Patent Publication Number: US-8522667-B2

Title: Pump liner retention device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Application Ser. No. 61/174,281, filed Apr. 30, 2009, which is incorporated herein by reference. 
    
    
     FIELD 
     Embodiments of the invention relate to accessories for reciprocating force delivery devices. More specifically, embodiments disclosed herein relate to devices and methods for maintaining a seal between a cylinder and a fluid manifold in a reciprocating piston and cylinder device. 
     BACKGROUND 
     Production of oil and gas is a trillion dollar industry. To get oil and gas out of the earth, large costly equipment is used under extreme conditions. For example, reciprocating pumps that generate very high pressures are used for pumping liquids into and out of holes that are miles deep. Such pumps are either pumping against the pressure of fluids trapped beneath millions of tons of rock or taking suction of those fluids, so they must be functional for long periods of time under extreme stress. 
     One example of a reciprocating pump that routinely develops pressures of several thousand pounds per square inch is a drilling fluid pump. Drilling fluid (also called “drilling mud”) is a dense, viscous substance pumped into an active drilling hole to cool the drilling bit, lubricate the drill stem, support the walls of the wellbore, discourage premature entry of fluids into the wellbore, reveal the presence of oil or gas in a drilling formation, and carry cuttings to the surface where they can be removed. Higher viscosity drilling fluid is able to carry more and heavier cuttings, so additives are frequently used to increase viscosity. Pumping a high viscosity, high density fluid into a highly pressurized wellbore through miles of pipe requires very high pressure. 
     Reciprocating force delivery devices such as drilling fluid pumps operate by guiding a piston along a cylinder. One end of the cylinder is coupled to a fluid manifold which admits fluid when the piston is retracted. When the piston is advanced the fluid is forced from the manifold under pressure. The piston is generally driven by a rod or rod assembly coupled to a motor. 
     The cylinder forms a seal with the fluid manifold that must be maintained by urging the cylinder against the fluid manifold. A retention device is used to apply the sealing force to the cylinder. Prior art retention devices rely on rings that must be bolted to the fluid manifold by applying balanced tensile loads to the bolts to avoid unbalanced sealing force resulting in a weak seal. Other prior art retention devices rely on complex hardware with numerous parts to enable use of hydraulic force to balance the load on the seal. In many cases, sealing and seating of prior art devices is aided by hydraulic mechanisms that require hydraulic fluids, use of which may harm local ecosystems. It is also common to use potentially unsafe methods of impulse torquing (i.e. hitting with a sledgehammer) to complete seating and sealing. Moreover, while it is desirable to apply a balanced load to seal the cylinder to the fluid manifold, oil field equipment often must be operated far from available supplies of parts. Equipment having few parts that are easily assembled is generally favored. 
     Thus, there remains a need for a cylinder retention device for a reciprocating force delivery device that provides a load-balanced seal with minimal parts and easy assembly. 
     SUMMARY 
     Embodiments described herein provide a retention assembly for a reciprocating force delivery device having a cylinder liner abuting a fluid manifold, comprising a collar rotatably disposed around the cylinder liner, a locking ring disposed around the cylinder liner and distal to the fluid manifold, a compression ring between the locking ring and the collar, and a plurality of fasteners that fasten the locking ring to the fluid manifold. 
     Other embodiments provide a reciprocating force delivery device, comprising a motor, a reciprocating drive that couples the motor with a piston assembly comprising a piston movably disposed within a cylinder, a fluid manifold abutting an end of the cylinder, and a cylinder retention assembly attached to the fluid manifold and disposed around the cylinder, comprising a locking ring attached to the fluid manifold by fasteners, and a rotatable collar disposed between the locking ring and a shoulder of the cylinder such that rotation of the collar applies an axial force to the cylinder and the locking ring. 
     Other embodiments provide a method of maintaining a seal between a reciprocating force delivery device comprising a piston movably disposed within a cylinder, and a fluid manifold coupled to the cylinder, comprising providing a rotatable element located between a shoulder on an external surface of the cylinder and a locking ring fastened to the fluid manifold with fasteners forming a variable topography interface between the rotatable element and a compression ring disposed between the rotatable element and the locking ring, and rotating the rotatable element with respect to the compression ring to apply an axial force to the cylinder and the locking ring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above-recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is an exploded isometric view of a cylinder liner retention assembly according to one embodiment. 
         FIG. 2  is a cross-sectional view of the cylinder liner retention assembly of  FIG. 1  in an assembled state. 
         FIG. 3A  is a perspective view of a collar of the cylinder liner retention assembly of  FIG. 1 . 
         FIG. 3B  is a detailed perspective view of a portion of the collar of  FIG. 3A . 
         FIG. 3C  is a detailed side view of a portion of the collar of  FIG. 3A . 
         FIG. 4A  is a perspective view of a compression ring of the cylinder liner retention assembly of  FIG. 1 . 
         FIG. 4B  is a detailed view of the compression ring of  FIG. 4A . 
         FIG. 4C  is another detailed view of the compression ring of  FIG. 4A . 
         FIG. 4D  is a detailed view of a compression ring according to another embodiment. 
         FIG. 5  is a detailed view of the collar and the compression ring of  FIGS. 3A and 4A . 
         FIG. 6  is a front view of the cylinder liner retention assembly of  FIG. 1  in an assembled state. 
         FIG. 7  is a schematic side view of a reciprocating force delivery device employing the cylinder retention assembly of  FIG. 1 . 
         FIG. 8A  is an exploded isometric view of a torque tool according to another embodiment. 
         FIGS. 8B-8D  are detailed views of components of the torque tool of  FIG. 8A . 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
     DETAILED DESCRIPTION 
     Embodiments described herein generally provide methods and apparatus for maintaining a seal between a cylinder and a fluid manifold in a reciprocating force delivery system such as a pump or compressor. Such a system generally comprises a motor, a reciprocating drive for converting the rotary motion of the motor into linear motion of a piston disposed within a cylinder, and a fluid manifold coupled to the cylinder and abutting one end of the cylinder. The opening through the cylinder generally mates with an opening in the fluid manifold. 
     The cylinder abuts the fluid manifold around the opening therein, and a seal is maintained between the cylinder and the manifold by a retention device which applies a compressive axial force to the cylinder. The retention device generally abuts a shoulder that extends from an external surface of the cylinder, applying the axial force to the shoulder of the cylinder. 
       FIG. 1  is an exploded isometric view of a cylinder liner retention assembly  100  according to one embodiment. A fluid manifold  102  abuts a cylinder  104 . A collar  106  fits over the cylinder  104  and abuts a shoulder on the cylinder  104 , as further described below in connection with  FIGS. 2-4C . A compression ring  108  fits over the collar  106 , and a locking ring  110  fits over the collar  106 . Fasteners  112  fasten the locking ring  110  to the fluid manifold  102  by positioning heads  114  through openings  120 , rotating the locking ring  110  to engage the fasteners  112 , and installing a clamp  118  to prevent any counter-rotation of the locking ring  110  after installation. The heads  114  of the fasteners  112  may be permanently attached to the fasteners  112  after installation by installing fasteners  116 , such as threaded bolts or screws, through the heads  114  into the fasteners  112 . 
       FIG. 2  is a cross-sectional view of the cylinder liner retention assembly of  FIG. 1  in an assembled state. The collar  106  has an inner surface  208  that slidably contacts an outer surface  210  of the cylinder  104 . The collar  106  has an outwardly extending flange  212  with a shoulder  204  that seats on an outwardly extending stop  202  of the cylinder  104 . The flange  212  also has a locking face  206  opposite the shoulder  204  that abuts a locking face  214  of the compression ring. A pressure face  216  of the compression ring opposite the locking face  214 , abuts a pressure face  218  of the locking ring  110 , and an outward face  220  of the locking ring  110  engages the heads  114  of the fasteners  112 . A portion of the collar  106  is positioned between the cylinder  104  and the compression ring  108 , so that the compression ring  108  fits over the collar  106 , an inner surface  222  of the compression ring  108  slidably contacting an outer surface  224  of the collar  106 . A portion of the collar  106  is also positioned between the cylinder  104  and the locking ring  110 , so that the locking ring  110  fits over the collar  106 , an inner surface  226  of the locking ring  110  slidably contacting the outer surface  224  of the collar  106 . The collar  106  is accessible at a second end  228  of the collar  106  to facilitate rotating the collar  106 , as described further below in connection with  FIG. 5 . 
       FIG. 3A  is a perspective view of the collar  106  of  FIGS. 1 and 2 . The locking face  206  of the collar  106  has one or more ridges  302  that form a variable topography surface abutting the locking face  214  of the compression ring  108 . The distance between the shoulder  204  and the locking face  206  of the collar  106  define a thickness of the flange  212  that varies about an average value by less than about 2%, such as less than about 1%, for example about 0.6%. The second end  228  of the collar  106  has fingers  304  and grooves  306 , which may have any convenient shape, to facilitate rotating the collar  106  when the retention assembly is in an assembled state. The flange  212  also has scalloped recesses  308  to accommodate the fasteners  112  installed around the collar  106 . 
       FIG. 3B  is a detailed perspective view of a portion of the collar  106  of  FIG. 3A . One of the ridges  302  is shown extending from a first edge  310  of the flange  212  to a second edge  312  of the flange  212 . The ridge  302  visible in  FIG. 3B  illustrates the variable topography of the locking face  206  of the flange  212 . The ridge  302  connects two portions of the locking face  206  having different elevation. The elevation difference between the two portions may be up to about 4% of the thickness of the flange  212  defined by the shoulder  204  and the locking face  206 , such as up to about 2% of the thickness, for example about 1.2% of the thickness. 
       FIG. 3C  is a detailed side view of a portion of the collar  106  of  FIG. 3A . The locking face  206  of the flange  212  is visible, along with a ridge  302  and a recess  308 . The locking face  206  forms an angle θ with a plane  314  defined by the shoulder  204  of the flange  212  ( FIG. 3B ). The locking face  206  is thus not parallel to the shoulder  204 . The angle θ may be up to about 2° in some embodiments, such as less than about 2°, or less than about 1°, for example about 0.7°. 
       FIG. 4A  is a perspective view of the compression ring  108  of  FIGS. 1 and 2 . The locking face  214  of the compression ring is shown. The compression ring has scalloped recesses  406  that enable installation of the fasteners  112 , and extensions  408  that prevent rotation of the compression ring  108  when the fasteners  112  are installed. Similar to the collar  106 , the compression ring  108  has one or more ridges  404  to give the locking face  214  of the compression ring  108  a variable topography for abutting the locking face  206  of the collar  106 . The locking face  214  and pressure face  216  of the compression ring  108  define a thickness of the compression ring  108  that varies about an average value by less than about 2%, such as by less than about 1%, for example about 0.6%. 
       FIG. 4B  is a detail view of the compression ring  108  of  FIG. 4A , showing the ridge  404  in a similar way to the view of  FIG. 3B .  FIG. 4C  is a detailed view, similar to the view of  FIG. 3C , of the compression ring  108 . As with the locking face  206  of the collar  106 , the ridge  404  connects portions of the locking face  214  of the compression ring  108  having different elevation. The difference in elevation may be up to about 4% of the thickness defined by the locking face  214  and pressure face  216  of the compression ring  108 , such as up to about 2% of the thickness, for example about 1.2% of the thickness. The locking face  214  of the compression ring  108  forms an angle θ with a plane  410  defined by the pressure face  216  of the compression ring  108  ( FIG. 4B ). Thus, similar to the collar  106 , the locking and pressure faces  214  and  216  of the compression ring  108  are not parallel. The angle θ may be up to about 2° in some embodiments, such as less than about 2°, or less than about 1°, for example about 0.7°. 
       FIG. 4D  is a detailed view of a compression ring  108  according to another embodiment. The compression ring  108  of  FIG. 4D  features the locking face  214  that forms an angle θ with respect to the pressure face  216 , as for the embodiment of  FIG. 4C . In addition, the locking face  214  of  FIG. 4D  forms an angle α with respect to the pressure face  216  in a direction orthogonal to the direction of the angle θ. The embodiment of  FIG. 4D  increases the contact surface between the locking face  214  and the locking face  206  of the collar  106  to spread the contact stress between the two articles over a larger surface. The angle α elevates one edge of the locking face  214  above the other, such that the two edges do not propagate together in the plane of the pressure face  216 . In the embodiment of  FIG. 4D , the inner edge of the locking face  214  is circular and progresses in a path parallel to the pressure face  216 , while the outer edge of the locking face  214  progresses generally helically with respect to the pressure face  216 . The angle α may have any value between about 0.1° anc about 25°, depending on the needs of individual embodiments. Generally, the angle α will be larger with higher pressure systems to increase the area over which the contact stress is distributed. 
     It should be noted that in some embodiments, the inner edge of the locking face  214  may progress in a helical pattern similar to the outer edge, but at a different angle θ′ of inclination. In the embodiment of  FIG. 4D , the angle θ′ is zero. In some embodiments, it may be advantageous for the angle of inclination of the inner edge helix θ′ to be larger than that of the outer edge helix θ. In other embodiments, the angles θ and θ′ may have opposite signs. That is, the inner edge may progress along a downward sloping helix while the outer edge progresses along an upward sloping helix, or vice versa. 
       FIG. 5  is a detailed view showing the collar  106  and the compression ring  108  spaced closely apart to illustrate the relationship between the locking faces  206  and  214  of the collar  106  and the compression ring  108 , respectively. In general, the ridges  302  and  404  will mate when the collar  106  is in a first position. When the ridges  302  and  404  are mated, the locking faces  206  and  214  of the collar  106  and the compression ring  108  are in their closest spaced relationship. If the collar  106  is rotated a short distance, the ridges  302  and  404  begin to diverge, and the locking faces  214  and  206  increase in distance from each other. This axial movement of the collar  106  and the compression ring  108  with respect to each other applies axial force to the locking ring  110  and the cylinder  104 , abutting the compression ring  108  and the collar  106 , respectively. The axial force urges the cylinder  104  against the fluid manifold  102  to maintain the seal between the cylinder  104  and the fluid manifold  102 . 
     In embodiments featuring a plurality of ridges  302  or  404 , the ridges will generally be symmetrically spaced around the collar  106  or the compression ring  108 . All the ridges  302  of the collar  106  have substantially the same height, and all the ridges  404  of the compression ring  108  have substantially the same height, but the ridges  302  of the collar  106  need not have substantially the same height as the ridges  404  of the compression ring  108 . The height, number, and spacing, of the ridges  302  and  404  will generally determine the degree of rotation and rotational force required to tighten the cylinder liner retention assembly of  FIG. 1 . In most embodiments, the height, number, and spacing of ridges  302  and  404  will be selected to provide a tight seal of the cylinder  104  against the fluid manifold  102  with a reasonable turning force and distance, which may be applied using a suitable tool, an example of which is discussed in more detail below in connection with  FIG. 8A-8D . In most embodiments featuring a plurality of ridges  302  or  404 , the number of ridges  302  of the collar  106  will be the same as the number of ridges  404  of the compression ring. In some embodiments, however, the number of ridges  302  of the collar may be an integer multiple of the number of ridges  404  of the compression ring. In other embodiments, the number of ridges  404  of the compression ring  108  may be an integer multiple of the number of ridges  302  of the collar  106 . 
       FIG. 6  is a front view of the retention assembly of  FIG. 1  in an assembled state. The collar  106  is disposed about the cylinder  104 , with the fluid manifold  102  shown at the rear. The compression ring  108  is visible through the openings  120  in the locking ring  110 . A portion of each opening  120  is obscured from view by one of the heads  114 . Whereas the portion of each opening  120  that is visible has a diameter greater than a diameter of each of the heads  114 , the portion of each opening  120  obscured by one of the heads  114  has a diameter smaller than that of each of the heads  114 . The openings  120  with two portions having two different diameters can be seen also in  FIG. 1 . The locking ring  110  is thus installed by positioning the installed heads  114  through the large portions of the openings  120  and turning the locking ring  110  to engage the heads  114  in the small portions of the openings  120 . The clamp  118  is then installed between the heads  114  to prevent counter-rotation of the locking ring  110 . The clamp  118  is permanently attached to the locking ring  110  after installation by applying a fastener  602 , such as a screw or bolt, that penetrates the clamp  118  and lodges in the locking ring  110 . As described above, the heads  114  of the fasteners  112  may be permanently attached to the fasteners  112  by applying the fasteners  116 . The fingers  304  and grooves  306  of the collar  106  are accessible from the front of the assembly to facilitate rotation of the collar  106  to tighten the assembly. Any suitable tool may be used to facilitate rotating the collar  106 , one example of which is discussed in more detail below in connection with  FIG. 8A-8D . 
     In general, all components of the retention assembly described herein are made of any hardened steel suitable for the service in which the assembly is deployed. One or both variable topology surfaces may be coated with a malleable material, such as a soft metal or other non-ferrous metal, for example copper, bronze (nickel-aluminum alloy), or titanium, to promote spreading of the force applied between the surfaces of the collar and the compression ring. A thin layer of malleable material will generally suffice, such as a thickness less than about 0.01 in., for example about 0.005 in. The layer may be deposited in any convenient manner, such as by plating, for example electroplating or electroless plating, sputtering, or plasma spraying. 
       FIG. 7  is a schematic side view of a reciprocating force delivery device  700  employing the retention assembly described above. The device  700  generally comprises a motor  702 , a reciprocating drive  704  comprising a piston assembly  706  with a piston  708  movably disposed inside a cylinder  710  that abuts a fluid manifold  712 . The cylinder  710  is urged against the fluid manifold  712  by a cylinder retention assembly  714  according to any of the embodiments described herein. The retention assembly  714  facilitates easy installation, comprising sliding a collar, a compression ring, and a locking ring over the cylinder  710  to seat against an outwardly extending stop of the cylinder (as shown in  FIG. 2 ), installing fasteners and fastener heads (as shown in  FIGS. 1 and 2 ), positioning a locking ring and turning to lock (as shown in  FIG. 6 ), and rotating the collar to tighten (as described in connection with  FIGS. 5 and 6 ). 
       FIG. 8A  is an exploded isometric view of a torque tool  800  according to an embodiment. The torque tool  800  is suitable for use with the retention assembly described elsewhere herein. The torque tool  800  comprises an engagement member  802  to which a handle  804  is coupled by a torque bit  806 . The torque bit  806  is inserted into openings  814  and  816  in the engagement member  802  and the handle  804 , respectively. Locking pins  810  are provided to lock the torque bit  806  into the device. One locking pin  810  is inserted into an opening  822  in the engagement member  802 , and another is inserted into a similar opening in the handle  804 , which is visible in the view of  FIG. 8C . An extender  808  may be used with the handle  818  to apply more torque. The engagement member  802  comprises fingers  812  that mate with the grooves  306  of the collar  106  ( FIG. 3 ). 
     The engagement member  802  is shown in the detailed view of  FIG. 8B . The engagement member mates with the collar  106  when the retention assembly is in an assembled state, as shown in  FIG. 6 , by fitting over the assembly such that the fingers  812  project into the grooves  306 . Applying torque to the tool turns the collar  106  and tightens the retention assembly as described above. The opening  814  is formed by two hexagonal bores rotated 15° with respect to each other. This provides a large number of engagement surfaces for the torque bit  806  ( FIGS. 8A and 8D ) to engage. 
     The handle  804  is shown in the detailed view of  FIG. 8C . The opening  816  for the torque bit  806  is formed in a similar manner to the opening  814  in the engagement member  802 . One of the locking pins  810  is inserted into the opening  820  to lock the torque bit  806  into the opening  816 . 
     The torque bit  806  is shown in the detailed view of  FIG. 8D . The torque bit  806  may be formed from a rod with hexagonal cross-section by forming scallops  824  in the facets of the hexagonal rod and locking rings  826  at either end of the torque bit  806 . The scallops  824  provide clearance for protrusions in the openings  814  and  816 , and the locking rings provide a mechanism for the locking pins  810  to engage with the torque bit  806 . 
     The configuration of the tool  800  is adjustable to allow use in confined spaces. The positional relationship of the handle  804  and the engagement member  802  may be adjusted by removing the torque bit  806 , adjusting the relative orientation of the handle  804  and engagement member  802 , and reinserting the torque bit  806 . The torque bit  806  and openings  814  and  816  of  FIGS. 8A-8D  allow for adjustment in 15° increments to facilitate use of the tool in areas where the long handle of a wrench may be constrained. The torque tool  800  of  FIGS. 8A-8D  is also capable of applying more torque than conventional socket wrenches due to the torque bit  806  and locking pins  810 . In an alternate embodiment, a suitable torque tool may be constructed with openings in the engagement member and handle formed by a square dual-bore with the two bores rotated 45°. The torque bit for such an alternative embodiment may be constructed in similar fashion to the torque bit  806  above, but starting with a rod of square cross-sectional shape. 
     As mentioned above, the tool  800  of  FIGS. 8A-8D  is an example of a tool that may be used with embodiments disclosed herein. It should be noted, however, that the tool  800 , and alternative embodiments thereof, may be configured to apply torque to any object by adjusting the mating features of the engagement member  802 . For example, the engagement member may be configured to mate with fasteners of many kinds, including square and hexagonal bolts. 
     While the foregoing is directed to embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof.