Patent Publication Number: US-10760569-B2

Title: Reciprocating pumps and closures therefore

Description:
RELATED CASE 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/510,470 filed on May 24, 2017 and incorporates said provisional application by reference into this document as if fully set out at this point. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to high pressure reciprocating pumps and to fluid end closures used in such pumps. 
     BACKGROUND OF THE INVENTION 
     High pressure reciprocating pumps are commonly used for high pressure oilfield applications, such as, for example, hydraulic fracturing. When such pumps are used for hydraulic fracturing, a reciprocating plunger causes the fracturing fluid to flow into and out of a fluid chamber which is formed in a “fluid end” body of the pump. As the plunger moves away from the fluid chamber, the fracturing fluid is drawn through an inlet valve into the fluid chamber. Then, when the plunger changes direction and moves toward the fluid chamber, the fracturing fluid is discharged from the pump through an outlet valve. 
     A high pressure reciprocating pump assembly  10  of the type heretofore used in the art is illustrated in  FIGS. 1A and 1B . The pump assembly  10  can be installed in fixed position or can be mounted on a trailer or skid for moving from site to site on land or offshore. The pump assembly  10  comprises a power end  12  and a fluid end body  20 . The fluid end body  20  is coupled with the power end  12  by a set of stay rods  16 . 
     The fluid end body  20  of the pump assembly  10  can have one or a plurality of internal fluid chambers  22 . For each of the internal fluid chambers  22 , the fluid end body  20  comprises: a suction bore  26  through which a fluid is drawn from a suction manifold  28  into the fluid chamber  22 ; a suction valve  24  within the suction bore  26 ; a discharge access bore  32 ; a discharge valve  30  accessible via the discharge access bore  32 ; a plunger bore (cylinder)  34  in communication with the fluid chamber  22 ; a plunger  36  which is slidably received in the plunger bore  34  for reciprocating movement toward and away from the fluid chamber  22 ; and an access bore  38  which provides access to the plunger bore  34  and to the suction bore  26 . 
     The suction bore  26  extends inwardly from a first face  25  of the fluid end body  20  to the internal fluid chamber  22 . The discharge access bore  32  extends inwardly from a second face  31  of the fluid end body  20  to the internal fluid chamber  22 . The plunger bore  34  extends inwardly from a third face  31  of the fluid end body  20  to the internal fluid chamber  22 . The access bore  38  extends inwardly from a fourth face  37  of the fluid end body  20  to the internal fluid chamber  22 . 
     The power end  12  of the pump assembly  10  comprises a drive assembly  13  which is contained within a power end housing  15 . The drive assembly  13  comprises: a crankshaft  50 ; a bull gear  52  which rotates the crankshaft  50 ; and a pinion gear  54  which engages and drives the bull gear  52 . An engine or motor (not shown) is connected or linked to the pinion gear  54  for directly or indirectly driving the pinion gear  54  during operation. 
     In the pump assembly  10  shown in  FIG. 1 , a connecting rod  56  mechanically connects the crankshaft  50  of the power end  12  to a cross head  58  via a wrist pin  60 . The crosshead  58  is mounted for reciprocating linear movement within a stationary crosshead housing  62 . A pony rod  64  is connected between the crosshead  58  and the plunger  36  for driving the reciprocating movement of the plunger  36  within the plunger bore (cylinder)  34  of the fluid end body  20 . It will be understood, however, that the plunger  36  can alternatively be directly coupled with the crosshead  58  such that the pony rod  64  would be eliminated. 
     As will also be understood by those in the art, the fluid end  20  of the pump assembly  10  can have a single reciprocating plunger  36  or can have multiple plungers  36  which operate in a corresponding number of cylinders  34 , depending upon the fluid flow capacity required. The reciprocating plunger pumps most commonly used for hydraulic fracturing are 3 cylinder (triplex) pumps and 5 cylinder (quintuplex) pumps. 
     As illustrated in  FIG. 1A , each plunger  36  used in the pump assembly  10  extends through a plunger bore (cylinder)  34  of the fluid end body  20  so as to interface with a corresponding internal fluid chamber  22 . As the plunger  36  moves longitudinally away from the chamber  22 , the pressure inside the fluid chamber  22  decreases, thus creating a differential pressure across the suction valve  24 . A biasing member  68  (e.g., a spring) located between the suction valve  24  and a valve stop  70  maintains a predetermined closing force on the suction valve  24 , thereby maintaining the suction valve  24  in a closed position until the differential pressure across the suction valve  24  reaches a point which is sufficient to overcome the force generated by the biasing member  68 . 
     When this point is reached, the suction valve  24  opens to allow the fluid to enter the fluid chamber  22  from the suction manifold  28 . The fluid then continues to be drawn into the fluid chamber  22  until the pressure differential between the fluid inside the chamber  22  and the fluid pressure inside the suction manifold  28  is reduced to a point at which the suction valve  24  automatically returns to its closed position (via, e.g., the biasing mechanism  68  of the suction valve  24  and/or the pressure within the chamber  22 ). 
     As the plunger  36  then changes direction and moves longitudinally toward the fluid chamber  22 , the fluid pressure inside the chamber  22  increases to produce a pressure differential across the discharge valve  30  which acts against the closing force of a biasing spring  74  to open the discharge valve  30  so that the fluid is discharged from the fluid chamber  22  of the fluid end body  20  via discharge bore  66  and a discharge port  65 . 
     The pump assembly  10  also includes: a pressure containing closure  80  for each plunger bore  34  of the fluid end body  20 ; a pressure containing closure  84  for each discharge access bore  32  of the fluid end body  20 ; a pressure containing closure  86  for each access bore  38  of the fluid end body  20 ; and a pressure closure  89  for the side bore  66  of the discharge port  65 .  FIG. 1B  also shows pressure gage connections  91  and  93  installed through the closures  84  of two of the discharge access bores  32 . 
     Heretofore, the pressure containing closures used in the industry in the fluid end bodies of high pressure reciprocating pumps have been either (a) threaded closures of the type illustrated in  FIG. 2  or (b) flanged closures with threaded studs as illustrated in  FIG. 3 . 
     When using a prior art threaded closure  90  of the type illustrated in  FIG. 2  (also referred to as a threaded retainer), the threaded closure  90  will be received within the outer end of the bore  34 ,  32 ,  38  or  66  of the fluid end body  20  for closing the outer end of the bore and for holding an internal seal member  92  (e.g., a cover  97  with a surrounding O-ring or other seal element  99 ) in contact with a radial retaining shoulder  94  formed within the bore  34 ,  32 ,  38  or  66 . The prior art threaded closure  90  includes threads  96  which are formed around the cylindrical exterior of the closure  90  and which mate with, and are received by, threads  98  which must be formed in the fluid end body  20  around the cylindrical interior wall  100  of the bore  34 ,  32 ,  38  or  66 . 
     It is also known in the art that the threaded closure (retainer)  90  and the cover  97  can alternatively be formed together as a single element. 
     When using a prior art flanged pressure containing closer  102  of the type illustrated in  FIG. 3  (also referred to as a flanged retainer), a cylindrical body portion  104  of the flanged closure  102  will be received within the outer end of the bore  34 ,  32 ,  38  or  66  of the fluid end body  20  for closing the outer end of the bore and for holding the internal seal member  92  (e.g., a cover  107  with an O-ring or other surrounding seal element  111 ) in contact with the radial retaining shoulder  94  formed within the bore  34 ,  32 ,  38  or  66 . In addition, the flanged closure  102  also comprises a radial flange  106  which is provided at the outer end of the cylindrical body portion  104  and which will extend over the exterior surface  105  of the fluid end body  20  around the outer end of the bore  34 ,  32 ,  38  or  66 . The flanged closure  102  is retained in closed position on the fluid end body  20  by at least 2 threaded studs  108  which extend through bores  112  provided in the radial flange  106 . As shown in  FIG. 3 , each of the stud connections requires that a corresponding threaded bore  110  for threadedly receiving a distal portion  109  of the stud  108  must be formed in the fluid end body  20  adjacent to the outer end of the bore  34 ,  32 ,  38  or  66 . 
     It is also know in the art that the flanged closure  102  and the cover  107  can alternatively be formed together as a single element. 
     Thus, the prior art threaded closure  90  and the prior art flanged closure (retainer)  102  which uses threaded studs  108  each require that attachment threads  98  or  110  for receiving the threaded closure  90  or the threaded studs  108  must be formed in the fluid end body  20  of the pump assembly  10 . The threads  98  or  110  formed in the fluid end body  20  are difficult and costly to machine and costly or impossible to repair if the threads  98  or  110  are damaged during machining or assembly. In addition, the prior art threaded closures are subject to thread fatigue failures due to the highly fluctuating pressure conditions produced in high pressure reciprocating pumps. 
     The cost of repairing or replacing a damaged fluid end body for a 3 cylinder (triplex) or 5 cylinder (quintuplex) pump will typically be at least $1,000.00 and can be as much as $100,000.00 or more. 
     Also, to sufficiently tighten the prior art threaded closures  90 , the closures must be hammered during assembly. This presents not only a further risk of damaging the fluid end body  20  of the reciprocating pump, but also poses a risk of injury to the workman if the correct procedure is not carefully followed. 
     Consequently, a need exists for improved fluid end closures for high pressure reciprocating pumps which (a) do not require the machining of attachment threads in the fluid end body, (b) do not require hammering during assembly, and (c) are less expensive to produce and install. 
     SUMMARY OF THE INVENTION 
     The present invention provides improved fluid end bodies and improved fluid end closures for high pressure reciprocating pumps which alleviate the problems and satisfy the needs discussed above. The inventive closures do not require that any retaining threads for the closures be machined or otherwise formed in the fluid end body. The inventive closures therefore also eliminate the need for hammering during assembly. In addition, because there are no threaded attachments between the inventive closures and the fluid end body, the inventive closures eliminate the possibility of a thread fatigue failure occurring during operation. 
     In one aspect, there is provided a closure for the fluid end body of a high pressure reciprocating pump wherein the closure comprises one or more plates or bars of any length needed to cover one or more bores in the fluid end body (e.g., to cover a single bore or to simultaneously cover a series of three bores as in a triplex pump or a series of five bores as in a quintuplex pump). The closure further comprises a mating slot which extends through or partially through the fluid end body over the outer ends of the one or more bores for slidably receiving the one or more closure plates or bars. 
     In another aspect, there is provided a fluid end apparatus for a reciprocating pump comprising: (a) a fluid end body having one or more bores which extend inwardly into a face of the fluid end body; (b) a closure slot which extends within the face of the fluid end body over an outer end of each of the one or more bores; (c) the closure slot having a longitudinal length which extends from a first side of the face of the fluid body to, or at least a portion of the distance to, a second side of the face which is opposite the first side, and the closure slot having an end opening in one or both of the first and the second sides of the face; (d) an outer access opening for the closure slot which extends inwardly to the closure slot from an outer surface of the face of the fluid end body and extends longitudinally with the closure slot from the first side of the face to, or at least a portion of the distance to, the second side of the face; (e) the outer access opening having a lateral width which is less than a lateral width of the closure slot but the same as or greater than a diameter of the one or more bores such that a sealing member (e.g., a cover with an O-ring or other sealing element) or other object can be placed in or removed from the outer end of each of the one or more bores via the access opening; and (f) a closure plate structure which is slidably receivable in the closure slot and has at least one width dimension which is greater than the lateral width of the outer access opening such that the closure plate structure can be placed and retained in the closure slot over the outer end of at least one of the one or more bores. 
     In another aspect, there is provided a fluid end apparatus for a reciprocating pump comprising: (a) a fluid end body having one or more bores which extend inwardly into a face of the fluid end body; (b) a sealing member for each of the one or more bores; (c) a closure slot which extends within the face of the fluid end body over an outer end of each of the one or more bores; (d) the closure slot having a longitudinal length which extends from a first side of the face of the fluid end body to, or at least a portion of the distance to, a second side of the face which is opposite the first side, and the closure slot having an end opening in one or both of the first and the second sides of the face; (e) an outer access opening for the closure slot which extends inwardly to the closure slot from an outer surface of the face of the fluid end body and extends longitudinally with the closure slot from the first side of the face to, or at least a portion of the distance to, the second side of the face; (f) the outer access opening having a lateral width which is the same as or greater than a diameter of the one or more bores such that the sealing member for each of the one or more bores can be placed in or removed from the outer end of each of the one or more bores via the access opening; (g) the lateral width of the outer access opening is less than a lateral width of the closure slot such that the outer access opening divides the closure slot into a longitudinally extending open central portion, a first longitudinally extending slot channel running adjacent to a first lateral side of the open central portion, and a second longitudinally extending slot channel running adjacent to a second lateral side of the open central portion which is opposite the first lateral side of the open central portion; (h) a first elongate bar which is slidably received in the first longitudinally extending slot channel over and in contact with a first outer edge portion of the sealing member; and (i) a second elongate bar which is slidably received in the second longitudinally extending slot channel over and in contact with a second outer edge portion of the sealing member. 
     Further aspects, features, and advantages of the present invention will be apparent to those of ordinary skill in the art upon examining the accompanying drawings and upon reading the following Detailed Description of the Preferred Embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic cutaway side view of a prior art, high pressure reciprocating pump assembly  10 . 
         FIG. 1B  is a perspective view of the prior art, high pressure reciprocating pump assembly  10 . 
         FIG. 2  is a cutaway elevational side view of one half of a prior art threaded closure  90  used in high pressure reciprocating pump assemblies. 
         FIG. 3  is a cutaway elevational side view of one half of a prior art flanged closure  102  used in high pressure reciprocating pump assemblies. 
         FIG. 4  is a plan view of a first embodiment  150  of the closure assembly provided by the present invention. 
         FIG. 5  is a lateral cutaway view of the inventive closure assembly  150  as seen from perspective A-A shown in  FIG. 4 . 
         FIG. 6  is a plan view of a second embodiment  200  of the closure assembly provided by the present invention. 
         FIG. 7  is a lateral cutaway view of the inventive closure assembly  200  as seen from perspective  7 - 7  shown in  FIG. 6 . 
         FIG. 8  is a cutaway view of the inventive closure assembly  200  as seen from perspective  8 - 8  shown in  FIG. 6 . 
         FIG. 9  is a plan view of a linear half  206  of a two piece cover plate  202  used in the inventive closure assembly  200 . 
         FIG. 10  is an end view of the linear half  206  of the two piece cover plate  202  used in the inventive closure assembly  200 . 
         FIG. 11  is a plan view of a third embodiment  250  of the closure assembly provided by the present invention. 
         FIG. 12  is a lateral cutaway view of the inventive closure assembly  250  as seen from perspective  12 - 12  shown in  FIG. 11 . 
         FIG. 13  is a side view of a closure bar  252  used in the inventive closure assembly  250 . 
         FIG. 14  is a plan view of a fourth embodiment  300  of the closure assembly provided by the present invention. 
         FIG. 15  is a lateral cutaway view of the inventive closure assembly  300  as seen from perspective  15 - 15  shown in  FIG. 14 . 
         FIG. 16  is a plan view of a cover plate  304  used in the inventive closure assembly  300 . 
         FIG. 17  is a cutaway view of the cover plate  304  as seen from perspective  17 - 17  shown in  FIG. 16 . 
         FIG. 18  is another plan view of the inventive closure assembly  300  as seen from perspective  18 - 18  shown in  FIG. 19 . 
         FIG. 19  is a lateral cutaway view of the inventive closure assembly  300  as seen from perspective  19 - 19  shown in  FIG. 18 . 
         FIG. 20  is a plan view of a fifth embodiment  350  of the closure assembly provided by the present invention. 
         FIG. 21  is a lateral cutaway view of the inventive closure assembly  350  as seen from perspective  21 - 21  shown in  FIG. 20 . 
         FIG. 22  is a plan view of a cover plate  352  used in the inventive closure assembly  350 . 
         FIG. 23  is a cutaway view of the cover plate  352  as seen from perspective  23 - 23  shown in  FIG. 22 . 
         FIG. 24  is a cutaway view of an embodiment  180  of the inventive closure assembly which is a variation of the embodiment  150  illustrated in  FIGS. 4 and 5 . 
         FIG. 25  is a plan view of an embodiment  240  of the inventive closure assembly which is a variation of the embodiment  200  illustrated in  FIGS. 6-10 . 
         FIG. 26  is a cutaway view of the inventive closure assembly  240  as seen from perspective  26 - 26  shown in  FIG. 25 . 
         FIG. 27  is a plan view of an embodiment  400  of the inventive closure assembly. 
         FIG. 28  is a cutaway view of the inventive closure assembly  400  as seen from perspective  28 - 28  shown in  FIG. 27 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment  150  of the inventive closure assembly is illustrated in  FIGS. 4 and 5 . The inventive closure assembly  150  comprises a cover plate  152  having a longitudinal length  153  which is sufficient to cover the outer end opening  154  of at least one bore  155 , or to cover the outer end openings  154  of a series of two, three, or more bores  155   a ,  155   b , and/or  155   c , which are provided in one face  156  of the fluid end body  158  of a high pressure reciprocating pump. The longitudinally extending lateral sides  160  and  162  of the cover plate  152  are preferably linear and can have a rectangular cross-sectional shape as indicated in  FIG. 5  or can be beveled or rounded or can have other cross-sectional shapes. In addition, the cross-sectional shapes of the longitudinally extending lateral sides  160  and  162  of the cover plate  152  can be the same (e.g., both squared) or different (e.g., one squared and one beveled). 
     It will be understood that, unless otherwise specified, the term “plate” as used in reference to element  152 , or in reference to other elements described herein, is an inclusive term covering structures of the type shown or described, regardless of whether the element was cut from or formed as a metal plate, cut from or formed as a metal bar, or cut or formed in any other manner from any desired material. 
     The cover plate  152  is slidably received in a cover plate slot  164  which is formed within the face  156  of the fluid end body  158  over, and preferably perpendicular to, the outer end openings  154  of the bore(s)  155  or  155   a ,  155   b , and  155   c . By way of example, but not by way of limitation, the slot  164  for the cover plate  152  can be formed in the fluid end body  158  by standard machining processes such as milling. 
     As seen in  FIG. 5 , the lateral cross-sectional shape of the cover plate slot  164  preferably corresponds to the lateral cross-sectional shape of the cover plate  152 . In addition, the slot  164  preferably has a longitudinal length which extends within the face  156  of the fluid end body  158  from one side  159  of the face  156  to the other side  161  so that the corresponding longitudinal ends  166  and  168  of the slot  164  are open for slidably receiving the cover plate  152 . Once inserted into either of the longitudinal ends  166  or  168  of the slot  164 , the cover plate  152  can be moved into a closing position over one or more of the bore openings  154 . 
     Alternatively, it will be understood that the cover plate slot  164  can be milled or otherwise formed such that the slot  164  does not extend the entire distance from side  159  to the other side  161  of the face  156  of the fluid end body  158  but instead has a closed end. The closed end will preferably be located between side  161  of the face  156  and the bore  155   a  which is closest to the side  161 . 
     The cover plate slot  164  is spaced inwardly below, and runs parallel to, the outer surface  170  of the face  156  of the fluid end body  158 . However, a centralized, longitudinally extending outer access opening  172  for the slot  164  extends inwardly from the outer surface  170  of the face  156  of the fluid end body  158  to the slot  164 . The lateral width  174  of the outer access opening  172  is the same as or preferably slightly greater than the diameter  177  of the outer end openings  154  of the bore(s)  155  or  155   a ,  155   b ,  155   c  so that sealing members  176  can be inserted through the outer access opening  172  into the bore(s)  155  or  155   a ,  155   b ,  155   c.    
     However, the lateral width  174  of the outer access opening  172  is less than the lateral width  178  of the slot  164  and is also less than the lateral width of the cover plate  154 . As a result, the longitudinally extending outer access opening  172  divides the longitudinally extending slot  164  into (a) a longitudinally extending open central portion  167 , (b) a first longitudinally extending slot channel  169  running adjacent to one lateral side of the open central portion  167 , and (c) a second longitudinally extending slot channel  173  adjacent the opposite lateral side of the open central portion  167 . The longitudinally extending slot channels  169  and  173  extend longitudinally within the face  156  of the fluid end body  158  either (a) from one side  159  of the face  156  to the other side  161  such that both ends of each of the slot channels  169  and  173  are open or (b) at least a portion of the distance from side  159  to side  161  such that the slot channels  169  and  173  each have a closed end, which will preferably be located between side  161  and bore  155   a . The slot channels  169  and  173  slidably receive and retain the longitudinally extending lateral side edges  160  and  162  of the cover plate  152 . 
     A variation  180  of the closure plate assembly  150  is illustrated in  FIG. 24 . In the assembly  180 , a slot channel  182  is milled or otherwise formed along only one lateral side of the longitudinally extending access opening  184 . In this variation  180 , the lateral depth of the slot channel  182  and the milling tolerances used for forming the slot channel  182  and the cover plate  186  prevent the cover plate  186  from the pivoting in the slot channel  182  so that that the cover plate  186  and the sealing member  188  are firmly retained in the bore  190 . 
     By way of example, but not by way of limitation, the inventive closure assemblies  150  and  180  can be used for closing the access bores, discharge bores, or valve cover bores of the fluid end body  158 . 
     A second embodiment  200  of the inventive closure assembly is illustrated in  FIGS. 6-10 . The inventive closure assembly  200  is similar to the inventive closure assembly  150  shown in  FIGS. 4 and 5  except that the cover plate  202  of the inventive closure  200  is a two piece cover plate having a first linear half  204  and a mating second linear half  206 . The two piece cover plate  202  can be used, for example, for covering a single bore opening in the fluid end body  208 , or for covering the center bore  210   b  of a series of bores  210   a ,  210   b , and  210   c , wherein the single bore or the central bore  210   b  of the series of bores includes, for example, a sealing element  212  having a seal piece extension  214  which must project from the attached closure assembly  200  for attaching a pressure gage or for attaching any other instrument, element or structure. The mating ends  216  and  218  of the first and second linear halves  204  and  206  of the two piece cover plate  202  have corresponding cavities  220  and  222  formed therein which, when assembled in the cover plate slot  224  of the fluid end body  208  over the bore(s)  210   a ,  210   b , and/or  210   c , form an aperture  226  having a circular shape or other shape suitable for retaining the seal piece extension  214 . 
     In addition to being useful, for example, for closing a single access bore having a seal piece extension  214 , or for closing a series of bores wherein a central one of the bores has a seal piece extension  214 , the inventive closure assembly  200  can also be used for closing a single bore or a series of bores wherein the single bore or a central one of the series of bores has, for example, a union fitting or other fitting projecting therefrom for attaching a flow line. 
     The longitudinally extending lateral side edges  228  and  230  of the mating first and second linear halves  204  and  206  of the two piece cover plate  202  shown in  FIGS. 6-10  have beveled outer surfaces  232  and  234 . However, as with the cover plate  152  of the closure assembly  150  shown in  FIGS. 4 and 5 , the side edge portions  228  and  230  of the two piece cover plate  202  can be rectangular or can have other lateral cross-sectional shapes. 
     The illustration of the inventive two piece cover plate assembly  200  in  FIGS. 6-10  also differs from the illustration of the one piece cover plate assembly  150  shown in  FIGS. 4 and 5  in that one or more, preferably a plurality, of bolts  236  may be used to secure each of the mating linear halves  204  and  206  of the two piece cover plate  202  in the cover plate slot  224 . In each of the bolt attachments, the bolt  236  is inserted through a non-threaded bore  238  which extends into the face  240  of the fluid end body  208  outside of the centralized outer linear access opening  242  and is threadedly received and tightened in a threaded bore  244  which is provided in one of the longitudinally extending lateral side edge portions  228  or  230  of the linear half  204  or  206  of the two piece cover plate  202 . 
     A variation  240  of the closure assembly  200  for covering a single bore  243  is illustrated in  FIGS. 25 and 26 . Variation  240  comprises a two piece cover having mating halves  241  and  242  sized to cover a single bore  243  having, e.g., a union fitting  244  or other fitting projecting therefrom for attaching a flow line, a seal piece projecting therefrom for attaching a pressure gage, or other structure projecting therefrom. A further variation of the closure assembly  240  is that the assembly  240  is secured in the slot  239  over the bore  243  using a plurality of bolts  246  (preferably 2 bolts  246  per each half  241  and  242  of the cover) which extend through non-threaded bores  245  provide through the halves  241  and  242  of the cover and are threadedly received and tightened in corresponding threaded bores  247  formed in a radial flange  248  provided at the base of the union fitting  244 . An O-ring or other sealing element  249  is also provided around the flange  248  of the union fitting  244  for sealing the bore  243 . 
     A third embodiment  250  of the inventive closure assembly is illustrated in  FIGS. 11-13 . The inventive closure assembly  250  is similar to the inventive closure assembly  150  shown in  FIGS. 4 and 5  except that, rather than using a cover plate  152 , the inventive closure assembly  250  uses a pair of longitudinally extending closure bars  252  and  254  which are slidably received in the laterally opposing side channels  256  and  258  of the cover slot  260 . The slot channels  256  and  258  extend longitudinally within the face  262  of the fluid end body  264  from one side  266  of the face  262  to, or at least a portion of the distance to, the other side  268  thereof such that the ends of the slot channels  256  and  258  at or approaching the side  268  of the face  262  can be open or closed. 
     The cross sectional shape of each channel  256  and  258  corresponds or substantially corresponds to the cross-sectional shape of the closure bar  252  or  254  or is otherwise suitably shaped for receiving the closure bar  252  or  254  therein. The cross-sectional shapes of the bars  252  and  254  can be the same or different. In the embodiment  250  illustrated in  FIGS. 11-13 , the closure bar  252  is entirely rectangular whereas the closure bar  254  has a greater thickness and also has a beveled outer surface  270 . 
     In the assembly  250 , the sealing member(s)  272  illustrated in  FIG. 12  each comprise a cover element  271  which is surrounded by an O-ring or other sealing element  273  for sealing the bore(s)  274 . The sealing members  272  can differ from the sealing members  176  used in the assembly  150  in that side notches  276  and  278  can optionally be formed in the outer end  280  of the cover element  271  for receiving the side edges  282  and  284  of the closure bars  252  and  254  so that (a) the closure bars  252  and  254  prevent the sealing member  272  from rotating in the fluid end bore  274  and (b) the notched sealing member  272  also assists in holding the closure bars  252  and  254  in the longitudinally extending slot channels  256  and  258 . 
     To further secure the components of the closure assembly  250  in operating position, the closure bar  254  is preferably bolted to the sealing member  272  using a bolt  288  which extends through a bore  290  formed through the closure bar  254  and is threadedly received and tightened in a corresponding threaded bore  292  provided in the outer end  280  of the sealing member  272 . In addition, a lateral holding plate  294  can also be bolted to the longitudinal ends  296  and  298  of the closure bars  252  and  254 . Preferably, a similar holding plate will also be bolted to the opposite ends of the closure bars  252  and  254  unless the opposite ends of the slot channels  256  and  258  are blind. 
     By way of example, but not by way of limitation, the inventive closure assembly  250  can be used for closing the access bores, discharge bores, or valve cover bores of the fluid end body  264 . 
     A fourth embodiment  300  of the inventive closure assembly is illustrated in  FIGS. 14-17 . The inventive closure assembly  300  is essentially the same as the inventive closure assembly  150  illustrated in  FIGS. 4 and 5  except that a threaded cylindrical bore  302  is provided through the rectangular cover plate  304  of the closure assembly  300 . By way of example, as shown in  FIG. 15 , the threaded bore  302  provided through the cover plate  304  allows a gland nut  306  or other element of a plunger stuffing box assembly to be threadedly installed in the cover plate  304  against one or more packing seal components  305 . Consequently, the closure assembly  300  can be used in a plunger bore  308  of the fluid end body  310  for receiving and allowing the reciprocating pumping movement of the plunger  312  through the cover plate  304 . 
     In addition to being used for closing a plunger bore  308 , the inventive closure assembly  300  can also be used as illustrated in  FIGS. 18 and 19 , for example, in a discharge bore  320  of the fluid end body  322  for threadedly receiving a union fitting  324  for attaching a discharge flow line (e.g., a high pressure flow line to a well head). The closure assembly  300  illustrated in  FIG. 19  also optionally includes a locking nut  326  on the fitting  324 . 
     A fifth embodiment  350  of the inventive closure assembly is illustrated in  FIGS. 20-23 . The inventive closure assembly  350  is essentially the same as the inventive closure assembly  300  illustrated in  FIGS. 14-19  except that, rather than being rectangular, the cover plate  352  of the closure assembly  350  has an opposing pair of flat sides  354  and  356  and an opposing pair of rounded, preferably semicircular, sides  358  and  360  wherein (a) the width  362  of the cover plate  352  between the flat sides  354  and  356  is less than the width  364  of the cover plate  352  between the rounded sides  358  and  360  and (b) the width  362  of the cover plate  352  between the flat sides  354  and  356  is also less than the lateral width  366  of the longitudinally extending access opening  368  of the cover retaining slot  370 . This allows the partially rounded cover plate  352  to be inserted through the slot access opening  368  onto the bore and then rotated such that the rounded sides  358  and  360  are received in the outer, longitudinally extending channels  374  and  376  of the slot  370 . 
     In this embodiment  350 , the cover retaining slot  370  in the face  380  of the fluid end body  382  preferably extends across the outer openings of all of the bores  389  in the face  380 ; however, the cover retaining slot can be open at both ends, open on one end and closed on the other, or closed at both ends. 
     To prevent the partially rounded cover plate  352  from rotating during operation, the rounded cover plate  352  is preferably bolted in place using a bolt  378  which (a) extends through a non-threaded bore  372  in the face  380  of the fluid end body  382  outside of the longitudinally extending access opening  368  and (b) is threadedly received and tightened in a threaded bore  385  which extends into the outer surface  384  of the rounded side portion  360  of the partially rounded cover plate  352 . 
     A sixth embodiment  400  of the inventive closure assembly for closing a single bore  402  in a fluid end body  404  is illustrated in  FIGS. 27 and 28 . The assembly  400  comprises a lobed pressure closure element  406  which is removably securable for retaining a sealing member  408  between the lobed element  406  and an interior radial shoulder  410  in the outer end of the bore  402 . 
     By way of example, but not by way of limitation, the sealing member  408  can comprise a cover body  412  having a surrounding seal element groove  414  formed therein in which an O-ring or other sealing element  416  is received. Alternatively, it will be understood that the lobed closure element  406  and the cover body  412  can be formed together as a single closure and sealing element. 
     The lobed closure element  406  is preferably substantially circular except for a single lobed portion  418  which projects radially outward on only one side of the closure element  406 . 
     A cavity  420  having an outer opening  421  with a shape corresponding to the shape of the lobed closure element  406  is provided in the face  422  of the fluid end body  404  for receiving the sealing member  408  and the lobed closure element  406 . The cavity  420  further includes a radially projecting lobe channel  425  provided on one side of the cavity  420  beneath the outer surface  426  of the face  422  of the fluid end body  404 . 
     Consequently, the closure element  406  can be inserted through the outer opening  421  of the cavity  422  over the sealing member  408  and then rotated so that the projecting lobe  418  of the closure  406  is received in the lobe channel  425  of the cavity  420  to thereby lock the closure  406  and sealing member  408  in place. 
     Thus, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those in the art.