Abstract:
Fluid end for high pressure reciprocating pump, in particular for hydraulic fracturing pumps, comprising: a body having a first bore ( 18 ) for receiving a reciprocating plunger ( 31 ), a second bore ( 19 ) for accommodating a suction valve ( 41 ), and a third bore ( 21 ) for accommodating a discharge valve ( 43 ), the second bore ( 19 ) and the third bore ( 21 ) being perpendicular to the first bore ( 18 ); at least a tubular sleeve ( 30 ) in said first bore ( 18 ); at least a tubular cartridge ( 30 ) in the second bore and/or third bore; and a fluid tight seal between contacting surfaces of said sleeve ( 30 ) and said cartridge ( 30 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from U.S. Non-Provisional application Ser. Nos. 14/210,931 and 14/211,017, each of which claims priority from U.S. Provisional Patent Application Ser. No. 61/800,852, filed Mar. 15, 2013, the disclosure of all of which are hereby incorporated by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to hydraulic fracturing pump systems and, more particularly, to the fluid ends of multiplex reciprocating fracturing pumps. 
     BACKGROUND 
     Multiplex reciprocating pumps are generally used to pump high pressure fracturing fluids into wells for recovery of oil and gas trapped in shale formations and the like. Typically, these pumps have two sections, a power end which is coupled to a diesel engine and transmission that drives the pump and plungers in the fluid ends in which a mix of water, sand and chemicals are pressurized up to 15,000 psi or more. 
     These multiplex reciprocating pumps are commonly in the form of triplex pumps having three fluid cylinders and quintuplex pumps that have five cylinders. It will be appreciated, however, that the present disclosure has application to pumps which can utilize the features thereof in forms other than the triplex and quintuplex pumps. The fluid ends of these pumps typically comprise a single block having cylinders bored therein and are commonly referred to as monoblock fluid ends or an assembly of individual bodies with cylinders, referred to as modular fluid ends. 
     The pumping cycle of a fluid end is composed of two stages, a suction cycle during which a piston moves outward in a bore, thereby lowering the fluid pressure in the inlet to a fluid end and a discharge cycle during which the plunger moves forward in the plunger bore, thereby progressively increasing the fluid pressure to a predetermined level for discharge through a discharge pipe to a well site. 
     Fluid ends used in well site applications for oil and gas exploration have limited service life due to fatigue crack failures. These failures are a result of operating pressures, mechanical stresses, erosion and corrosion of the internal passages which have been addressed in prior art efforts with limited success. 
     Discussion of the Prior Art 
     International Application No. PCT/IB2011/002771 (International Publication No. WO 2012 052842 A2 entitled “Fluid End Reinforced With Abrasive Resistant Insert, Coating or Lining”) describes the use of inserts in wear prone areas only and, as such, does not provide erosion, corrosion and fatigue crack protection throughout the entire flow passages in the fluid end. 
     U.S. Patent Publication 2008/0080994 A1, “Fluid End Reinforced With a Composite Material,” is directed to a fluid end of a reciprocating pump wherein carbon steel thin base material is formed into three tubes which are welded and then hydroformed to give a cross-like configuration. That structure is reinforced with a composite that provides some additional stress resistance and reduced weight, however, it does not utilize the inherent benefits of the originally designed high strength steel in the fluid block. 
     U.S. Pat. No. 3,786,729 is directed to a liner seal for the plunger bore and does not address the protection of high stress areas such as those associated with intersecting bores. 
     SUMMARY OF THE INVENTION 
     This disclosure is generally directed to systems for substantially protecting the portions of the fluid end body flow passages from impingement by high pressure fracking fluid passing therethrough to provide enhanced erosion and corrosion resistance as well as improved fatigue properties and extended service life. 
     A first aspect of this disclosure is directed to one or more sleeve components sleeve components and/or one or more cartridge components which cooperate to protect flow passages in fluid end body portions surrounding the outer surface thereof from direct impingement thereon by high pressure fracking fluid passing through said fluid end. 
     A further aspect of this disclosure is directed to a sleeve that is received in a plunger bore of a fluid end body which sleeve includes a pair of apertures that are connected to, and in flow communication with, the outlet of the suction bore and the inlet of in the discharge bore. 
     In accordance with another aspect of the disclosure, a kit which includes one or more sleeves, and/or one or more cartridges are provided for installation in a conventional fluid end steel body which, when installed therein, cooperate to protect the fluid end body portions surrounding the outer surfaces thereof from impingement by high pressure fracking fluid passing through said fluid end. 
     A further aspect of the present invention is directed to a method of installing one or more components in the flow passages of a fluid end body of a reciprocating pump used in the recovery of oil and gas for the purpose of extending the service life thereof and to minimize the effects of erosion, corrosion and fatigue, such components being configured and located within one or more bores in said fluid end body to protect the portions of said fluid end body surrounding those components including portions thereof associated with high stress areas such as the corners of intersecting bores. 
     It is to be understood that the foregoing general description and the following detailed description are exemplary and provided for purposes of explanation only and are not restrictive of the subject matter claimed. Further features and objects of the present disclosure will become apparent in the following description of the example embodiments and from the appended claims. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       In describing the preferred embodiments, reference is made to the accompanying drawing figures or in like parts have like reference numerals and wherein: 
         FIG. 1  is a schematic illustration of a power end and fluid end of a reciprocating pump used in the recovery of oil and natural gas; 
         FIG. 2  is a perspective view of the block component of the fluid end shown in  FIG. 1 ; 
         FIG. 3  is a side elevational view as seen from the mounting flange surface of the fluid end block shown in  FIGS. 2 and 3 ; 
         FIG. 4  is a top plan view of the fluid end block shown in  FIG. 2 ; 
         FIG. 5  is a sectional view of the fluid end block shown in  FIG. 3  taken along the sectional line  5 - 5  of  FIG. 3  which has been modified to accept the components of the first embodiment described herein, but prior to the installation of such components; 
         FIG. 6  is a perspective view of a sleeve component suitable for use in accordance with the first embodiment of the present disclosure; 
         FIG. 7  is an end view of the sleeve shown in  FIG. 6 ; 
         FIG. 8  is a side elevational view of the sleeve shown in  FIGS. 6 and 7 ; 
         FIG. 9  is a sectional view of the sleeve shown in  FIGS. 6-8  taken along the section line  9 - 9  of  FIG. 7 ; 
         FIG. 10  is a perspective view of a cartridge component suitable for use in the first embodiment of this disclosure; 
         FIG. 11  is a front elevational view of the cartridge shown in  FIG. 10 ; 
         FIG. 12  is an end view of the cartridge component shown in  FIGS. 10-11 ; 
         FIG. 13  is a side elevational view of the cartridge shown in  FIGS. 10-12 ; 
         FIG. 14  is a sectional view of the cartridge shown in  FIGS. 10-13  taken along the line  14 - 14  of  FIG. 11 ; 
         FIG. 15  is a perspective view of a tubular plug suitable for use in the first embodiment of this disclosure; 
         FIG. 16  is a top plan view of the tubular plug (spacer) shown in  FIG. 15 ; 
         FIG. 17  is a side elevational view of the component shown in  FIGS. 15 and 16 ; 
         FIG. 18  is a bottom plan view of the component shown in  FIGS. 15-17 ; 
         FIG. 19  is a sectional view of the component shown in  FIGS. 15-18  taken along the section line  19 - 19  of  FIG. 16 ; 
         FIG. 20  is a schematic sectional view illustrating a procedure of installing the sleeve component shown in  FIGS. 7-10  in a fluid end in accordance with the first embodiment of the present disclosure; 
         FIG. 21  is a schematic view illustrating a procedure for installing the cartridge of  FIGS. 10-14  in a fluid end block in accordance with the first embodiment of the present disclosure; 
         FIG. 22  is a schematic view, partially in section, illustrating the assembly of the components of the first embodiment of the present disclosure; 
         FIG. 23  is an assembly drawing, partially in section, illustrating another embodiment of the present disclosure which utilizes a single sleeve component; 
         FIG. 24  is a perspective view of a sleeve which can be used in accordance with the embodiment of  FIG. 23 ; 
         FIG. 25  is a perspective view of a retainer nut suitable for use with the embodiment shown in  FIG. 23 ; 
         FIG. 26  is a perspective view of a sleeve component suitable for use in a further embodiment of the present invention; 
         FIG. 27  is a front elevational view of the sleeve of  FIG. 26 ; 
         FIG. 28  is a side elevational view of the sleeve shown in  FIGS. 26 and 27 ; 
         FIG. 29  is a bottom plan view of the sleeve shown in  FIGS. 26-29 ; 
         FIG. 30  is a sectional view of the sleeve shown in  FIGS. 26-30  taken along the section line  30 - 30  of  FIG. 29 ; 
         FIG. 31  is a perspective view of a lower cartridge component of said further embodiment; 
         FIG. 32  is a top plan view of the lower cartridge component of  FIG. 31 ; 
         FIG. 33  is a sectional view of the lower cartridge component shown in  FIGS. 32 and 33 , taken along the section line  33 - 33  of  FIG. 3C ; 
         FIGS. 34 and 35  are side elevational views of the lower cartridge component shown in  FIGS. 31-33 ; 
         FIG. 36  is a bottom plan view of the lower cartridge component shown in  FIGS. 31-35 ; 
         FIG. 37  is a perspective view of the upper cartridge component of said further embodiment of the present invention; 
         FIG. 38  is a top plan view of the upper cartridge component shown in  FIG. 37 ; 
         FIG. 39  is a sectional view of the upper cartridge component shown in  FIGS. 37 and 38  taken along the line  39 - 39  of  FIG. 40 ; 
         FIGS. 40 and 41  are side elevational views of the upper cartridge components shown in  FIGS. 37-39 ; 
         FIG. 42  is a bottom plan view of the upper cartridge component shown in  FIGS. 37-42 ; 
         FIG. 43  is a perspective view of a locking ring component for said further embodiment; 
         FIG. 44  is a side elevational view of the locking ring component of  FIG. 43 ; 
         FIG. 45  is a top plan view of the locking ring shown in  FIGS. 43 and 44 ; 
         FIG. 46  is a sectional view of the sleeve spacer shown in  FIGS. 43-46  taken along the section line  46 - 46  of  FIG. 45 ; 
         FIG. 47  is a schematic view, partially in section, illustrating a procedure for installing the upper and lower cartridges in a fluid end block in accordance with said further embodiment of the present invention; 
         FIG. 48  is a schematic view, partially in section, illustrating a procedure for installing the sleeve component in a fluid end block in accordance with said further embodiment of the present invention; and 
         FIG. 49  is a schematic view, partially in section, illustrating the assembly of the components of said further embodiment of the present invention installed in a fluid end cylinder assembly together with the internal working elements. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with an important aspect of the present disclosure, the subject invention is particularly suited for use in existing fluid end designs, however, it is not restricted to those designs and can be utilized in other high pressure pumping applications where operating pressures, mechanical stresses, erosion and corrosion of internal passages are a concern. For the purpose of illustration, however, it will be described in conjunction with a conventional triplex fluid end such as is generally shown in  FIGS. 1-5 . 
     Referring to  FIG. 1 , a triplex reciprocating pump system is generally designated by the reference numeral  10  and includes a power end  11 , typically driven by a diesel engine and transmission, which is coupled to a pump body or fluid end  12  that is supplied with water and other ingredients for the fracking fluid via an inlet  13 . It is pressurized in the fluid end and discharged through a high pressure outlet  14  therein. Fluid end  12  includes a mounting surface  16  which can be used to directly secure the fluid end to the power end by plurality of bolts  17 . 
     As best shown in  FIGS. 2-5 , the fluid end  12  includes, a block  12   a  formed from a high strength steel forging, which is machined to provide a first or plunger bore  18 , a second or suction bore  19 , center chamber  20  for pressurization of the fracking fluid and a third bore or high pressure discharge bore  21 . Each of the high pressure discharge bores  21  shown in  FIG. 5  feeds into a common internal high pressure discharge passage  22  which directly communicates with the high pressure discharge outlet  14 . 
     The components of this first disclosed embodiment include a sleeve component, the details of which are shown in  FIGS. 6-9 , a cartridge component, the details of which are shown in  FIGS. 10-14 , a combination retainer/positioning plug, the details of which are shown in  FIGS. 15-19  and the assembly of these components with conventional internal valves, seals, etc. are shown in  FIG. 22 . 
     In  FIGS. 6-9 , the cylindrical sleeve component of the first disclosed embodiment is designated by the reference numeral  25  and can be composed of stainless steel, Inconel® and Incoloy® and other metal and alloys exhibiting suitable corrosion and erosion resistance and strength. If desired, coatings and surface treatments may be applied to the surfaces of the sleeves to improve the corrosion and erosion characteristics thereof. As shown, sleeve component  25  includes a first sleeve portion  25   a , a second sleeve portion  25   b  which are coupled to each other by integral interconnecting bridge portion  25   c  and  25   d . The outer surfaces of the first and second sleeve portions  25   a  and  25   b  are configured to be respectively received in direct contact with a first portion of the first bore, the plunger bore and a second portion of the first bore that can also be referred to as an access bore. 
     Sleeve  25  also includes a pair of flow passage apertures  26  and  27  defined by inner edges of bridge portions  25   c  and  25   d  which are configured to be in alignment with the second or suction bore  19  and third or high pressure discharge bore  21  when the sleeve is installed in a fluid cylinder of the fluid end  12 . 
     If desired, first tubular sleeve portion  25   a  and second tubular sleeve portion  25   b  may be in the form of two separate sleeves (without the interconnecting bridge portions) which are respectively received in the first and second portions of the first bore, namely the plunger and access bores. 
     In  FIGS. 10-14 , the cylindrical cartridge component of the first disclosed embodiment is designated by the reference numeral  30 . As shown, cartridge component includes a first portion  30   a  which is configured to be received in the second or suction bore  19 , a pair of apertures  30   b  and  30   c , an upper portion  30   d  are configured to be received in the third or high pressure discharge bore  30   d  and a bottom edge  30   e  that engages a removable plug which will be more fully described below. As with sleeve  25 , the cartridge  30  can be composed of stainless steel, Inconel®, Incoloy® as well as other metals and alloys. Correspondingly, coatings and surface treatments may be applied to the surfaces of the cartridge to improve the corrosion and erosion characteristics thereof. Apertures  30   b  and  30   c  are positioned to be in alignment with the first and second portions of the first bore and the center chamber  20  for accommodating the reciprocal movement of a plunger  31  ( FIG. 23 ). 
     As will be described more fully later in conjunction with  FIG. 22 , the perimeter of each aperture  30   a  and  30   b  includes a full perimeter groove in which a gasket is received. These gaskets can be formed from a suitable material which can withstand the high pressures, chemicals and other conditions associated with fracking operations and can include elastomers and synthetic fluorocarbon polymers which exhibit these properties. 
     In accordance with an important aspect of this disclosure, the sleeves and cartridges can be machined and/or surface treated prior to their assembly into the block. This feature provides greater flexibility in shaping the internal cylinder contours, resulting in improved performance and durability of the fluid end. 
     In some applications, it may be preferred to machine the mating fluid end bore surfaces and the outside surfaces of the sleeves and cartridge inserts to standard dimensions while machining the internal surfaces to address the required configurations. If desired, stress in the fluid end block may be reduced by increasing the thickness of the sleeve and cartridge cylinder to optimize the contours of the interfacing surfaces of the fluid end block. For example, by having a larger radius between intersecting bores of the block. 
     The tubular plug component of this disclosed embodiment is separately shown in  FIGS. 15-19  and designated by the reference numeral  32  which includes top end face having an annular rim  32   a  configured for direct contact with cartridge bottom edge  30 ( e ) and a threaded annular sidewall  32   b  that is matingly received in the threaded lower end of the second or suction bore  19  of fluid end  20 . Plug  32  is sized to secure cartridge  30  in a fixed operating position in the second and third bores with the apertures  30   b  and  30   c  in alignment with the first or plunger bore  18 . As shown, wrench-receiving recesses  33 - 36  can be provided in the bottom end face  32   c  of plug  32  to facilitate its installation and removal in and to the fluid end  12 . 
     Installation of the sleeve  25  into the first or plunger bore can be made from either end. For example, in the sleeve installation step shown in  FIG. 20  of the illustrated embodiment, since the diameters of first bore  18  and sleeve  25  are larger than the diameter of the open end of the bore opposite the mounting flange, access to the bore can be made through the mounting flange surface  16  ( FIGS. 2-4 ). It will be appreciated, however, that if the relative dimensions of bore  18  and sleeve  25  are appropriate, access to the interior of the bore and insertion of the sleeve could be done by removal of the retainer nut  53  ( FIG. 22 ) covering at that open end. 
     The surface of the bore  18  and sleeve  25  are machined to provide a smooth surrounding surface and to an equally smooth outer surface of the sleeve. In order to insure intimate surface-to-surface direct contact between the bore and sleeve, the sleeve can, if desired, have a slightly larger outer diameter than the bore. A differential temperature between the two is created to provide the necessary clearance during insertion and an interference fit when the temperature of both are normalized. 
     As schematically depicted in  FIG. 21 , after the sleeve  25  is installed, the cartridge is also machined to have outer diameter which is again slightly larger than the machined diameters of the second and third bores. A differential temperature between the cartridge and these bores is then created to provide the assembly clearance during this insertion and, when allowed to normalize, to provide a tight, interference fit between the cartridge and the second and third bores. 
       FIG. 22  illustrates a fluid end cylinder assembly  40  in which the sleeve, cartridge and plug components have been incorporated along with the internal working elements (e.g., plunger, suction valve, high pressure discharge valve, etc.). As shown, plunger  31  is received in the first bore  18  and reciprocates to effect pressurization in the chamber  20  to draw fracking fluid therein, at low pressure from the second or suction bore  19  containing a suction valve  41  and associated intake mechanism  42 . Correspondingly, the third high pressure discharge bore  21  receives pressurized fracking fluid from chamber  20  and discharges the same into the internal high pressure passage  22  via discharge valve  43  and associated discharge mechanism  44 . 
     Plunger packing assembly  49  and associated O ring seals in seal carriers  46  and  47  function to prevent or at least minimize passage of fracking fluid to the fluid body portions which surround the sleeve  25  and cartridge  30  components. As shown in  FIG. 22 , corrosion resistant material strips and beads  48  composed of a titanium-reinforced epoxy putty such as Devcon® (ITW Devon, Danvers, Mass.) can be utilized to minimize or eliminate seepage of tracking fluid into the portions of the fluid end body portions surrounding the sleeve  25  and cartridge  30 . 
     As schematically depicted in  FIG. 22 , during operation, the regions designated by reference numeral  51  represent the highest stress location in the assembled sleeve and cartridge. Correspondingly, the region designated by the reference numeral  52  represents the highest stress location in the block which is lower than the stress at region  51 . Since the sleeve and cartridge components by reason of their composition (e.g., high strength stainless steel, Inconel®, Incoloy®, etc.) provide greater resistance to erosion and corrosion as well as mechanical stresses and fatigue than is provided by the forged steel block, it follows the greater service life results. 
     Correspondingly, because the stress at the  52  location is less than that at the  51  location it follows that the overall stress on the block is reduced. 
     As previously noted, each of apertures  30   b  and  30   c  in the cartridge  30  has a perimeter groove in which a gasket is received. Those gaskets provide an effective seal between the outer surface of the cartridge and the edges of apertures  26  and  27  of the sleeve  25  which withstand the high pressure of the fracking fluid in the flow passages. 
     As shown, an access opening  18   a  at one end of bore  18  receives a removable retaining nut  53  to provide selective access to the interior of the first bore, when desired. 
       FIGS. 23-25  depict a further embodiment of the present invention where like parts have like reference numerals. This embodiment is designated by the reference numeral  60  and includes a modified block  61  formed from a high strength steel forging, a modified first plunger bore  62  and a modified sleeve  63 , composed of high strength stainless steel, Inonel®, Incolon® and equivalent metals and alloys. It does not require a cartridge like the cartridge  30  of the first embodiment. 
     As shown in  FIG. 23 , the modified bore includes a first section  62   a  with an enlarged diameter and a second co-axially aligned reduced diameter section  62   b . The sleeve  63  includes a first portion  63   a  which is sized to be tightly received in the bore section  62   a  and a second portion  63   b  sized to be received in bore section  62   b  with an interference fit between surfaces of bore sections  62   a  and  62   b  and the corresponding cylindrical surface of sleeve portions  63   a  and  63   b.    
     A seal carrier plate  64  has a lip  64   a  which contacts an outer end face of sleeve portion  63   a . As shown, an annular shoulder  62   c  in the bore  62  between bore section  62   a  and  62   b  is in direct contact with an annular back face  63   e . Lip  64   a  of seal carrier  64  and the shoulder  62   c  serve to maintain the sleeve  63  in a fixed position during fracking operations. 
     In accordance with an important feature of this disclosure, sleeve  63  has a pair of apertures  63   c  and  63   d , each of which is defined by a full perimeter groove in which a gasket is received. As with cartridge  30  of the first embodiment, the gaskets are formed from a suitable material which can withstand the high pressures and chemical erosion associated with fracking operations and can include elastomers and synthetic fluorocarbon polymers that exhibit these properties which are known to those skilled in the art. 
     As shown in  FIGS. 23 and 24 , the sleeve apertures  63   d  and  63   c  can be located in the outer surface of bore  62   a  at locations designated by reference numeral  65  and  66  and provide an effective seal between the sleeve and fluid end body portions in contact therewith. 
     The reference numerals  67  and  68  identify high stress locations in the sleeve interior portions in the area adjacent the sleeve apertures  63   d  and  63   c  and pressurization chamber  20 . As such, these areas are in locations wherein the resistance to erosion, corrosion, high stress and fatigue provided by high-strength stainless steel, Inconel®, Incoloy® and equivalents as contemplated by this disclosure is important. 
     As shown, an access opening  70  is enclosed by a removable retaining nut  69 . 
     The components of the third disclosed embodiment include a sleeve component, the details of which are shown in  FIGS. 26-30 , a lower cartridge component, the details of which are shown in  FIGS. 31-36 , an upper cartridge component, the details of which are shown in  FIGS. 37-42 , a locking ring component, the details of which are shown in  FIGS. 43-46 . The assembly of these components together with conventional internal valves, seals, etc. are shown in  FIG. 49 . 
     As shown in  FIGS. 26-30 , the cylindrical sleeve component of this third embodiment is designated by the reference numeral  75  and can be composed of stainless steel, Inconel® and Incoloy®, as well as other metals and alloys known to those skilled in the art which provide suitable corrosion and erosion resistance and strength. Additionally, coatings and surface treatments may be applied to the surfaces of the sleeves to improve the corrosion and erosion resistant characteristics thereof. In this illustrated embodiment, sleeve component  75  includes a first sleeve portion  75   a  which extends radially outwardly into a second, enlarged sleeve portion  75   b  via a shoulder  75   c . The outer surfaces of the first and second sleeve portions  75   a  and  75   b  are configured to be respectively received in surface-to-surface contact with a first portion of the first bore (the plunger bore) and a second portion of that bore which can be referred to as an access bore. 
     Sleeve  75  includes a pair of apertures  75  and  76  which respectively communicate with an outlet of the second bore suction bore  19  and the inlet to the third bore high pressure discharge bore  21  when the sleeve is installed in a fluid cylinder of a fluid end  12  (see  FIG. 49 ). If desired, the first and second tubular sections  75   a  and  75   b  may be in a form of two separate sleeves which are respectively received in first and second portions of the first bore. 
     In accordance with the present disclosure, the perimeter of each aperture  76  and  77  is respectively defined by a full perimeter groove  76   a  and  77   a  in which a gasket is received. These gaskets can be formed of a suitable material which can withstand the high pressures, chemicals and other conditions associated with fracking operations and can include synthetic fluorocarbon polymers that exhibit these properties as well as hydrogenated nitrile butadiene rubbers (HNBR), also known as highly saturated nitrile (HSN) rubbers. 
     In this embodiment, a lower cartridge component  80  is received in the suction bore  19  and a separate upper cartridge component  81  is received in discharge bore  21  (see  FIG. 49 ). As shown, lower cartridge component  80  has a generally cylindrical shape which extends upwardly from an end face  80   a  into a threaded section  80   b  which is configured to mate with a threaded section  19   a  in section bore  19 . A pair of notches  83  in end face  80   a  facilitate installation and removal of the lower cartridge component  80  in the suction bore  19 . As shown, the upper end of lower cartridge  80  terminates in an annular end face  80   d  and includes a groove  80   e  for receiving an “O-ring” (not shown). 
     Upper cartridge component  81  is sized to be tightly received in high pressure discharge bore  21  and includes an annular top end face  81  which extends into a cylindrical body  81   b  having a circular bottom end face  81   c  and groove  81   d  for receiving an “O-ring” (not shown). 
     In accordance with an important aspect of this disclosure, the circumferential seals in the groove  76   a  and  77   a  of sleeve  75  respectively cooperate with the upper annular end face  80   d  and the lower annular end face  81   a  of upper cartridge components to form a fluid-tight seal between these contacting surfaces of the sleeve and cartridges. 
     As with sleeve  75 , lower cartridge component  80  and upper cartridge component  81  can be composed of stainless steel, Inconel® and Incoloy® and other metal alloys exhibiting suitable corrosion and erosion resistance and strength. Correspondingly, coatings and surface treatments known to those skilled in the art may be applied to the surfaces of these components to improve the erosion and corrosion characteristics thereof. 
     If desired, a locking ring  82 , separately shown in  FIGS. 43-46 , may be provided to secure or fix the position of sleeve  75  in the plunger bore  18  as generally shown in  FIG. 49 . Locking ring component  82  has an annular shape with external threads  82   a  and internal threads  82   b . An end face  82   c  is sized to engage an end face  75   d  of sleeve  75  (see  FIGS. 30 and 49 ). The external threaded portion  82  is sized to mate with the threaded access opening in the plunger bore  18  and secure the sleeve in a fixed operating position therein. The internal threads  82   b  provide a securement facility for a plug or cover (not shown). 
     In accordance with an important aspect of this disclosure, the sleeve and cartridge components can be machined and/or surface treated prior to their assembly into the block. This affords greater flexibility in shaping of the internal cylinder contours and results in improved performance and durability of the fluid end. In some applications, it may be preferred to machine the fluid end bore surfaces and the outside surfaces of the sleeve and cartridge components to standard dimensions while machining the internal surfaces to address the required configurations. If desired, stress in the fluid end block may be reduced by increasing the thickness of the sleeve and cartridge components to optimize the contours of the inner facing surfaces of the fluid end block. For example, by having a larger radius between intersecting bores of the block. 
     As illustratively shown in  FIG. 47 , the upper and lower cartridge components can be initially installed followed by further machining to accept the subsequently installed sleeve as shown in  FIG. 48 . 
     These machining operations are done in order to assure a smooth surrounding surface on the individual bores and an equally smooth surrounding surface on the individual components. In order to insure intimate surface-to-surface direct contact between the components and the bores, the cartridge components can have a slightly larger outer diameter than the suction and discharge bores. A differential temperature between the two is then created to provide the necessary clearance during insertion and the interference fit results when the temperatures of both are normalized. 
     As schematically depicted in  FIG. 48 , after the cartridge components are installed, finish machining of the internal passageways is achieved to assure that the desired surface-to-surface contact. Again, differential temperatures between the sleeve and the bores are utilized to provide assembly clearance during insertion. Upon cooling, these differential temperatures normalize to provide a tight, interference fit between the outer surfaces of the sleeve and the inner surfaces of the plunger board  18 . 
       FIG. 49  illustrates the fluid end cylinder assembly of the third embodiment in which the dual cartridge and single sleeve components have been incorporated along with the internal working elements (e.g., plunger, suction valve, high pressure discharge valve, etc.). As shown, plunger  31  is received in the first bore  18  and reciprocates to effect pressurization in the chamber  20  to draw fracking fluid therein at low pressure from the suction bore  19  containing a suction valve  41  and associated intake mechanism  42 . Correspondingly, the high pressure discharge bore  21  receives a pressurized fracking fluid from chamber  20  and discharges the same into the high pressure passage  22  via discharge valve  43  and associated discharge mechanism  44 . 
     Plunger packing assembly  49  and associated O-ring seals in seal carriers  46  and  47  function to prevent or at least minimize passage of fracking fluid to the fluid body portions which surround the sleeve and cartridge components. As shown in  FIG. 49 , corrosion resistant material strips or beads composed of a titanium-reinforced epoxy putty such as Devcon® can be utilized to minimize or eliminate seepage of fracking fluids into the portions of the fluid end bodies surrounding the sleeve end cartridge components. 
     As schematically depicted in  FIG. 49 , during operation, the regions designated by reference numeral  51  represent the highest stress location in the assembled sleeve and cartridge. Correspondingly, the regions designated by reference numeral  52  represent the highest stress locations in the block which is lower than the stress at regions  51 . Since the sleeve and cartridge components, by reason of their composition, provide greater resistance to erosion and corrosion, as well as mechanical stresses and fatigues than that provided by the forged steel block, greater service life results. 
     As previously noted, each of the apertures  76  and  77  in sleeve  75  has a perimeter groove  76   a  and  77   a  in which a gasket is received. Those gaskets provide an effective fluid-tight seal between the gaskets contained in the sleeve apertures and the upper end of face  80   d  of lower cartridge component  80  and the lower end face  81   c  of upper cartridge component  81   c.    
     While the subject invention has been disclosed and described with illustrative examples, it will be appreciated that modifications and/or changes may be made to those examples by those skilled in the art without departing from the spirit and scope of this invention as defined by the appended claims.