Patent Publication Number: US-2023160402-A1

Title: Retainer Nut Assembly for Pump and Methods

Description:
TECHNICAL FIELD 
     The present disclosure relates to pump assemblies and, in particular, retainer nut assemblies for such pump assemblies and methods of assembly. 
     BACKGROUND 
     In hydraulic fracturing, and other similar applications, the pumping equipment used to pump fluid media into a well is an important part of the fracturing system and process. Reciprocating pump systems have been used for decades to propel a fluid media, typically a mixture of water, sand and chemicals, for example, into a well at high pressures and flow rates. Increasing demands of pressure pumping has required such pumps to evolve by increases in size, horsepower rating, and pressure capabilities. As a result, designing pump assemblies to be reliable and easily maintained has become an increasingly important consideration. 
     Reciprocating pump systems typically include fluid end blocks with fluid inlet and outlet passages for the fluid media. Each of the fluid inlets and fluid outlets include a check valve to control the flow of fluid through the fluid end block. Such pump systems have a plunger that generates the substantial pumping pressures required to pump the fluid media through the pump. Pump systems typically have both a cover assembly and a retainer nut for access to the inner workings of the fluid end of the pump for initial assembly and maintenance. 
     Current hydraulic fracturing fluid ends typically require a threaded retainer nut to retain a suction cap in position in the fluid end block. To tighten the retainer nut, the use of a hammer wrench and a sledgehammer are typically required to generate a preload in the threads. The use of the hammer can give an imprecise result and is a swinging mass that exposes the user to harm. Due the nature of the pumping process and high forces generated in the fluid end block, the retainer nut can work loose. This creates the potential of the retainer nut being forcefully ejected from the fluid end block and/or may cause damage to the block itself. 
     U.S. Pat. No. 8,402,880 discloses a pump system with a fluid block. A retaining system secures a closure at an installed position within a bore of the fluid block. The bore has screw threads along at least a portion thereof. The closure has an internally threaded hold extending therein. The closure in the installed position closes the bore. The retaining system includes a retaining cover or nut for holding the closure in the bore. The retaining nut has external threads that are engageable with the screw threads of the bore such that the cover is rotatable relative to the housing in a tightening direction for movement of the cover into the bore toward the closure and rotatable in an opposite, loosening direction for movement of the cover out from the bore away from the closure. 
     There is a need for an easily assembled and reliable retainer nut for a fluid end of a pump system. Devices and methods according to the disclosure satisfy the need. 
     The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the innovations described herein, nor to limit or expand the prior art discussed. Thus, the foregoing discussion should not be taken to indicate that any particular element of a prior system is unsuitable for use with the innovations described herein, nor is it intended to indicate that any element is essential in implementing the innovations described herein. The implementations and application of the innovations described herein are defined by the appended claims. 
     SUMMARY 
     In one aspect, the disclosure includes a retainer nut assembly for a fluid end of a pump system including a fastener comprising a generally cylindrical configuration, first and second ends, external threads configured to engage corresponding threads of a fluid end block, and a cavity formed at the first end. A suction cap is shaped and sized to sealingly fit to the fluid end block. A load piston is movably disposed in the cavity and adjacent the suction cap. A bore is formed through the fastener in communication with the cavity and provided with a hydraulic fluid. A pressure piston is movably disposed in the bore. A threaded passageway is formed through the fastener in communication with the bore and open to the second end and a locking bolt is disposed in the threaded passageway configured, when inserted into the threaded passageway to contact the pressure piston and generate fluid pressure on the load piston with the hydraulic fluid. 
     In another aspect, the disclosure includes a fluid end for a reciprocating pump system including a fluid end block defining a fluid chamber. A plunger is reciprocally disposed in the fluid chamber to generate fluid pressure therewithin. An outlet fluid passage is formed in the fluid end block in fluid communication with the fluid chamber, the outlet fluid passage including an outlet valve. An inlet fluid passage is formed in the fluid end block in fluid communication with the fluid chamber, the inlet fluid passage including an inlet valve. A retainer nut assembly for the fluid end of the pump system includes a fastener including a generally cylindrical configuration, first and second ends, external threads configured to engage corresponding threads of a fluid end block, and a cavity formed at the first end. A suction cap is shaped and sized to sealingly fit to the fluid end block. A load piston is movably disposed in the cavity and adjacent the suction cap. A bore is formed through the fastener in communication with the cavity and provided with a hydraulic fluid. A pressure piston is movably disposed in the bore. A threaded passageway is formed through the fastener in communication with the bore and open to the second end and a locking bolt is disposed in the threaded passageway configured, when inserted into the threaded passageway to contact the pressure piston and generate fluid pressure on the load piston with the hydraulic fluid. 
     In yet another aspect, the disclosure includes a method of installing a retainer nut assembly into a fluid end block for a reciprocating pump system, the method including threading a fastener portion into the fluid end block, tightening a locking bolt disposed in the fastener and engaged therewith via threads, engaging and advancing a pressure piston disposed in a bore of the fastener with the locking bolt, generating fluid pressure in the bore with the pressure piston, applying the fluid pressure to a load piston, and generating, with the load piston, a force on a section cap installed in the fluid end block. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an elevation view of a reciprocating pump system according to an exemplary embodiment, the reciprocating pump system including a fluid end. 
         FIG.  2    is a section view of the fluid end of  FIG.  1    according to an exemplary embodiment, the fluid end including a fluid end block or housing and inlet and outlet valves. 
         FIG.  3    is a perspective view of a retaining nut assembly positioned in a fluid end block. 
         FIG.  4    is a perspective cross section view of the retaining nut of  FIG.  3    positioned in a fluid end block. 
         FIG.  5    is a cross section view of the retaining nut of  FIG.  3    positioned in a fluid end block. 
         FIG.  6    is a perspective view of a retaining nut engaged with a tool. 
         FIG.  7    is a method of installing a retaining nut according to embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Now referring to the drawings, wherein like elements refer to like reference numbers, there is illustrated in  FIG.  1    an exemplary embodiment of a reciprocating pump system (generally referred to by the reference numeral  10 ) including a power end portion  12  and a fluid end portion  14  operably coupled thereto. The power end portion  12  includes a housing  16  in which a crankshaft (not shown) is disposed, as is known, the crankshaft being operably coupled to an engine or motor (not shown), as is known, which is configured to drive the crankshaft. The fluid end portion  14  includes a fluid end block  18 , which is connected to the housing  16  via a plurality of stay rods  20 . The fluid end block  18  includes a fluid inlet passage  22  and a fluid outlet passage  24 , which are spaced in a parallel relation. A plurality of fluid end retainer nut assemblies  26 , one of which is shown in  FIG.  1   , is connected to the fluid end block  18  opposite the stay rods  20 . A plurality of cover assemblies  28 , one of which is shown in  FIG.  1   , is connected to the fluid end block  18  opposite the fluid inlet passage  22 . A plunger rod assembly  30  extends out of the housing  16  and into the fluid end block  18 . Other configurations of a reciprocating pump system  10  are contemplated. 
     In embodiments, as illustrated in  FIG.  2    with continuing reference to  FIG.  1   , the plunger rod assembly  30  includes a plunger  32 , which extends through a bore  34  formed in the fluid end block  18 , and into a fluid chamber  36  formed in the fluid end block  18 . The plunger  32  is reciprocally disposed in the fluid chamber  36  to generate fluid pressure therewithin. In embodiments, a plurality of parallel-spaced bores may be formed in the fluid end block  18 , with one of the bores being the bore  34 , a plurality of fluid chambers may be formed in the fluid end block  18 , with one of the fluid chambers being the fluid chamber  36 , and a plurality of parallel-spaced plungers may extend through respective ones of the bores and into respective ones of the fluid chambers, with one of the plungers being the plunger  32 . 
     The fluid end block  18  includes inlet and outlet fluid passages  38  and  40  formed therein, which are generally coaxial along a fluid passage axis  42 . Under conditions to be described below, fluid flows from the inlet fluid passage  38  toward the outlet fluid passage  40  along the fluid passage axis  42 . The fluid inlet passage  22  is in fluid communication with the fluid chamber  36  via the inlet fluid passage  38 . The fluid chamber  36  is in fluid communication with the fluid outlet passage  24  via the outlet fluid passage  40 . 
     The inlet fluid passage  38  may include an enlarged-diameter portion  38   a  and a reduced-diameter portion  38   b  extending downward therefrom (as in the figure), which direction may also be considered the upstream direction. Downstream from the enlarged-diameter portion  38   a  is an inlet fluid passage neck  38   c , which is reduced in diameter relative to the enlarged-diameter portion. 
     The enlarged diameter portion  38   a  defines a tapered internal shoulder  43  and thus a frusto-conical surface  44  of the fluid end block  18 . The reduced-diameter portion  38   b  defines an inside surface  46  of the fluid end block  18 . Similarly, the outlet fluid passage  40  includes an enlarged-diameter portion  40   a  and a reduced-diameter portion  40   b  extending downward therefrom. The enlarged-diameter portion  40   a  defines a tapered internal shoulder  48  and thus a frusto-conical surface  50  of the fluid end block  18 . The reduced-diameter portion  40   b  defines an inside surface  52  of the fluid end block  18 . The frusto-conical surfaces  44 ,  50  form valve seats for respective inlet and outlet valves  54 ,  56 . 
     An inlet valve  54  is disposed in the inlet fluid passage  38 , and engages at least the frusto-conical surface  44  and the inside surface  46 . Similarly, an outlet valve  56  is disposed in the outlet fluid passage  40 , and engages at least the frusto-conical surface  50  and the inside surface  52 . In an exemplary embodiment, each of valves  54  and  56  is a spring-loaded valve that is actuated by a predetermined differential pressure thereacross. 
     A counterbore  58  is formed in the fluid end block  18 , and is generally coaxial with the outlet fluid passage  40  along the fluid passage axis  42 . In embodiments, the fluid end block  18  may include a plurality of parallel-spaced counterbores, one of which may be the counterbore  58 , with the quantity of counterbores equaling the quantity of plunger throws included in the pump system  10 . The cover assembly  28  shown in  FIGS.  1  and  2    includes at least a plug  64  and a fastener  66 . In embodiments, the cover assembly  28  may be disconnected from the fluid end block  18  to provide access to, for example, the counterbore  58 , the fluid chamber  36 , the plunger  32 , the outlet fluid passage  40  or the outlet valve  56 . In embodiments, the pump system  10  may include a plurality of plugs, one of which is the plug  64 , and a plurality of fasteners, one of which is the fastener  66 , with the respective quantities of plugs and fasteners equaling the quantity of plunger throws included in the pump system  10 . 
     A counterbore  60  is formed in the fluid end block  18 , and is generally coaxial with the bore  34  along an axis  62 . The counterbore  60  defines an internal shoulder  60   a  and includes an internal threaded connection  60   b  adjacent the internal shoulder  60   a . In embodiments, the fluid end block  18  may include a plurality of parallel-spaced counterbores, one of which may be the counterbore  60 , with the quantity of counterbores equaling the quantity of plunger throws included in the pump system  10 . The counterbore  60  is sized and shaped to receive a retainer nut assembly  26  (see  FIGS.  3 - 6   ) according to embodiments disclosed herein. In embodiments, the retainer nut assembly  26  may be disconnected from the fluid end block  18  to provide access to, for example, the counterbore  60 , the fluid chamber  36 , the plunger  32 , the inlet fluid passage  38 , or the inlet valve  54 . The retainer nut assembly  26  may then be reconnected to the fluid end block in accordance with the foregoing. In several exemplary embodiments, the pump system  10  may include a plurality of plugs, one of which is the plug  68 , and a plurality of fasteners, one of which is the fastener  70 , with the respective quantities of plugs and fasteners equaling the quantity of plunger throws included in the pump system  10 . 
     Focusing now on the inlet fluid passage  38 , a biasing member  71  is positioned within the inlet fluid passage  38 . The biasing member  71  may be a coil spring. In one embodiment the biasing member  71  is a conical coil spring. The biasing member  71  may be retained in place by a spring stop  72  as is known. When installed as shown in  FIG.  2   , the biasing member  71  exerts a selected biasing force on the inlet valve  54  that holds the inlet valve against the frusto-conical surface  44  to create a closed or sealed condition. When a pressure differential on the inlet valve  54  exceeds the closing force generated by the biasing member  71 , the inlet valve opens and permits fluid media to enter the fluid chamber  36 . 
     Turning to  FIGS.  3 - 6   , the retainer nut assembly  26  includes a fastener  70  that is sized and shaped to be threaded, i.e., advanced, into the fluid end block  18  via an external thread  70   a  of the fastener  70 . The external thread  70   a  is configured to engage with the internal threads  60   b  of the counterbore  60 . The external thread  70   a  is formed at a first end  70   b  of the generally cylindrical fastener  70 . The thread  70   a  may be segmented to permit fluid to escape from inside the fluid chamber  36 . The fastener  70  holds a load piston  104 , which abuts and holds in place a suction cap or plug  68  in the fluid end block  18  when installed. 
     The retainer nut assembly  26  includes a mechanism to preload the assembly when installed in the fluid end block  18  to reduce cyclical changes in force on the threaded connection  70   a ,  60   b  due to the large changes in pressure generated inside the fluid end block. The large changes in pressure can cause alternating stress on the threaded connection  70   a ,  60   b , which can cause the retainer nut assembly to loosen and the threads of the fastener to fatigue. Moreover, failure of the fluid end portion  14  can occur from the large amplitude of alternating stress and resulting damage caused to the retainer nut assembly  26 . For example, cracks can develop in the fluid end portion  14  from high cyclic stress. The retainer nut assembly  26  also may include a mechanism to determine if the assembly is preloaded a specified amount. Both of these mechanisms will be detailed hereinbelow. 
     The plug  68  is sized and shaped to be disposed in the counterbore  60 , engaging the internal shoulder  60   a  and sealingly engaging an inside cylindrical surface defined by the reduced-diameter portion of the counterbore  60 . In an exemplary embodiment, the plug  68  may be characterized or referred to as a suction cap. The load piston  104  may be provided with an annular load seal  110  disposed in an annular load groove  112  that is formed on the outer, circular periphery of the load piston. 
     The fastener  70  may include two or more outwardly extending tabs or lugs  80  configured to be engaged and rotated by a tool  82  ( FIG.  6   ). The tabs  80  may each be a generally rectangular, outwardly extending part attached to the fastener  70 , for example by welding, in a configuration suitably spaced apart so as to enable the application of a sufficient amount of torque to rotate and secure the fastener  70  in place using the tool  82 . Each of the tabs  80  may have an opening  84  formed therethrough for receiving the tool  82 . 
     For example, a pair of tabs  80   a ,  80   b  are arranged across from each other on opposite sides of or adjacent the outer periphery of the outer surface or second end  86  of the fastener  70  such that the openings  84  sufficiently align to enable the tool  82  to be inserted through both of the tabs. Applying a torque via the tool  82  conveys the torque through the tabs  80   a ,  80   b  to the fastener  70 . A clockwise torque (as viewed in  FIG.  6   ) with right-handed threads  70   a  formed on the fastener  70  would have the effect of advancing the fastener into the fluid end block  18 , and vice versa. Two pairs of tabs  80  may be arranged at 90 degree orientations about and adjacent the periphery of the second end  86  to enable easy access via the tool  82 . Other configurations of tabs or engageable features are contemplated. The tool  82  may be a cylindrical bar, for example, or any suitable means of engaging the tabs  80  and exert a suitable amount of torque to advance the fastener  70  into the fluid end block  18 . 
     The second end  86  of the fastener  70  also, as seen in  FIG.  3   , includes a lock piece or locking bolt  88 , which may be a threaded fastener such as a hex bolt. Insertion and rotation of the lock piece  88  applies the preload to the retainer nut assembly  26  as will be explained below. As shown in  FIGS.  4 - 5   , the lock piece  88  is threaded into the fastener  70  by engaging an internally threaded passage  90  formed in or through the fastener  70 . The internally threaded passage  90  may be formed in the center of the fastener, i.e., centered on an axial center  92  of the fastener  70 . 
     The fastener  70  also may include a lock indicator  93 , which may include a piston or pressure transducer, sensor, or any suitable mechanism that responds to pressure as will be explained more fully herein and provides an indication when a specified preload force is being applied to the retainer nut assembly  26 . The lock indicator  93  may be biased by a spring  106 , wavy washer, or cone washer, or any suitable mechanism such that until a specified amount of force is acting on the lock indicator, the lock indicator does not extend from the second end  86 . The lock indicator  93  extends outwardly from the second end  86  when a specified preload force acts on the indicator. In alternative embodiments, the lock indicator  93  may be a sensor that generates a signal indicative of the forces being sensed thereby. In alternative embodiments, the lock indicator  93  may be a green-red hydraulic bypass indicator. 
     In embodiments, the lock indicator  93  includes a post portion  114  disposed in a bore  115  formed in or through the fastener  70  and a piston portion  116  that is disposed in a port  117 . The port  117  has a greater diameter than that of the bore  115  so as to retain the lock indicator  93  when the lock indicator is being urged outwardly by fluid pressure in the port  117 . 
     The fastener  70  includes formed in the first end  70   a , opposite the second end  86 , a cavity  96  with an annular groove  100  formed in the sidewall of the fastener adjacent the end opposite the outer surface. The groove  100  is sized and shaped to retain a snap ring  102 . The cylindrical cavity  96  is sized and shaped to movably receive the load piston  104  and, when the load piston is positioned within the cavity, the snap ring  102  is positioned to retain the load piston therein. The snap ring  102  may retain the load piston  104  by stopping against a shoulder  108  formed at the inner edge of the load piston. The shoulder  108  is configured to permit a limited amount of axial movement of the load piston  104  in the cavity  96  such that the load piston can be moved against the suction cap  68 . 
     The fastener  70  also includes a pressure piston  94  disposed in a bore  96  formed in the fastener along the axis  92 . The pressure piston  94  is provided with two or more seals  101 . The seals  101  may include elastomeric O-rings, or any suitable means of sealing the bore  96  and pressure piston  94 . The bore  96  is also formed on the axial center  92  and is in communication with or open to the internally threaded passage  90  such that the lock piece  88  when inserted inwardly contacts the pressure piston  94  and can exert a force against the piston. The piston  94  has an axial length that is less than the length of the bore  96  and the bore is filled with a hydraulic fluid, such as grease for example. 
     When the lock piece  88  is threaded inwardly and presses against the piston  94 , hydraulic pressure is generated within the bore  96 , which in turn is conveyed to the load piston  104 . When the load piston  104  is loaded via hydraulic pressure generated by advancing the lock piece  88  pressing against the piston  94 , the load piston generates pressure via the hydraulic fluid in the bore  96 , and the load piston  104  exerts pressure on the cap  68 . In return, a force opposite in direction is generated that urges the fastener  70  outwardly from the fluid end block  18 , which preloads the threads  70   a . Fluid pressure generated by the pressure piston  94  pushes fluid into the space between the cavity  96  and the load piston  104  and acts on the piston portion  116  of the indicator  93  to urge the indicator outwardly to provide an indication of hydraulic pressure being generated. 
     Changes in pressure generated by the plunger  32  within the fluid chamber  36  act indirectly on the fastener  70 . When the threads  70   a  are not preloaded, the threaded connection  70   a ,  60   b  between the fastener  70  and the fluid end block  18  experiences cyclical changes of stress. When the threads  70   a  are preloaded, static stress is increased and peak to peak cyclic stress amplitude is greatly reduced. As a result, the threaded connection is more reliable, the status of the fluid end retainer nut assembly  26  is easily discernable, and the need for frequent maintenance is reduced. 
     INDUSTRIAL APPLICABILITY 
     The industrial applicability of the system described herein will be readily appreciated from the forgoing discussion. The foregoing discussion is applicable to fluid ends of reciprocating pump assemblies, in particular, for pumping fluid media in fracturing operations and similar applications. 
     One example of the industrial application of the system according to embodiments of the disclosure, and referring also to  FIGS.  1 - 6   , a method of installing a retainer nut assembly  26  includes manually threading the retainer nut assembly into a fluid end block  18  of a fluid end  14  of a reciprocating pump system  10 . In embodiments, with the suction cap  68  in position in the fluid end block  18 , and the load piston  104  positioned on the fastener  70 , in step  120 , the installation includes engaging a fastener portion  70  with a tool  82  and rotating/threading the fastener into the fluid end block  18 . Once the retainer nut assembly  26  is fully threaded into the fluid end block  18 , in step  122 , a locking bolt  88  is tightened. The locking bolt  88  may be tightened by rotating and advancing the locking bolt into the fastener  70 . In step  124 , advancement of the locking bolt  88  engages a pressure piston  94 , the advancement of which generates fluid pressure on a load piston  104 . The load piston  104 , in step  126 , generates a force on a suction cap  68 , which presses the suction cap into the fluid end block  18 . In step  128 , the fluid pressure generated also imparts a reaction load or force on the fastener  70 , which loads the fastener threads  70   a , in the outward direction relative to the fluid end block  18 . In step  130 , a lock indicator  93 , which is configured to respond to the generated fluid pressure and provide an indication whether a specified installation pressure is reached, provides an indication of the generated fluid pressure. 
     It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated. 
     Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. 
     Unless explicitly excluded, the use of the singular to describe a component, structure, or operation does not exclude the use of plural such components, structures, or operations or their equivalents. The use of the terms “a” and “an” and “the” and “at least one” or the term “one or more,” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B” or one or more of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B; A, A and B; A, B and B), unless otherwise indicated herein or clearly contradicted by context. Similarly, as used herein, the word “or” refers to any possible permutation of a set of items. For example, the phrase “A, B, or C” refers to at least one of A, B, C, or any combination thereof, such as any of: A; B; C; A and B; A and C; B and C; A, B, and C; or multiple of any item such as A and A; B, B, and C; A, A, B, C, and C; etc. 
     Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.