Abstract:
A valve assembly suitable to flowing through the fluid carrying solid particles or liquid drops. A closure element is provided for performing rotational or sliding linear operation in a body housing of the valve having inlet and outlet passageways therein. The initial stroke length of the present invention closure element from fully closed position to the position just permitting the fluid flow is lengthened so that a portion of its upstream surface engaged with the sealing surface of seat ring in fully closed position will not or less suffer the erosion of such erosive fluid during shut off or throttling.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to valves resistant to erosion for the fluid carrying solid particles or liquid drops, and more particularly to a closure element in the valves. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is frequently needed to use a valve assembly to control flow of the fluid in the pipelines which incorporates the solid particles or liquid drops. Upstream surface of the closure element in a prior art valve will be damaged by impingement of such fluid for a short period of time during rotational or linear sliding motion between open and closed positions, so that the closure element loses the sealing capability engaged with upstream seat ring after the valve is closed and the valve begins to leak. And then they will still attack leaking paths formed on the upstream sealing surface of the closure element much stronger in fully closed position and cause them into heavy leaking openings rapidly, the valve has to be removed from the pipelines. 
         [0003]    Valve manufacturers have being devoted themselves to improving surface hardness of the closure element made of metallic materials or employed the closure element made of or coated with high hardness ceramics in the prior art valve, in order to enhance its capacity of erosion resistant. It is effective only that hardened surface hardness of the metallic closure element is higher than the hardness of the solid particles, or disadvantage of micro fracture characteristic occurred easily in the ceramics has to be overcome after they are impacted by the solid particles or liquid drops carried in the fluid. The means improving surface hardness of the closure element will greatly increase material cost, expense of hardening process and processing charge machining hardened surface, and is neither a sole nor an universal choice solving erosion resistant. 
         [0004]    The magnitude of the impact angles included between the particle flow directions in the fluid and the eroded surface of the different places on surface of the valve closure element, is various during a valve opening or closing operation, and different kinds of materials have their own impact angles at which it is high resistance to erosion, so that it is rather difficult to find out a material for the closure element which can resist the erosion at various impact angles simultaneously. 
         [0005]    Additionally, the erosion loss of material is affected by shape, size, hardness and brittleness of the solid particles, as well as velocity and concentration of the particle flow. The solid particle erosion impinged on the surface of materials can be avoided only that the particles are flowing at a very slow velocity, but this way would not be adopted generally, because it will decrease the fluid conveying efficiency. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a longitudinal elevation sectional view of a prior art ball valve in fully open position. 
           [0007]      FIG. 2  is simplified top view of the prior art ball valve in  FIG. 1 , only showing upstream and downstream seat rings, and a ball closure element in fully closed position. 
           [0008]      FIG. 3  is a fragmentary top view similar to  FIG. 2 , and shows an example of the upstream surface of partly opened ball closure element being eroded by the abrasive fluid. 
           [0009]      FIG. 4  is an embodiment of the present invention, only showing simplified fragmentary top view of the relationship between the ball closure element and seat rings in fully closed position. 
           [0010]      FIG. 5  is a longitudinal elevation sectional view of a prior art gate valve in fully closed position. 
           [0011]      FIG. 6  is a simplified fragmentary side view of  FIG. 5 , only showing the relationship among a gate closure element, a seat ring and a stem of the gate valve in fully closed position. 
           [0012]      FIG. 7  is another embodiment of the present invention, only showing simplified fragmentary side view of the gate valve with the gate closure element, a seat ring and a stem in fully closed position. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    Surfaces of the ball closure element both in V-port ball valve and in semi-spherical ball valve have a regular curvature, because they are a segmental spheroid with a V-notch flowway or one portion of an entire spheroid respectively, and additionally, the closure element of a plug valve is a truncated cone or a cylinder and its surface also has a regular curvature. Although all of the closure elements are not an entire spheroid and have not a cylindrical flowway there through, they have a similar sealing principle and configuration to the ball valve, and rotate about an axis of their stems between fully open and fully closed positions; therefore the ball valve will be taken as representative of them. 
         [0014]    The ball valve and gate valve are described and cited in their illustrations respectively hereinafter. 
         [0015]      FIG. 1  is a cross-section in elevation view of a ball valve constructed in accordance with the prior art, which consists of a valve housing  1 , a ball closure element  17 , a stem  19  and two seat rings  14 . The valve housing  1  is formed by the interconnection of a left-hand housing section  2  and a right-hand housing section  3  equipped with flanges  4  and  5  on its external ends respectively, used to be connected with pipelines by plurality of bolts and nuts (not shown) threading through holes  6  and  7  on them, and with other flanges  8  and  9  on its internal ends respectively, between which is disposed a gasket  10  used to effect a seal. One end of stud bolts  11  is screwed into tapped holes in flange  8  on the housing section  2 , and the other end of them extended through registering holes in the flange  9  on the housing section  3 . Nuts  12  are screwed onto the free ends of the stud bolts  11 , make the flanges  8  and  9  join together. The gasket  10  will be compressed, and the flanges  8  and  9  meet together tightly when fastened together by the nuts  12 , thereby two housing sections  2  and  3  form an unitary valve housing  1 . 
         [0016]    A pair of annular seat rings  14  are received within recesses  15  and  16  of the left-hand housing section  2  and the right-hand housing section  3  surrounding passageways  13  respectively, and are defined between the valve housing  1  and the ball closure element  17 , and have the same inner diameter as the port of the passageways  13  of the housing sections  2  or  3  adjacent to it generally. 
         [0017]    The ball closure element  17  is mounted between the two seat rings  14 , and has a cylindrical flowway  18  extending there through which axis passes through the center of the ball closure element  17  and is normal to the axis of the stem  19 . The flowway  18  of the ball closure element  17  is aligned with the passageways  13  of the housing sections  2  and  3 , and permits the fluid to flow through smoothly when the valve  1  is in fully open position as shown in  FIG. 1 . The surface of the ball closure element  17  blocks the passageways  13  completely when the valve  1  is in fully closed position after the stem  19  turns the ball closure element  17  through  90 ° about its longitudinal axis, as shown in  FIG. 2 . 
         [0018]      FIG. 2  is a simplified top view of the ball valve  1  in accordance with the prior art, showing the relationship between the seat rings  14  and the ball closure element  17  in fully closed position. The flowway position of the ball closure element  17  is plotted in full lines  18 b, the flowway position in fully open position in dashed line  18 a is imaginary. The points A and B are intersections intersected by the surface of the ball closure element  17  between the flowway  18 b and  18 a with the plane through the center ◯ of the ball closure element  17  and perpendicular to the axis of the stem  19  (not shown). The angle included between two radiuses linked the center ◯ of the ball closure element  17  and the points A and B respectively is an initial angle α of the ball closure element  17 . The circular arc length  20  between the points A and B facing the angle a is an initial stroke length of it, and is also the narrowest length in the common surface between two passageways  18   b  and  18   a , which is equal to the sealing surface radial width  21  of the seat ring  14 . Magnitude of the diameter of a ball closure element is only related to the radial width of the sealing surface of the seat ring, namely its initial stroke length or to the initial angle facing it after determined the inner diameter of the flowway of the ball closure element (same as the passageways specified in the standards issued by various standard organizations in the world). 
         [0019]    An imaginary annular spherical surface surrounding the flowway  18   a  plotted in dotted line, which inner diameter is the same as the upstream seat ring  14 , the radial width is equal to the initial stroke length  20  and center of the circle is the point P intersected by the axis  30  of flowway  18   a  and the upstream surface  22  of the ball closure element  17  in fully closed position, could be constructed on the upstream surface  22  of the ball closure element  17 . This annular spherical surface is the sealing surface of the ball closure element  17  engaged with the sealing surface  21  of the upstream seat ring  14  in fully closed position. The point B is located at periphery of the imaginary annular spherical surface. 
         [0020]    A lot of tests demonstrated that the needed radial width of the sealing surface of a seat ring depends on leakage classes of a valve, the maximum pressure differential across the valve when it is closed, fluid categories and nature, material of the sealing surface and the coefficients related to the material of the sealing surface. The annular spherical surface of the ball closure element and the sealing surface of the seat ring are a pair of matched sealing surfaces, so the radial width of the annular spherical surface has to be equal to, or just a bit longer than the one of the sealing surface of the seat ring after the radial width of the sealing surface of the seat ring has been determined according to the prior art mentioned above, in order to ensure that an effective sealing between the ball closure element and the seat ring can be achieved. That is to say, the initial stroke length of the ball closure element is the same as the radial width of the seat ring at least. 
         [0021]    The initial stroke length of a ball closure element relates to its diameter closely, overlong initial stroke length will not only lengthen the diameter of a ball closure element unduly, and cause cost of production to be raised further, but also increase the actuated torque of the valve, therefore the valve manufacturers always select a diameter for a ball closure element having an initial stroke length just equal to the radial width of sealing surface of the seat ring in fact for meeting the sealing requirement of the valve in a prior art. 
         [0022]    The points A and C are two intersections intersected by the flowway  18   a , the upstream surface  22  of the ball closure element  17  and the plane through the center ◯ of the ball closure element  17  and normal to the axis of the stem  19  (not shown). The angle included between two radiuses linked such two points and the center ◯ of the ball closure element  17  respectively, is the flowway angle β of the ball closure element  17 . The circular arc length between the points A and C facing the flowway angle β is a flowway stroke length of the ball closure element opposite to the inner port diameter of the passageways  13 . 
         [0023]    As shown in  FIG.3 , disengaged with the sealing surface of the seat ring  14 , the point B on the periphery has entered into the passageway  13 , and the flowway  18  of the ball closure element  17  starts to communicate with the passageways  13  in the housing sections  2  and  3  allowing the fluid to flow through valve opening after the ball closure element  17  has been turned through the initial angle a or the initial stroke length  20  from fully closed position actuated by the stem  19  counterclockwise. The diameter of the prior art ball closure element is calculated on the base of the radial width of the seat ring sealing surface, its initial stroke length is much shorter than the flowway stroke length. 
         [0024]    The point B, which is in the position disengaged with the seat ring finally when opening the valve or the position blocking the passageway at last when closing the valve on the surface of the ball closure element, on the periphery of the annular spherical surface is beside the opening of the ball valve. The area around the point B is exposed to the fluid flowing in upstream passageway for the longest time and eroded at the highest velocity relatively during opening or closing operation. A velocity of the fluid flowing across the point A on the inside edge of the annular spherical surface is higher and time is longer too as it is near the point B for reasons of the narrow initial stroke length. On the other hand, a velocity flowing across the area away from the point B will be much lower, and the time also much shorter than the point B. Whenever the fluid carries the solid particles or liquid drops, the annular spherical surface around the point B will be eroded the most severely because of the highest velocity and the longest time. The damaged annular spherical surface keeps effective engaging with the sealing surface of the seat ring no longer and the valve becomes a much more severe leakage after staying in fully closed position for a short time. 
         [0025]      FIG. 4  is an embodiment of the present invention which only illustrates the relationship between the ball closure element  17  and the seat rings  14  in a ball valve. The diameter of the ball closure element  17  has been lengthened, therefore the initial stroke length between the points A and B has been become longer in comparison with the prior art ball valve. One portion of the initial angle a facing the lengthened initial stroke is an angle γ which faces the sealing surface radial width  21  of the seat ring  14 , and the remainder of the lengthened initial angle a is a differential angle θ between the angles α and γ. Accordingly, the length of the lengthened initial stroke between the points A and B could be imaginarily divided in two portions. The interior annular spherical surface constructed by taking the point P intersected between the axis  30  of the passageway  13  and the upstream surface  22  in fully closed position as the center ◯ of the annulus, the inner  25  bore diameter of the seat ring  14  as its inner diameter and the circular arc length between the points A and D facing the angle γ as a radial width, is the sealing surface in the upstream surface  22  of the ball closure element engaged with the sealing surface  21  of the seat ring  14  when the valve is in fully closed position. The exterior annular spherical surface constructed by taking the circular arc length between the points D and B facing the angle θ as a radial width is nested outside the former concentrically, so the interior annular spherical surface is spaced out with the opening by the exterior annular spherical surface and away from the point B. 
         [0026]    The point B enters into the passageway  13  and the fluid starts to flow through the valve after the ball closure element  17  is turned through the initial stroke length from fully closed position counterclockwise. Provided  1 o that the angle θ is smaller than the angle β, some area of not only the exterior but the interior annular spherical surface is exposed to the fluid flowing in the upstream passageway  13 , both of the annular spherical surfaces will be eroded severely whenever the fluid carries the solid particles or liquid drops. Differing from the prior art valve, the area around the point B eroded the easiest has not been on the outside edge of the interior annular spherical surface engaged with the sealing surface of seat ring  14  in fully closed position now, but on the periphery of the exterior annular spherical surface not engaged with the sealing surface of seat ring  14  in fully closed position, as a result, the exterior annular spherical surface bears the most severe erosion that should be borne by the interior annular spherical surface, and protects the interior one from much erosion, and it causes the eroded area, time and velocity for the interior annular spherical surface exposed to the fluid flowing in the upstream passageway  13  to be less and slower than the prior art ball valve. The bigger the θ is, the shorter the time is, the less the area is, the slower the velocity that the fluid flows across the area is, so the less the suffered erosion is. Provided that the angle θ is equal to or larger than the angle β, only some area on the exterior annular spherical surface exposed to the upstream passageway  13  will be eroded by the flowing fluid now, any area on the interior annular spherical surface relating to angle γ just leaves or has been moved out of the passageway  13  and would not be eroded. Consequentially the time, area and velocity eroded by the flowing fluid on the interior annular spherical surface depend on the length of the lengthened initial stroke mainly. 
         [0027]    In reverse, when the ball closure element  17  starts to be turned from fully open position toward closed direction clockwise, and the area around the point B on the exterior annular spherical surface enters into the valve lo upstream passageway  13  firstly and is eroded by the flowing fluid immediately. 
         [0028]    Provided that the angle θ is larger than or equal to the angle β, any area on the inner annular spherical surface has not entered into the passageway  13  yet or just wants to do it when the upstream surface  22  of the ball closure element  17  is rotated to the position where the point B touches the sealing surface  21  of the seat ring  14  and the flow starts to be blocked, so the erosion of the inner annular spherical surface would not take place. During the period of time to keep rotating the ball closure element  17  until it arrives in fully closed position, the inner annular spherical surface entered into the upstream passageway  13  would not be also eroded naturally because the fluid has been blocked by the exterior annular spherical surface and cannot flow. 
         [0029]    Provided that the angle θ is smaller than the angle β, some area on the interior annular spherical surface also enters into the passageway  13  following the exterior annular spherical surface and is eroded by the flowing fluid before the point B touches the seat ring  14  and the passageway  13  has been blocked, but the position eroded firstly and severely is still the area around the point B on the exterior annular spherical surface, so that the interior annular spherical surface gets protected by the exterior annular spherical surface to some extent, and it causes the eroded time, area and velocity for the interior annular spherical surface exposed to the fluid flowing in the upstream passageway  13  to be less than the prior art ball valve, until the upstream passageway  13  is blocked by the upstream surface  22  of the ball closure element  17  completely. The factors affecting the extent of the erosion of the interior spherical surface are the same as the description of opening the valve above, and also depend on the magnitude of the angle θ lo or the initial stroke length. 
         [0030]    The inner annular spherical surface entered into the passageway  13  would not be eroded yet even through the area around the point B on the exterior annular spherical surface has been damaged somewhat and cannot engage with the sealing surface of the seat ring perfectly after many times of opening and closing operation. The slight leakage between them only lasts a short period of time in which the damaged exterior annular spherical surface is brought into touch with the sealing surface of the seat ring  14 , and the velocity of the fluid leaking across the leakage paths is slow, therefore it is not enough to constitute an erosive threat to any area on the interior spherical surface which has entered into the upstream passageway  13 . The reason is that the velocity flowing across any area on the inner annular spherical surface should be much lower than the area around point B as it is at a distance from the damaged surface on the exterior annular spherical surface, 
         [0031]    The position eroded the most severely on the upstream surface  22  of the ball closure element  17  is the area around point B on the periphery of the exterior annular spherical surface, and a degree of the erosion tapers off from the point B on the exterior annular spherical surface towards the interior annular spherical surface along the upstream surface  22  of the ball closure element  17 . Therefore the longer the diameter of a ball closure element is, the longer its initial stroke length is, and the longer the circular arc length facing the angle θ in the initial stroke length is also, the better the interior annular spherical surface will get protected by the exterior annular spherical surface, and the ball closure element becomes much erosion resistant. 
         [0032]      FIG. 5  is an elevation cross-sectional view of a prior art gate valve without guiding port (Gate valves with guiding port have the same principle) in fully closed position, which consists of a valve housing  27 , a stem  28  (not shown), a gate closure element  26  and two annular seat rings  23 , etc. The valve housing  27  includes two cylindrical passageways  24  in generally, and a chamber between the passageways  24  in which is disposed a gate closure element  26  for controlling flow of the fluid. The gate closure element  26  is reciprocated within the valve chamber by means of the valve stem  28  and a suitable operator mechanism, not shown. A pair of annular seat rings  23  is received within appropriate annular recesses  29  in the passageways  24  by two sides of the gate closure element  26  respectively. 
         [0033]    A planar radial end face of the annular seat rings  23  establishes sliding engagement with the planar sealing surface of the gate closure element  26 . The other rear radial end face is abutted on a shoulder  30  in the annular recesses  29 . The valve housing  27  is provided with either wafer or flanges at each end thereof as traditional ways for connected to a pipeline. 
         [0034]    A length at the bottom of the upstream surface of the gate closure element  26  from the end edge  25  along the axis of the stem  28  upwards, which is equal to the radial width of the sealing surface of the seat ring  23  normally, is an initial stroke length of the gate closure element  26 . Another length being equal to the inner bore diameter of the seat ring  23  on the initial stroke length along the axis of the stem  28  upwards is a flowway stroke length of the gate closure element  26 . A length of gate closure element  26  of the prior art gate valve along the axis of the stem  28  is equal to or a little longer than the sum of the radial width of the sealing surface of the seat ring  23  and the inner diameter of the seat ring  23 , excluding the length for connecting the stem  28  with the gate closure element  26 , after the inner diameter of the passageway  24  has been determined as the description of the ball valve in  FIG. 2  above. 
         [0035]    For the same reason as the ball valve described above, an overlong gate closure element can also increase a weight and production cost of the valve, thereby the length of a gate closure element of a prior art gate valve along the axis of a stem is exactly the sum of the radial width of the sealing surface and the inner diameter of the seat ring. 
         [0036]      FIG. 6  is a simplified side cross-sectional view of a prior art gate valve without guiding port, which only illustrates a stem  28 , a seat ring  23  and a gate closure element  26  in fully closed position. The diameter of the inner bore of the seat ring  23  surrounding a passageway  24  and disposed in an annular recess of a valve housing  27  (not shown) is the same one as the port of the passageways  24  adjacent to it generally. The gate closure element  26  has completely blocked the passageway  24 . The length of the gate closure element has been designed to be as short as possible in the prior art gate valve as well, so that an initial stroke length h of a gate closure element is much shorter than a flowway stroke length DN of the gate valve. The fluid starts flowing through the valve after the middle point B of the end edge  25  of the gate closure element  26  has slid across an initial stroke length equal to the radial width b of the sealing surface of the seat ring  23  and enters into the passageway  24  surrounded by the seat ring  23  when the gate closure element  26  is pulled upwards by the stem  28 , and all the upstream area of the gate closure element  26  exposed to the passageway  24  will be eroded by the flowing fluid to different extent until the middle point B has slid across the flowway stroke DN again and reached the fully open position at last, and in which the area around the middle point B of the end edge  25  will be eroded the longest and the most severely. 
         [0037]    It has the same situation during closing the valve also. The area around the middle point B of the end edge  25  starts to be eroded by the flowing fluid as long as it enters into the passageway  24 . The area exposed to the passageway  24  gets larger and larger with the valve being closed further, all of the area will be eroded, but the area around the middle point B will be eroded the longest and the velocity of the fluid flowing there through is the highest, so that it suffers the most severe erosion. The fluid stops flowing and the erosion ends after the middle point B of the end edge  25  has slid across the flowway stroke DN and touches the sealing surface of the seat ring  23 . The valve arrives in fully closed position after the gate closure element  26  is pushed downwards further and has slid across an initial stroke h (being equal to the radial width b of sealing surface of the seat ring  23 ) again. 
         [0038]    The upstream sealing surface around the middle point B of the end edge  25  of the gate closure element  26  has been severely eroded by the solid particles or the liquid drops incorporated in the fluid repeatedly after many cycles of operating the valve, and the length of its sealing surface engaged with the seat ring  23  has been shortened, the sealing capability between them fails in fully closed position, the valve starts leaking uninterruptedly. The solid particles or the liquid drops will attack and expand the leakage paths rapidly within a relatively short period of time when the gate closure element stays in fully closed position, and cause the valve to be damaged severely. 
         [0039]      FIG. 7  is a simplified view of another embodiment of the present invention applied to gate valves without guiding port (Gate valves with guiding port have the same principle); it has the same principle as the ball valve described above. The initial stroke length H of the improved gate closure element  26   a  has been lengthened compared with the initial stroke length h of the prior art gate valve, and is still located at the bottom of its upstream sealing surface from the end edge  25  upwards along the axis of the stem  28 . The rectangular area formed by taking the initial stroke length H as a width and the width of the gate closure element  26   a  as a length, could be divided into two imaginary upper and lower portions which boundary between them is normal to the axis of the stem  28 , in which the surface of rectangular area of the lower portion close to the end edge  25  is used for bearing erosion during opening or closing operation, its width is expressed as a letter L; and the upper portion on it, which width of the rectangular area is b, is the area engaged with a part of the sealing surface of the seat ring  23  in fully closed position of the valve. 
         [0040]    The longer the initial stroke length H of the gate closure element  26   a  is lengthened after determined the size of the valve, the wider the width of rectangular area of the lower portion is, the better the surface of the rectangular area of the upper portion engaged with the sealing surface of the seat ring in fully closed position will be protected, so that the gate closure element  26   a  can get longer life. 
         [0041]    The middle point B of end edge  25  in lower portion of the lengthened gate closure element  26   a  starts to be disengaged with the sealing surface of the seat ring  23  and the fluid flows through the passageway  24 , as long as that it enters into the passageway  24  during opening the valve (lifting the stem  28  upwards). The upper and lower portions are both eroded by the fluid, provided that the width L of the rectangular area of the lower portion is shorter than the flowway stroke DN of the valve (being equal to the inner bore diameter of the seat ring  23 ) during operating the valve, but the lower portion shall be eroded more severely than the upper portion because it is near the point B, so the upper portion can be protected by the lower portion in part. The upper portion is protected by the lower portion completely and will not be eroded by the fluid at all, provided that the width L of the rectangular area of the lower portion is equal or longer than the flowway stroke length DN. The reason is that any area of the upper portion has left or just wants to leave the passageway  24  when the middle point B of end edge  25  enters into the passageway  24 . 
         [0042]    The principle of closing operation related to the gate closure element of the present invention will not be described, since it is the reverse of the opening valve described above and similar to the description for the ball valve too. 
         [0043]    Although the present invention was described in terms of specific embodiments, it is obvious to a person skilled in the art that various alterations and additions are possible without departing from the spirit of the invention which is set out in the appended claims, therefore the extent disclosed in the embodiments above is only for purpose of illustration and not intended to be limited by this description. The art of the present invention valve closure elements are also applicable to full bore ball valve, reduced bore ball valve, V-port ball valve, semi-spherical ball valve, floating ball valve, trunnion ball valve, plug valve, parallel-slide gate valve, knife gate valve and sliding gate valve, etc.