Abstract:
A balanced plug valve having substantially reduced shut-off force requirements due to an integral dual seating arrangement of the valve plug within a valve housing having slanted inlet and outlet ports and wherein the inlet port forms an elliptical opening for fluid control which is selectively exposed by a cylindrical portion of a sliding valve plug.

Description:
TECHNICAL FIELD  
       [0001]     The control valve described herein makes known an apparatus enabling the control of high-pressure fluids without the requirements of excessive actuator forces, by providing a low cost balanced plug and without resorting to expensive and more difficult cages and seat rings.  
       BACKGROUND  
       [0002]     Control valves are commonly used to control the fluid passing through a pipe. As known to those skilled in the art, a control valve regulates the rate of fluid flow as the position of the valve plug is changed by an actuator. There are three important features of a control valve, such as a globe valve, that it must contain the fluid without external leakage, that it must be able to withstand the pressure and temperature of the fluid, and that the fluid forces acting on the plug should not cause instability nor prevent the plug from shutting the valve off.  
         [0003]     Quite often control valves have to perform under elevated pressure and temperature conditions. While valves with a single seat shut-off configuration and an un-balanced plug provide good service in these applications, they do require substantial forces that have to be provided by an actuator in order to overcome the effects of high fluid pressure acting on such un-balanced plug surfaces. For example, a one inch valve plug needs more than 800 lbs force to close against 1000 psi fluid pressure.  
         [0004]     Such actuator force requirements can be quite expensive and such valves face other problems such as stability of operation. A typical example of such a single seated valve is shown in U.S. Pat. No. 4,474,356.  
         [0005]     One typical way of alleviating these problems in prior art is the use of a cage with dual seating surfaces for the plug. My prior inventions, shown in U.S. Pat. Nos. 6,536,472 B2 and 3,805,839, describe such a solution. While capable of performing the required tasks, this is a very expensive solution due to the extra, precision machined, parts and due to the extra heavy bonnet bolting that is required to lock the cage within the valve housing. Finally, these valves have an additional problem of absorbing thermal expansion of the cage, especially if cage and housing have to be made of different materials.  
       SUMMARY  
       [0006]     The object of my invention is a control valve assembly of low cost and compact configuration, requiring neither cage nor seat rings  
         [0007]     A further object is to provide for substantial balancing of fluid pressure acting on the valve plug thereby eliminating the need for larger and expensive actuating devices. Yet another object of my invention is to provide a control valve with parts that can be made from similar materials and, utilizing the use of one flexible valve seat, can overcome the adverse effects of thermal expansion on the sealing capabilities of the valve plug.  
         [0008]     In accordance with another aspect of my invention, a gradual enlarging flow passage provides a desired flow characteristic by utilizing the elliptical opening of a slanted inlet port co-operating with a cylindrical portion of the valve plug.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a central, cross-sectional view of a preferred embodiment of my invention.  
         [0010]      FIG. 2  is a cross-sectional side view of the invention depicted in figure one and taken along the lines  2 - 2 .  
         [0011]      FIG. 3  is a central, cross-sectional view illustrating a flexible upper seating arrangement, and where the valve plug incorporates a lower, contoured portion.  
         [0012]      FIG. 4  is an enlarged, partial, cross-sectional view of the elastic seating arrangement. 
     
    
     DETAILED DESCRIPTION  
       [0013]     Referring to  FIG. 1 , my balanced plug valve comprises a housing  5  preferably made from stainless steel, and having a central bore  6 , a slanted inlet port  7 , and a slanted outlet port  8 . Both ports intersect said central bore  6 . The angle of the slant is dependent on the size of the housing and its width. Typical slant angles α are 30 degrees to 50 degrees. Housing  5  is configured to fit between a pair of pipeline flanges. Suitable indentations  9  are provided to accommodate bolts required to clamp the housing  5  between said flanges. A bonnet is threaded into the upper portion  11  of housing  5 . Said bonnet furthermore has a lower, flattened surface  12  engaging a similar configured portion within the housing and retained there between a suitable gasket  13 .  
         [0014]     Bonnet  10  features a hollow indenture  14  and an adjustable packing box  15 .  
         [0015]     Central bore  6  has a number of steeped diameter portions  16 ,  17 , and  18  respectively and wherein the intersection between diameter  17  and  18  constitutes a lower seating surface  17   a  straddling the inlet port  7  and the outlet port  8 .  
         [0016]     A slide able valve plug  19  made from a hard stainless steel, or, having a chrome plated surface, and having a larger diameter portion  20 , engaging indentation  14  and diameter portion  16 . Said plug  19  furthermore has a lower, reduced diameter  21  closely fitting within diameter portions  17 , and having a beveled portion  22  capable of sealingly engaging the seating surface  17   a . The plug furthermore has a central bore  23 , an upper threaded bore  24 , and a fluid conducting opening  25 . The intersection  20   a  between diameters  20  and  21  likewise is beveled and sealingly engages the corner of diameter portions  14  and  16  when the plug is in its lowest sliding position.  
         [0017]     A valve stem  26  whose lower end is fastened to the threaded portion  24  of plug  19  while the upper end is able to attach to an actuating device (not part of the invention) after passing through packing box  15 .  
         [0018]     Finally, there is an enlarged fluid collecting void  27  commencing at a distance of about one-third the diameter of inlet port  7  along diameter portion  17  and extending from there to a point of intersection with the upper surface of inlet port  7 .  
         [0019]     As can be seen in  FIG. 2 , the terminating opening  28  of inlet port  7  has the general shape of an ellipse which is partially uncovered by the cylindrical diameter  21  of plug  19  when in the highest sliding position, as shown in  FIG. 2 .  
         [0020]      FIG. 3  represents a modified version of my invention wherein gasket  13  is replaced by a flat metal washer  29 , preferably made from hardened stainless steel or of a high nickel alloy. This washer has a reduced diameter which is only slightly larger than diameter portion  17  and which is able to contact intersection  20   a  when the plug  19  is in the lowest position. Notice that the inner circumference of washer  29  is able to deflect somewhat after contact by intersection  20   a . This will enable washer  29  to absorb a sudden differential expansion of plug  19  following the admission of hot fluid in to my valve. The plug configuration shown in  FIG. 3  furthermore has a lower, terminating profiled portion  30  closely engaging diameter portion  18  of housing  5 . This configuration is advantageous when a different flowing area characteristic is desired than the one provided by area  28 .  
         [0021]     The functioning of my valve is as follows: Fluid coming from a piping system enters port  7  and from there flows into void  27 . Further fluid flow is prevented when the plug  19  is in the lowest sliding position by sealing contact surfaces at  17   a  and  26 . Note, that hydrostatic forces generated by the fluid are minimized since only the area between diameter  20  and  21  are subjected to pressure. These generated minor forces are directed towards opening of the plug, therefore contributing to the dynamic stability of the plug. However fluid flow will commence once plug  19  will begin to lift off the seats. Here fluid flow will commence very gradually, since only a small portion  28   a  of inlet port  7  becomes exposed. The width and therefore the flow area of  28   a  becomes progressively larger with increased plug travel till finally the lower seating surface of plug  19  disengages from diameter portion  17  and therefore adds an additional flow area  31  allowing additional fluid to pass from void  27  into diameter portion  18  and from there into outlet port  8 . This gradual opening of the flow areas with plug travel is highly desirable for automatic control purposes. However, the additional contour portion  30  may be employed if a special characteristic is desired.  
         [0022]     Fluid is able to communicated freely between lower diameter portion  18  and area  14  once the plug is unseated in order to maintain the nearly complete balance of fluid forces acting on plug  19 .  
         [0023]     While the invention has been explained in preferred configurations, the description is not intended to be construed in a limiting sense. Various modifications and combinations will be apparent to those skilled in the art. For example, the bonnet may be attached by suitable bolting instead of being threaded. Also, it is foreseen that the housing may incorporate flanges able to connect to similar flanges of a piping system. It is also foreseen that the inlet and outlet ports may be threaded in order to connect to the piping and that the direction of flow might be reversed from that shown.  
         [0024]     Finally, the stem seal may be in form of a bellows instead of a packing box.