CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of U.S. provisional patent application Ser. No. 62/138,865 filed Mar. 26, 2015, which is incorporated by reference into this application in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure is related to the field of modular stops for valves, in particular, ball valves used in drill stem safety valves in a drill string. 
       BACKGROUND 
       [0003]    Drill stem safety valves (“DSSV”) typically have two primary purposes: a) they are safety devices that can be closed to prevent mud and/or well fluid from flowing back up the interior of the drill pipe in the event of an unbalanced pressure in the mud column; and b) they can be used as a flow control device to turn on and off the flow of mud while making and breaking connections during drilling operations for top drives. 
         [0004]    When used for blow out prevention, these valves are only used during testing or in emergencies. However, in mud control, they can be operated several hundred times in the drilling of a single well. 
         [0005]    Drilling mud is an abrasive, highly engineered fluid that is used to balance pressure in the string against pressure in the pay zone upon point of penetration. The abrasiveness of the fluid is due to entrained solids such as sand. Well fluids are any hydrocarbons in the pay zone, and can include a mixture of oil, gas and solids. 
         [0006]    To operate a DSSV, it is simply turned from the open to closed position and back again, by applying torque to the DSSV stem. This torque can be applied manually, or by an actuator. The stem in the valve is a part which penetrates the pressure envelope. It typically has a hexagonal interface to receive a wrench that can be used to open or close the valve. 
         [0007]    The body of the valve is the part which houses all the internal parts. The body is typically constructed of high strength carbon steel alloy due to the extremely high pressure, torque and tension it is subjected to as part of the drill string. This type of alloy is selected for its strength, but as such is not very corrosion resistant and cannot be welded because welding introduces localized hardening that can cause premature failure under high loads. 
         [0008]    Under pressure, the valve takes a significant amount of torque to operate. Some valves require upwards of 2000 foot-pounds (“ft-lbs”) to operate. This torque can be applied manually by wrench, or by actuator. Because of this, there is substantial load on the hexagonal stem, and conversely when the valve reaches its full travel, this load is transferred to the “valve stop”. 
         [0009]    The stops in the valve are the contact areas between the stem and, typically, a stop ring or the body itself. The stops must have enough surface area to withstand the load applied either by wrench or by actuator. The ability of these stops to handle the loads applied is critical to proper function of the valves. If the stops are too weak, i.e. there is not enough “stopping power”, they will quickly yield under load. As the stops yield, they allow the ball to travel further and further from its optimal position in both the open and closed direction. This is referred to as “over travel”. Any over travel can have significant, negative effects on valve performance and life, and can result in infantile failure. 
         [0010]    Currently, for any DSSV, the correct alignment of the ball in the open and closed position is critical to optimal valve life. Without correct alignment in the open position, the leading edge of the ball and the trailing edge of the lower seat will be exposed to abrasive mud flow, causing premature wear and potentially vortices that can accelerate erosion. The resulting deflected flow path and resulting accelerated erosion can lead to infantile failure. 
         [0011]    There are several methods to ensure alignment of the ball in the open and closed positions. Early stop systems incorporated a “stop ring”. This ring is a removable ring on the interior of the valve exposed to the drilling fluid, usually adjacent to the upper seat, which provides a flat surface for the stem to come into contact with. Due to the nature and design of the ring, the amount of surface area available to stop against is typically very low. Because of the low amount of surface area, these stop rings cannot resist significant amounts of torque and therefore do not have much stopping power. After only a few uses, any yielding in the stop area will allow the ball to over travel in the open and closed direction. However, one advantage of using stop rings is that they are replaceable. Any yielding of the ring can easily be fixed by simply replacing the ring during regular service. 
         [0012]    To improve stopping power, “cam style” stops were invented. These types of stops are typically used in higher pressure valves, and are typically single sided (as opposed to dual stops mentioned below). Typically, these types of stops comprise a cam lobe incorporated into the stem, which mates with a cam feature milled directly into the body. The utilization of a cam allows for much more surface area in the stop, resulting in more accurate, reliable and repeatable alignment under high torque applications. However, by incorporating or integrating the stop into the body itself, either by machining or fabricating the stop in the valve body, they are difficult to inspect, not very corrosion-resistant and non-repairable because they cannot be welded. If the body wears out, it must be replaced which shortens the useful life of the valve at great expense. 
         [0013]    A recent innovation to cam style stops is the Dual Stop™ stem, as manufactured by Hi-Kalibre Equipment Limited of Edmonton, Alberta, Canada. In this design, the stem lobes are doubled, for double the stopping power. While this provides even further reliability and improved life in the field, these lobes are still difficult to inspect, not very corrosion resistant and when they eventually wear out, they cannot be repaired. 
         [0014]    It is, therefore, desirable to provide a stop mechanism for DSSVs that overcomes the shortcomings of the prior art. 
       SUMMARY 
       [0015]    A modular stop can be provided that incorporates the stops into a removable part. The stops can be integrated into a stem insert. The material of the stem insert can be made from more corrosion resistant alloys, to improve or lengthen the service life of the stop. 
         [0016]    In some embodiments, the stops can be manufactured to be either single-sided, or dual-sided. In some embodiments, the modular stop can still comprise a cam and, thus, can provide as much stopping power as conventional cam style stems. In addition, they can have the same repeatability and reliability as the current state of the art. 
         [0017]    In some embodiments, the modular stops can be easily removed for inspection or replacement. Replacement of a worn modular stop with a new modular stop can return the valve travel to normal as the wear is contained in the removable insert, which will eliminate replacement of the valve body due to integral stops being worn. 
         [0018]    In some embodiments, existing prior art valves can be upgraded or retrofitted to incorporate the modular stop. By machining existing bodies to receive a modular stop, the modular stop can be incorporated into previously manufactured equipment, using the same stems and a new insert and, thus, extend the service life of the valve and improve the accuracy of its operation. 
         [0019]    Broadly stated, in some embodiments, a modular stop can be provided for use in a valve, the valve comprising a tubular body and at least one opening disposed through a sidewall thereof, the at least one opening providing communication to a valve chamber disposed within an interior of the body, the at least one opening providing access to a stem configured for turning a ball valve disposed in the tubular body, the stem comprising a cylindrical portion comprising a longitudinal axis extending therethrough, and a cam plate disposed on one end of the cylindrical portion wherein the cam plate is substantially perpendicular to the longitudinal axis, the cam plate comprising at least one cam lobe, the body further comprising a first relief disposed around the at least one opening in the interior adjacent to the valve chamber, the modular stop comprising: a tubular neck portion comprising a first end and a second end, the first end configured for slidable fit into the at least one opening when inserted therein, the tubular neck portion defining a first passageway between the first and second ends, the first passageway configured for slidable fit with the cylindrical portion of the stem when the cylindrical portion is inserted therein; and a base portion disposed on the second end, the base portion larger in diameter than the tubular neck portion, the base portion configured for insertion into the first relief when the tubular neck portion is inserted into the at least one opening, the base portion comprising a second relief configured for receiving the cam plate when the cylindrical portion is inserted into the first passageway, the second relief further comprising at least one stop configured for contacting the at least one cam lobe wherein the stem is limited to approximately 90 degrees of rotational movement about the longitudinal axis when inserted into the modular stop. 
         [0020]    Broadly stated, in some embodiments, a valve can be provided for use with a drill string, the valve comprising a tubular body and at least one opening disposed through a sidewall thereof, the at least one opening providing communication to a valve chamber disposed within an interior of the tubular body, the at least one opening providing access to a stem configured for turning a ball valve disposed in the body, the stem comprising a cylindrical portion comprising a longitudinal axis extending therethrough, and a cam plate disposed on one end of the cylindrical portion wherein the cam plate is substantially perpendicular to the longitudinal axis, the cam plate comprising at least one cam lobe, the body further comprising a first relief disposed around the at least one opening in the interior adjacent to the valve chamber, the valve comprising a modular stop further comprising: a tubular neck portion comprising a first end and a second end, the first end configured for slidable fit into the at least one opening when inserted therein, the tubular neck portion defining a first passageway between the first and second ends, the first passageway configured for slidable fit with the cylindrical portion of the stem when the cylindrical portion is inserted therein; and the modular stop further comprising a base portion disposed on the second end, the base portion larger in diameter than the tubular neck portion, the base portion configured for insertion into the first relief when the tubular neck portion is inserted into the at least one opening, the base portion comprising a second relief configured for receiving the cam plate when the cylindrical portion is inserted into the first passageway, the second relief further comprising at least one stop configured for contacting the at least one cam lobe wherein the stem is limited to approximately 90 degrees of rotational movement about the longitudinal axis when inserted into the modular stop. 
         [0021]    Broadly stated, in some embodiments, the modular stop can further comprise a seal disposed between it and the tubular body. 
         [0022]    Broadly stated, in some embodiments, the second relief can comprise a first stop and a second stop to define the start and stop of the rotational movement. 
         [0023]    Broadly stated, in some embodiments, the modular stop can further comprise means for preventing rotation of the base portion when inserted into the first relief. 
         [0024]    Broadly stated, in some embodiments, the means can comprise the base portion comprising a cross-sectional shape that is non-circular, wherein the first relief is configured to receive the base portion wherein the modular stop cannot substantially rotate when the base portion is inserted into the first relief. 
         [0025]    Broadly stated, in some embodiments, the rotation preventing means can comprise an interference fit between the base portion and the body when the base portion is inserted into the first relief. 
         [0026]    Broadly stated, in some embodiments, the rotation preventing means can comprise complimentary splines disposed on the base portion and in the first relief wherein the complimentary splines mesh with each other when the base portion is inserted into the first relief. 
         [0027]    Broadly stated, in some embodiments, the rotation preventing means can comprise at least one pin disposed between the body and the base portion wherein the modular stop cannot substantially rotate when the base portion is inserted into the first relief. 
         [0028]    Broadly stated, in some embodiments, a method can be provided for manufacturing a valve for use with a modular stop wherein the valve comprises a tubular body and at least one opening disposed through a sidewall thereof, the at least one opening providing communication to a valve chamber disposed within an interior of the tubular body, the at least one opening providing access to a stem configured for turning a ball valve disposed in the body, the stem comprising a cylindrical portion comprising a longitudinal axis extending therethrough, and a cam plate disposed on one end of the cylindrical portion wherein the cam plate is substantially perpendicular to the longitudinal axis, the cam plate comprising at least one cam lobe, the method comprising the steps of: fabricating a first relief disposed around the at least one opening in the interior adjacent to the valve chamber; providing a modular stop, further comprising: a tubular neck portion comprising a first end and a second end, the first end configured for slidable fit into the at least one opening when inserted therein, the tubular neck portion defining a first passageway between the first and second ends, the first passageway configured for slidable fit with the cylindrical portion of the stem when the cylindrical portion is inserted therein, and a base portion disposed on the second end, the base portion larger in diameter than the tubular neck portion, the base portion configured for insertion into the first relief when the tubular neck portion is inserted into the at least one opening, the base portion comprising a second relief configured for receiving the cam plate when the cylindrical portion is inserted into the first passageway, the second relief further comprising at least one stop configured for contacting the at least one cam lobe wherein the stem is limited to approximately 90 degrees of rotational movement about the longitudinal axis when inserted into the modular stop; inserting the tubular neck portion into the at least one opening, wherein the base portion is substantially seated in the first relief; and inserting the cylindrical portion into the first passageway, wherein the cam plate is substantially disposed in the second relief. 
         [0029]    Broadly stated, in some embodiments, a method can be provided for retrofitting an existing valve for use with a modular stop wherein the valve comprises a tubular body and at least one opening disposed through a sidewall thereof, the at least one opening providing communication to a valve chamber disposed within an interior of the tubular body, the at least one opening providing access to a stem configured for turning a ball valve disposed in the body, the stem comprising a cylindrical portion comprising a longitudinal axis extending therethrough, and a cam plate disposed on one end of the cylindrical portion wherein the cam plate is substantially perpendicular to the longitudinal axis, the cam plate comprising at least one cam lobe, the method comprising the steps of: fabricating a first relief disposed around the at least one opening in the interior adjacent to the valve chamber; providing a modular stop, further comprising: a tubular neck portion comprising a first end and a second end, the first end configured for slidable fit into the at least one opening when inserted therein, the tubular neck portion defining a first passageway between the first and second ends, the first passageway configured for slidable fit with the cylindrical portion of the stem when the cylindrical portion is inserted therein, and a base portion disposed on the second end, the base portion larger in diameter than the tubular neck portion, the base portion configured for insertion into the first relief when the tubular neck portion is inserted into the at least one opening, the base portion comprising a second relief configured for receiving the cam plate when the cylindrical portion is inserted into the first passageway, the second relief further comprising at least one stop configured for contacting the at least one cam lobe wherein the stem is limited to approximately 90 degrees of rotational movement about the longitudinal axis when inserted into the modular stop; inserting the tubular neck portion into the at least one opening, wherein the base portion is substantially seated in the first relief; and inserting the cylindrical portion into the first passageway, wherein the cam plate is substantially disposed in the second relief. 
         [0030]    Broadly stated, in some embodiments, the methods can further comprise the step of fabricating at least one O-ring groove disposed around the tubular neck portion and installing an O-ring into the at least one O-ring groove prior to inserting the tubular neck portion into the at least one opening. 
         [0031]    Broadly stated, in some embodiments, the methods can further comprise the step of fabricating a first stop and a second stop in the second relief, to define the start and stop of the rotational movement, prior to seating the base portion in the first relief. 
         [0032]    Broadly stated, in some embodiments, the methods can further comprise the step of providing means for preventing rotation of the base portion when inserted into the first relief. 
         [0033]    Broadly stated, in some embodiments, the methods can further comprise the steps of: fabricating the base portion to comprise a cross-sectional shape that is non-circular; and fabricating the first relief to receive the base portion wherein the modular stop cannot substantially rotate when the base portion is inserted into the first relief. 
         [0034]    Broadly stated, in some embodiments, the methods can further comprise the step of fabricating the base portion such that there is an interference fit between the base portion and the first relief when the base portion is inserted into first relief. 
         [0035]    Broadly stated, in some embodiments, the methods can further comprise the step of fabricating complimentary splines disposed on the base portion and in the first relief wherein the complimentary splines mesh with each other when the base portion is inserted into the first relief. 
         [0036]    Broadly stated, in some embodiments, the methods can further comprise the step of providing a pin disposed between the body and the base portion wherein the modular stop cannot substantially rotate when the base portion is inserted into the first relief. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIG. 1  is a cross-sectional side elevation view depicting a ball valve comprising modular stops. 
           [0038]      FIG. 2  is a front elevation view depicting one embodiment of a modular stop comprising a single-sided stop. 
           [0039]      FIG. 3  is a side elevation view depicting the modular stop of  FIG. 2 . 
           [0040]      FIG. 4  is a bottom plan view depicting the modular stop of  FIG. 2 . 
           [0041]      FIG. 5  is a perspective view depicting the modular stop of  FIG. 2 . 
           [0042]      FIG. 6  is a front elevation view depicting another embodiment of a modular stop comprising a dual-sided stop. 
           [0043]      FIG. 7  is side elevation view depicting the modular stop of  FIG. 6 . 
           [0044]      FIG. 8  is a bottom plan view depicting the modular stop of  FIG. 6 . 
           [0045]      FIG. 9  is a perspective view depicting the modular stop of  FIG. 6 . 
           [0046]      FIG. 10  is a cross-sectional side elevation view depicting a valve comprising the modular stop of  FIG. 2 . 
           [0047]      FIG. 11  is a cross-sectional side elevation view depicting a valve comprising the modular stop of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0048]    Referring to  FIG. 1 , one embodiment of modular stops  10  are shown installed in valve  11 . In some embodiments, modular stop  10  can be inserted into opening  30  disposed through sidewall  31  of tubular valve body  32 , wherein base portion  36  of modular  10  can seat in relief  58  disposed in sidewall  31 . In some embodiments, stem  12  can be disposed in passageway  48  disposed through modular stop  10 . 
         [0049]    In some embodiments, stem  12  can be mechanically connected to ball valve  18  via u-joint  16 , which can be position in valve chamber  28  and held in position by lower ball seat  20  and upper ball seat  22 , which can be further held in position by split ring  24  and lock ring  26 . In some embodiments, u-joint  16  can comprise key  17  that can fit into key slot  19  of ball valve  18 . Similarly, u-joint  16  can comprise another key (not shown) configured to fit into a corresponding key slot  56  (as shown in  FIG. 8 ) as well known to those skilled in the art, wherein ball valve  18  can be rotated to close valve  11  by inserting a hex wrench (not shown) into hex opening  14  and rotating the hex wrench approximately 90 degrees to close off passageway  15  extending through valve body  32 . 
         [0050]    Referring to  FIGS. 2 to 5 , one embodiment of modular stop  10  is shown, wherein this embodiment can comprise a singular or single-sided stop. In this embodiment, modular stop  10  can comprise neck portion  34  and base portion  36 , which can be larger in diameter than neck portion  34 . In some embodiments, modular stop  10  can comprise a seal placed between it and valve body  32  and/or relief  58  to provide means to prevent produced substances, such as fluids and gases from passing through opening  30  when modular stop  10  is installed therein. In some embodiments, this seal can comprise neck portion  34  comprising at least one O-ring groove  38  disposed therearound to receive an O-ring (not shown), as well known to those skilled in the art, to provide sealing means when neck portion  34  is inserted into opening  30  of valve body  32 . Stem  12  can comprise cylindrical portion  13 , which can be configured to be inserted into passageway  48  disposed through neck portion  34 . In some embodiments, stem  12  can comprise key  52  extending outwardly from cam plate  40 , which can serve as means to engage key slot  19  on ball valve  18  without the need of u-joint  16 . In some embodiments, base portion  36  can comprise cam profile or relief  44 , which can be configured to receive cam plate  40 . In this embodiment, cam plate  40  can comprise a single cam lobe  42 , which can be configured to contact stops  46  when stem  12  is rotated approximately through 90 degrees of rotation about longitudinal axis  60  from one stop  46  to the other stop  46 . As shown in  FIG. 4 , stem  12  can rotate in a clockwise direction from contacting right-hand stop  46  to left-hand stop  46 , which represents approximately 90 degrees of rotation about longitudinal axis  60 . In some embodiments, to prevent modular stop  10  from rotating when inserted into relief  58  disposed in valve chamber  28  of valve body  32 , base portion  36  can comprise a cross-sectional shape that is non-circular, as represented by reference numeral  50 , that can be inserted into relief  58 , wherein relief  58  can be configured to receive cross-sectional shape  50  of base portion  36  and prevent the rotation thereof about longitudinal axis  60 . 
         [0051]    Referring to  FIGS. 6 to 9 , another embodiment of modular stop  10  is shown, wherein this embodiment can comprise a dual or double-sided stop. In this embodiment, modular stop  10  can comprise neck portion  34  and base portion  36 , which can be larger in diameter than neck portion  34 . In some embodiments, modular stop  10  can comprise a seal placed between it and valve body  32  and/or relief  58  to provide means to prevent produced substances, such as fluids and gases from passing through opening  30  when modular stop  10  is installed therein. In some embodiments, this seal can comprise neck portion  34  comprising at least one O-ring groove  38  disposed therearound to receive an O-ring (not shown), as well known to those skilled in the art, to provide sealing means when neck portion  34  is inserted into opening  30  of valve body  32 . Stem  12  can comprise cylindrical portion  13 , which can be configured to be inserted into passageway  48  disposed through neck portion  34 . In some embodiments, stem  12  can comprise key slot  56  extending across cam plate  40 , which can serve as means to engage u-joint  16  that, in turn, can engage key slot  19  on ball valve  18 , as shown in  FIG. 1 . In some embodiments, base portion  36  can comprise cam profile or relief  44 , which can be configured to receive cam plate  40 . In this embodiment, cam plate  40  can comprise two cam lobes  42 , which can be placed diagonally opposed to each other across cam plate  40 , as shown in  FIG. 8 . In some embodiments, cam lobes  42  can be configured to contact stops  46  when stem  12  is rotated approximately through 90 degrees of rotation about longitudinal axis  60  from one stop  46  to the other stop  46 . As shown in  FIG. 8 , stem  12  can rotate in a clockwise direction from contacting stops  46  located on the upper right and lower left of  FIG. 8 , to stops  46  located on the upper left and lower right, wherein the rotation represents approximately 90 degrees of rotation about longitudinal axis  60 . In some embodiments, to prevent modular stop  10  from rotating when inserted into relief  58  disposed in valve chamber  28  of valve body  32 , base portion  36  can comprise a cross-sectional shape that is non-circular, as represented by reference numeral  50 , that can be inserted into relief  58 , wherein relief  58  can be configured to receive cross-sectional shape  50  of base portion  36  and prevent the rotation thereof about longitudinal axis  60 . 
         [0052]    In some embodiments, the non-circular cross-sectional shape of base portion  36  can represent means for preventing the rotation of modular stop  10  when inserted into relief  58 . In some embodiments, the rotation prevention means can comprise an interference fit between base portion  36  and relief  58  when modular stop  10  is inserted into relief  58 . In other embodiments, the rotation prevention means can comprise complimentary splines disposed about base portion  36  and in relief  58 , as well known to those skilled in the art, wherein the complimentary splines engage each other when base portion  36  is inserted into relief  58 . In other embodiments, the rotation prevention means can comprise at least one pin disposed between modular stop  10  and valve body  32  when base portion  36  is inserted into relief  58 , wherein the at least one pin is configured to engage both modular stop  10  and valve body  32  and prevent the rotation of modular stop  10  about longitudinal axis  60 . 
         [0053]    Referring to  FIG. 10 , an illustration of a single-sided modular stop  10  installed in relief  58  of valve body  32  is provided. As shown in  FIG. 10 , stem  12  can rotate in a counter-clockwise direction from contacting upper stop  46  to lower stop  46 , wherein the rotation represents approximately 90 degrees of rotation about longitudinal axis  60 , and wherein key  52  would move from a substantially horizontal orientation to a substantially vertical orientation. 
         [0054]    Referring to  FIG. 11 , an illustration of a double-sided modular stop  10  installed in relief  58  of valve body  32  is provided. As shown in  FIG. 11 , stem  12  can rotate in a counter-clockwise direction from contacting stops  46  located on the upper left and lower right of  FIG. 11 , to stops  46  located on the upper right and lower right, wherein the rotation represents approximately 90 degrees of rotation about longitudinal axis  60 , and wherein key slot  56  would move from a substantially horizontal orientation to a substantially vertical orientation. 
         [0055]    In some embodiments, modular stop  10  can be comprised of bronze, as well as other wear-resistant materials, such as copper alloys, stainless steel, monel and iconel as well known to those skilled in the art. In so doing, modular stop  10  can be manufactured of materials that have better wear characteristics than the high strength carbon steel used in the manufacture of valve body  32 . In some embodiments, stem  12  can be comprised of 17-4 stainless steel, as well as other wear-resistant materials, such as copper alloys, bronze alloys, monel and iconel as well known to those skilled in the art. 
         [0056]    Although a few embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications can be made to these embodiments without changing or departing from their scope, intent or functionality. The terms and expressions used in the preceding specification have been used herein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the invention is defined and limited only by the claims that follow.
A modular stop is provided for ball valves, such as those used as drill stem safety valves. The modular stop can be a replaceable component in valves for use with stems used to rotate a ball valve in the valve's body. The modular stop can bear the wear associated with the operation of ball valves and when the modular stop has exceeded its usable service life, it can be replaced without replacing the whole of the valve body. The modular stop can be used in new valve manufacture as well as in the retrofitting or remanufacturing of existing valves.