Patent Publication Number: US-2023135605-A1

Title: Fluid end of a hydraulic fluid pump and method of assembling the same

Description:
FIELD OF THE INVENTION 
     The present invention relates to a hydraulic fluid pump and, more particularly, to a fluid end assembly of a hydraulic fluid pump. Hydraulic fluid pumps are used to provide high pressure fluids for drilling and fracturing operations. The fluid pumps typically include reciprocating plungers or pistons that provide the necessary high pressure fluid. 
     BACKGROUND OF THE INVENTION 
     Plug locks or retaining assemblies for pumps may be used to secure plug members (e.g., valve covers, liners, pistons, stuffing boxes, plungers, etc.) within or proximate to bores in a fluid end housing/module of a pump. These retaining assemblies secure the valves and plug members within or proximate to the fluid end housing of a pump, while also enabling access to the valves and other fluid end components for servicing. Conventional retaining assemblies often impart a preload onto the plug members in order to create an effective and reliable seal during operation of the pump. Thus, conventional retaining assemblies typically require tools for installation/removal of the retaining assemblies on/from the fluid end housing of a pump. The tools needed to remove and/or install the conventional retaining assemblies include, but are not limited to, hydraulic pumps, torque wrenches, drills, and/or impact guns. Because tools are required for installing/removing the conventional retaining assemblies, the process for removing and/or installing these conventional retaining assemblies is both time-consuming and may be dangerous. In addition, conventional retaining assemblies are often constructed from materials that have a limited degree of corrosion resistance, which sometimes results in the conventional retaining assemblies becoming unusable or stuck in the sealed position. Thus, what is needed is a retaining assembly capable of a tool-free operation, that does not impart a preload on the plug members to secure the plug members in place, and that is constructed from materials having a high degree of corrosion resistance. 
     SUMMARY 
     In some aspects, the apparatus described herein relates to a fluid end assembly of a hydraulic fluid pump including: a housing having a bore; a plug member positioned at least partially within the bore; a lock cover coupled to the housing and configured to retain the plug member within the bore during operation of the fluid end assembly; and a magnetic retention pin extending at least partially through a portion of the lock cover to retain the lock cover in a position that retains the plug member at least partially within the bore. 
     In some aspects, the apparatus described herein relates to a fluid end assembly, wherein the plug member is a valve cover that is configured to seal the bore. 
     In some aspects, the apparatus described herein relates to a fluid end assembly, wherein the plug member is a liner that at least partially extends through the lock cover, the liner including: a first end; a second end opposite the first end; a sidewall spanning from the first end to the second end and defining a conduit that spans through the liner from the first end to the second end; and a flange extending radially outward from the sidewall more proximate to the second end than the first end. 
     In some aspects, the apparatus described herein relates to a fluid end assembly, further including: a piston movably disposed within the conduit of the liner. 
     In some aspects, the apparatus described herein relates to a fluid end assembly, further including: a lock coupled to the housing, the lock defining a threaded bore, wherein the lock cover is configured to threadedly engage the threaded bore of the lock to couple the lock cover to the housing. 
     In some aspects, the apparatus described herein relates to a fluid end assembly, wherein each of the lock cover and the threaded bore of the lock includes broken zero-pitch threads. 
     In some aspects, the apparatus described herein relates to a fluid end assembly, wherein, when the lock cover is threadedly engaged with the threaded bore of the lock, the magnetic retention pin is disposed within a post bore of the lock to prevent the lock cover from rotating with respect to the lock. 
     In some aspects, the apparatus described herein relates to a fluid end assembly, wherein the bore is an axial bore defined by a central axis, wherein the central axis extends through the plug member and the lock cover such that the lock cover is axially aligned with the plug member. 
     In some aspects, the apparatus described herein relates to a fluid end assembly, wherein, when the lock cover is coupled to the housing, the lock cover does not apply a preload against the plug member. 
     In some aspects, the apparatus described herein relates to a fluid end assembly, wherein the lock cover further includes: a first end; a second end opposite the first end, the first end being disposed proximate the plug member when the lock cover is coupled to the housing; a sidewall extending from the first end to the second end; and a flange extending radially outward from the sidewall between the first end and the second end, wherein the magnetic retention pin at least partially extends through a cutout disposed within the flange. 
     In some aspects, the apparatus described herein relates to a fluid end assembly, wherein the lock cover further includes: a handle coupled to the flange and extending beyond the first end of the lock cover. 
     In some aspects, the techniques described herein relate to a method of assembling a fluid end of a hydraulic fluid pump, the method including: inserting a plug member into a bore of a housing of the fluid end; coupling a lock cover to the housing such that the lock cover is positioned over the plug member and retaining the plug member in the bore; and inserting a magnetic retention pin at least partially through the lock cover. 
     In some aspects, the techniques described herein relate to a method, wherein coupling the lock cover to the housing includes threading the lock cover into a lock, wherein the lock is coupled to the housing of the fluid end. 
     In some aspects, the techniques described herein relate to a method, wherein the lock cover and the lock include broken zero-pitch threads, wherein threading the lock cover to the lock includes axially inserting the lock cover within the lock and then rotating the lock cover relative to the lock. 
     In some aspects, the techniques described herein relate to a method, wherein, when the lock cover is coupled to the housing, the lock cover does not apply a preload against the plug member. 
     In some aspects, the techniques described herein relate to a method, wherein the plug member is a valve cover that includes a circumferential seal, and wherein inserting the valve cover into the bore includes engaging the circumferential seal against the bore of the housing. 
     In some aspects, the techniques described herein relate to a method, wherein the plug member is a liner that at least partially extends through the lock cover and that defines a conduit configured to receive a piston. 
     In some aspects, the apparatus described herein relates to a fluid end assembly of a hydraulic fluid pump including: a housing having a bore; a plug member positioned at least partially within the bore; a lock cover axially aligned with the bore of the housing and configured to rotate between an unlocked position and a locked position, where the lock cover is configured to retain the plug member within the bore when in the locked position; and a magnetic retention pin extending at least partially through a portion of the lock cover to retain the lock cover in the locked position. 
     In some aspects, the apparatus described herein relates to a fluid end assembly, wherein the lock cover further includes: a first end; a second end opposite the first end, the second end being disposed proximate the plug member when the lock cover is coupled to the housing; a sidewall extending from the first end to the second end; a flange extending radially outward from the sidewall between the first end and the second end, wherein the magnetic retention pin at least partially extends through a cutout disposed within the flange; and a handle coupled to the flange and extending beyond the first end of the lock cover. 
     In some aspects, the apparatus described herein relates to a fluid end assembly, further including: a lock coupled to the housing, the lock defining a threaded bore that is axially aligned with the bore of the housing, wherein the lock cover is configured to threadedly engage the threaded bore of the lock to axially align the lock cover to with the bore of the housing and to couple the lock cover to the housing. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The apparatuses, systems, devices, modules, and/or components presented herein may be better understood with reference to the following drawings and description. It should be understood that some elements in the figures may not necessarily be to scale and that emphasis has been placed upon illustrating the principles disclosed herein. In the figures, like-referenced numerals designate corresponding parts throughout the different views. 
         FIG.  1    illustrates a perspective view of a hydraulic fluid pump. 
         FIG.  2    illustrates a perspective view of retainer assemblies coupled to a fluid end assembly of a hydraulic fluid pump. 
         FIG.  3    illustrates a cross-sectional view taken along line A( 1 )-A( 1 ) of the fluid end assembly and retainer assemblies illustrated in  FIG.  2   . 
         FIGS.  4 A and  4 B  illustrate perspective views of a valve cover for use within the fluid end assembly and the retainer assemblies illustrated in  FIG.  2   . 
         FIG.  5    illustrates a cross-sectional view taken along line A( 2 )-A( 2 ) of the retainer assembly illustrated in  FIG.  2   . 
         FIG.  6    illustrates a perspective view of a lock of the retainer assembly of  FIG.  2   , the lock shown with associated fasteners. 
         FIG.  7    illustrates a perspective view of the lock of  FIG.  6    shown without the associated fasteners. 
         FIG.  8    illustrates a perspective view of a lock cover of the retainer assembly illustrated in  FIG.  2   . 
         FIG.  9    illustrates a perspective isolated view of the main body of the lock cover illustrated in  FIG.  8   . 
         FIG.  10    illustrates a perspective isolated view of the handle of the lock cover illustrated in  FIG.  8   . 
         FIGS.  11 A and  11 B  illustrate perspective views of the retention pins of the retainer assembly illustrated in  FIG.  2   . 
         FIG.  12    illustrates a top view of the retainer assembly illustrated in  FIG.  3   . 
         FIG.  13    illustrates a perspective view of a second embodiment of a retainer assembly coupled to a fluid end assembly of a hydraulic fluid pump. 
         FIG.  14    illustrates a perspective view of the second embodiment of the retainer assembly illustrated in  FIG.  13   . 
         FIG.  15    illustrates a cross-sectional view taken along line A( 3 )-A( 3 ) of the second embodiment of the retainer assembly illustrated in  FIG.  13   . 
         FIGS.  16 A and  16 B  illustrate perspective views of a liner of the second embodiment of the retainer assembly illustrated in  FIG.  14   . 
         FIGS.  17 A and  17 B  illustrate perspective views of a piston of the second embodiment of the retainer assembly illustrated in  FIG.  14   . 
         FIG.  18    illustrates a top view of the second embodiment of the retainer assembly illustrated in  FIG.  14   . 
         FIG.  19    illustrates a perspective view of a third embodiment of a retainer assembly coupled to a fluid end assembly of a hydraulic fluid pump. 
         FIG.  20    illustrates a perspective view of the third embodiment of the retainer assembly illustrated in  FIG.  19   . 
         FIG.  21    illustrates a cross-sectional view taken along line A( 4 )-A( 4 ) of the third embodiment of the retainer assembly illustrated in  FIG.  19   . 
         FIG.  22 A  illustrates a top perspective view of the main body of the lock cover of the third embodiment of the retainer assembly illustrated in  FIG.  20   . 
         FIG.  22 B  illustrates a bottom perspective view of the main body of the lock cover of the third embodiment of the retainer assembly illustrated in  FIG.  20   . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying figures which form a part hereof wherein like numerals designate like parts throughout, and in which is shown, by way of illustration, embodiments that may be practiced. It is to be understood that other embodiments may be utilized, and structural or logical changes may be made without departing from the scope of the present disclosure. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of embodiments is defined by the appended claims and their equivalents. 
     Aspects of the disclosure are disclosed in the description herein. Alternate embodiments of the present disclosure and their equivalents may be devised without parting from the spirit or scope of the present disclosure. It should be noted that any discussion herein regarding “one embodiment”, “an embodiment”, “an exemplary embodiment”, and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, and that such particular feature, structure, or characteristic may not necessarily be included in every embodiment. In addition, references to the foregoing do not necessarily comprise a reference to the same embodiment. Finally, irrespective of whether it is explicitly described, one of ordinary skill in the art would readily appreciate that each of the particular features, structures, or characteristics of the given embodiments may be utilized in connection or combination with those of any other embodiment discussed herein. 
     Various operations may be described as multiple discrete actions or operations in turn, in a manner that is most helpful in understanding the claimed subject matter. However, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations may not be performed in the order of presentation. Operations described may be performed in a different order than the described embodiment. Various additional operations may be performed and/or described operations may be omitted in additional embodiments. 
     For the purposes of the present disclosure, the phrase “A and/or B” means (A), (B), or (A and B). For the purposes of the present disclosure, the phrase “A, B, and/or C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C). 
     The terms “comprising,” “including,” “having,” and the like, as used with respect to embodiments of the present disclosure, are synonymous. 
       FIG.  1    illustrates a hydraulic fluid pump  10  (e.g., a drill pump) of the type often used during drilling and/or hydraulic fracturing operations such as hydrocarbon or oil fracturing. The hydraulic fluid pump  10  includes a power end or drive end or drive end assembly  12  that is largely enclosed within a casing  18 . A fluid end or fluid end assembly  14  attaches to the drive end  12  and the casing  18 , and includes at least one fluid end block or drilling module  16 . In the embodiment illustrated in  FIG.  1   , three drilling modules  16  are shown. However, the hydraulic fluid pump  10  may include any number of drilling modules  16  that make up the fluid end assembly  14 . A drive shaft  20  extends out of the casing  18  and provides for a connection point for a prime mover such as a motor or engine. The prime mover drives the drive shaft  20  at a desired speed to power the drive end  12 . The drive end  12  typically includes a transmission (e.g., gears, belts, chains, etc.) that serve to step down the speed of the drive shaft  20  to a speed appropriate for the fluid end  14 . The drive end  12  includes a series of reciprocating mechanisms that in turn drives a piston or plunger within a respective bore of the fluid end block  16  to pump a fluid. 
     An example embodiment of a fluid end assembly  14  of a hydraulic fluid pump  10  is illustrated in  FIG.  2   , while  FIG.  3    illustrates a cross-sectional view of the fluid end assembly  14  illustrated in  FIG.  2    taken along line A( 1 )-A( 1 ). As illustrated, the fluid end assembly  14  includes a housing  100  with valve covers  200  and retainer assemblies  300  coupled thereto. 
     As best illustrated in  FIG.  3   , the housing  100  defines the main body of the fluid end assembly  14  surrounding an interior volume  110 , the housing having an inlet bore  120 , an outlet bore  122 , a piston bore  124 , and first and second service bores  126 ,  128 . When the fluid end assembly  14  is installed on a hydraulic fluid pump  10 , an inlet manifold  22  (shown in  FIG.  1   ) of the hydraulic fluid pump  10  distributes fluid to an inlet bore  120  to interior volume  110  of the housing  100 . An inlet valve  130  may be positioned in the inlet bore  120  to control flow from the inlet manifold  22  into the interior volume  110  of the housing  100  of the fluid end  14 . The outlet bore  122  directs pressurized fluid from the interior volume  110 , past an outlet valve  132 , and to an outlet manifold  24  (shown in  FIG.  1   ) fastened to the fluid end  14  and aligned with the outlet bore  122  of the fluid end  14 . Thus, the outlet manifold  24  is in fluid communication with the interior volume  110  of the housing  100  via the outlet bore  122  and outlet valve  132 . 
     As further illustrated in  FIG.  3   , the piston bore  124  extends perpendicular to the inlet bore  120 , and supports a packing arrangement having a plurality of seals and a piston retainer  134 . A reciprocating piston (not shown) is movable to pressurize fluid within the interior volume  110  and to the outlet manifold  24  (shown in  FIG.  1   ). 
     With continued reference to  FIGS.  2  and  3   , the first service bore  126  is formed in the housing  100  adjacent the outlet valve  132  and in fluid communication with the outlet bore  122  at all operative times (i.e., the first service bore  126  is not separated from the outlet bore  122  by the outlet valve  132 ). The first service bore  126  is axially aligned with the inlet bore  120  and extends into the housing  100  such that it intersects the outlet bore  122 . The first service bore  126  provides access to the interior volume  110  for insertion and removal of the outlet valve  132  from the housing  100 , and is therefore sized to permit insertion and removal of the outlet valve  132 . A second service bore  128  is formed in the housing  100  parallel with, and also axially aligned with, the piston bore  124 . The second service bore  128  provides access to the interior volume  110  of the housing  100  without removal of the valves  130 ,  132 , the piston retainer  134 , or piston (not shown). The second service bore  128  may additionally provide access for insertion and removal of the piston and/or the inlet valve  130  from the housing  100 , and is sized accordingly. 
     As shown in  FIGS.  2 ,  3 ,  4 A,  4 B, and  5   , both of the service bores  126 ,  128  include valve covers  200  and retainer assemblies  300  that are configured to retain the valve covers  200  within the service bores  126 ,  128 . The valve covers  200  seal against the housing  100  to prevent fluid from the interior volume  110  of the housing  100  from passing through the respective service bores  126 ,  128 . Each retainer assembly  300  covers a respective valve cover  200  (or other type of plug member, the valve cover  200  being one of many types of plug members) to retain the valve cover  200  in a sealing position within its respective bore  126 ,  128 . When the reciprocating piston increases the pressure of the fluid within the interior volume  110  of the housing  100 , a force is applied on the valve covers  200 . While  FIGS.  4 A and  4 B  illustrate a single valve cover  200 , and while  FIGS.  5 - 10 ,  11 A,  11 B, and  12    illustrate a single retainer assembly  300  associated with a valve cover  200 , the description of the valve cover  200  and the retainer assembly  300  below applies to both of the valve covers  200  and the retainer assemblies  300  illustrated in  FIGS.  2  and  3    because they are substantially identical to one another. 
     Turning to  FIGS.  4 A and  4 B , illustrated are perspective views of a valve cover  200 . As illustrated, the valve cover  200  is a cylindrical plug sized to engage the first service bore  126  of the housing  100 . The valve cover  200  may have a first end  202  and an opposite second end  204 . The valve cover may further include a first portion  210  disposed more proximate to the first end  202 , and a second portion  220  that is disposed more proximate to the second end  204 . As illustrated in  FIGS.  4 A and  4 B , the first portion  210  may have a larger diameter than the second portion  220 . The differing diameters of the first and second portions  210 ,  220  may define an outer periphery of the valve cover  200  that is stepped, which may facilitate the valve cover  200  to rest against a lip  127  (best shown in  FIGS.  3  and  5   ) of first service bore  126  of the housing  100  when inserted in an axial (insertion) direction such that the second end  204  of the valve cover  200  is disposed within the interior volume  110  of the housing  100 . As best illustrated in  FIG.  4 A , the first portion  210  includes a planar top or upper surface  212  that may form the first end  202  of the valve cover  200 . Thus, the upper surface  212  of the valve cover may be configured to be engage by the lock cover  340  of the retainer assembly  300 , as described in greater detail below. As best illustrated in  FIG.  4 B , the first portion  210  may further include a sidewall  214  and an underside surface or stepped face  216 , where the sidewall  214  spans from the underside surface  216  to the upper surface  212 . When the valve cover  200  is inserted into the first service bore  126  in an axial (insertion) direction such that the second end  204  of the valve cover  200  is disposed within the interior volume  110  of the housing  100 , the underside surface  216  may rest against or abut the lip  127  of the first service bore  126  of the housing  100 . 
     The second portion  220  of the valve cover  200  may be axially aligned with the first portion  210 , and, as best illustrated in  FIG.  4 B , may include bottom surface  222  and a cylindrical peripheral surface or sidewall  224  that spans from the bottom surface  222  of the second portion  220  to the underside surface  216  of the first portion  210 . Thus, the bottom surface  222  may form the second end  204  of the valve cover  200 . Furthermore, the cylindrical peripheral surface  224  may define a groove or cutout  226 . A circumferential ring seal  228  (e.g., elastomeric seal) may be positioned within the groove  226  of the valve cover  200  to seal the valve cover  200  relative to the service bore  126 . As best illustrated in  FIGS.  3  and  5   , the seal  228  may be positioned at an axial interface between the valve cover  200  and the housing  100 . In other words, the seal  228  is positioned on the cylindrical peripheral surface  224  of the second portion  220  of the valve cover  200  and engages the cylindrical inner surface of the service bore  126 . Therefore, the seal  228  is energized with its placement within the service bore  126  of the housing  100  by its frictional engagement with the service bore  126 . In contrast, a seal that is located on the underside surface or stepped face  216  of the first portion  210  (not the cylindrical peripheral surface  224  of the second portion  220 ) of the valve cover  200  and engaging the lip  127  of the service bore  126  of the housing  100  that is, for example, perpendicular to the axial direction of the service bore  126 , is only energized by preloading the valve cover  200  against the housing  100 . 
     As further illustrated in  FIG.  4 B , the second portion  220  of the valve cover  200  further includes a protrusion  230  that extends from the bottom surface  222  of the second portion  220  of the valve cover  200 . The protrusion  230  may contain an opening or channel  232  that extends through the protrusion  230  and at least a portion of the second portion  220  of the valve cover  200 . As best illustrated in  FIG.  5   , the channel  232  may be configured to slidably receive a portion or valve shaft  240  of the outlet valve  132 , while a spring or resilient member  242  extends from the outlet valve  132 , around the protrusion  230 , and engages the bottom surface  222  of the second portion  220  of the valve cover  200 . The resilient member  242  is configured to retain and position the outlet valve  132  within the outlet bore  122  of the interior volume  110  of the housing  100 . The resilient member  242  biases a valve member  244  of the outlet valve  132  in a closing direction. 
     As  FIG.  5    further illustrates, and with continued reference to  FIGS.  2 ,  3 ,  4 A and  4 B , the first service bore  126  of the housing  100  of the fluid end  14  is aligned with, and provides access to, the outlet valve  132  positioned within the interior volume  110  of the housing  100 . The outlet valve  132  may be configured to control a flow of fluid within the interior volume  110  of the housing  100 . The first service bore  126  is sealed by the valve cover  200 , which is held in place via the retainer assembly  300 . As illustrated and further detailed below, the retainer assembly  300  may include a lock  310 , a lock cover  340 , and one or more retention pins  410 . The retainer assembly  300  retains the valve cover  200  within the first service bore  126  of the housing  100  and counteracts the force applied on the valve cover  200  by pressurized fluid within the interior volume  110  of the housing  100 . However, unlike conventional retainer assemblies, the retainer assembly  300  does not apply a preload on the valve cover  200 . As previously explained, conventional retainer assemblies apply a preload to an associated valve cover to counteract the force applied by the pressurized fluid and to prevent unseating of the valve cover seal, which is typically a face seal, from the housing/bore of the housing. In contrast to the prior art, the retainer assemblies  300  illustrated in  FIGS.  2 ,  3 , and  5    do not require a preload to counteract the force applied by the pressurized fluid, and do not require a preload to prevent unseating of an valve cover seal  228  of the valve cover  200  from the housing  100 . 
     Turning to  FIGS.  6  and  7   , illustrated is an embodiment of the lock  310  of the retainer assembly  300 , where the lock  310  is a ring having a substantially cylindrical shape. In other embodiments, the lock  310  may be non-cylindrical, or may be formed as a plate that is associated with a plurality of valve covers  200  along a length of the fluid end  14 . The illustrated lock  310  includes a sidewall  312  that extends between a first axial end  314  and a second axial end  316 . The lock further includes a lock cover bore  320  extending through the lock  310  from the first axial end  314  to the second axial end  316 . The lock cover bore  320  is therefore a through-bore extending entirely through the axial length of the lock  310 . As shown, the lock cover bore  320  is centered on the lock  310  such that the lock cover bore  320  is coaxial with a central axis B of the lock  310 . 
     As illustrated in  FIGS.  6  and  7   , the lock cover bore  320  may be a threaded bore, and more specifically, may include a plurality of broken, zero-pitch threads or lugs  322 . As shown, the lock cover bore  320  may include twelve threads  322  spaced apart along the length of the bore between the first and second axial ends  314 ,  316  of the lock  310 . In other embodiments, the lock cover bore  320  may include more or less threads  322  (e.g., at least one, at least two, etc.). The threads  322  may have no pitch and are therefore not interconnected with one another as a spiral. Rather, each thread  322  may be flat or planar and may be defined within a plane that is perpendicular to the central axis B of the lock cover bore  320  and parallel with the respective plane of each additional thread  322 . In other embodiments, the threads  322  of the lock cover bore  320  may have a pitch along the axial length of the lock  310 . 
     Each of the plurality of threads  322  is broken or interrupted such that each thread  322  is non-continuous, but instead defines a gap  324  at intervals along the thread  322 . As shown in  FIGS.  6  and  7   , each thread  322  of the plurality of threads is broken into four broken thread segments  326  each spanning 45 degrees about the lock cover bore  320 , with a gap  324  in between each 45 degree segment. In other embodiments, each thread  322  may be broken into more or less segments  326  (e.g., two broken thread segments  326  each spanning 90 degrees about the lock cover bore  320  and separated by 90 degree gaps  324 , three broken thread segments  326  each spanning 60 degrees about the lock cover bore  320  and separated by 60 degree gaps  324 , etc.). Further, in some embodiments, the sizes of the gaps  324  may be dissimilar to the sizes of the broken thread segments  326 . Each thread  322  of the respective broken thread segment  326  is axially aligned with every other thread of the respective broken thread segment  326  such that the gaps  324  are axially aligned. Therefore, each axial gap  324  extends through the entire lock cover bore  320  between the adjacent broken thread segments  326 . In other embodiments, the threads  322  of the lock cover bore  320  may have a pitch along the axial length of the lock  310 , and may continuously extend around the lock cover bore  320  (i.e., the threads  322  may not contain any gaps  324 ). 
     The lock  310  further includes a plurality of fastener bores  330 , which are best shown in  FIG.  7   , that positioned around the lock cover bore  320 . As shown, twelve fastener bores  330  are positioned radially outward from the lock cover bore  320 , extending axially through the lock  310  from the first axial end  314  to the second axial end  316 . Central axes C of the fastener bores  330  extend parallel to one another and parallel to the central axis B of the lock cover bore  320 . The fastener bores  330  may be spaced equidistant from one another about the lock cover bore  320 . In the embodiment illustrated, each fastener bore  330  may be spaced apart from the next adjacent bores  330  by approximately 30 degrees. 
     As shown in  FIG.  6   , fasteners  332  (e.g., threaded fasteners such as bolts, threaded studs, etc.) may extend through the fastener bores  330 . The fasteners  332  may be longer than the fastener bores  330  (i.e., longer than the axial length of the lock  310 ) such that when the second axial end  316  of the lock  310  is positioned on the housing  100  of the fluid end  14 , the fasteners  332  extend through the fastener bores  330  of the lock  310  and into respective threaded fastener bores (not shown) of the fluid end housing  100 . As shown, the fasteners  332  may each be a threaded stud, and each fastener  332  may further include an associated nut  334  that is threaded onto the fastener  332  and into engagement with the first axial end  314  of the lock  310 . The fasteners  332  may couple the lock  310  to the housing  100  of the fluid end  14 . 
     The lock  310  further includes a plurality of pin bores or retainer bores  336 , which extend axially from the first axial end  314  of the lock  310  toward the second axial end  316 . The retainer bores  336  are located radially between the lock cover bore  320  and the sidewall  312  of the lock  310  and extend in an axial direction that is parallel to the central axis B of the lock cover bore  320 . As shown, the retainer bores  336  may be located more proximate to the lock cover bore  320  than to the sidewall  312  of the lock  310 . The retainer bores  336  may be blind holes or blind bores that are formed in the first axial end  314  and may terminate prior to the second axial end  316 . As shown, the retainer bores  336  may be unthreaded. In the illustrated embodiment, the lock  310  may contain four retainer bores  336 , each offset from one another by ninety degrees about the lock cover bore  320 . In some embodiments, the number of retainer bores  336  may correspond to the number of broken thread segments  326  of the lock cover bore  320 . The retainer bores  336  will be described in greater detail below with respect to the retention pins  410 . 
     Turning to  FIGS.  8 - 10   , illustrated is the lock cover  340  of the retainer assembly  300 . The lock cover  340  is configured to be inserted into the lock cover bore  320  of the lock  310  and may be generally cylindrical to facilitate rotation of the lock cover  340  within the lock cover bore  320  and with respect to the lock  310 . As best illustrated in  FIG.  8   , the lock cover  340  may include a main body  350  and a handle  390  coupled to the main body  350 . 
       FIG.  9    illustrates an isolated (i.e., with the handle  390  removed) perspective view of the main body  350  of the lock cover  340 , the main body  350  being sized and shaped to fit within the lock cover bore  320  of the lock  310 . The main body  350  may have a first axial end  352  and a second axial end  354  opposite the first axial end  352 . The main body  350  may also include a central bore  356  that extends through the main body  350  from the first axial end  352  to the second axial end  354 . 
     As further illustrated in  FIG.  9   , the main body  350  may further include an upper portion  360  and a lower portion  370 . The upper portion  360  may be smaller in diameter than the lower portion  370 . The upper portion  360  may be substantially cylindrical with a sidewall  362  extending from a first end  364  to a lower end  366 . The first end  364  of the upper portion  360  may form the first axial end  352  of the main body  350 . The upper portion  360  may further includes various assembly features, such as radial apertures  368  (extending transverse to the central bore  356  of the main body  350  of the lock cover  340 ) that assist in the installation of the lock cover  340  within the lock  310 . 
     The lower portion  370  may include a substantially cylindrical sidewall  372  that extends from a first end  374  to a second end  376 . The second end  376  of the lower portion  370  may form the second axial end  354  of the main body  350 . Moreover, the first end  374  of the lower portion  370  may be coupled to the second end  366  of the upper portion  360 . Disposed at the coupling of the first end  374  of the lower portion  370  to the second end  366  of the upper portion  360  is a flange  378 , which may have a diameter that is larger than both that of the upper portion  360  and the lower portion  370 . Thus, the flange  378  may extend radially outward from the main body  350  of the lock cover  340 . Disposed on the upper surface of the flange  378  may be a plurality of attachment openings  379  (e.g., threaded bores). 
     As further illustrated in  FIG.  9   , the lower portion  370  may be a threaded portion and may include external threads  380  that are similar to the internal threads  322  of the lock cover bore  320 . Thus, the external threads  380  may be broken zero-pitch threads sized to engage the broken zero-pitch threads  322  of the lock cover bore  320 . As shown, the lower portion  370  of the main body  350  of the lock cover  340  may include eleven threads  380  that are configured to engage within the twelve threads  322  of the lock cover bore  320 . The threads  380  are broken such that the broken thread segments  382 , which are separated from one another by gaps  384 , of the external threads  380  fit within the gaps  324  between the broken thread segments  326  in the lock cover bore  320  (i.e., the external broken thread segments  382  of the lock cover  340  are equal to or less than the size of the gaps  324  in the lock cover bore  320 ) and the arrangement of the external broken thread segments  382  allow them to each be aligned with, and placed within, respective gaps  324  in the lock cover bore  320 . As the external threads  380  are broken, the external threads  380  of the lock cover  340  are engaged with the lock cover bore  320  by first axially inserting the lock cover  340  into the lock cover bore  320  with the external broken thread segments  382  of the lock cover  340  positioned in the gaps  324  defined between the internal broken thread segments  326  of the lock cover bore  320 . Once the lock cover  340  is axially positioned within the lock cover bore  320  of the lock  310 , the lock cover  340  may be rotated relative to the lock cover bore  320  so that the threads  322 ,  380  engage one another. For the illustrated embodiment, this includes rotating the lock cover  340  by 45 degrees with respect to the lock cover bore  320 . In some embodiments, one pair of mating threads  322 ,  380  (e.g., the lowest threads) of the lock cover bore  320  and the lock cover  340 , respectively, may be larger and/or spaced apart at a greater distance from one another than the remainder of threads  322 ,  380  so that the lock cover  340  is only capable of engaging the lock cover bore  320  at one axial position along the axial length of the lock cover bore  320 . In other embodiments, the length of the lower portion  370  (i.e., the length between the first and second ends  374 ,  376  of the lower portion  370 ) may be sized (e.g., have a predetermined length) so that the threads  322 ,  380  of the lock cover bore  320  and the lock cover  340 , respectively, are aligned to facilitate a mating engagement of the threads  322 ,  380  when the flange  378  of the main body  350  of the lock cover  340  is in abutment with the first axial end  314  of the lock  310 . In other embodiments, the threads  380  of the lock cover  340  may have a pitch along the axial length of the lower portion  370  of the lock cover  340 , and may continuously extend around the lower portion  370  of the lock cover  340 . 
     In even further embodiments, the lock cover bore  320  of the lock  310  and the lock cover  340  may contain a complementary grove/track and cam arrangement, where one component contains at least one groove, and the other component contains at least one complementary cam that may be received by the at least one groove. In some embodiments, this grove may be L-shaped, while in other embodiments, the groove may spiral around the lock cover bore  320  or lock cover  340 . In these embodiments, when the lock cover  340  is inserted into the lock cover bore  320 , the cam may be disposed in the groove. As the lock cover  340  descends into the lock cover bore  340  and is placed in a locked position (i.e., fully inserted into the lock cover bore  320 , the cam may follow along the groove. 
     As illustrated in  FIGS.  5 ,  8 , and  9   , the second axial end  354  (i.e., the second end  376  of the of the lower portion  370 ) of the main body  350  of the lock cover  340  defines an abutment surface  386  for contacting the first end  202  (e.g., the upper surface  212  of the first portion  210 ) of the valve cover  200  when the lock cover  340  is installed within the lock cover bore  320  of the lock  310 . As shown, the abutment surface  386  directly contacts the valve cover  200 , and specifically, as shown in  FIG.  5   , contacts the radial periphery of the upper surface  212  of the first portion  210  of the valve cover  200 . In other embodiments, the abutment surface  386  may indirectly contact the valve cover  200  via an intermediate component. 
     As previously explained, and as best shown in  FIGS.  8  and  10   , the lock cover  340  includes a handle  390  that is coupled to the main body  350 . The handle  390  may include a lower ring portion  392  and an upper engagement portion  400 . As best illustrated in  FIG.  10   , the lower ring portion  392  may have a substantially ring shape. In other embodiments of the of the handle  390 , the lower ring portion  392  may be of any other shape. The lower ring portion  392  may include a central opening  394  and a series of attachment apertures  396 . As best illustrated in  FIG.  8   , when the handle  390  is coupled to the main body  350 , the upper portion  360  of the main body  350  may be inserted through the central opening  394  of the lower ring portion  392  such that the lower ring portion surrounds the upper portion  360  of the main body  350 . Moreover, when the handle  390  is coupled to the main body  350 , the lower ring portion  392  may be in abutment with the upper surface of the flange  378  of the main body  350 , and the attachment apertures  396  may be aligned with the attachment openings  379  of the flange of the main body  350 . As further illustrated in  FIG.  8   , fasteners  398  may be inserted through the attachment apertures  396  of the lower ring portion  392  of the handle  390  and into the attachment openings  379  of the main body  350  to secure the handle  390  to the main body  350 . As further illustrated, the lower ring portion  392  may also include one or more cutouts  399  disposed in an outer edge of the lower ring portion  392 . When the handle  390  is coupled to the main body  350 , the lower ring portion  392  may be a flange of the lock cover that extends radially outward from the main body  350  of the lock cover  340 . 
     Continuing with  FIGS.  8  and  10   , the upper engagement portion  400  of the handle  390  may include a series of upstanding members  402  that extend upwardly from the top surface of the lower ring portion  392 . The embodiment of the handle  390  illustrated in  FIG.  10    contains four upstanding member  402 . The handle  390  may further include two elongated members  404  that extend across the handle  390 , where each elongated member  404  is coupled to the ends of two upstanding members  402 . The elongated members  404  may be substantially parallel to one another. The handle  390  may further include cylindrical members  406  that extend between opposing ends of the two elongated members  404  to create a handle engagement area of a user. Thus, the handle  390  presents the user with two engagement areas (e.g., the cylindrical members  406 ) that are opposed to one another and are configured to facilitate ease of rotation of the lock cover  340 . In other embodiments, the cylindrical members  406  may be of any shape. In further embodiments, the handle  390  may be of any other shape, structure, and orientation that facilitates ease of insertion and rotation of the lock cover  340 . In even further embodiments, the handle  390  may be integrally formed with the main body  350 . In yet even further embodiments, the lock cover  340  may not contain a handle  390 , and instead the cutouts  399  may be formed in the flange  378  of the main body  350  of the lock cover  340 . 
     Turning to  FIGS.  11 A and  11 B , illustrated is an example embodiment of the retention pin  410 . The pin  410  may be substantially elongated with a first end  412  and an opposite second end  413 . Disposed between the first end  412  and the second end  413  may be an intermediate portion  414  that may be substantially cylindrical in shape. As illustrated in  FIGS.  11 A and  11 B , the pin  410  includes an engagement flange portion  415  disposed at the first end  413 , where the engagement flange portion  415  extends radially outward from the intermediate portion  414 . The engagement flange portion  415  may be shaped to facilitate engagement with an operator&#39;s/user&#39;s finger. The pin  410  may further include a shank or shank portion  416  that descends from a bottom face or bottom surface  417  of the intermediate portion  414 . As illustrated, the shank  416  may be smaller in diameter than the intermediate portion  414 . As best illustrated in  FIG.  11 B , the bottom surface  417  of the intermediate portion  414  of the pin  410  may include a magnet  418 . 
     As best illustrated in  FIGS.  5  and  12   , when the lock cover  340  is inserted into the lock cover bore  320  of the lock  310 , and the lock cover  340  has been rotated such that external threads  380  of the lock cover  340  engage the internal threads  322  of the lock cover bore  320  of the lock  310  and such that the cutouts  399  of the lower ring portion  392  are aligned with the retainer bores  336  on the first end  314  of the lock  310 , the shanks  416  of the pins  410  may be inserted through, and at least partially disposed within, both the cutouts  399  of the lower ring portion  392  and the retainer bores  336  on the first end  314  of the lock  310 . This rotation prevention positioning of the pins  410  prevents rotation of the lock cover  340  with respect to the lock cover bore  320 . In other words, the shanks  416  of the pins  410  being engaged with both the cutouts  399  of the lower ring portion  392  of the lock cover  340  and the retainer bores  336  of the lock  310  rotatably lock the lock cover  340  relative to the lock  310  in a position that prevents axial removal of the lock cover  340  from the lock  310  (due to the engagement of the external threads  380  of the lock cover  340  with the internal threads  322  of the lock cover bore  320  of the lock  310 ). 
     As further illustrated in  FIG.  5   , the bottom surface  417  of the intermediate portion  414  of the pins  410  may be in abutment with the lower ring portion  392 . In some embodiments, the lower ring portion  392  may be constructed from ferromagnetic metals or other magnetically attractive materials such that the magnet  418  of the intermediate portion  414  of the pin  410  is attracted to the lower ring portion  392 , which serves to secure the pins  410  in the rotation prevention position (i.e., the position shown in  FIGS.  5  and  12    where the pins  410  prevent rotation of the lock cover  340  with respect to the lock cover bore  320  of the lock  310 ). The magnetic attraction between the magnet  418  of the pins  410  and the lower ring portion  392  may be strong enough to withstand and overcome vibrations imparted onto the lock  310  and the lock cover  340  by a hydraulic fluid pump  10 . 
     In operation, as shown in  FIGS.  2 ,  5 , and  12   , to assemble and secure the outlet valve  132  within the first service bore  126  of the fluid end  14 , the lock  310  is fastened to the housing  100  of the fluid end  14  such that the lock  310  surrounds the first service bore  126  into which the outlet valve  132  and valve cover  200  will be inserted. Fasteners  332  may be inserted through the fastener bores  330  of the lock  310  to thread into the fastener bores (not shown) of the housing  100  of the fluid end  14 . Nuts  334  may be threaded onto the fasteners  332  and may be tightened against the first axial end  314  of the lock  310 , thereby securing the lock  310  to the housing  100  of the fluid end  14 . The outlet valve  132  may be positioned through the lock  310  (i.e., inserted through the lock cover bore  320 ) and within the outlet bore  122  of the fluid end  14 , and the first service bore  126  may then be sealed by the valve cover  200 , which may also be inserted through the lock cover bore  320  of the lock  310 . In some embodiments, the outlet valve  132  and valve cover  200  can be installed within the first service bore  126  prior to installation of the lock  310 , though, as shown, the valve cover  200  and outlet valve  132  are removable and insertable through the lock  310  for replacement and initial assembly without removing the lock  310  from the housing  100  of the fluid end  14 . The circumferential seal  228  on the cylindrical peripheral surface  224  of the valve cover  200  is energized by its placement within the first service bore  126 , and does not need to be preloaded during installation. 
     The lock cover  340  is positioned above the lock cover bore  320  of the lock  310  and is rotatably aligned such that the gaps  324  between the broken thread segments  326  of the lock  310  are axially aligned with the broken thread segments  382  of the lock cover  340 , and such that the broken thread segments  326  of the lock  310  are axially aligned with the gaps  384  between the broken thread segments  382  of the lock cover  340 . The lock cover  340  is axially inserted (i.e., along central axis B) into the lock cover bore  320  of the lock  310  until the flange  378  of the main body  350  of the lock cover  340  abuts the first axial end  314  of the lock  310 . As previously explained, the length of the lower portion  370  of the main body  350  of the lock cover  340  may be configured such that, when the flange  378  is in abutment with the first axial end  314  of the lock  310 , the threads  380  of the lock cover  340  are axially displaced into alignment with the appropriate openings between threads  322  of the lock  310 . When the threads  380  are axially positioned to be aligned as desired, the operator/user rotates the lock cover  340  relative to the lock  310 , thereby engaging the threads  322 ,  380  with one another. When the threads  322 ,  380  are engaged with one another, the lock cover  340  is axially locked (prohibited from moving axially along central axis B) with respect to the lock cover bore  320  of the lock  310 . Conversely, when the threads  322 ,  380  are not engaged with one another, the lock cover  340  is axially unlocked (free to move axially along central axis B) with respect to the lock cover bore  320  of the lock  310 . The operator/user may rotate lock cover  340  until the cutouts  399  of the lower ring portion  392  of the handle  390  of the lock cover  340  are aligned with the retainer bore  336  in the first axial end  314  of the lock  310 . The operator/user may then insert the shank  416  of each pin  410  into a cutout  399  and aligned retainer bore  336  until the bottom surface  417  of the intermediate portion  414  abuts the lower ring portion  392  of the handle  390  of the lock cover  340 . As explained previously, when the shanks  416  of the pins  410  are inserted into both the cutouts  399  and the retainer bores  336 , the lock cover  340  cannot be rotated relative to the lock  310  and cannot be axially removed from the lock cover bore  320  of the lock  310 . Therefore, the pins  410  serve as a rotational lock that prohibits rotation of the lock cover  340  relative to the lock  310 . The magnetic attraction between the magnet  418  of the intermediate portion  414  of the pins  410  and the lower ring portion  392  of the handle  390  of the lock cover  340  secures the pins  410  in the inserted position (i.e., the shanks  416  of the pins  410  being inserted into both the cutouts  399  and the retainer bores  336 ) until the operator/user manually removes the pins  410 . When secure, the abutment surface  386  of the lock cover  340  is positioned in proximity to and/or in contact with the upper surface  212  of the first portion  210  of the valve cover  200 , thereby preventing axial translation of the valve cover  200  away from the fluid end housing  100 , even in response to increased pressure within the fluid end  14 . 
     In operation, to remove the valve cover  200  or the outlet valve  132 , the operator lifts pulls the pins  410  out of the cutouts  399  and the retainer bores  336 . The interaction between the threads  322 ,  380  of the lock  310  and the lock cover  340  counteract the magnetic force between the magnet  418  and the lower ring portion  392  of the handle  390  of the lock cover  340  to facilitate removal the pins  410  from the retainer bores  336  and the cutouts  399 . With the shanks  416  of the pins  410  removed from at least the retainer bores  336 , the operator/user can rotate the lock cover  340  until the threads  322 ,  380  are disengaged from one another such that the threads  322  of the lock  310  are aligned with the gaps  384  of the lock cover  340  and the threads  380  of the lock cover  340  are aligned with the gaps  324  in the lock cover bore  320  of the lock  310 . The lock cover  340  may then be axially removed from the lock cover bore  320  of the lock  310 , and the valve cover  200  and outlet valve  132  are accessible for service and/or removal and replacement. 
     Turning to  FIG.  13   , illustrated is a fluid end assembly  14  with two first embodiment retainer assemblies  300  (as described above with respect to  FIGS.  2 ,  3 ,  4 A,  4 B,  5 - 10 ,  11 A,  11 B , and  12 ) coupled to the housing  100  of the fluid end assembly  14 , and one second embodiment of the retainer assembly  300 ′ that is coupled to the housing of the fluid end assembly  14  proximate to the piston bore  124 . Both the first and second embodiments of the retainer assembly  300 ,  300 ′ described herein may be utilized to secure various types of plug members within bores  120 ,  122 ,  124 ,  126 ,  128  of the housing  100 . These plug members include the valve covers  200 , as described above with respect to  FIGS.  4 A and  4 B , but also include the liner  500  and piston  520  illustrated in  FIGS.  16 A,  16 B,  17 A, and  17 B . The second embodiment of the retainer assembly  300 ′ illustrated in  FIGS.  13 - 15  and  18    may be substantially similar in structure and operation to the first embodiment of the retainer assembly  300  (i.e., the second embodiment of the retainer assembly  300 ′ may contain the same or similar components as described above with respect to the first embodiment of the retainer assembly  300 , including, but not limited to, the lock  310 , the lock cover  340 , and the pins  410 ) except that the second embodiment of the retainer assembly  300 ′ may secures a liner  500  and piston  520  to the housing  100  instead of a valve cover  200 . 
     As best illustrated in  FIGS.  16 A and  16 B , the liner  500  may be a substantially elongated plug member having a first end  502  and an opposite second end  504 . The term liner as used herein may refer to a liner, a stuffing box, and/or a gland package that are configured to prevent the leakage of fluids between sliding or turning parts (e.g., pistons, plungers, etc.). While the illustrated embodiment of the liner  500  is substantially cylindrical, the liner  500  may be of any other shape. The liner  500  may further include a sidewall  506  spanning from the first end  502  to the second end  504 . As further illustrated in  FIGS.  16 A and  16 B , the liner  500  may also include a central conduit  508  spanning through the liner  500  from the first end  502  to the second end  504 . The central conduit  508  may be centrally disposed in the liner  500  such that the central conduit  508  is coaxial with a central axis D of the liner  500  that extends through the first and second ends  502 ,  504  of the liner  500 . In addition, the embodiment of the liner  500  illustrated may further include a flange  510  that extends radially outward from the sidewall  506  more proximate to the second end  504  than to the first end  502  of the liner  500 . The flange  510  may define an upper surface  512  and an opposite lower surface  514 . As best illustrated in  FIGS.  14 ,  15 , and  18   , the diameter of the flange  510  may be greater than the diameter of the central bore  356  of the main body  350  of the lock cover  340 , while the diameter of the remaining portions of the liner  500  may be substantially equal to, or slightly smaller than, the diameter of the central bore  356  of the main body  350  of the lock cover  340 . Thus, when installed on the housing  100  as best illustrated in  FIG.  15   , the abutment surface  386  of the lock cover  340  may be disposed proximate to, or in abutment with, the upper surface  512  of the flange  510  of the liner  500 , while the portion of the liner  500  disposed between the first end  502  and the flange  510  may extend through the central bore  356  of the main body  350  of the lock cover  340 . 
     As best illustrated in  FIGS.  17 A and  17 B , illustrated is a piston  520  that may be disposed within the central conduit  508  of the liner  500 , and configured to slide or translate along the central conduit  508  of the liner  500  (i.e., along the central axis D of the liner  500 ). The term piston as used herein may refer to a piston or plunger that is configured to slide and/or turn through a liner, stuffing box, or gland package. The piston  520  may be substantially cylindrical in shape, and may have a first end  522  and an opposite second end  524 . The piston  520  may further include a sidewall  526  spanning from the first end  522  to the second end  524 . As best illustrated in  FIG.  17 A , the second end  524  of the piston  520  may include a cavity  528  and a protrusion  530  extending centrally through the cavity  528 . Because the protrusion  530  extends centrally through the cavity  528 , the cavity  528  may have an annular shape. As further illustrated in  FIGS.  17 A and  17 B , the piston  520  further includes a central conduit  532  that extends through the piston  520  from the first end  522  to the second end  524 . The central conduit  532  may be centrally disposed in the piston  520  such that the central conduit  532  is coaxial with a central axis E of the piston  520  that extends through the first and second ends  522 ,  524 , as well as the protrusion  530  in the cavity  528 , of the piston  520 . Thus, the central conduit  532  extends through the protrusion  530  that extends through the cavity  528  of the piston  520 . In other words, the protrusion  530  defines the circumference of portion of the central conduit  532  that extends through the cavity  528  of the piston  520 . The sidewall  526  of the piston  520  may further include a channel  534  that extends circumferentially around the sidewall  526  proximate to the first end  522  of the piston  520 . The channel  534  may be configured to receive a seal (not shown) that is configured to seal the piston  520  relative to the central conduit  508  of the liner  500 . Thus, the seal may be energized with its placement within the central conduit  508  of the liner  500  by its frictional engagement with the central conduit  508 . As best illustrated in  FIGS.  14  and  15   , the central conduit  532  of the piston  520  may be configured to receive a piston rod  540  that is configured to facilitate translation/movement of the piston  520  through the central conduit  508  of the liner  500 . 
     The second embodiment of the retainer assembly  300 ′ illustrated in  FIGS.  13 - 15 ,  16 A,  16 B,  17 A,  17 B, and  18    may be secured to the housing  100  of the fluid end  14  proximate to the piston bore  124  of the housing of the fluid end  14  to removably secure the liner  500  and piston  520  to the housing  100  at the piston bore  124 . In  FIG.  15   , the frame  550  of the pump  10 , a portion of which may be disposed between the second axial end  316  of the lock  310  and the outer surface of the housing  100 , is shown in phantom for illustrative purposes only. During assembly, the lock  310  may be fastened to the housing  100  of the fluid end  14  such that the lock  310  surrounds the piston bore  124  into which at least a portion of the liner will be inserted. The fasteners  332  may then be passed through the fastener bores  330  of the lock  310  to thread into the fastener bores (not shown) of the housing  100  of the fluid end  14 . The nuts  334  may then be threaded onto the fasteners  332  and may then be tightened against the first axial end  314  of the lock  310 , thereby securing the lock  310  to the housing  100  of the fluid end  14 . The liner  500  may then be inserted through the lock cover bore  320  of the lock  310 , and at least partially into the piston bore  124  such that the bottom surface  514  of the flange  510  of the liner  500  engages with piston retainer  134  disposed within the piston bore  124 . In this position, the portion of the liner  500  disposed between the flange  510  and the first end  502  of the liner  500  may extend through the lock cover bore  320  of the lock  310 . In some embodiments, the portion of the liner  500  disposed between the flange  510  and the second end  504  of the liner  500  or the bottom surface  514  of the flange  510  may contain a seal that is energized by its placement against the piston retainer  134  disposed within the piston bore  124 . 
     Once the liner  500  has been placed within the piston bore  124 , the lock cover  340  may be positioned above the lock cover bore  320  of the lock  310  and rotatably aligned such that the gaps  324  between the broken thread segments  326  of the lock  310  are axially aligned with the broken thread segments  382  of the lock cover  340 , and such that the broken thread segments  326  of the lock  310  are axially aligned with the gaps  384  between the broken thread segments  382  of the lock cover  340 . The lock cover  340  may be axially inserted (i.e., along central axis B) into the lock cover bore  320  of the lock  310  such that the liner  500  is inserted into the central bore  356  of the lock cover  340 , and until the flange  378  of the main body  350  of the lock cover  340  abuts the first axial end  314  of the lock  310 . As previously explained, the length of the lower portion  370  of the main body  350  of the lock cover  340  may be configured such that, when the flange  378  is in abutment with the first axial end  314  of the lock  310 , the threads  380  of the lock cover  340  are axially displaced into alignment with the openings between the appropriate threads  322  of the lock  310 . When the threads  380  are axially positioned to be aligned as desired, the operator/user rotates the lock cover  340  relative to the lock  310 , thereby engaging the threads  322 ,  380  with one another. When the threads  322 ,  380  are engaged with one another, the lock cover  340  is axially locked (prohibited from moving axially along central axis B) with respect to the lock cover bore  320  of the lock  310 . Conversely, when the threads  322 ,  380  are not engaged with one another, the lock cover  340  is axially unlocked (free to move axially along central axis B) with respect to the lock cover bore  320  of the lock  310 . The operator/user may rotate the lock cover  340  until the cutouts  399  of the lower ring portion  392  of the handle  390  of the lock cover  340  are aligned with the retainer bore  336  in the first axial end  314  of the lock  310 . Rotation of the lock cover  340  with respect to the lock  310  may also rotate the lock cover  340  with respect to the liner  500  at least partially disposed within the central bore  356  of the main body  350  of the lock cover  340 . As previously described, the operator/user may then insert the shank  416  of each pin  410  into a cutout  399  and aligned retainer bore  336  until the bottom surface  417  of the intermediate portion  414  abuts the lower ring portion  392  of the handle  390  of the lock cover  340  in order to rotationally lock the rotational position of the lock cover  340  relative to the lock  310 . The magnetic attraction between the magnet  418  of the intermediate portion  414  of the pins  410  and the lower ring portion  392  of the handle  390  of the lock cover  340  secures the pins  410  in the inserted position (i.e., the shanks  416  of the pins  410  being inserted into both the cutouts  399  and the retainer bores  336 ) until the operator/user manually removes the pins  410 . Once the lock cover  340  is secured both rotationally and axially within the lock cover bore  320  of the lock  310 , and, as a result, the liner  500  is secured to the housing  100 , the piston  520  and the piston rod  540  may be inserted into the central conduit  508  of the liner  500 . However, in other embodiments, the piston  520 , and the piston rod  540  may be inserted into the liner  500  prior to installation of the liner  500  in the piston bore  124  of the housing, or prior to the lock cover  340  being inserted into the lock cover bore  320  of the lock  310 . Once installed, the piston  520  may be movable along the central conduit  508  of the liner  500  to pressurize fluid within the interior volume  110  of the housing  100 . 
     Turning to  FIG.  19   , illustrated is a fluid end assembly  14  with two first embodiment retainer assemblies  300  (as described above with respect to  FIGS.  2 ,  3 ,  4 A,  4 B,  5 - 10 ,  11 A,  11 B , and  12 ) coupled to the housing  100  of the fluid end assembly  14 , and one third embodiment of the retainer assembly  300 ″ that is coupled to the housing  100  of the fluid end assembly  14  proximate to the piston bore  124 . While the first and second embodiments of the retainer assembly  300 ,  300 ′ described above may be utilized to secure various types of plug members (e.g., valve covers  200 , liners  500 , pistons  520 , stuffing boxes, plungers, etc.) within bores  120 ,  122 ,  124 ,  126 ,  128  of the housing  100 , the third embodiment of the retainer assembly  300 ″ integrates the liner and the main body  610  of the lock cover  600  into one uniform structure and may be configured secure a piston  520  in proximity to the piston bore  124  via the central bore  616  of the lock cover  600 . Outside of the lock cover  600 , the third embodiment of the retainer assembly  300 ″ illustrated in  FIGS.  19 - 21    may be substantially similar in structure and operation to the first and second embodiments of the retainer assembly  300 ,  300 ″ (i.e., the third embodiment of the retainer assembly  300 ″ may contain the same or similar components as described above with respect to the first and second embodiments of the retainer assembly  300 ,  300 ″ including, but not limited to, the lock  310  and the pins  410 ). 
     The lock cover  600  of the third embodiment of the retainer assembly  300 ″, like the lock cover  340 , may include both a main body  610  and a handle  390  attached to the main body  610 , but the main body  610  of the third embodiment of the retainer assembly  300 ″ may differ from the main body  350  of the lock cover  340  while the handle  390  of the lock cover  600  remains substantially similar to the handle  390  of the lock cover  340 . 
     As best illustrated in  FIGS.  22 A and  22 B , illustrated are isolated (i.e., with the handle  390  removed) perspective views of the main body  610  of the lock cover  600 . As best illustrated in  FIGS.  20  and  21   , the main body  610  of the lock cover  600  may be sized and shaped to fit within the lock cover bore  320  of the lock  310 . As illustrated in  FIGS.  22 A and  22 B , the main body  610  may have a first axial end  612  and a second axial end  614  opposite the first axial end  612 . The main body  610  may also include a central bore  616  that extends through the main body  610  from the first axial end  612  to the second axial end  614 . The diameter of the central bore  616  of the main body  610  of the lock cover  600  may be smaller than the diameter of the central bore  356  of the main body  350  of the lock cover  340 . More specifically, the diameter of the central bore  616  of the main body  610  of the lock cover  600  may be substantially equal to the diameter of the central conduit  508  of the liner  500 . Thus, as best illustrated in  FIG.  21   , the central bore  616  of the main body  610  may be configured to receive the piston  520  and at least a portion of the piston rod  540 , which may be configured to translate or move along the central bore  616  of the main body  610 . 
     As further illustrated in  FIGS.  22 A and  22 B , the main body  610  may further include an upper portion  620  and a lower portion  640 . The upper portion  620  may be substantially cylindrical with a sidewall  622  extending from a first end  624  to a lower end  626 . The upper portion  620  may be a stepped structure with a first stepped segment  628  and a second stepped segment  629 , the first stepped segment  628  having a larger diameter than the second stepped segment  629 . As best illustrated in  FIG.  22 A , the first stepped segment  628  may have first concentric upper surface  630 , and the second stepped segment  629  may have a second concentric upper surface  632 . The second concentric upper surface  632  may form the first end  624  of the upper portion  620 , which in turn may form the first axial end  612  of the main body  610 . In other embodiments, the upper portion  620  may not have a stepped structure, and may include only a single upper surface that defines an opening to the central bore  616 . In even further embodiments, the upper portion  620  may have a stepped structure with a larger number of stepped segments and concentric upper surfaces. 
     The lower portion  640  may also be substantially cylindrical with a sidewall  642  that extends from a first end  644  to a second end  646 . Similar to the upper portion  620 , the lower portion  640  may also be a stepped structure, but the lower portion  640  may include a first stepped segment  650 , a second stepped segment  652 , and a third stepped segment  654 . The first stepped segment  650  may have a larger diameter than the second stepped segment  652  and the third stepped segment  654 , while the second stepped segment  652  may have a larger diameter than the third stepped segment  654 . Moreover, the first stepped segment  650  of the lower portion  640  may have a larger diameter than the first and second stepped segments  628 ,  629  of the upper portion  620 . As best illustrated in  FIG.  22 B , the first stepped segment  650  may have first concentric lower surface  660 , the second stepped segment  652  may have a second concentric lower surface  662 , and the third stepped segment  654  may have a third concentric lower surface  664 . The third concentric lower surface  664  may form the second end  646  of the lower portion  640 , which in turn may form the second axial end  614  of the main body  610 . In other embodiments, the lower portion  640  may not have a stepped structure, and may include only a single horizontal lower surface that defines an opening to the central bore  616 . In even further embodiments, the lower portion  640  may have a stepped structure with a larger or smaller number of stepped segments and concentric lower surfaces. In some even further embodiments, the lower portion  640  may have a tapered or substantially conical surface that tapers from the sidewall towards a central axis of the main body  610 . 
     Continuing with  FIGS.  22 A and  22 B , the first end  644  of the lower portion  640  may be coupled to the second end  626  of the upper portion  620 . Disposed at the coupling of the first end  644  of the lower portion  640  to the second end  626  of the upper portion  620  is a flange  648 , which may have a diameter that is larger than the first stepped segment  650  of the lower portion  640 . Thus, the flange  648  may extend radially outward from main body  610  of the lock cover  600 . Disposed on the upper surface of the flange  648  may be a plurality of attachment openings  649  (e.g., threaded bores) for securing the handle  390  to the main body  610 . 
     As further illustrated in  FIGS.  22 A and  22 B , the first stepped segment  650  of the lower portion  640  may be a threaded portion like that of the lock cover  340 . Thus, the first stepped segment  650  of the lower portion  640  may include external threads  670  that are similar to the internal threads  322  of the lock cover bore  320  and the external threads  380  of the lock cover  600 . Thus, the external threads  670  may be broken zero-pitch threads sized to engage the broken zero-pitch threads  322  of the lock cover bore  320 . In the embodiment shown, the first stepped segment  650  of the lower portion  640  of the main body  610  of the lock cover  600  may include eleven threads  670  that are configured to engage within the twelve threads  322  of the lock cover bore  320 . In other embodiments, the lower portion  640  of the main body  610  may include any number of threads  670 . The threads  670  are broken such that broken thread segments  672 , which are separated from one another by gaps  674 , of the external threads  670  fit within the gaps  324  between the broken thread segments  326  in the lock cover bore  320  (i.e., the external broken thread segments  672  of the lock cover  600  are equal to or less than the size of the gaps  324  in the lock cover bore  320 ) and the arrangement of the external broken thread segments  672  allow them to each be aligned with, and placed within, respective gaps  324  in the lock cover bore  320 . As the external threads  670  are broken, the external threads  670  of the lock cover  600  are engaged with the lock cover bore  320  of the lock  310  by first axially inserting the lock cover  600  into the lock cover bore  320  with the external broken thread segments  672  of the lock cover  600  positioned in the gaps  324  defined between the internal broken thread segments  326  of the lock cover bore  320 . Once the lock cover  600  is axially positioned within the lock cover bore  320  of the lock  310 , the lock cover  600  may be rotated relative to the lock cover bore  320  so that the threads  322 ,  670  engage one another. For the illustrated embodiment, this includes rotating the lock cover  600  by 45 degrees with respect to the lock cover bore  320 . In some embodiments, one pair of mating threads  322 ,  670  (e.g., the lowest threads) of the lock cover bore  320  and the lock cover  600 , respectively, may be larger and/or spaced apart at a greater distance from one another than the remainder of threads  322 ,  670  so that the lock cover  600  is only capable of engaging the lock cover bore  320  at one axial position along the axial length of the lock cover bore  320 . In other embodiments, the length of the lower portion  640  (i.e., the length between the first and second ends  644 ,  646  of the lower portion  640 ) may be sized (e.g., have a predetermined set length) so that the threads  322 ,  670  of the lock cover bore  320  and the lock cover  600 , respectively, are aligned to facilitate a mating engagement of the threads  322 ,  670  when the flange  648  of the main body  610  of the lock cover  600  is in abutment with the first axial end  314  of the lock  310 . As best illustrated in  FIG.  21   , the second and third concentric lower surfaces  662 ,  664  of the of the lower portion  640  of the main body  610  of the lock cover  600  abuts or contacts the piston retainer  134  when the lock cover  600  is installed within the lock cover bore  320  of the lock  310 . 
     Installation and operation of the third embodiment of the retainer assembly  300 ″ onto the housing  100  of the fluid end  14  may be substantially similar to that of the second embodiment of the retainer assembly  300 ′. The third embodiment of the retainer assembly  300 ″ illustrated in  FIGS.  19 - 21    may be secured to the housing  100  of the fluid end  14  proximate to the piston bore  124  of the housing of the fluid end  14  to removably secure the piston  520  to the housing  100  proximate to the piston bore  124 . In  FIG.  21   , the frame  550  of the pump  10 , a portion of which may be disposed between the second axial end  316  of the lock  310  and the outer surface of the housing  100 , is shown in phantom for illustrative purposes only. During assembly, the lock  310  may be fastened to the housing  100  of the fluid end  14  such that the lock  310  surrounds the piston bore  124 . The fasteners  332  may then be passed through the fastener bores  330  of the lock  310  to thread into the fastener bores (not shown) of the housing  100  of the fluid end  14 . The nuts  334  may then be threaded onto the fasteners  332  and may then be tightened against the first axial end  314  of the lock  310 , thereby securing the lock  310  to the housing  100  of the fluid end  14 . The lock cover  600 , which, as described above, may incorporate an integrated piston liner, may be positioned above the lock cover bore  320  of the lock  310  and rotatably aligned such that the gaps  324  between the broken thread segments  326  of the lock  310  are axially aligned with the broken thread segments  672  of the lock cover  600 , and such that the broken thread segments  326  of the lock  310  are axially aligned with the gaps  674  between the broken thread segments  672  of the lock cover  600 . The lock cover  600  may be axially inserted (i.e., along central axis F illustrated in  FIG.  21   ) into the lock cover bore  320  of the lock  310  such that the flange  648  of the main body  610  of the lock cover  600  abuts the first axial end  314  of the lock  310 . The length of the lower portion  640  of the main body  610  of the lock cover  600  is set/predetermined such that, when the flange  648  is in abutment with the first axial end  314  of the lock  310 , the second and third concentric lower surfaces  662 ,  664  of the lock cover  600  may be disposed proximate to, or in abutment with, the piston retainer  134 . In addition, in this axially lowered position, the threads  670  of the lock cover  600  are axially displaced into alignment with the appropriate openings between threads  322  of the lock  310 . When the threads  670  are axially positioned to be aligned as desired, the operator/user may then rotate the lock cover  600  relative to the lock  310 , thereby engaging the threads  322 ,  670  with one another. When the threads  322 ,  670  are engaged with one another, the lock cover  600  is axially locked (prohibited from moving axially along central axis F) with respect to the lock cover bore  320  of the lock  310 . Conversely, when the threads  322 ,  670  are not engaged with one another, the lock cover  600  is axially unlocked (free to move axially along central axis F) with respect to the lock cover bore  320  of the lock  310 . The operator/user may rotate the lock cover  600  until the cutouts  399  of the lower ring portion  392  of the handle  390  of the lock cover  340  are aligned with the retainer bore  336  in the first axial end  314  of the lock  310 . As previously described, the operator/user may then insert the shank  416  of each pin  410  into a cutout  399  and aligned retainer bore  336  until the bottom surface  417  of the intermediate portion  414  abuts the lower ring portion  392  of the handle  390  of the lock cover  600  in order to rotationally lock the rotational position of the lock cover  600  relative to the lock  310 . The magnetic attraction between the magnet  418  of the intermediate portion  414  of the pins  410  and the lower ring portion  392  of the handle  390  of the lock cover  600  secures the pins  410  in the inserted position (i.e., the shanks  416  of the pins  410  being inserted into both the cutouts  399  and the retainer bores  336 ) until the operator/user manually removes the pins  410 . Once the lock cover  600  is secured both rotationally and axially within the lock cover bore  320  of the lock  310 , the piston  520  and the piston rod  540  may be inserted into the central bore  616  of the main body  610  of the lock cover  600 . However, in other embodiments, the piston  520 , and the piston rod  540  may be inserted into the central bore  616  of the main body  610  of the lock cover  600  prior to installation of the lock cover  600  into the lock cover bore  320  of the lock  310 . Once installed, the piston  520  may be movable along the central bore  616  of the lock cover  600  to pressurize fluid within the interior volume  110  of the housing  100 . 
     In even further embodiments, the lock covers  340 ,  600  described herein may be secured directly (without the lock  310  described herein) to the housing  100  to secure plug members (e.g., valve covers  200 , liners  500 , pistons  520 , stuffing boxes, plungers, etc.) in positions proximate to, or within, the bores  120 ,  122 ,  124 ,  126 ,  128  of the housing  100 . In these embodiments, the bores  120 ,  122 ,  124 ,  126 ,  128  may be sized and shaped to directly receive the lock covers  340 ,  600 . Moreover, the bores  120 ,  122 ,  124 ,  126 ,  128  may contain the same or similar broken zero-pitch thread arrangement (i.e., thread segments and gaps, etc.) described above with respect to the lock cover bore  320  of the lock  310  to facilitate axially insertion and rotation of the lock covers  340 ,  600  within the bores  120 ,  122 ,  124 ,  126 ,  128 . In this embodiment, the housing  100  may contain retainer bores disposed proximate to the bores  120 ,  122 ,  124 ,  126 ,  128 , and that are configured to receive the shank  416  of the pins  410  to rotational lock the lock covers  340 ,  600  within the bores  120 ,  122 ,  124 ,  126 ,  128 . 
     In some even further embodiments, the components (especially the threads  322 ,  380 ,  670 ) of the retainer assemblies  300 ,  300 ′,  300 ″ described herein may be constructed from corrosion resistant materials, including, but not limited to, being nickel plated. By constructing the components of the retainer assemblies  300 ,  300 ′,  300 ″ from corrosion resistant materials, the life of the retainer assemblies  300 ,  300 ′  300 ″ is extended. 
     While the apparatuses presented herein have been illustrated and described in detail and with reference to specific embodiments thereof, it is nevertheless not intended to be limited to the details shown, since it will be apparent that various modifications and structural changes may be made therein without departing from the scope of the inventions and within the scope and range of equivalents of the claims. For example, the lock presented herein may be modified to be of any shape, and contain any number of fastener openings, lock cover bores, retainer bores, threads, thread segments, and/or gaps between thread segments. Moreover, the lock cover presented herein may also be of any shape, and may contain any number of handles, cutouts, threads, thread segments, and/or gaps between thread segments. In addition, the main body and the handle of the lock cover presented herein may also be integrally formed from one uniform material (rather than being two structures fastened to one another). 
     In addition, various features from one of the embodiments may be incorporated into another of the embodiments. That is, it is believed that the disclosure set forth above encompasses multiple distinct inventions with independent utility. While each of these inventions has been disclosed in a preferred form, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. The subject matter of the inventions includes all novel and non-obvious combinations and subcombinations of the various elements, features, functions, and/or properties disclosed herein. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure as set forth in the following claims. 
     It is also to be understood that terms such as “left,” “right,” “top,” “bottom,” “front,” “rear,” “side,” “height,” “length,” “width,” “upper,” “lower,” “interior,” “exterior,” “inner,” “outer” and the like as may be used herein, merely describe points of reference and do not limit the present invention to any particular orientation or configuration. Further, the term “exemplary” is used herein to describe an example or illustration. Any embodiment described herein as exemplary is not to be construed as a preferred or advantageous embodiment, but rather as one example or illustration of a possible embodiment of the invention. Additionally, it is also to be understood that the components of the fluid pump described herein, the fluid end assembly described herein, the plug members described herein, the retainer assemblies described herein, or portions thereof may be fabricated from any suitable material or combination of materials, such as, but not limited to, plastic or metals (e.g., nickel, copper, bronze, aluminum, steel, etc.), as well as derivatives thereof, and combinations thereof. In addition, it is further to be understood that the steps of the methods described herein may be performed in any order or in any suitable manner. 
     Finally, when used herein, the term “comprises” and its derivations (such as “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc. Similarly, where any description recites “a” or “a first” element or the equivalent thereof, such disclosure should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Meanwhile, when used herein, the term “approximately” and terms of its family (such as “approximate”, etc.) should be understood as indicating values very near to those which accompany the aforementioned term. That is to say, a deviation within reasonable limits from an exact value should be accepted, because a skilled person in the art will understand that such a deviation from the values indicated is inevitable due to measurement inaccuracies, etc. The same applies to the terms “about”, “around”, “generally”, and “substantially.”