Abstract:
A method and apparatus for controlling fluid flow with a quarter-turn ball valve with seats operated to lift off the sealing surface of the ball valve prior to ball rotation and to reseat upon completion of the ball rotation. One embodiment shown relates to a quarter-turn ball valve having a rotatable cam with an eccentric camming disk that engages a cam pocket in the ball seats to reciprocally lift off the sealing surface of the ball valve prior to ball rotation and to reseat upon completion of the ball rotation. An embodiment is also shown that provides filler pieces that restrict that flow around the ball valve whenever the ball seats are lifted off the surface of the ball valve.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit under USC 119 of the filing date of provisional application Ser. No. 61/906,254 filed Nov. 19, 2013 entitled “Quarter Turn Ball Valve with Lift-Off Seats.” 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to a method and apparatus for controlling fluid flow using a rotary ball valve. More particularly, the invention relates to a quarter turn rotary ball with cam actuated reciprocating seats for controlling fluid flow in abrasive or high pressure conditions. 
     2. Description of the Related Art 
     Certain types of on/off valves have severely attenuated lives due to very concentrated flows with non-axial components during the initial stages of valve opening and final stages of valve closing. In particular, the seats of ball valves and rotary plug valves are susceptible to damage from this type of flow. A second problem which impacts valve actuation is high actuation forces and seat wear due to friction from relative motion of the seats and the sealing plug. This type of problem is common to ball valves, rotary plug valves, and gate valves. 
     Conventional quarter turn ball valves are commonly used for on/off control of fluid flows. Such conventional valves offer the advantages of simplicity, low fabrication costs, and a full bore flow path with attendant low pressure drops across the flowing valves. The seats of the conventional ball valves are spring loaded and also frequently pressure biased to bear against the ball, but their movement in service is negligible. The conventional valves are directly operated by 90° rotations of their directly connected stems. 
     However, the conventional valves do not perform well in abrasive flows or under high differential pressures. In such situations, when the valve is rotated sufficiently from its closed position so that an initial flow path is created between the bore of the ball and its seat, a high pressure differential flow is directed across the lenticular gap between the adjacent seating surface and the lip of the through hole of the ball. The same condition occurs during valve closure. The consequence of this situation is rapid erosive wear in the exposed region of the ball and seat. Such wear can quickly cause functional failure of the valve. Abrasive fluids further contribute to such erosive wear. 
     A critical need exists for a ball valve which is resistant to seat and ball erosion in high pressure and abrasive operation. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention involve a ball valve that separates the valve seats from the ball sealing plug prior to and following rotation of the valve plug for actuation. The valve of this invention seals for pressure from either direction by using both upstream and downstream seats. 
     The disclosed valve will reciprocably separate the valve seat(s) from the sealing plug (e.g., a ball or plug) prior to actually moving the sealing plug, move the sealing plug to its new position, and reseat the valve seat(s) onto the sealing plug. This unseating/reseating of the valve seats is done for both opening and closing operations. The disclosed valve permits a considerable reduction in valve operating force, even under high pressures, and provides a temporary flow path during operation which is less susceptible to abrasive and cavitational wear than standard, non-reciprocating valves. 
     A third embodiment of the present invention The foregoing has outlined rather broadly several aspects of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or redesigning the structures for carrying out the same purposes as the invention. It should be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is an oblique view of the quarter turn reciprocating seat ball valve of the present invention. 
         FIG. 2  is a longitudinal cross-sectional view of the open valve of  FIG. 1 . 
         FIG. 3  is an oblique view of the exploded cam assembly of the present invention. The view is of the side which normally abuts the upper transverse surface of the ball. 
         FIG. 4  is a view looking axially upwardly at the side of cam which contacts the flat of the ball. 
         FIG. 5  is a view looking downwardly on the axis of the ball. This view shows the angular relationship of the arcuate slot of the ball with the through hole flow axis of the ball. 
         FIG. 6  is an oblique view of the ball of the present invention, showing the arcuate slot on an upper transverse surface of the ball. 
         FIG. 7  is an exploded view of the cavity seal assembly. 
         FIG. 8  is a transverse sectional view of the cavity seal assembly taken perpendicular to the axis of the valve. 
         FIG. 9  is an exploded view of the ball, the ball seat assemblies, and the cam assembly. 
         FIG. 10  is a longitudinal view of the ball, its seat assemblies, and the cam assembly, wherein the ball is in its open position. 
         FIG. 11  is an oblique partially exploded view of the keeper ring and valve stem assemblies. 
         FIG. 12  is a view looking downwardly along the valve axis at the ball and cam in their closed position, wherein the cam has not displaced the seats from the surface of the ball. 
         FIG. 13  is a view looking downwardly along the valve axis at the ball and cam with the ball in its closed position, with the cam having been rotated 90° counterclockwise from its position in  FIG. 12  to displace the seats from the surface of the ball. 
         FIG. 14  is a view looking downwardly on the valve axis at the ball and cam with the ball having been rotated 90° counterclockwise from its position in  FIG. 13  to its open position by further 90° counterclockwise rotation of the cam. The additional rotation of the elliptical cam has permitted the seats to reseal against the ball. 
         FIG. 15  corresponds to  FIGS. 12, 13, and 14 , wherein the cam has been rotated clockwise from its position in  FIG. 14  in order to prepare to reclose the valve. The rotation of the elliptical cam has displaced the seats from the surface of the ball. 
         FIG. 16  is a plan view of the ball, cam, and seat assemblies, wherein the ball has been closed and the seats reseated by a clockwise rotation of the cam. 
         FIG. 17  corresponds to  FIG. 16 , but shows the cam having been rotated 90° counterclockwise to lift the seats off the ball preparatory to valve opening. 
         FIG. 18  corresponds to  FIG. 17 , but both the ball and the cam have been rotated counterclockwise an additional 90° in order to open the ball. 
         FIG. 19  corresponds to  FIG. 18 , but the cam has been rotated 90° clockwise and the seats displaced from the ball preparatory to closing the ball. 
         FIG. 20  is a longitudinal section taken through the assembly of  FIG. 16  on the section line  20 - 20 . 
         FIG. 21  is a longitudinal section taken through the assembly of  FIG. 17  on the section line  21 - 21 . 
         FIG. 22  is a longitudinal section taken through the assembly of  FIG. 18  on the section line  22 - 22 . 
         FIG. 23  is a longitudinal section taken through the assembly of  FIG. 19  on the section line  23 - 23 . 
         FIG. 24  is a transverse sectional view of the valve assembly with the seats cammed off the ball, but the ball still in its closed position. 
         FIG. 25  is a cross-sectional view taken on the horizontal plane through the flow axis the closed valve and perpendicular to the axis of the transverse port of the valve. The valve seats are shown cammed off from the surface of the ball preparatory to rotating the ball to its open position. 
         FIG. 26  corresponds to  FIG. 25 , but is taken at a distance approximately one sixth of the valve bore outwardly in the direction of the transverse port of the valve body. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention involve a ball valve that separates the valve seats from the surface of the ball valve preparatory to and during rotation. 
     For the present invention, the term “quarter turn” refers to the motion of the ball, rather than the motion of its valve stem. The quarter turn reciprocating seat ball valve of the present invention utilizes a rotary cam having a lost motion linkage to a ball valve to separate the seats of the valve from the ball prior to its rotation to either a fully open or fully closed position. The cam is rotated 180° by the valve stem, either simultaneously or following completion of the ball valve rotation, and the seats are reseated against the ball. The present invention is not suitable for metering flow. 
     When the seats are cammed off the surface of the ball valve preparatory to and during rotation, the flow passing between the seats and the ball is limited due to the placement of static structural elements which constrict the bypassing flow around both the outer spherical ball surface and the cam during the valve rotation. These flow restrictions limit the flow between the ball and its seats as the seats are separated from the ball, thereby minimizing potential wear of the ball and seats. The valve is housed in a bonneted body and can be serviced in-line. The valve is particularly suited for use with abrasive fluids or high pressure gas service. 
     The lost motion linkage used to operate the valve of the invention requires a 180° rotation of the valve stem, rather than the conventional 90° rotation. The valve can be operated either manually or by means of an actuator. In the case of the manually operated valve, a two-to-one motion multiplying gear box is used to convert the desired 90° motions of the handle to the 180° motions required for the valve stem to operate the valve. If a mechanical actuator is used, it can either provide a longer stroke or utilize a two-to-one motion multiplying gear box. 
     The materials of construction of the valve  10  of the present invention are high strength low alloy steel and stainless steel. Typically, the valve stem, the ball and its seats, the seat bias springs, and the bonnet seal ring will be stainless steel, while the body, bonnet, and other components will be high strength low alloy steel. Other than the bonnet seal ring, the seals of the valve will be elastomeric O-rings and backup rings. The bonnet seal ring is a commercially available stem seal. 
     Referring to  FIG. 1 , the assembled valve  10  of the present invention is seen in an oblique view. The general configuration of the body  11  corresponds to that of a conventional top entry quarter turn ball valve, with the top entry transverse port  19  closed by a bolted bonnet flange assembly  104  and an operating valve stem  94  extending through a central hole in the bonnet  105 . Two of the bonnet studs  115  are elongated in order to permit an actuator to be mounted thereon. 
     The actuator is not otherwise described herein, but it provides a selectably reversible 180° rotation for actuating the valve  10 . The transverse flow outlet body ends  25  of the body  11  are each provided with seal grooves  26  and a circular array  27  of drilled and tapped mounting bolt holes. The valve may thus be connected into a flanged piping system by means of an array of threaded studs with nuts and a sealing ring on each end. 
       FIG. 2  shows a longitudinal sectional view of the open valve  10 . The body  11  has a main cylindrical section intersected perpendicularly at midlength by an enlarged bonnet extension  17 . A longitudinally extending through bore has symmetrically opposed flow passages  12 , with the inner portion of the flow passages having stepwise enlarged counterbores providing opposed seat pockets  13  intersecting the central cavity  15  of the body. 
     The seat pockets  13  each have, from their outer ends, a short first counterbore, a slightly larger diameter relatively long central second counterbore to house the central portion of the seat assembly  31 , and a further enlarged diameter third counterbore to house the enlarged outer end of a seat  31 . Each seat pocket  13  has a short rectangular cross-section keyway  14  extending outwardly from the transition between the second and third seat counterbores on the upper side of the seat pockets  13 . The keyways  14  are located on the bonnet side of the seat pockets  13 . 
     The centrally positioned transverse port  19  extends upwardly from the flow axis of the body  11 . At its inner end and concentric both with midpoint of the flow axis of the valve and the axis of the transverse port, the lower central cavity  15  of the body  11  has a hemispherical bore  18 . The hemispherical bore  18  of the central cavity  15  is a close fit to the spherical outer surface of the ball  46 . 
     As seen in  FIG. 24 , coaxial with the transverse port  19  of the body  11  and extending outwardly and downwardly from the hemispherical bore of the central cavity  15  is a cylindrical pivot hole  16 . The pivot hole  16  is concentric with the central cavity  15  and provides a rotational and translational support to the lower pivot pin  49  of the ball  46 . Slightly above the horizontal plane intersecting the flow passages  12  of the body  11 , a first counterbore  101  of the transverse port  19  extends upwardly and outwardly approximately half of the diameter of the ball  46 , where it meets an outwardly facing transverse internal shoulder  20 . The first counterbore  101  is cylindrical and slightly larger than the diameter of the ball. 
     A short enlarged intermediate bore  21  extends outwardly from the shoulder  20 , where it is joined by a thread relief and then an upwardly extending female threaded bore  22 . At the outer end of the threaded bore  22  of the transverse port  19 , a female seal groove  23  is sealingly engagable by a metallic seal ring  103  to permit sealing between the body  11  and the bonnet  105 . The transverse bonnet mounting face  29  at the outlet of the transverse port has a concentric array of drilled and tapped bonnet bolt holes  27 . 
     A pair of identical tubular seat assemblies  31  are mounted in opposed positions in the seat pockets  13  of the body  11 . As seen in  FIGS. 9 and 10 , each seat assembly  31  consists of a main seat  32 , a seat extension  40 , a male O-ring  43  with a backup ring  44 , and a helical seat bias spring  45 . 
     The seat  32  is cylindrical with a straight bore equal to the bores of both the body  11  and the ball  46 . At its inner end which will abut the ball  46 , the seat  32  has an enlarged upset cylindrical head  34  having a transverse inner end adjoined on its inward side by a spherical seating face  36  sealingly compatable with the ball  46  of the valve. The spherical face  36  on its inward side intersects the bore of the seat  32 . 
     Although the spherical seating faces  36  of the seats  32  can provide metal-to-metal sealing, in highly abrasive environments, provision of an annular molded-in elastomeric seat in the central portion of each spherical face  36  is often desirable, although it is not shown herein. Such a modification is well understood by those skilled in the art and would not change the basic behavior of the valve  10 , although it would improve sealing with abrasive fluids. 
     A reduced diameter external cylindrical body section  33  having an intermediate O-ring groove  37  extends radially outwardly from the enlarged cylindrical head  34  of the seat to an inwardly extending intermediate transverse shoulder. The O-ring groove  37  contains male O-ring  43  and backup ring  44 . A further reduced diameter shank  38  then extends from that intermediate shoulder outwardly to a transverse outer end of the seat. A rectangular cross-section external antirotation key  39  extends outwardly a short distance from the outer transverse face of the upset head  34 . The key  39  has a slip fit with the keyway  14  of the seat pocket  13  of the body  11 . The length of the key  39  is equal to or slightly less than the length of the keyway  14 . 
     The upset head  34  of the seat  32  has a slightly smaller diameter than that of the third counterbore of the seat pocket  13 . The cylindrical body  33  of the seat  32  has a close slip fit to the second counterbore of the seat pocket  13  so that the O-ring  43  can seal between the seat pocket  13  and the body  33  of the seat  32 . The reduced diameter shank  38  of the seat  32  has a slip fit to the counterbore  41  of the inward end of the seat extension  40 . 
     Coplanar with the antirotation key  39  of the seat  32  and on the opposed transverse face where the spherical seating face  36  is, a cam pocket  35  is located. The cam pocket  35  is relatively shallow and symmetrical about the midplane of the antirotation key  39 . The inner end of the cam pocket  35  is spaced a short distance outwardly of the outer diameter portion of the spherical seating face of the seat  32 . The pocket  35  extends to the outer diameter of the upset head  34  of the seat. Looking radially along the midplane of the antirotation key  39 , the profile of the cam pocket  35  is slightly elliptical to match the elliptical minor diameter region of the cam  56 . 
     The inner end of the seat extension  40  has the same outer diameter as that of the cylindrical body  33  of the seat  31 . The outer end of the seat extension  40  has a loose slip fit to the helical compression seat bias spring  45 . The external outwardly facing shoulder of seat extension  40  is abutted by the seat bias spring  45  in order to bias the seat assembly  31  against the ball  46 . The outward end of the seat bias spring  45  abuts the inwardly facing transverse shoulder of first counterbore of its seat pocket  13 . Because the outer diameter of the spherical sealing face  36  is less than the outer diameter of the cylindrical body  33  of the seat  32 , the upstream seat also is biased against the ball  46  by retained pressure when the ball is closed. 
     The ball  46 , seen in  FIGS. 5, 6, and 9 , has a smooth spherical sealing surface  47  with a radially projecting reduced diameter cylindrical lower pivot pin  49  on its lower side. The lower pivot pin  49  is journaled in the pivot bore of the body  11 . A diametrically extending through bore flow passage  48  is perpendicular to the axis of the lower pivot pin  49 . On its upper side, the ball has a transverse face  52  perpendicular to the pivot axis and sufficiently offset from the midheight of the ball to permit the spherical sealing face  36  of the seat  32  to comate with and fully seal with the seat assemblies  31 . 
     A cylindrical upper pivot pin  50  extends radially upwardly from the transverse face  52  of the ball. The upper transverse end of the upper pivot pin  50  has a central drilled and tapped extraction hole  51  to simplify insertion and extraction of the ball  46  from the central cavity  15  of the valve  10 . 
     An arcuate, constant radius camming slot  53  extending 90° is located on the outwardly facing upper transverse face  52  of the ball  46 . The camming slot  53  has a close slip fit to the camming pin  68  of the cam assembly  55 . The distal ends of the camming slot are rounded with a radius which closely matches the radius of the camming pin  68 . 
     The cam assembly  55  of the valve  10 , seen most clearly in  FIGS. 3, 4 , and  9 , consists of a cam  56 , an O-ring  67 , and a camming pin  68 . The cam  56  has an elliptical disk  57  having a central constant diameter bore  58  normal to and extending upwardly from its lower face. The bore  58  has a close slip fit with the upper pivot pin  50  of the ball  46 . A face seal O-ring groove  59  concentric with the lower bore  58  is located on the lower face of the disk. O-ring  67  is mounted in groove  59 . 
     Referring to  FIGS. 3 and 4 , a short upwardly extending cylindrical blind hole  60  which serves as a mounting point for the camming pin  68  is perpendicular to the lower face of the cam  56  and offset from the bore  58 . The radius extending from the center of cam  56  to the center of the camming pin hole  60  is at an angle A from the major axis of the elliptical disk  57  of the cam. Stepped cylindrical camming pin  68  is press-fitted into the hole  60 . 
     The upper face of the elliptical cam  56  has a central round upper pivot pin  61  extending upwardly from the disk  57  of the cam  56 . The upper end of the pivot pin  61  has a regular hexagonal extension  62 . As seen in  FIG. 4 , the angle between the radius to the camming pin hole  60  and the hexagonal extension  62  is fixed at 45° and is independent of the value of angle A. The transverse upper end of the pivot pin  61  has a central drilled and tapped hole  63  for manipulation and extraction of the cam  56 .  FIG. 6  also shows with a dashed line a circle having a diameter equal to the minor diameter of the ellipse of the cam  56 . The eccentricity of the cam is relatively small, but it is sufficient to cause the seats  32  to displace from contact with the ball  46 . 
     The cavity seal assembly  69  is seen in an exploded view in  FIG. 7  and a transverse cross-sectional view in  FIG. 8 . The cavity seal assembly  69  consists of a cavity seal disk  70 , two opposed filler pieces  79 , mounting dowel pins  84  for the filler pieces, and both male and female O-rings  85  and  87  with backup rings  86  and  88 . 
     The cavity seal disk  70  has a constant diameter central through hole  71  having a female O-ring groove housing O-ring  87  and backup ring  88 . On its external cylindrical face, the cavity seal disk  70  has a reduced diameter lower section  73 , a downwardly facing transverse shoulder  74 , and an enlarged upper cylindrical section  75  with a male O-ring groove  76 . O-ring  85  and backup ring  86  are mounted in the O-ring groove  76 . 
     The upper face of the cavity seal disk  69  has a shallow diametrical alignment groove  77 , along with a pair of diametrically opposed drilled and tapped extraction holes  120 . The alignment groove  77  permits the cavity seal disk assembly  69  to be closely aligned during assembly with the through bores  12  of the body  11  of the valve  10 . 
     The lower face of the cavity seal disk  70  has a pair of mirror image regularly spaced mounting holes  78  for a pair of filler pieces  79 . The holes  78  are symmetrical about the alignment groove  77 . The mounting holes  78  are all at the same radius from the center of the cavity seal disk  70 , and the two sides of the pattern of mounting holes are symmetrical about the alignment groove  77 . 
     The filler pieces  79  are best seen in  FIGS. 7 and 8 . The filler pieces  79  are made to have externally cylindrical outer faces  81  which have a close slip fit into the straight first counterbore  101  of the body  11  of the valve  10 . The upper and lower ends of the filler pieces  79  are perpendicular to the cylindrical axis of the parts. The lower interior faces of the filler pieces have a spherical surface which is a close fit to the diameter of the ball valve  46 . The center of the spherical cut face  80  is on the cylindrical axis of the filler piece  79  a short distance below its lower end. 
     On the upper interior side of the filler pieces  79 , a short cylindrical counterbore extends downwardly to a transverse shoulder to form a cam pocket  82 . The radius of the cam pocket  82  is slightly more than half of the major diameter of the elliptical disk  57  of the cam  56 , and the depth of the cam pocket is also slightly more than the thickness of the elliptical disk  57 . 
     The upper transverse face of each filler piece  79  has a regular array of dowel pin mounting holes  83  positioned on the same radius as the mounting holes  78  of the cavity seal disk  70 . The mounting holes  83  are on the same pattern as the mounting holes  78  on the lower face of the cavity seal disk  70 . Dowel pins  84  are used to cojoin the filler pieces  79  to the lower side of the cavity seal disk  70 . 
     The keeper ring assembly  89  shown in  FIG. 11  consists of a threaded keeper ring  90  and a pair of radial needle bearings  92 . The keeper ring  90  retains by clamping the cavity seal disk  70 , thereby preventing both axial and rotary motion of the disk. The threaded keeper ring  90  is a concentric right circular ring having a counterbore  91  on its upper side. The external threads are compatable with the threads of the bore  22  near the outer end of the transverse port  19 . A pair of diametrically opposed drilled and tapped holes is on the upper transverse face of the keeper ring  90  for applying torque and easing insertion and removal in the body  11 . Two radial needle bearings  92  are pressed into the counterbore of the ring  91 . 
     The valve stem assembly  93  shown in  FIG. 11  consists of the valve stem  94 , and a pair of hardened thrust washers  99  with a caged needle thrust bearing  100  located between the thrust washers. The valve stem  94  has an enlarged cylindrical lower head  95  with an elongated coaxial cylindrical upper extension. The lower end of the lower head  95  of the valve stem has an upwardly extending coaxial hexagonal socket  96  for engagement with the hexagonal extension  62  of the cam  56 . The length of the lower head  95  is generally about 70% of its diameter. 
     Immediately above the lower head  95 , the valve stem  94  has a short constant diameter pilot section  97  which has a close slip fit with the two hardened thrust washers  99 . A caged needle thrust bearing  100  is positioned between the thrust washers  99  and then both the washers and the thrust bearing are positioned around the pilot section to bear against both the upper transverse end of the lower head  95  of the valve stem  94  and also against the lower face of the bonnet  105 . At its upper end, the valve stem has a coaxial upper male hexagonal section  98  for engagement by a handle, an intermediate gear box, or a valve actuator. The attachments for rotating the valve stem assembly  93  are not shown herein. The corner to corner dimension of the upper hexagonal section  98  is equal to or less than the diameter of the upper portion of the valve stem. The upper transverse end of the valve stem  94  has a concentric drilled and tapped hole for retention of a handle or actuator. 
     A commercially available metallic seal ring  103  has a straight bore and two symmetric opposed frustoconical exterior faces. The seal ring has opposed narrow transverse ends. When the metallic seal  103  is installed in the seal groove  23  of the body  11  and the bonnet flange  105 , the seal is radially compressed to provide metal to metal sealing against the seal grooves  23  of the body  11  and  106  of the bonnet  105 . 
     The bonnet assembly  104  consists of the bonnet  105 , a shaft seal  112 , a shaft seal retainer nut  113 , standard length bonnet mounting studs  113 , elongated bonnet mounting studs  115  for actuator mounting, and hex nuts  116  for the studs. The bonnet  105  is a disk having a concentric seal groove  106  on its lower side. The seal groove  106  has a short frustoconical outer face, a transverse interior end, and a cylindrical interior side to accommodate the metallic seal ring  103 . The bonnet  105  has a coaxial stepped shaft hole  107 , the lower end of which has a close fit to the upper cylindrical end of valve stem  94 . 
     The middle portion of the shaft hole  107  has a short right circular cylindrical shaft seal counterbore  108  for housing the commercially available shaft seal  112 . The upper portion of the shaft hole has an enlarged female thread to engagement by the threads of the shaft seal retainer nut  113 . 
     The bonnet  105  is mounted onto the body  11  of the valve  10  by means of threaded studs  114  and  115  with hex nuts  116 . The bonnet has a regular circular array of through mounting bolt holes corresponding to the pattern on the bonnet mounting face  29  of the body  11  of the valve  10 . The threaded studs  114  and  115  are engaged in the tapped holes array  27  of the body  11  and the hex nuts  116  are then used to mate the bonnet  105  to the body. With the bonnet bearing on the outer end of the bonnet extension  17 , the seal ring  103  is engaged to prevent leakage in the joint. 
     Operation of the Invention 
     In many ways, the quarter turn reciprocating seat ball valve  10  of the present invention is structurally and operationally similar to a conventional quarter turn ball valve. Such conventional valves are suited for on/off service but are not well suited for metering flows. The conventional valves also are not well suited for very high pressure applications, particularly with gas. The conventional valves generally do not perform well in high pressure gas or abrasive flow situations when opening and closing under pressure. However, the quarter turn reciprocating seat ball valve  10  of the present invention will be able to operate successfully both in gas and abrasive flows with high pressure differentials. 
     Because during seat displacement the cam  56  applies forces to the seats  32  which are eccentric from the centerlines of the seats, the seat extensions  40  are used to extend the length of the seat assemblies  31  and thereby reduce the transverse reactions on the seat assemblies produced by the eccentric cam loads. The lengths of the seat and seat extension  40  are limited by what can pass through the transverse port  19  of the body  11  for installation in a seat pocket  13 . Combining a seat  32  with a seat extension  40  permits easy installation while reducing transverse loads on the seat assembly  32 . 
     When the ball  46  of the present invention is in its initially closed position as seen in  FIG. 10 , the seats  32  are biased to abut the ball by their respective seat bias springs  45 , thereby preventing flow. This condition is shown in  FIGS. 2, 10, 12, 16 , and  20 . Additionally, if the ball valve  10  is closed and is retaining upstream pressure, then a pressure bias urges the upstream seat  32  against the ball  46 . This is because the outer diameter of the cylindrical body  33  of the seat  32  is greater than the outer diameter of the spherical seating face  36  of the seat. 
     In the following description of valve operation, it is assumed that the closed valve is initially retaining pressure. The views of the of the ball  46  and the cam  56  assemblies in  FIGS. 12 to 15  are taken looking down the axis of the valve stem assembly  93  to the ball  46 . Likewise,  FIGS. 16 to 19  are taken with the same orientation. 
     When the ball valve  10  is closed and the initial relationship of the cam  56 , the seats  32 , and the ball  46  are as shown in  FIGS. 12, 16, and 20 , the valve opening operation can be begun. First, the valve stem assembly  93  and its connected cam assembly  55  are initially rotated 90° without causing the ball  46  to open. The rotation of the cam assembly  55  does not entail rotation of the ball  46  during this initial operation because the camming pin  68  is able to move freely in the camming slot  53  of the ball  46 . This initial rotation would be counterclockwise from the position shown in  FIG. 12 . 
     Due to necessary allowances for fabrication tolerances, the minor axis portion of the elliptical cam  56  typically is initially almost in contact with the cam pockets  35  of the seats  32  prior to the initiation of rotation of the valve stem  94  and cam  56 . The initial valve stem  93  rotation first results in the elimination of any clearance gap between the cam  56  and the cam pockets  35  of the seats  32 . A relatively initial high torque then is applied to the cam assembly  55  through the further rotation of the valve stem assembly  93 . 
     This high initial torque is due to friction from relative motion between the cam  56  and the cam pocket  35  of the seats  32 . If there is a high differential pressure sealed by the valve  10 , the high contact force between the cam  56  and the cam pockets  35  on the upstream seat  32  is due to the pressure induced seating forces on the contact between the upstream seat and the ball  46 . The resultant forces from the cam  56  on the seats  32  cause the seats  32  to be displaced from the surface of the ball  46  so that sealing is lost between the seats  32  and the ball  46 . The torque required to displace the seats  32  from the ball  46  when the closed valve  10  is pressure balanced is much less than if the valve is sealing a differential pressure. 
     Because the loads applied to the seats  32  by the cam  56  are eccentric, the relative movement between the seats and the cam result in torques being applied to the seats about their centerlines. These torques are resisted by the antirotation keys  39  of the seats  32 . The antirotation keys transfer their induced loads to the keyways  14  of the seat pockets  132  of the body  11 . Additionally, the lengthening of the seat assemblies  31  by the provision of the seat extensions  40  reduces lateral frictional reactions on the seat assemblies. 
     When sealing is lost between the seats  32  and the ball  46 , the forces required to further displace the seats are reduced and the torque on the valve stem assembly  93  from that source is reduced, although additional torque results from the shaft seal  112  of the bonnet assembly  105  on the valve stem  94 , the bearings  92  and  100 , and the pressure induced frictional resistance of the O-ring  87  of the cavity seal assembly  69 . 
     With the seats  32  separated from the spherical surface  47  of the ball  46  but prior to ball  46  rotation by the cam assembly  55 , some flow bypasses the closed ball  46  through clearance gaps between the ball, the valve body  11 , the cavity seal assembly  69 , and the cam  56 . These gaps can be seen in the transverse cross-sectional view through the valve stem  94  axis in  FIG. 24 . However, this flow is comparatively restricted due to the small size of those bypass gaps in comparison to the size of the gaps between the ball and its cammed-off seats. The spherical sealing surface  47  of the ball  46  is a close fit to both the spherical lower portion of the central cavity  15  of the body  11  and the inner spherical faces  80  of filler pieces  70  of the cavity seal assembly  69 . Likewise, the flow gap between the cam  56 , the filler pieces  79 , and the cavity seal disk  70  is also relatively small and severely restricts erosive flow through that gap. 
     Referring to  FIGS. 24, 25 and 26 , the relative sizes of the bypass flow areas around the ball  46  and cam  56 , seen in  FIG. 24 , can be compared with the relatively much larger circular flow gaps between the seats  32  and the ball  46  when the seats are fully displaced from the ball by the cam  56 . The eccentricity of the cam  56  is such that the gaps between the fully displaced seats and the ball  46  are more than an order of magnitude larger than the bypass flow areas. 
     The consequence of this difference in gap sizes is that bypassing flow velocities are much larger and more erosive between the ball  46  and cam  56  and their surrounding components than between the ball and its seats  32 . The resulting wear is mainly on the portions of the elliptical cam disk  57  and the inner cylindrical surfaces of the filler pieces  79 . The portions of the cam elliptical disk  57  which are most exposed to erosive wear are normally lightly loaded during valve operation. Hence, such wear on the cam  56  is more tolerable than if it were on a highly loaded portion of the disk. Likewise, the resulting bypass wear on the body  11  and ball  46  is not in a portion of the ball which bears on the seat when the ball is closed. 
     The ball  46  in  FIGS. 25 and 26  is not rotated from its closed position when the opening movement of the cam  56  causes the camming pin  68  to move from its position shown in  FIG. 12  to that shown in  FIG. 13 . A small amount of coupled rotation of the cam  56  and the ball  46  from the position shown in  FIGS. 13, 25, and 26  causes the bore  48  of the ball  46  to become sufficiently aligned with the bores of the seats  32  and the body  11  to permit flow through the bore  48  of the ball. The opening of that additional bore flow path during ball rotation from the position shown in  FIG. 13  to that in  FIG. 14  causes the velocities in the aforementioned flow bypass channels to rapidly drop to non-erosive levels. 
     When the camming pin  68  encounters the end of the 90° slot  53  of the ball  56  as seen in  FIGS. 13, 17, and 21 , rotation of the ball can initiate. This ball rotation results from further rotation of the cam counterclockwise from the position shown in  FIG. 13 . As the ball  46  is being rotated by the further rotation of the elliptical cam  56 , the diameter of the cam sections bearing on the cam pockets  35  of the seats  32  decreases, so that the gaps between the seats  32  and the ball  46  decrease and eventually are eliminated as the ball becomes fully open. The valve stem  94  rotates 180° in order to move the ball  46  from its fully closed position to its fully open position. 
     The closure of the ball  46  from its open position is somewhat similar to the ball opening operation. During ball closure, the initial 90° of rotation of the valve stem  94  again shifts the valve seats  32  out of sealing engagement with the spherical surface  47  of the ball  46 . The starting position for the initial cam  56  rotation to lift the seats  32  off the ball prior to the initiation of ball closure is shown in  FIGS. 18 and 22 . Following this initial 90° of closing rotation of the valve stem  94  and cam  56 , the camming pin  68  encounters the other end of the camming slot  53  of the ball  46 . 
     During the subsequent 90° of additional rotation from the position with the seats  32  cammed off the ball  46  as shown in  FIGS. 19 and 23 , the flow passage  48  of the ball is also rotated 90° with the cam  56  so that it is perpendicular to the flow passages of the seats  32  and the body  11 . At that point, the cam  56  has simultaneously rotated sufficiently so that the spring biased seats  32  can reseal against the ball. 
     Due to fabrication tolerance variations, some initial clearance gap is unavoidable between the cam  56  and the cam pockets  35  of the engaged seats  32  during the initiation of valve closing. This results in the necessity to rotate the cam  56  a few degrees before the cam  56  can begin to displace the seats  32  from the ball  46 . 
     As shown in  FIG. 4 , the angle between the elliptical minor axis of the cam  56  and the radius to the camming pin mounting hole  60  is A. Angle A in the drawings is shown as 45°. However, using a value of angle A which is slightly larger than 45° causes a delayed liftoff of the seats  32  with the surface of the valve  10  prior to full valve opening. Likewise with angle A slightly larger than 45°, for the closing of the valve  10 , the reseating of the seats  32  is achieved slightly prior to the valve flow passage  48  being aligned at 90° from the through flow passages for the valve  10 . While using a value of the angle A slightly greater than 45° leads to slightly more friction during valve closure, this situation may be preferable for minimizing erosion in high pressure operation. As a practical matter, the value of A probably should be limited to no more than 50°. 
     The actuator used for operation of the ball  46  and cam  56  of this valve  10  will be provided with travel stops to ensure that the valve stem  94  and the cam assembly  55  are only rotated 180 degrees, rather than the usual 90 degrees. If manual actuation with a rotary handle is desired, a one-to-two motion multiplying gearbox will be located between the upper hex  98  of the valve stem  94  and the handle. Neither style of actuation is shown herein, but both types are readily understood by those skilled in the art. The provision of bearings to support the valve stem markedly lowers the friction associated with valve operation under pressure. Use of a rapid acting actuator is highly desirable to further minimize wear during valve shifting. 
     ADVANTAGES OF THE INVENTION 
     Like conventional quarter turn ball valves, the ball is reversibly rotatable between its two end positions. However, the provision of valve seats which can be reciprocably moved out of sealing engagement with the ball prior to valve movement and then reseated when movement is complete results in much improved valve life. This is particularly desirable in the case when the fluid media passing through the valve is either abrasive or is high pressure gas. 
     When the seats  32  are lifted off the closed ball  46  during opening, a potential flow path is opened. However, as may be seen in  FIG. 24 , the additional flow restriction path resulting from the close clearances existing between the ball  46 , the filler pieces  79 , the cam  56 , the cavity seal disk  70 , and the body  11  is relatively small compared to the maximum size of the flow path between the seats  32  and the ball  46 . Accordingly, the relatively small flow bypass restrictions between the other valve components serve to highly restrict the flow between the seats  32  and the ball  46 . 
     Additionally, the pressure drop for the valve with the seats cammed off is also shared by the gap between the ball  46  and both of its seats  32 . The same flow restriction situation occurs when the ball  46  is nearing closure. The limiting of the flow thus reduces flow induced erosion of the ball  46  and its seats  32  when the ball opening sequence initiates. Likewise, the limiting of the flow thus reduces flow induced erosion of the ball  46  and its seats  32  when the ball closing sequence is being completed. 
     The fabrication costs of the quarter turn ball valve of the present invention are reduced in comparison to the costs of a gate valve having the same bore and capable of performing at the same service pressures. The quarter turn ball valve of the present invention is also readily serviceable through its bonnet opening while still connected in its flow circuit. 
     The foregoing has described several aspects of the present invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or redesigning the structures for carrying out the same purposes as the invention. 
     For example, various changes can be made to the construction of the quarter turn reciprocating seat ball valve or different materials can be used for reasons of corrosion or temperature resistance. Furthermore, different spring types such as wave springs can be substituted for the coiled seat bias springs shown herein. Elastomeric seals integral with the seats can be used provided operating pressures are not excessive. Other minor changes can render the valve fire safe. These and other changes do not depart from the spirit and scope of the invention as set forth in the appended claims.