Abstract:
A gate valve seal for a gate valve including a body having an inlet aperture and an outlet aperture, and a gate closure reciprocally disposed within the body between a closed valve position where the gate closure blocks the apertures and an open valve position where the gate closure does not block the apertures. The seal includes a first resilient seat for placement in the inlet aperture of the gate valve body and a second resilient seat for placement in the outlet aperture of the gate valve body. The seats sealingly engage one another and the gate closure when the closure cycles between the valve positions. Each of the seats includes an inner diametrical surface which generates sealing pressure that increases as internal pipeline pressure increases.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to slurry valves, and in particular, to a knife-gate valve designed especially for handling abrasive, high-density slurries, the valve having a seal configuration that utilizes the fluid pressure in the pipeline to energize resilient seats contained therein.  
         BACKGROUND OF THE INVENTION  
         [0002]    Valves designed especially for abrasive, high-density slurry service must be resistant to the abrasive wear of the slurry and have a minimum number of cavities, which can collect solids and cause jamming of the closure member. Single seated knife-gate valves have been used for slurry service for many years but are subject to wear and jamming unless equipped with special seats and flushing systems.  
           [0003]    Dual, rubber seated knife-gate valves have evolved as an effective, alternative means for minimizing wear and jamming effects. The basic structure of such a valve is described in U.S. Pat. No. 5,464,035. The dual, rubber seats provide a wear resistant valve body liner, tight shutoff, and a minimal number of cavities for solids buildup. In this design, the gate closure is retracted from the slurry flow stream when the valve is open, resulting in no wear on the gate when the valve is open. To close the valve, the gate closure is pushed between the rubber seats, separating and compressing the rubber, until the gate closure extends through the portway and stops the flow of the slurry. The gate closure is retracted when the valve is to be opened.  
           [0004]    Although dual, rubber seated knife-gate valves have good wear characteristics and resistance to jamming, the inherent leakage rates during the valve&#39;s opening and closing cycle are a problem in many applications. More specifically, the shape of the leading edge of the gate closure, the configuration of the seats, and the properties of the material used for the seats (typically rubber) effect how much fluid leaks when the gate closure pushes through and separates the seats as the gate closure closes the valve, when the gate closure pulls away from between the seats as the gate closure opens the valve, and when the gate closure fully withdraws from between the seats as the gate closure fully opens the valve. Current designs rely, in a large measure, on the memory and recovery rate properties of the seat rubber to cause the seat to decompress and reseat and seal against the gate closure as the gate closure is retracted. Unfortunately, reseating is typically delayed thereby resulting in leakage.  
           [0005]    Therefore, an improved knife-gate valve seal configuration which reduces leakage during cycling is needed.  
         SUMMARY OF THE INVENTION  
         [0006]    A gate valve seal for a gate valve including a body having an inlet aperture and an outlet aperture, and a gate closure reciprocally disposed within the body between a closed valve position where the gate closure blocks the apertures and an open valve position where the gate closure does not block the apertures. The seal comprises a first resilient seat for placement in the inlet aperture of the gate valve body and a second resilient seat for placement in the outlet aperture of the gate valve body. The seats sealingly engage one another and the gate closure when the closure cycles between the valve positions. Each of the seats includes an inner diametrical surface which generates sealing pressure that increases as internal pipeline pressure increases.  
           [0007]    In another aspect of the present invention, a gate valve assembly comprises a body having an inlet aperture and an outlet aperture; resilient seats disposed in the apertures; and a gate closure reciprocally disposed within the body between a closed valve position where the gate closure blocks the apertures and an open valve position where the gate closure does not block the apertures. The seats sealingly engage one another and the gate closure when the closure cycles between the valve positions. Each of the seats includes an inner diametrical surface which generates sealing pressure that increases as internal pipeline pressure increases. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The advantages, nature, and various additional features of the invention will appear more fully upon consideration of the illustrative embodiments now to be described in detail in connection with accompanying drawings wherein:  
         [0009]    [0009]FIG. 1 is a perspective view of a gate valve assembly according to an exemplary embodiment of the present invention;  
         [0010]    [0010]FIG. 2 is a perspective view of an exemplary embodiment of a seat made according to the principles of the present invention;  
         [0011]    [0011]FIG. 3 is a cross-sectional view through the seat of the present invention in an uncompressed state;  
         [0012]    [0012]FIG. 4A is a perspective cross-sectional view through the gate valve assembly of FIG. 1 showing the gate closure fully retracted from between the seats in the fully opened valve position;  
         [0013]    [0013]FIG. 4B is a perspective cross-sectional view through the gate valve assembly of FIG. 1 showing the gate closure in midstroke of an opening or closing cycle;  
         [0014]    [0014]FIG. 4C is an enlarged perspective cross-sectional view through the gate valve assembly of FIG. 4B showing the relationship between gate closure and the seats; and  
         [0015]    [0015]FIG. 4D is a perspective cross-sectional view through the gate valve assembly of FIG. 1 showing the gate closure between the seats and completely separating them in the fully closed valve position. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    Referring to FIG. 1, there is shown an exemplary knife-gate valve assembly made according to the principles of the present invention. The valve assembly  20  includes an open bottom or closed bottom body  22  (open bottom body is depicted in FIG. 1) having a front wall  24 , a rear wall  26 , a first side wall  28 , and a second side wall  30 . The walls  24 ,  26 ,  28 ,  30  cooperate to define therewithin a chamber (not visible). The first side wall  28  has a first aperture  32  formed therein and the second side wall  30  has a second aperture  34  formed therein, the apertures  32 ,  34  defining a portway  35 . A gate valve seal formed by a pair of annular, resilient seats  36  are disposed in the first and second apertures  32 ,  34 . The seats  36  may be composed of any material having adequate strength and resilience, such as rubber or plastic. Pipeline bolting flanges  40  (only one of which is shown) rim the first and second apertures  32 ,  34 .  
         [0017]    A sliding gate closure  44  is reciprocably disposed in the chamber for opening and closing the portway  35  defined by the apertures  32 ,  34 . An operator  46 , such as a handwheel, effects translation of the gate closure  44  via a threaded rod  48  and yoke  50 . The gate closure  44  may also be translated via a fluid actuator and linkage arrangement (not shown).  
         [0018]    In operation, the valve assembly  20  is typically bolted between two pipeline mating flanges (not shown). The resilient seats  36  are held in the body  22  and the apertures  32 ,  34  by the mating flanges, and are compressed against the gate closure  44  and mating flanges to effect a seal at both locations. When the valve assembly  20  is fully opened such that the portway  35  is no longer occluded and the gate closure  44  is fully withdrawn from between the seats  36  (FIG. 4A), the flanges compress the seats  36  against one another thereby providing a seal against internal pipeline pressure. One of ordinary skill in the art should recognize that when the valve is in the “fully opened” position the gate closure  44  may not be fully withdrawn from between seats  36 . In particular, the leading edge of the gate closure  44  may remain between the upper portions of the seats  36  but not within the portway  35  in the fully opened valve position.  
         [0019]    To close the valve assembly  20 , the handwheel operator  46  pushes the gate closure  44  into and through the seats  36 , separating the seats  36  but effecting a seal against the gate closure surface  45 . To open the valve, the handwheel operator  46  pulls the closure gate  44  back through the seats  36  until it is retracted from the portway  35 .  
         [0020]    The gate valve seal configuration formed by the resilient seats  36  of the present invention achieves a reduction in leakage during cycling because the seats  36  are configured to be energized by fluid pressure in an associated pipeline, thereby overcoming the memory and recovery problems inherent in the resilient material used for the seats  36 . More specifically, the seats  36  are configured so that internal pipeline pressure pushes them against the gate  44 , thereby overcoming any memory loss inherent in the composition of the seats  36  caused by the seats  36  being compressed and strained.  
         [0021]    [0021]FIGS. 2 and 3 show in detail an exemplary embodiment of one of the annular resilient seats  36  made according to the principles of the present invention. The seat  36  includes an outer diametrical aperture seating surface  52 , an inner diametrical surface  54  with a concave segment or chord  56  disposed opposite the aperture seating surface  52 , a flange engagement surface  58 , and an inclined gate engagement surface  60  disposed opposite the flange engagement surface  58 . A seal nose  64  is defined at the junction of the inclined gate engagement surface  60  and the concave segment or chord  56  (or inner diametrical surface  54 ). The seal nose  64  extends beyond the inclined gate engagement surface  60 . The seat  36  is reinforced by a stiffener ring  62  molded therein in the upper and outer quadrant of the seat  36 . The stiffener ring  62  may be made of metal or plastic and configured to prevent collapse of the seat  36  due to gate closure forces, or extrusion of the seat due to pipeline pressure.  
         [0022]    As shown in FIG. 3, the seat  36  has a height h, a width w, a chord radius cr, a chord length cl, a chord undercut d, a seal nose radius nr, and a relief angle a. These dimensions are interrelated to effect an optimized seal. For example, in a preferred embodiment, the length of the chord cl may be 72% +/−15% of the height h. The depth of the chord undercut d may be 0.115 inches +/−0.030. The radius of the chord cr may be 100% +/−50% of the height h. The seal nose radius nr may be 20% +/−5% of the seal width w. The relief angle a may be 65 degrees +/−15 degrees.  
         [0023]    [0023]FIG. 4A shows the seats  36  with gate  44  fully retracted from between the seats  36  such that the valve is fully opened. As can be seen, the opposing seal nose sealing surfaces  64  of the seats  36  sealingly contact each other. FIGS. 4B and 4C show the seats  36  when the gate  44  is in the midstroke of the opening or closing cycle. In the midstroke position, the opposing seal nose sealing surfaces  64  of the seats  36  not separated by the gate closure  44  remain in sealing contact with each other, and in the transition area  65  (where the leading edge of the gate closure  44  separates the seats  36  as seen in FIG. 4C), the seal nose sealing surfaces  64  of the seats  36  sealingly contact the gate closure  44 . Note that the transition area  65  at the leading edge of the gate  44  is the area where more leakage typically occurs when conventional seats are employed. FIG. 4D shows the seats  36  when the gate closure  44  is closed and the opposing seal nose sealing surfaces  64  are compressed and in contact with the gate closure  44 .  
         [0024]    The shape of the concave segment or chord  56  of the seat  36  allows internal pipeline pressure to push the seal nose sealing surfaces  64  of the seats  36  against each other in the open position, and against the gate closure  44  in the transition and closed position, providing a tighter and faster responding seal. The concave segment or chord  56  of the seat  36  also reduces the stress and strain, extending the seat life, by allowing the seat  36  to bend rather than being put under the direct compression initiated by the gate cycling to the closed position or internal pipeline pressure pushing the gate closure  44  into the seat  36 . The resulting hydrostatic force acting on the resilient seal nose sealing surface  64  overcomes the relatively slow rate of recovery of the material, which occurs as the gate closure  44  is retracted and the compressed resilient seat  36  is relaxed and must quickly seal against the mating seat  36  to prevent external leakage. There is also another beneficial effect in that there is an increase in sealing pressure as pipeline pressure increases, making it a pressure compensating seal.  
         [0025]    The valve assembly  20  of the present invention is applicable to any fluids piping system that will allow some external leakage when the valve is cycled open or closed, but requires tight shutoff in the closed position, and an unobstructed portway in the open position. The valve assembly  20  is also useful in applications that contain fluid slurries and where a valve configuration is required that has a minimal number of internal pockets for solids to settle or collect.  
         [0026]    Typical applications may include mining and power industries. In particular, the valve assembly  20  of the present invention is suitable for those mining and power industry applications that have high slurry densities or slurry properties resulting in problems with other valve configurations.  
         [0027]    While the foregoing invention has been described with reference to the above embodiments, various modifications and changes can be made without departing from the spirit of the invention. Accordingly, all such modifications and changes are considered to be within the scope of the appended claims.