36  of plug  24 , are chamfered to allow plug  24  to tightly close against seals without damaging the seals. This feature is described in more detail below. 
     A sliding seal o-ring  38  is positioned within a groove  40  of guide  32 , sealing plug  24  at perimeter wall  30  to block fluid passage between the exterior of the perimeter wall  30  of plug  24  and guide  32 . A close-off o-ring seal  42  is positioned within a groove  44  of bonnet  14  to block fluid passage between the exterior of the perimeter wall  30  of plug  24  and bonnet  14  when plug  24  is in a closed position. 
     Along an interior end  46  of bonnet  14  there is a ridge  48  having an internal contoured wall  50 . Ridge  48  has a similar perimeter shape as that of plug  24 , but is sized slightly larger such that perimeter wall  30  of plug  24  may fit snugly within an interior of ridge  48 . Contour  50  of ridge  48  begins proximal to bonnet groove  44  and close-off o-ring seal  42 , and curves outward in a direction away from valve stem  20 . 
     Contour  50  has a radius of curvature that may vary at different locations along contour  50 . For example, contour  50  may have a constant radius of curvature. Alternatively, contour  50  may have a relatively large radius of curvature at a location proximal to bonnet groove  44  which gradually decreases until contour  50  ends at a location along a rim  54  of ridge  48  (see FIGS.  4  &amp;  5 ). In a further embodiment, contour  50  may have a relatively small radius of curvature at a location proximal to bonnet groove  44  which gradually increases until contour  50  ends at a location along rim  54  of ridge  48  (see FIGS.  2  &amp;  3 ). 
     The gradual increase and/or decrease of the curvature profile of contour  50  may be determined by formula, or may be determined empirically. For example, the curvature profile may be defined such that the radius of curvature fluctuates up and down along various locations of a single contoured wall  50 . In addition, the overall length of contour  50  and the depth of ridge  48  may vary from a relatively smaller ridge  48  and shorter contour  50  to a relatively larger ridge  48  and longer contour  50 . 
     The valve body and parts can be made from any of the conventional valve materials, including but not limited to cast iron, brass, stainless steel, other metallic materials, polymers, or composites. 
     The particular combination of elements making up contoured plug valve  10  allow the valve to be constructed relatively compact in size. The actual contoured wall  50  itself can be manufactured using a lathe process or screw machines rather than being machined or cast like tapered V-gaps require. This ease of manufacture makes for a more economical cost efficient manufacturing process, and therefore a less expensive balanced plug valve relative to the aforementioned circular seat balanced plug valve devices. 
     Operationally, contoured wall  50  of the bonnet  14  characterizes the flow of a fluid through valve  10 . In a basic flow pattern, the fluid enters the valve, flows through a first port  56 , passes through plug  24  (while in an open position), and exits the valve through a second port  58 . More particularly, after passing through plug  24 , the fluid passes inbetween the chamfered edge  34  of plug  24 , and contoured wall  50 . The positioning of chamfered edge  34  relative to contour  50  forms a gap  60  through which the fluid must flow. As plug  24  is moved toward bonnet  14  via a force acting on the valve stem  20 , gap  60  becomes narrower and the flow is modulated to a lower rate. As plug  24  continues toward contour  50 , the flow rate gradually drops, until such time as chamfered edge  34  of plug  24  makes sealing contact with close-off seal  42  and blocks fluid flow. In this position (represented by dotted lines in FIG.  1 ), valve  10  is closed and there is a tight shutoff of the fluid flow. 
     The flow rate can likewise be modulated upwards by moving plug  24  toward a fully open position. As plug  24  is lifted off of the close-off seal  42 , the flow rate increases at a rate at least partially dependent upon the shape of contour  50 . As plug  24  continues toward a fully open position, the flow rate will increase until valve  10  is fully open. The flow rate can be modulated at all points along the valve stroke between the fully opened and fully closed positions through adjustments of the position of plug  24 . 
     By altering the curvature and length dimensions of the contoured edge  52 , the dimensions of the gap  60  change. These variations significantly affect the sensitivity and overall ability in controlling the modulation of the flow rate. 
     Take, for example, an embodiment where contour  50  has a relatively large radius of curvature at a location on contour  50  proximal to groove  44  in bonnet  14  which gradually decreases as contour  50  extends toward rim  54  (see FIG.  5 ). Here, plug  24  and valve stem  20  must travel a relatively large distance at the bonnet  14  end of contour  50  to affect the width dimension of gap  60 . Thus, there is a relatively large leeway in the position required of the plug  24  to achieve a requisite gap  60  width and flow rate. A relatively significant portion of the valve stroke may be traveled while the flow rate of the fluid is marginally affected. 
     In an alternative embodiment, contour  50  has a relatively small radius of curvature at a location on contour  50  proximal to groove  44  in bonnet  14  which gradually increases as contour  50  extends toward rim  54  (see FIG.  3 ). Here, plug  24  and valve stem  20  need only travel a relatively small distance at the bonnet  14  end of contour  50  to affect the width dimension of gap  60 . Thus, there is almost no leeway in the position required of plug  24  to achieve a requisite gap  60  width and flow rate. However, valve stem  20  need only be moved a small distance to achieve a desired change in the flow rate. 
     A laboratory test was conducted using a prototype 2-inch balanced plug valve with contoured walls. The contour had a radius of curvature of 0.485 inches. As can be seen in FIG. 11, between approximately 0% and 25% of valve stroke, the flow coefficient (Cv in (gpm)/(sqrt. psi)) increased from 0 to approximately 2.5. This is a slope of approximately 0.1; the slope being a comparative indication of the rate at which the flow rate increases relative to an increase in the gap caused by the actuator moving the plug. This first 25% of valve stroke represents the portion of the curve during which the fluid was flowing around the contoured wall before exiting the port. From approximately 26% valve stroke to 100% valve stroke, the gap provided between the contoured wall and the plug was large enough that the contour had little affect on the flow rate. Between approximately 26% and 68% of valve stroke, the flow coefficient increased from approximately 2.6 to 22. This is a slope of approximately 0.46. The increase in the flow coefficient began to diminish beyond 68% of valve stroke due to other limiting factors such as friction coefficients, shape and size of the ports, and other generally known flow factors not discussed here. 
     The possible applications of contour  50  for use in valves are plentiful. FIGS. 2-10 are various embodiments in which a contoured wall  50  is useful for the control and modulation of flow rates. FIGS. 2-5 are the same valve structure as that of FIG. 1, but with different variations of the shape of the contoured wall  50 . It should be noted that these figures are only representative samples of a few of the multitude of possible contoured wall 50 shapes. A contour shape can have any combination of an infinite number of radii of curvature along a single perimeter edge, which results in the inability to depict herein all possible contoured wall shapes. 
     FIGS. 6 and 8 are external plug configurations. In such embodiments, an interior portion of bonnet  62  is sized to fit within perimeter wall  64  of plug  66 . Plug  66  is chamfered on its internal edge  68  such that it fits snugly around contoured wall  70 . Again, contoured wall  70  can be varied in its shape and size to achieve desired flow characteristics relative to valve stroke. 
     In FIGS. 7 and 8, valve stem  21  is configured such that plug  24  is mounted closer to the internal valve stem end  22  than in valve  10  of FIG.  1 . In addition, valve stem  21  does not slide through bonnets  15  and  63 . 
     FIG. 9 is a 3- way balanced mixing valve  72 . The contoured walls  50  and  51  are similar to those of the valve  10  of FIG. 1, however, there are two contoured walls  50  and  51  due to the additional port  74 . The valve  76  of FIG. 10 is mechanically identical to FIG. 9, but the flow direction is reversed, making valve  76  a diverting valve. 
     There are many advantages associated with the use of balanced plug valves having contoured walls over conventional valves. With regard to flow control, there exists an ability to close and open the valve against virtually any pressure-to-body rating. There is also an increased rangeability for controlling low flows. Physical improvements include no seat damage due to chattering impact at closing; less guide damage and noise due to vibration in the plug guide; long seat life due to reduced erosion; and greatly improved packing life due to reduced stem loads and smooth stem motion. The balanced plug prevents slamming shut of the valve and hammering regardless of flow direction. The actuator for a balanced plug valve with contoured walls can be smaller, lighter and less expensive because the force requirements are less than those of conventional valves. The variation in the contour of the wall provides for customized response and better control of the flow rates. In fact, the contoured wall creates innumerable possibilities for creating different flow characteristics within a given valve body relative to the stroke distance of the plug and the input from the actuator. 
     Certain changes may be made in the above described, without departing from the spirit and scope of the invention herein involved. It is intended that all of the subject matter of the above description or shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein. The description and illustrations shall not be construed as limiting the invention. Rather, it is intended that the invention be limited only to the extent required by the appended claims and the applicable rules of law.

Technology Category: 2