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FIELD OF THE INVENTION 
     The present invention pertains to well pump rod, including a rod commonly known as a sinkerbar, which is provided with a high density polyethylene sleeve disposed thereover to minimize wear on the rod and well tubing in which it is disposed. The invention also pertains to preferred methods and apparatus for applying a polyethylene sleeve to a pump rod or “sinkerbar”. 
     BACKGROUND 
     Downhole well pumps which utilize elongated strings of so-called “sucker rods” as the pump actuating mechanism are widely used for various well pumping applications. Although it was once and long-considered a suitable design to provide a pump rod string, with rod sections having the smallest diameter disposed in the string directly above the pump, with progressively increasing rod diameters in the rod string near the earth&#39;s surface, this configuration produces a tendency to significantly buckle and bend the rod string at the rod sections of smallest diameter, that is just above the pump, and cause substantial abrasion of the rod string as well as the tubing string in which the rod and pump are disposed. Consequently, more recent design techniques have utilized rod sections of larger diameter near the bottom of the rod string and directly above the pump, and commonly known as “sinkerbars”. 
     By way of example, a pump rod string including 1.50 inch diameter sinkerbars connected end to end in the bottom 300 feet to 500 feet of the string, directly above the pump, allows the rod string to maintain tension and allows the highest compressive or buckling forces to occur in the relatively larger diameter sinkerbar sections. Accordingly, sinkerbar sections having a larger diameter, compared to the rest of the rod string, are less likely to buckle in compression and when elastic deflection of the sinkerbars occurs and the well tubing is engaged thereby, the contact is disposed over a greater surface area and tends to reduce wear which ultimately requires replacement of the rod and/or the tubing string. 
     Even with the development of larger diameter rod sections or so-called sinkerbars, there have been efforts to reduce wear on the tubing string by providing, for example, a high or ultra-high density polyethylene liner inside the tubing string, which minimizes wear and friction caused by engagement with a deflected pump rod string. However, certain drawbacks are associated with this approach to reducing wear on tubing as well as rod strings, namely, a reduction in the effective inside diameter of the tubing string due to the thickness of the polyethylene liner and the requirement to install substantial lengths, up to several thousand feet, of lined tubing string in the well in order to accommodate the entire length of pump rod string which is likely to be deflected into engagement with the tubing string as a result, for example, of changing the position of the pump within the tubing string from time to time. U.S. Pat. No. 5,511,619 issued to William E. Jackson on Apr. 30, 1996 describes an example of the aforementioned approach. However, the present invention contemplates an alternative, improved solution to the problems associated with rod actuated well pumps, as discussed hereinabove. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved elongated pump rod section or sinkerbar for use with downhole rod actuated well pumps and the like. 
     In accordance with one aspect of the invention, an elongated pump rod or “sinkerbar” is provided which includes a sleeve of polymer material disposed over a major portion of the exterior of the rod or sinkerbar and preferably comprises polyethylene, high density polyethylene or ultra high density polyethylene. This sleeve provides a bearing surface which reduces friction and wear on the well tubing and the pump rod or sinkerbar in the event of engagement between the sinkerbar and the well tubing. 
     By placing a sleeve of polymer material, such as polyethylene, on the exterior of the pump rod or sinkerbar and in accordance with methods contemplated by the invention, there is no requirement to utilize non-standard tubing string sizes, and/or limit well fluid flow resulting from a reduced internal diameter of the tubing string. At the same time, the ability to maintain tension in the pump rod string and reduce wear on the pump rod string and the tubing string is provided. Moreover, by utilizing only a few hundred feet (200 feet to 500 feet) of pump rod or sinkerbar string incorporating the polyethylene or other polymer sleeve thereover, the cost of providing a wear-reducing arrangement for rod actuated well pumps is reduced. 
     The present invention also contemplates the provision of methods and apparatus for applying a polymer sleeve over a substantially cylindrical elongated section of a pump rod or sinkerbar. One embodiment of the method and apparatus utilizes a hydraulic cylinder which is operable to engage one end of the rod or sinkerbar and forcibly displace it within a section of stationary polyethylene tubing. Another embodiment contemplates a method and apparatus which holds the rod or sinkerbar stationary and utilizes a hydraulic cylinder actuator to forcibly displace the polyethylene sleeve over the outer diameter of the rod, still further, a third embodiment of a method and apparatus for applying a polyethylene sleeve to a sinkerbar contemplates utilizing a hydraulic cylinder actuator for displacing the sleeve over a stationary rod or sinkerbar and wherein the sleeve is applied from a continuous roll of polyethylene tubing. 
     Those skilled in the art will further appreciate the above-mentioned advantages and features of the invention together with other important aspects thereof upon reading the detailed description which follows in conjunction with the drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a longitudinal side elevation, partially sectioned, of a pump rod or sinkerbar including a wear resistant polymer sleeve in accordance with the present invention; 
     FIG. 2 is a side elevation of a first embodiment of an apparatus for applying a polymer sleeve to a sinkerbar or pump rod in accordance with the invention; 
     FIG. 3 is a plan view of a second embodiment of an apparatus for applying a polymer sleeve to a sinkerbar; 
     FIG. 4 is a side elevation of the apparatus shown in FIG. 3; 
     FIG. 5 is a plan view of a third embodiment of an apparatus for applying a polymer sleeve to a sinkerbar in accordance with the invention; and 
     FIG. 6 is a side elevation of the apparatus shown in FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the description which follows, like parts are marked throughout the specification and drawing with the same reference numerals, respectively. The drawing figures may not be to scale and certain features may be shown in somewhat schematic or generalized form in the interest of clarity and conciseness. 
     Referring to FIG. 1, there is illustrated an elongated pump rod or sinkerbar in accordance with the invention and generally designated by the numeral  10 . The sinkerbar  10  comprises an elongated cylindrical rod section  12 , extending over a major portion of the length of the sinkerbar and extending between a reduced diameter elevator section  14  and a first wrench flat section  16 . A cylindrical collar  18  is interposed the wrench flat section  16  and an externally threaded end part  20 . A wrench flat section  22  is provided adjacent the opposite end of the sinkerbar and a cylindrical collar  24  is interposed the wrench flat section  22  and a second externally threaded end part  26 . The aforedescribed configuration of a pump rod section or sinkerbar is somewhat conventional. By way of example, the sinkerbar  10  may be manufactured of alloy steel, such as SAE 1045 or SAE 4623 cold finished bar, in approximately twenty-five foot lengths. Further, by way of example, the rod section  12  may have an outside diameter of about 1.375 inches, the elevator section or neck  14  having a diameter of about 1.0 inches and the wrench flats  16  and  22  also having a cross-sectional dimension of about 1.0 inches. Conventional coupling threads are provided on the externally threaded end parts  20  and  26 . 
     The sinkerbar  10  differs from prior art sinkerbars in that an elongated polymer sleeve  28  extends over a major portion of the length of the bar and substantially covers the entire length of the rod section  12 , as shown. The sleeve  28  is preferably formed of a heat and abrasion resistant polymer which also exhibits good lubricity or low friction characteristics in contact with certain other materials, such as steel tubing. High density polyethylene or ultra high density polyethylene, for example, is preferred. A preferred configuration of a sleeve  28  for a sinkerbar having a diameter of 1.375 inches for the rod section  12  is provided by a cylindrical sleeve having an inside diameter of about 1.380 inches and an outside diameter of about 1.562 inches. The inside diameter of the sleeve  28  may be slightly less than the diameter of the rod section  12  so that the sleeve is required to be stretched and then forms a slight interference fit with the rod section after being sleeved over the rod section. Alternatively, the polymer sleeve  28  may be shrink-fitted onto the rod section  12  after application thereto. However, by providing the inner diameter of the sleeve  28  to be approximately a line-to-line fit with respect to the outer diameter of a rod section  12 , frictional engagement between the inner surface  28   b  of the sleeve and surface  12   a  of the rod section  12  and over a substantial length, i.e., about 25.0 feet, will maintain the sleeve in place and the difference between the coefficients of thermal expansion of the steel rod section  12  and the polyethylene sleeve will also provide for maintaining the sleeve securely on the rod section  12 . 
     Those skilled in the art will appreciate that a pump rod section or sinkerbar according to the invention, enjoys substantial benefits. The sleeve  28  will prevent rapid wear of the sinkerbar section  12  as well as a tubing string which may come into contact with the outer surface of the sleeve. Moreover, the sleeve  28  will protect a substantial portion of the rod or sinkerbar  10  against corrosion in the highly corrosive environment of hydrocarbon wells, for example. Still further, by providing the sleeve  28 , which exhibits a low coefficient of friction in contact with many materials, a pump rod string which may be deflected into engagement with the inside wall of a well tubing string will exhibit lower resistance to reciprocation in normal operation of a pumping system in which the rod is being used. 
     Referring now to FIG. 2, there is illustrated an apparatus and method for installing a sleeve, such as the sleeve  28 , over a cylindrical rod section, such as the rod section  12  of the pump rod or sinkerbar  10 . Referring to FIG. 2, a sinkerbar/sleeve assembly apparatus  40  is illustrated comprising spaced apart, vertically extending supports  42 ,  44  and  46  for suitably supporting a rigid tube  29 , closed at one end  29   a,  and operable to receive a section of polymer tubing  28   a  therein and which will become the sleeve  28  when assembled in sleeved relationship over a pump rod or sinkerbar  10 . The sinkerbar  10  is supported on one or more support members such as the support or steadyrest  48 , one shown, having one or more rollers  50  mounted thereon for engagement with the sinkerbar in supportive relationship. The steadyrest  48  may be supported on a track  52  for traversal therealong to support the sinkerbar  10  as it is displaced into the interior of the tubing  28   a.  A suitable expander member or mandrel  54  may be temporarily secured to one end of the sinkerbar  10  by threaded engagement with one of the external threaded parts  20  or  26  to facilitate insertion of the sinker bar within the tubing  28   a.    
     The sinkerbar  10  is pushed into the length of tubing  28   a,  which is held stationary within tube  29 , by an elongated hydraulic cylinder and piston actuator  58  having a stationary cylinder member  60  and a linearly extensible and retractable piston rod  62  connected to a piston  64  slidably disposed in the cylinder  60 . Actuator  58  is mounted on suitable spaced apart supports  88 ,  89  and  90 . A hydraulic pump unit  66  is operably connected to the cylinder actuator  58  in a conventional manner for extending the piston rod  62  to displace the sinkerbar  10  into the tubing  28   a  and to retract the piston rod to the position shown in FIG. 2 for a subsequent operation. A second steadyrest  69  is mounted on the track  52  and engageable with the distal end  62   a  of piston rod  62  for movement therewith to steady the piston rod and minimize the risk of deflection of the piston rod as it inserts the sinkerbar  10  into the tubing section  28   a.  The distal end  62   a  of piston rod  62  may be provided with a suitable adapter, not shown, for engaging one end of the sinkerbar during the displacement procedure. 
     Referring now to FIGS. 3 and 4, an alternate embodiment of an apparatus for installing a tubing section  28   a  in sleeved relationship over a sinkerbar  10  is illustrated and generally designated by the numeral  70 . The apparatus  70  includes an actuator unit  72  comprising two side-by-side hydraulic cylinder actuators  58  between which is mounted the rigid tube  29  for holding the polyethylene tubing section  28   a  therein, as shown in FIG.  3 . The hydraulic cylinder actuators  58  and the tube  29  are suitably supported on spaced apart vertically extending support legs  71 ,  73  and  75 , FIG.  4 . Hydraulic pump unit  66  is operably connected to both of the actuators  58  in a suitable manner for extending and retracting side-by-side linearly extensible piston rods  62 . The piston rods  62  are connected at their distal ends  62   a,  respectively, to a pusher member  63  and a support  65  therefor. Support  65  is mounted on suitable rollers for linear traversal along track  52 . An intermediate support or steadyrest  49 , similar to the support  48 , includes an extensible rest member  51  comprising a pneumatic cylinder, for example, to align and steady the sinkerbar  10  as it is pushed into the tubing section  28   a  which is held stationary in the tube  29 . An expander mandrel  54  is temporarily secured to one end of the sinkerbar  10  to facilitate insertion of the sinkerbar as it is pushed into the tubing section  28   a  by retracting the piston rods  62 , simultaneously, into their respective cylinders  60 . 
     Referring now to FIGS. 5 and 6, another embodiment of an apparatus for sleeving a section of polyethylene tubing over a sinkerbar  10  is illustrated and generally designated by the numeral  80 . The apparatus  80  includes the roller track  52 , at least one support or steadyrest  48  for a sinkerbar  10  and an abutment  82  mounted on a suitable support  84 . The abutment  82  is engageable with one end of the sinkerbar  10  to hold the sinkerbar stationary when a section  28   a  of polyethylene tubing is sleeved thereover. The tubing section  28   a  may be unreeled from a suitable storage spool or reel  28   b  of a continuous length of tubing and the tubing section is traversed through spaced apart sets of straightening rollers  85  and  87 , which are suitably mounted on spaced apart supports  88 ,  89  and  90 . 
     Side-by-side cylinder actuators  58  are also mounted on the supports  88 ,  89  and  90  and their respective linearly extensible piston rods  62  are connected at distal ends  62   a  to a head  92 , which is also connected to one end of tubing section  28   a  for pulling the tubing section  28   a  from reel  28   b  and sleeving it over the sinkerbar  10  as the piston rods  62  are extended toward the abutment  82 . A steadyrest  69  is also connected to the piston rods  62  adjacent their distal ends  62   a  and traverses the track  52  to reduce deflection of the rods as they are extended from the respective cylinders  60 . 
     Accordingly, a sleeve  28  may be extended in sleeved relationship onto a sinkerbar  10  over its rod section  12  by one of several methods as described and illustrated. 
     Although a preferred embodiment of a well pump rod or sinkerbar has been described herein together with preferred embodiments of methods and apparatus for assembling a polymer sleeve over a pump rod section or sinkerbar, those skilled in the art will recognize that various substitutions and modifications may be made to the invention without departing from the scope and spirit of the appended claims.

Summary:
An elongated pump rod or sinkerbar for use in a pump rod string for a downhole reciprocating well pump is provided with an elongated sleeve of high density or ultra high density polyethylene over a major portion of the length of the sinkerbar to minimize wear on the sinkerbar and a well tubing string as a consequence of deflection of the sinkerbar into engagement width the tubing string and to minimize frictional drag on the pump actuating mechanism as a result of such engagement. The polyethylene sleeve may be assembled over the sinkerbar by apparatus including an elongated hydraulic actuator which may be configured to push a sinkerbar into the sleeve while the sleeve is held stationary within a support tube, or by holding the sinkerbar stationary on a support and pulling the sleeve over the sinkerbar and from a continuous length of tubing from which the sleeve is formed.