Abstract:
A connector assembly comprising a housing and a tensile member disposed within the housing. The tensile member comprises first and second end portions. Each end portion sealingly engages the housing to form a hydraulic chamber therebetween. A first connector pivotally coupled to the first end portion. The axial position of the first connector relative to the housing is controlled by pressure within the hydraulic chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Application No. 60/653,605, filed Feb. 16, 2005, and titled “Hydraulic Self-Aligning Piston Rod Retention System,” which is hereby incorporated by reference herein for all purposes. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     Embodiments of the present invention relate to reciprocating equipment, particularly high-pressure mud pumps used in the oil production industry. More particularly, embodiments of the present invention relate to a novel method and apparatus for coupling components used in reciprocating equipment, such as mud pumps. 
     High pressure mud pumps commonly found in the oil production industry are generally large reciprocating pumps. The components of a mud pump can be divided into a power end and a fluid end. The power end components comprise a plurality of reciprocating connecting rods and crossheads connected to a rotating crankshaft. The fluid end components comprise a plurality of piston and cylinder assemblies along with the valves needed to control the flow of fluid into and out of the cylinders. In many pumps, an extension rod extends from each crosshead and is coupled to a piston via a piston rod. The power end serves to convert rotational motion of the crankshaft into a linear, reciprocating motion of the pistons within the cylinders. The reciprocating motion of the pistons generates pressurized fluid. 
     The drilling fluid pressurized by the mud pump often contains a high volume of solid material and can be highly abrasive. When operating with high pressure, abrasive fluid, mud pumps tend to have very high wear rates, especially in the fluid end components, such as the pistons. Because high pressure mud pumps experience high wear rates on pistons and other components, it is often necessary to replace the components on a regular basis. When replacing these components, the mud pump must necessarily be deactivated, which often results in interruption of the drilling process. Therefore, in order reduce downtime, it beneficial to be able to remove and replace worn components quickly and efficiently. 
     In many mud pump designs, the piston rods, which connect to the pistons, are connected to the extension rods via retention apparatus, such as piston rod clamps or links. These piston rod clamps can simplify the removal and replacement of a piston. Because field conditions are frequently less than ideal, and the components wear during operation, there is often some degree of misalignment between the reciprocating components. This misalignment can lead to complications and delays in installing a conventional piston rod clamp and making the connection between an extension rod and a piston rod. Therefore, there exists a need for a retention apparatus which allows for an efficient replacement of worn pistons and other high wear components while accommodating misalignment between the mud pump components, such as the extension rod and the piston rod. 
     Thus, the embodiments of the present invention are directed to piston rod retention systems that seek to overcome these and other limitations of the prior art. 
     SUMMARY OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention include methods and apparatus comprising a connector assembly comprising a housing and a tensile member disposed within the housing. The tensile member comprises first and second end portions. Each end portion sealingly engages the housing to form a hydraulic chamber therebetween. A first connector is pivotally coupled to the first end portion. The axial position of the first connector relative to the housing is controlled by pressure within the hydraulic chamber. 
     In certain embodiments a rod retention system comprises a connector assembly having a tensile member disposed within a housing. The tensile member has first and second end portions that sealingly engage the housing to form a hydraulic chamber therebetween. A first connector is coupled to the first end portion and disposable within a first receptacle disposed within a first rod. A second connector is coupled to the second end portion and disposable within a second receptacle disposed with a second rod. The first and second connectors are coupled to the tensile member so as to pivot or swivel with respect to the tensile member in order to compensate for misalignment of the connector assembly and the first and second rods. The axial distance between the first connector and the second connector is controlled by pressure within the hydraulic chamber. 
     Thus, the embodiments of present invention comprise a combination of features and advantages that enable substantial enhancement of rod retention systems. These and various other characteristics and advantages of the present invention will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention and by referring to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more detailed understanding of the present invention, reference is made to the accompanying Figures, wherein: 
         FIG. 1  is a partial sectional view of a mud pump comprising a rod retention system constructed in accordance with embodiments of the invention; 
         FIG. 2  is an isometric view of a rod retention system constructed in accordance with embodiments of the invention; 
         FIG. 3  is a partial sectional view of the rod retention system of  FIG. 2 ; 
         FIG. 4  is an isometric view of a connector assembly constructed in accordance with embodiments of the invention; 
         FIG. 5  is a partial sectional view of the connector assembly of  FIG. 4 ; 
         FIG. 6  is a partial sectional view of a tensile member constructed in accordance with embodiments of the invention; 
         FIG. 7  is an isometric view of a swivel connector constructed in accordance with embodiments of the invention; 
         FIG. 8  is a partial sectional view showing a connector assembly in an installation position; and 
         FIG. 9  is a partial sectional view showing a connector assembly in an operating position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. 
     Referring now to  FIG. 1 , mud pump  10  comprises fluid end  20  and power end  30 . Fluid end  20  comprises piston  22 , cylinder liner  24 , module  26 , intake valve  27 , and outlet valve  28 . Power end  30  comprises crankshaft  32 , connecting rod  34 , and crosshead  36 . Fluid end  20  is coupled to power end  30  by retention system  40 . Retention system  40  comprises extension rod  42 , piston rod  44 , and connector assembly  46 . Extension rod  42  connects to crosshead  36  and is coupled, via connector assembly  46  to piston rod  44 , which connects to piston  22 . Piston  22  is removed from pump  10  by disconnecting connector assembly  46  so as to decouple piston rod  44  from extension rod  42 . 
     Retention system  40  is shown in more detail in  FIGS. 2 and 3 . Retention system  40  further comprises pins  48  and  50 . Connector assembly  46  comprises end connectors  52  and  56  that interface with receptacles  54  and  58  on extension rod  42  and piston rod  44 , respectively. The interfaces between connectors  52  and  56  and their respective receptacles  54  and  58  are configured so as to compensate for misalignment between rods  42 ,  44  and connector assembly  46  during the assembly of retention system  40 . Pin  48  engages connector  52  and receptacle  54  so as to couple extension rod  42  to connector assembly  46 . Pin  50  engages connector  56  and receptacle  58  so as to couple connector assembly  46  to piston rod  44 . Each pin allows its associated connector to rotate about the pin&#39;s longitudinal axis so as to compensate for misalignment in a plane that is parallel to the longitudinal axis. Therefore, pins  48  and  50  are arranged perpendicular to each other so as to allow misalignment in more than one plane. 
     One embodiment of connector assembly  46  is shown in  FIGS. 4 and 5 . Connector assembly  46  comprises housing  60 , tensile member  62 , swivel connectors  64 , spherical sockets  66 , and hydraulic fitting  68 . Tensile member  62  is disposed within housing  60  with seals  70  sealingly engaged with the housing to form hydraulic chamber  72 . Hydraulic fitting  68  is disposed within the wall of housing  60  and provides fluid communication with hydraulic chamber  72 . 
     A swivel connector  64  is disposed on each end of tensile member  62 . Compliant member  74  is disposed between swivel connector  64  and tensile member  62 . Spherical socket  66  is coupled to tensile member  62  via threaded connection  76 . Spherical socket  66  engages swivel connector  64  and allows the swivel connector to pivot or swivel relative to tensile member  62  and housing  60 . Retaining rings  78  engage housing  60  limit the axial translation of tensile member  62 . 
     Referring now to  FIG. 6 , tensile member  62  may be formed from a unitary tubular member  88  having a helical slot  90 . Slot  90  penetrates the wall of tubular member  88  so as to reduce the axial strength and allow the tubular member to expand in response to an axial load as well as provide sufficient resiliency to create the desired loads on the connected components. The open ends  92  of tubular member  88  can be sealed by plugs  94 . In other embodiments, slot  90  may be replaced by other wall penetrations. Tensile member  62  may also be formed from solid bar material that has a sufficient strength and flexibility to allow axial expansion. In certain embodiments, the diameter of the bar material could be reduced in selected regions to achieve the desired expansion and resiliency. 
     Referring now to  FIG. 7 , swivel connector  64  comprises body  96  having spherical base  98 , groove  100 , pin receptacle  102 , and spherical pilot diameter  104 . Pin receptacle  102  has a longitudinal axis that intersects the center of curvature of spherical pilot diameter  104 . Spherical base  98  and spherical pilot diameter  104  allow swivel connector  64  to move in response to misalignment between mating components. In certain embodiments, a swivel connector could be formed with cylindrical surfaces or other curved surfaces to provide for misalignment in particular planes or directions. 
     In order to assemble connector assembly  46 , as shown in  FIG. 5 , pipe plugs  94  (or other suitable sealing means) are threaded into each end of tensile member  62 . A swivel connector  64  and resilient member  74  are then placed at each end of tensile member  62 . A spherical socket  66  is threaded onto each end of tensile member  62  to retain swivel connector  64 . As previously described, swivel connectors  64  and spherical sockets  66  have mating surfaces that are rounded, spherical, or otherwise formed with mating curved surfaces that allow the swivel connector to pivot or swivel relative to tensile member  62 . After the ends of tensile member  62  have been sealed and swivel connectors  64  installed, these components are installed into housing  60  along with seals  70 . 
     To install tensile member  62 , a retaining ring  78  is installed in a groove in one end of housing  60 . Tensile member  62  is then slid into housing  60  from the opposite end of the installed retaining ring  78 . After tensile member  62  and its associated components are installed into housing  60 , a second retaining ring  78  is installed on the other end of the housing so as to secure the tensile member within the housing. The assembly is completed by the installation of hydraulic fitting  68 . 
     To operate connector assembly  46 , a hydraulic fluid source, such as a pump, is coupled to hydraulic fitting  68  such that the fluid source is in fluid communication with hydraulic chamber  72 . Tensile member  62  will elongate axially in response to the application of pressurized hydraulic fluid to hydraulic chamber  72 . In certain embodiments, a hydraulic fluid pressure of 3000 psi may be applied to hydraulic chamber  72 . The elongation of tensile member  62  increases the extension of swivel connectors  64  from housing  60  of connector assembly  46 . Therefore, the axial position of swivel connectors  64  relative to housing  60  is dependent on the pressure within hydraulic chamber  72 . 
     Connector assembly  46  is constructed such that, when hydraulic chamber  72  is not pressurized (as shown in  FIG. 5 ), the distance between the receptacles in swivel connectors  64  is less than the distance between the corresponding receptacles in the piston rod  44  and the extension rod  46  when the rods contact housing  60  (as shown in  FIG. 2 ). Thus, pressurization of hydraulic chamber  72  is utilized to stretch tensile member  62  and allow the receptacles of swivel connectors  64  to become aligned with the corresponding receptacles in the connected rods. 
     Thus, connector assembly  46  is pressurized to stretch tensile member  62  and allow swivel connectors  64  to become axially aligned with the receptacles in the piston rod and extension rod. This is accomplished by removing inserting a hydraulic nozzle (not shown) into hydraulic fitting  68  (see  FIG. 5 ). The hydraulic nozzle can then be connected to a hydraulic pump, or other pressurized fluid source, and hydraulic chamber  72  of connector assembly  46  pressurized. In certain embodiments, the assembly will be pressurized to a maximum of 3,000 psi. A relief valve in the nozzle assembly may be used to prevent overpressurization of the connector assembly  46 . 
       FIG. 8  illustrates one end of connector assembly  46  in an installation position where hydraulic chamber  72  has been pressurized. It is understood that both ends of connector assembly will operate in substantially the same manner and substantially in unison. In certain embodiments, it may be possible to connect one end of connector assembly  46  without pressurizing the system, but pressurization is required to connect both ends. In  FIG. 8 , receptacle  80  and rod  82  are used to generically describe any rod to which the connector assembly is attached. For example, receptacle  80  and rod  82  may be, for example, a piston rod or an extension rod as described above 
     Pressurized fluid in hydraulic chamber  72  causes tensile member  62  to elongate. The elongation of tensile member  62  extends swivel connector  64  from housing  60 . The extended swivel connector  64  is inserted into receptacle  80  of rod  82 . Once the through holes in rod  82  and swivel connector  64  are axially aligned pin  84  is inserted to couple swivel connector  64  to rod  82 . 
     The extension of swivel connector  64  creates a gap  86  between housing  60  of connector assembly  46  and rod  82 . Gap  86  allows swivel connector  64  to compensate for misalignment between connector assembly  46  and rod  82 . Swivel connector  64  can rotate within receptacle  80  about the longitudinal axis of pin  84 . As discussed above, since each swivel connector  64  can only rotate about the longitudinal axis of its respective pin  84 , the swivel connector and pins on opposite ends of connector assembly  46  should be oriented perpendicular to each other so as to allow compensation of misalignment in more than one plane. 
     As swivel connector  64  moves relative to receptacle  80 , compliant member  88  is compressed between the connector and the receptacle and helps center the connector within the receptacle. Swivel connector  64  can also rotate relative to tensile member  62  along the spherical interface between the connector and spherical socket  66 . Compliant member  74  is compressed between swivel connector  64  and tensile member  62  as the swivel connector moves and helps return the swivel connector to its original position relative to the swivel connector. 
     The flexibility of swivel connector  64  allows the swivel connector to move in response to misalignment between the connector assembly  46  and rod  82 , which makes it easier to align the holes through the swivel connector and the rod so that pin  84  can be easily installed. Once pin  84  is installed, the connection between connector assembly  46  and rod  82  is completed by relieving the pressure within hydraulic chamber  72 . As the pressure within hydraulic chamber  72  is reduced, tensile member  62  will axially contract, drawing swivel connector  64  toward housing  60 . 
     As shown in  FIG. 9 , the contraction of tensile member  62  draws rod  82  toward connector assembly  46  such that gap  86  (see  FIG. 8 ) closes and the rod bears against housing  60 . As rod  82  contacts housing  60 , the continued contraction of tensile member  62  imparts a shear load on pin  84 . This shear load on pin  84  maintains the connection between rod  82  and connector assembly  46  during reciprocal motion. 
     To disconnect rod  82  from connector assembly  46 , a pressurized fluid source is hydraulically coupled to hydraulic fitting  68  such that the fluid source is in fluid communication with hydraulic chamber  72 . Tensile member  62  will elongate axially in response to the application of pressurized hydraulic fluid to hydraulic chamber  72 . The elongation of tensile member  62  increases the extension of swivel connectors  64  from housing  60  of connector assembly  46 , releasing the loads on pins  84 . Once pins  84  are unloaded, they can be removed, thus disconnecting rod  82  from swivel connector  46 . 
     Disclosed within is a novel method and apparatus for retaining components in reciprocating equipment such as mud pumps used in earthen drilling operations. Among the numerous advantages of this retention apparatus is the ability to accommodate some degree of misalignment among the components to which it is connected. The apparatus accomplishes this by incorporating mating surfaces between components which have surfaces that are rounded or formed with a spherical radius. In addition, the two retaining pins that connect the retention apparatus to the adjacent components (i.e., the extension rod and piston rod) are oriented at 90 degrees from each other. This allows the retention apparatus to accommodate misalignment in multiple planes. Other advantages of the apparatus include the ability to connect and disconnect components with lower hydraulic pressures than are typically necessary in prior art, hydraulically actuated devices. 
     While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. In addition, use of the term “between” when describing the location of a component should not be construed such that the component must be directly contacting the adjacent members. Furthermore, other embodiments may incorporate different configurations than the tensile member disclosed above, including the use of compression springs that act on surfaces to reduce the distance between the swivel connectors. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.