Abstract:
Methods and apparatus for securing a cylinder liner to a pump module. A tension body is disposed about the cylinder liner and attached to the pump module. A locking body engages the cylinder liner and is threaded to the tension body. A hydraulic load cell is removably attached to the tension body and includes a hydraulic ram arranged to impart a compressive load to the cylinder liner and a tension load in the tension body. The locking body can be adjusted axially to contact the cylinder liner and maintain the applied loads, which act as a pre-load to keep the cylinder liner in contact with the pump module.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not Applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable.  
       FIELD OF THE INVENTION  
       [0003]     The present invention relates generally to mud pumps and particularly relates to a system and apparatus for aligning and securing the cylinder liners of such pumps to their respective pumping modules. More particularly, the present invention relates to a hydraulic retention system and apparatus for aligning and securing the cylinder liner that includes a removable pre-loading system.  
       BACKGROUND  
       [0004]     In extracting hydrocarbons from the earth it is common to drill a borehole into the earth formation containing the hydrocarbons. A drill bit is attached to a drill string, including joined sections of drill pipe, suspended from a drilling rig. As the drill bit rotates, the hole deepens and the string is lengthened by attaching additional sections of drill pipe. During drilling operations, drilling fluid, or “mud” as it is also known, is pumped down through the drill pipe and into the hole through the drill bit. Drilling fluids are used to lubricate the drill-bit and keep it cool. The drilling mud also cleans the bit, and balances pressure by providing weight downhole, as well as bringing up to the surface sludge and cuttings created during the drilling process.  
         [0005]     Slush or mud pumps are commonly used for pumping the drilling mud. Because of the need to pump the drilling mud through several thousand feet of drill pipe, such pumps typically operate at very high pressures. Moreover, it is necessary for the mud to emerge from the drill bit downhole at a relatively high velocity to lubricate and cool the bit and to effectively remove cuttings from the hole. Lastly, the fluid pressure generated by the mud pump contributes to maintaining a predetermined total downhole pressure, which is necessary in order to prevent dangerous and costly well blowouts.  
         [0006]     The pistons and cylinders used for such mud pumps are susceptible to a high degree of wear during use because the drilling mud is relatively dense and has a high proportion of suspended abrasive solids. As the cylinder in which the piston reciprocates becomes worn, the small annular space between the piston head and the cylinder wall increases substantially and sometimes irregularly. This decreases the efficiency of the pump. To reduce the effect of this wear, the cylinder typically is provided with an expendable cylinder liner, which can be easily replaced.  
         [0007]     It is the usual practice to replace the cylinder liner at end of its useful life. The pump cylinder liner in a duplex pump typically has an average life of 1200 to 1500 pump hours, or about 90 to 100 days. A duplex pump has two reciprocating pistons that each force fluid into a discharge line. The average life of the cylinder liners in a triplex pump is about 500 to 900 hours or about 50 to 60 days of service life at a normal duty cycle. Triplex reciprocating pumps have three pistons that force fluid into a discharge line. These fluid pumps can be single acting, in which fluid is discharged on alternate strokes, or double acting, in which each stroke discharges fluid.  
         [0008]     In the course of installing or replacing a cylinder liner, the cylinder liner may become misaligned. Misaligned contact between the metal piston head and the cylinder creates considerable friction, abrasion, and heat. This, in turn, causes the cylinder liner, as well as other various pump parts, such as seals, to be susceptible to an increased rate of wear. In some cases, the frictional forces may even cause the seal to detach from the piston. For these reasons, the alignment of the cylinder liner of such pumps is critical.  
         [0009]     Further, changing a cylinder liner in a mud pump is typically a difficult, dirty, and heavy job. Still further, because drilling rig time is very expensive, frequent replacement of cylinder liners causes considerable inconvenience if the system and apparatus for releasing the old cylinder liners and fitting the replacement cylinder liners are slow or difficult to operate. Thus, it is important that the system and method for aligning and securing the cylinder liners may be implemented without undue effort and down-time.  
         [0010]     Some original pump designs include a large threaded “hammer nut” that is hammered on and off to hold the liner in place. Such a system for securing cylinder liners to respective pumping modules is difficult to operate with precision for a variety of reasons, including the involvement of heavy components, the handling of which may be dangerous for operators. These types of systems require considerable strength, skill and reliability of operators, together with the use of heavy tools in confined spaces. Thus, it is difficult to apply a specified torque to within a desired preset tolerance. Further, the securing force is dependent on the extent of wear and the general condition of the securing components.  
         [0011]     There are several alternative ways to attach cylinder liners to their respective pumping modules, and these may vary according to make of pump in which they are used. One embodiment presently known employs a tapered concentric clamp, while another uses a concentric screw clamping arrangement. The tapered clamp is susceptible to corrosion and wear, which diminish its effectiveness. Other pump designs require large wrenches or impact socket tools to remove large nuts from studs so as to release the retainer. Not only is this not as precise way to load the liner seal, but in some models the rotation effect can dislodge and fail the seal mechanism. In all of these systems, the force securing the cylinder liner is difficult to control precisely, causing the cylinder liner to be susceptible to misalignment.  
         [0012]     In still another known design, a replacement device involves removal of some of the original parts and uses hydraulics and Belleville washers to load, hold, and restrain the liner. This system relies on a spring lock, and therefore the securing force is dependent on the ability of the spring to retain its stiffness against the securing components. In addition, it relies on nuts secured on studs spaced about the circumference of the cylinder. Thus, this system causes the cylinder liner to be susceptible to misalignment arising from unequal securing forces at each stud, which can be caused by unequal tightening of each nut.  
         [0013]     Accordingly, there remains a need to develop a new and improved system and apparatus for retaining and replacing a cylinder liner which overcomes certain of the foregoing difficulties while providing more advantageous overall results.  
       SUMMARY OF THE PREFERRED EMBODIMENTS  
       [0014]     The embodiments of the present invention are directed to methods and apparatus for securing a cylinder liner to a pump module. A tension body is disposed about the cylinder liner and attached to the pump module. A locking body engages the cylinder liner and is threaded to the tension body. A hydraulic load cell is removably attached to the tension body and includes a hydraulic ram arranged to impart a compressive load to the cylinder liner and a tension load in the tension body. The locking body can be adjusted axially to contact the cylinder liner and maintain the applied loads, which act as a pre-load to keep the cylinder liner in contact with the pump module.  
         [0015]     In one embodiment, an assembly for attaching a liner to a pump module comprises a bushing attached to the pump module and a liner having a first end disposed within the bushing and a second end projecting from the bushing. The first end sealingly engages the pump module. An annular shoulder is disposed on the cylindrical liner. A tension body is connected to the bushing and a locking body is threadably engaged with the tension body and has a first end in contact with the annular shoulder so as to maintain the sealing engagement between the liner and the pump module. The assembly may also include a load cell operable to simultaneously apply a compressive load to the liner and a tension load to the tension body. In certain embodiments the assembly may also include a hydraulic body connected to the tension body and a piston disposed within the hydraulic body and operable to engage the second end of the liner and urge the liner into sealing engagement with the pump module.  
         [0016]     In an alternate embodiment, a device for securing a liner to a pump module comprises: an alignment member connected to the pump module and engaged with one end of the liner; a tension member extending axially from the bushing; a locking member having a first end threadably engaged with the tension member and a second end in contact with the liner, wherein the locking member is operable to maintain the position of the liner relative to the pump module; a hydraulic member connected to the tension member; and a piston disposed within the hydraulic member and adapted to urge the liner into engagement with the pump module, wherein the piston acts to separate the second end of the locking member from the liner.  
         [0017]     A method for securing a liner to a pump module, may include disposing a liner in a bushing connected to the pump module; attaching a tension body to the bushing; adjustably engaging a locking ring to contact the liner; attaching a hydraulic body to the tension body; applying hydraulic pressure to a piston disposed in the hydraulic body so as to compress the liner against the pump module; and adjusting the locking ring to maintain contact with the liner. The method may also include removing hydraulic pressure from the piston; and detaching the hydraulic body from the tension body.  
         [0018]     Thus, the present invention comprises a combination of features and advantages that enable it to overcome various shortcomings of prior devices. The various characteristics described above, as well as other features, 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  
       [0019]     For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein:  
         [0020]      FIG. 1  is a cross-sectional view of the fluid end of a conventional pump module;  
         [0021]      FIG. 2  is a cross-sectional view of one embodiment of a cylinder liner securing system in accordance with one embodiment of the present invention;  
         [0022]      FIG. 3  is an isometric view of a sub-assembly of the securing system of  FIG. 2 ;  
         [0023]      FIG. 4  is an isometric view of the load cell of  FIG. 2 ; and  
         [0024]      FIG. 5  is an isometric view of the cylinder liner securing system of  FIG. 2 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]     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. The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results.  
         [0026]     In particular, various embodiments described herein thus comprise a combination of features and advantages that overcome some of the deficiencies or shortcomings of prior art cylinder liner securing apparatus or systems. The various characteristics mentioned above, as well as other features and characteristics described in more detail below, will be readily apparent to those skilled in the art upon reading the following detailed description of preferred embodiments, and by referring to the accompanying drawings.  
         [0027]     Referring to  FIG. 1 , an exemplary prior art mud pump  10  includes retention member  12 . Retention member  12  preferably comprises a substantially cylindrical retention sleeve  14  that includes a front face  16  and an outer surface  18 . A cylinder liner  20  is disposed within retention member  12 , preferably contacting the inner surface  13  of retention member  12 . A wear plate  22  provides a renewable surface for liner  20 . A liner seal  26  is preferably positioned between end  24  of cylinder liner  20  and wear plate  22 . A piston  28  is disposed within liner  20  and is connected to a rod  30  which, in turn, is connected to a slider crank mechanism (not shown) driven by an electric motor or engine (not shown).  
         [0028]     In operation, the piston  28  reciprocates within liner  20 . The orientation of the piston  28  may be reversed from that shown in  FIG. 1 , depending on the configuration of the pump. Between the cylinder liner  20  and the piston  28  is a small annular space  32 . The piston  28  includes a piston head  34  having an annular seal  36  is disposed thereon. Seal  36  contacts the inside surface  21  of cylinder liner  20 . Pump fluid is located in chamber  38  defined by liner  20 , piston  28 , and wear plate  22 . Chamber  38  is in fluid communication with a passageway (not shown) through a pump manifold (not shown). The pump fluid is pressurized by the movement of the piston head  34  within the liner  20 . Seal  36  is provided to seal the annular space  32  and thereby prevent the fluid from leaking behind piston head  34 . Seal  36  also preferably helps keep the piston  28  centered so as to maintain the annular space  32  separating piston  28  from cylinder liner  20 .  
         [0029]     After operation of some duration, piston  28  and liner  20  will become worn, particularly if piston  28  and liner  20  come into contact as a result of misalignment. At some point, the degree of wear will be so great that operation of the pump will be impaired. For this reason, it is desirable to have a liner retention system that is reliable and easy to install, operate, and disassemble.  
         [0030]     Referring now to  FIG. 2 , one embodiment of a retention apparatus or system  100  includes load cell  110 , liner bushing  112 , liner body  114 , tension body  116 , and locking ring  118 . Liner bushing  112  is connected to a pump module  105 . Seal  107  is disposed between liner body  114  and pump module  105 . During operation, it is desired that liner body  114  maintain a compressive load on seal  107  in order to maintain seal energization. One method of maintaining this compressive load is to apply a pre-load to liner body  114  during assembly that is sufficient to maintain a compressive load on seal  107  as the forces acting on liner body  114  change during normal operations.  
         [0031]     Bushing  112  includes flange  119 , inner bore  120 , and neck  121  having an annular shoulder  122 . The inner bore  120  of bushing  112  supports and aligns liner body  114  with pump module  105 . Liner body  114  is laterally inserted into bushing  112 , with a gap  113  maintained between end  111  of bushing  112  and annular shoulder  115  of liner body  114 .  
         [0032]     Tension body  116  has a substantially cylindrical body with a first end having an inwardly-projecting mating shoulder  124 , a middle portion having slots  156  through the body, and a second end having a inner threads  128  and outwardly projecting locking grooves  126 . Annular shoulder  122  of bushing  112  engages mating shoulder  124  of tension body  116  forming an annular area  123  between tension body  116  and liner body  114 .  
         [0033]     Locking ring  118 , a substantially cylindrical sleeve member, is disposed in the annular area  123  between tension body  116  and liner body  114 . Locking ring  118  has outer threads  130  for engaging threads  128  of tension body  116 . Locking ring  118  also has holes  132  on one end that are adapted to accept a bar or handle  134 , which can be used to rotate the locking ring. The other end of locking ring  118  has a bearing face  136  that presses against shoulder  115  of liner body  114 .  
         [0034]     Load cell  110  includes hydraulic body  138 , piston  140 , retainer  142 , and springs  144 . Hydraulic body  138  has one end for receiving piston  140 , an elongate body  139  including windows  160 , and inwardly projecting locking tabs  146  that interface with locking grooves  126 . Piston  140  includes seals  148  that create a hydraulic chamber  150  between the piston and hydraulic body  138 . Pressurized fluid can be injected into chamber  150  through ports  152  to move piston  140  outward to contact liner body  114 .  
         [0035]     Referring now to  FIG. 3 , a perspective view of an assembly  152  is shown, including liner bushing  112 , liner body  114 , tension body  116 , and locking ring  118 . Bar  134  engages holes  132  on locking ring  118  to provide leverage for rotating the ring. Bolt pattern  154  on liner bushing  112  enables the bushing to be connected to a pump module (not shown). Tension body  116  may include handle  158 , which can be used to rotate the tension body into engagement with liner bushing  114  and maintain the position of the tension body while locking ring  118  is being rotated.  FIG. 3  also illustrates one arrangement of locking grooves  126  on tension body  116 . Locking grooves  126  are intermittently, and preferably equally, spaced around tension body  116 .  
         [0036]     Tension body  116  may include slots  156 , which serve to decrease the stiffness of the tension body, and thus lessen its resistance to elongating when loaded. By decreasing the stiffness of tension body  116 , the distribution of the pre-load can be more closely controlled, which allows for a more consistent application of the pre-load force. Once pre-loaded, tension body  116  then acts as a spring, forcing locking ring  118  against liner body  114  and maintaining the engagement of the liner body and the pump module. It is understood that any arrangement of slots, holes, or other aperture geometry could be similarly utilized to alter and control the stiffness of a tension body, and that a tension body without any stiffness controlling features could also be used.  
         [0037]     Referring now to  FIG. 4 , load cell  110  is shown, including hydraulic body  138 , piston  140 , and retainer  142 . Hydraulic body  138  includes locking tabs  146 , windows  160 , and handle  162 . Locking tabs  146  are arranged to interface with locking grooves  126  of tension body  116 , which are shown in  FIG. 3 . To assembly load cell  110  and tension body  116 , the load cell is rotated so that locking tabs  146  align with the spaces between locking grooves  126 . Load cell  110  is slid laterally over tension body  116  until tabs  146  and grooves  126  align and then rotated until the tabs and the grooves engage.  
         [0038]     Load cell  110  is shown installed with assembly  156  in  FIG. 5 . Windows  160  provide access to holes  132  for bar  134  and allow for observation of the engagement of tabs  146  and grooves  126 . Windows  160  also allow observation of the extension of piston  140  and its engagement with liner body  114 .  
         [0039]     Referring again to  FIG. 2 , once load cell  110  has been assembled onto tension body  116 , hydraulic pressure can be applied to chamber  150  through ports  152 . This hydraulic pressure urges piston  140  against the end of liner body  114 . The extension of piston  140  applies a compressive load that pushes liner body  114  into the pump module. The attachment of load cell  110  to tension body  116  creates a corresponding tension load in the tension body, causing tension body  116  to stretch. The stretching of tension body  116  separates face  136  of locking ring  118  from shoulder  115 . Locking ring  118  can then be rotated along threads  128  to maintain the contact between the face and the shoulder. As shown in  FIG. 5 , bar  134  can be inserted through a window  160  and into one of holes  132  to provide a lever suitable for rotating locking ring  118 .  
         [0040]     The pressure in chamber  150  can be monitored to determine when the desired pre-load force has been applied to liner body  114 . Piston  140  provides a pressure area that allows a relatively low pressure applied to the piston to generate a large force. Therefore, when compared to previous hydraulic systems, a lower pressure can be used to generate the same pre-load force. This allows lower pressure hydraulic systems to be used in assembling the pump components. In certain embodiments, chamber  150  may be fitted with a pressure relief valve to limit the pressure in the chamber.  
         [0041]     Once the desired pre-load is achieved, pressure can be released from chamber  150  and springs  144  will retract piston  140 . Load cell  110  can then be removed from tension body  116 . The loads in tension body  116  and liner body  114  are maintained by threads  130  holding locking ring  118  in bearing engagement against shoulder  115 . Thus, the pre-load on seal  107  is maintained by a positive mechanical engagement.  
         [0042]     Liner body  114  can disassembled from the pump module by reversing the installation procedure. First, load cell  110  is installed and used to apply a load to liner body  114 , as described above. The application of this load allows locking ring  118  to be loosened and removed along with tension body  116  and liner body  114 . In certain embodiments, locking ring  118  can be disengaged from tension body  116 , allowing liner body  114  to be removed while the tension body  116  remains installed.  
         [0043]     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. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied, so long as the hydraulic retention system and apparatus retain the advantages discussed herein. 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.