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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION  
         [0001]    The present invention has to do with wellhead equipment used in connection with a pumping oil well, preferably one pumped with a rotated rod string. For years, a typical conventional pumping wellhead for a rotary pumping oil well has been constructed as shown in FIG. 1. The assembly comprises from the bottom up: a flanged casing head attached to the well casing; a flanged tubing head having an internal hanger from which the well tubing string is suspended; a tubing head adapter having a flanged connection at its bottom end and a threaded connection of smaller diameter at its top end; a production blow-out preventer (B.O.P) body having top and bottom threaded connections and including side openings for receiving the B.O.P. ram components; a flow tee body having threaded bottom and top connections and a threaded or flanged side opening for connecting with a flow line; a polished rod stuffing box; and a rotary drive assembly for rotating the well&#39;s rod string to power a downhole progressive cavity pump. These components, except for the rotary drive assembly, combine to form a vertical central bore extending therethrough. The polished rod of the rod string extends through this central bore.  
           [0002]    The combination of the tubing head adapter, B.O.P. body and flow tee body components is commonly collectively referred to as a ‘pumping tree’.  
           [0003]    The assembly of wellhead components above the tubing head is usually referred to collectively as the ‘Christmas tree’.  
           [0004]    A recent improvement in the production wellhead art is disclosed in Canadian patent 2,197,584, issued Jul. 7, 1998 and re-issued May 16, 2000. This patent is owned by the present applicant. More particularly, this patent teaches integrating the tubing head adapter, B.O.P. body and flow tee body into a unitary structure, referred to as an ‘integral or composite pumping tree’, by forging, casting or machining a single steel body. The composite pumping tree is illustrated in prior art FIGS. 2 and 2 a  and forms the lower end of the Christmas tree.  
           [0005]    Another recent improvement in the production wellhead art is disclosed in Canadian patent application 2,280,581, filed by the present applicant. This patent application teaches integrating a tubing head adapter, shut-off valve body, B.O.P. body, and flow tee body into a composite pumping tree. This pumping tree is illustrated in prior art FIG. 3.  
           [0006]    As previously stated, the rotary drive assembly usually has a stuffing box at its bottom end. The primary function of the stuffing box is to prevent upward leaking of fluid around the rotating polished rod. The stuffing box comprises a body or housing containing annular packing, which seals between the housing and the polished rod of the rod string.  
           [0007]    Rotation of the polished rod eventually produces wear of the stuffing box packing. Therefore, changing the packing is part of the regular oilfield maintenance program.  
           [0008]    Prior art FIGS. 1, 2 and  3  show a rotary drive assembly mounted to the stuffing box by an ‘open’ frame. The frame has side ‘windows’ which enable access to the stuffing box packing gland, so as to change out the packing. However this frame introduces significant vertical separation between the rotary drive assembly and the pumping tree. This is undesirable as the rotary drive assembly vibrates when operating and applies offset forces that can create damage to the wellhead below. It is desirable to minimize the spacing between the rotary drive assembly and the pumping tree.  
           [0009]    A modified rotary drive assembly is shown in FIG. 4. In this unit, the stuffing box housing is now integral with the rotary drive assembly. This variation has had the benefit of shortening the distance between the rotary drive assembly and the pumping tree.  
           [0010]    However, it is more difficult to change out the packing of the stuffing box illustrated in FIG. 4. This process now requires:  
           [0011]    shutting off the rotary drive assembly;  
           [0012]    closing the production B.O.P by rotating the ram screws to advance the B.O.P rams into engagement with the polished rod;  
           [0013]    providing a service rig having a line which is attached to the polished rod to suspend the rod string;  
           [0014]    disconnecting the rod clamp normally suspending the rod string from and drivably connecting it with the rotary drive assembly;  
           [0015]    disconnecting the rotary drive assembly from the pumping tree;  
           [0016]    lifting the rotary drive assembly up using a second line from the service rig;  
           [0017]    securing a rod clamp to the polished rod below the rotary drive assembly, to secure the rod string;  
           [0018]    then fully removing the rotary drive assembly;  
           [0019]    replacing the packing; and  
           [0020]    re-assembling the equipment.  
           [0021]    This process can also be dangerous. Since the rod string is driven and rotated, it has a built-in torque. This torque can generate a back-spin force, which can cause injury to personnel in various situations.  
           [0022]    With this background in mind, it is an objective of the present invention to provide a polished rod locking assembly, forming part of the pumping tree and preferably being an integral component of the tree, which locking assembly can be actuated to clamp onto the polished rod to prevent back-spin and to grip the polished rod with sufficient force so as to suspend the weight of the rod string.  
           [0023]    It is another objective to provide a leverage assembly in conjunction with the locking assembly, which is operative to apply high axial torque to the locking means to better secure the rod string.  
           [0024]    It is another objective to provide a locking means capable of functioning like a blind ram to seal off the vertical bore of the wellhead, when the polished rod has parted in the stuffing box.  
         SUMMARY OF THE INVENTION  
         [0025]    In accordance with one aspect of the invention, a polished rod locking assembly (“PRL assembly”) is provided for inclusion as part of the pumping tree of a wellhead. This PRL assembly can be closed to clamp onto and frictionally engage the polished rod, to prevent back-spin, and to grip it with sufficient force so as to be able to suspend the rod string from the wellhead during stuffing box maintenance. These actions and results are hereafter collectively referred to as “securing” the polished rod.  
           [0026]    More particularly, the PRL assembly comprises:  
           [0027]    body means, which may be a separate component in a pumping tree formed of connected components or which preferably is integrated into a one piece integral pumping tree;  
           [0028]    the body means forms a central bore (which forms part of the pumping tree vertical bore) and a pair of opposed, preferably horizontal, radial side openings. The side openings are internally threaded along part of their length and extend between the body means&#39; outer peripheral surface and the central bore;  
           [0029]    an externally threaded locking member is positioned in each body side opening. These locking members can be radially advanced to frictionally engage the polished rod. Each locking member preferally comprises an inner cylindrical member and an outer, rotatable, threaded shaft. The shaft functions, when rotated or screwed, to advance or retract the inner member. The cylindrical member and shaft are interconnected so that the inner member does not rotate while the rotating shaft pushes or pulls it. The inner member has a vertically grooved inner end face which will embrace the polished rod as it contacts and frictionally engages it. More preferably, the inner member is formed in two parts. The innermost part is horizontally pivotally connected to the outer part and there is a slight clearance between the two parts. The outer part closely fits the internal surface of the side opening and remains stationary. The innermost part can tilt to a limited extent to accommodate misalignment of the polished rod. Each locking member seals against the surface forming the side opening in which it is contained. The outer end of the locking member protrudes from the body means;  
           [0030]    the inner end of an external lever arm is connected, preferably at right angle, with the protruding outer end of one of the locking members, for rotation or turning thereof. Movement of the outer end of the arm will cause the locking member to turn to a limited extent about its axis. Threaded means, such as a swing bolt having an annular head, is pivotally connected by means, such as a bolt, with the outer end of the arm. A post is anchored to the body means or tree. The post supports a rotatable sleeve at its outer end. The swing bolt extends through the opening formed by the sleeve. A nut, threaded on the end of the swing bolt, can be turned with relatively low torque to induce a relatively powerful lineal pull by the swing bolt on the arm. This causes relatively high torque to be applied to the locking member which in turn applies high lineal, inwardly directed force on the polished rod.  
           [0031]     As a consequence, the locking members can be activated by hand turning their outer ends, to bring their inner end faces into firm contact with the polished rod. The arm and swing bolt assembly can then be introduced and operated to bias the locking member with considerable lineal force against the polished rod to ensure sufficient frictional engagement to secure the heavy rod string.  
           [0032]     The specific described assembly provides a lever arm for turning the locking member and a mechanical means for biasing the arm&#39;s free end with a powerful lineal force to cause the locking member to secure the polished rod.  
           [0033]    In another aspect, the PRL assembly is constructed so that it can operate as a “blind ram” to close the vertical bore of the pumping tree. More particularly, the body means and locking members are modified so that one locking member can retract sufficiently to enable the other locking member to extend across the vertical bore to close it. The other locking member carries seal means suitable for sealing the vertical bore from the radial openings when the locking member is in the closed position. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0034]    [0034]FIG. 1 is a side view of a prior art wellhead for a rotary pumping well comprising a pumping tree formed of interconnected separate components, the wellhead having a rotary drive assembly at its upper end;  
         [0035]    [0035]FIG. 2 is a side view of a prior art wellhead for a rotary pumping well, incorporating an integral or composite pumping tree;  
         [0036]    [0036]FIG. 2 a  is a partly broken away perspective view of a prior art composite pumping tree;  
         [0037]    [0037]FIG. 3 is a side view of a prior art wellhead incorporating an integral pumping tree having an integral shut-off valve;  
         [0038]    [0038]FIG. 4 is a side view of a wellhead for a rotary pumping well comprising an integral pumping tree and having a PRL assembly constructed as an integral part of the tubing head adapter, the wellhead having a rotary drive assembly incorporating an integral stuffing box;  
         [0039]    [0039]FIG. 5 is a side view of a wellhead incorporating an integral pumping tree having a shut-off valve and a PRL assembly constructed as an integral part of the tubing head adapter section of the tree;  
         [0040]    [0040]FIG. 6 is a side view of a wellhead incorporating an integral pumping tree having a PRL assembly located above the production rod B.O.P.;  
         [0041]    [0041]FIG. 7 is a side view in section of one embodiment of the PRL assembly;  
         [0042]    [0042]FIG. 8 is a plan view in section of the assembly of FIG. 7;  
         [0043]    [0043]FIG. 9 is a sectional side view showing part of the PRL assembly of FIG. 7, positioned within a partly shown housing or body and engaging a polished rod;  
         [0044]    [0044]FIG. 10 is a sectional side view showing a self-aligning locking member positioned within a partly shown housing and engaging a polished rod;  
         [0045]    [0045]FIG. 11 is a sectional plan view of the assembly of FIG. 10;  
         [0046]    [0046]FIG. 12 is a sectional plan view showing a locking member connected with a leverage assembly;  
         [0047]    [0047]FIG. 13 is a sectional side view showing an upper PRL assembly coupled with a leverage assembly, together with a lower production rod B.O.P.;  
         [0048]    [0048]FIG. 14 is an external side view of part of the assembly of FIG. 13;  
         [0049]    [0049]FIG. 15 is a sectional plan view of a PRL assembly, adapted to convert to a blind ram assembly covering the vertical bore, in an open position;  
         [0050]    [0050]FIG. 16 is a sectional plan view of the PRL assembly of FIG. 15, in a closed rod-engaging position; and  
         [0051]    [0051]FIG. 17 is a sectional plan view of the PRL assembly of FIG. 16, in a closed blind ram position.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0052]    One embodiment of the PRL assembly  1  is illustrated in FIGS. 4, 5,  7 ,  8  and  9 . This PRL assembly  1  comprises a body means  2  having a vertical central bore  3  extending therethrough. The PRL assembly  1  forms part of the bottom connection  31  of an integral production pumping tree  4 . The bottom connection  31  is adapted to mate and connect with the top connection  5  of a wellhead tubing head  6 . The PRL assembly bore  3  forms part of the vertical internal bore  67  of the wellhead  7 , through which the polished rod  8  extends and through which fluid is produced.  
         [0053]    The body means  2  forms a pair of opposed horizontal radial openings  9  extending between its outer peripheral surface means  10  and the bore  3 . Each radial opening  9  has inner and outer sections  11 ,  12 . The opening sections  11 ,  12  have offset centerlines  14 ,  13 . The outer opening section  12  has a larger diameter than the inner opening section  11 , so that a shoulder  15  is formed at their junction.  
         [0054]    A pair of cylindrical members  16  are positioned in the radial opening inner sections  11  and are slidable therealong. Each cylindrical member  16  has inner and outer ends  17 ,  18 . The inner end  17  of the cylindrical member  16  has an end face  19  forming a vertical groove  100 , for conforming with and engaging the polished rod  8 .  
         [0055]    A pair of tubular gland assemblies  20  are threaded into the opening outer sections  12 . The gland assemblies  20  form part of the body means  2 . In the embodiment of FIGS. 8 and 9, each gland assembly  20  comprises an externally threaded tube  21 , an outer ring  22 , packing  23  and an inner ring  24  abutting the shoulder  15 . The threaded tube  21  can be actuated to energize the packing  23 . The tube  21  is also internally threaded.  
         [0056]    A pair of screws or shafts  26 , having externally threaded outer ends  27 , extend through the gland assemblies  20  and engage the outer ends  18  of the cylindrical members  16 . The outer end  27  of each shaft  26  protrudes out of its associated gland assembly  20  so that it is accessible for rotation. The shaft  26  and cylindrical member  16  together make up a unit referred to as a locking member  50 .  
         [0057]    Each shaft  26  has a T-shaped head  25  at its inner end, which is received in a correspondingly T-shaped slot  28  formed in the outer end  18  of its associated cylindrical member  16 . As a result of this connection and the offset centerlines, the shaft  26  and cylindrical member  16  are connected for axial movement together but the shaft can be turned without rotating the cylindrical member.  
         [0058]    As illustrated, the PRL assembly radial openings  9  are positioned between stud holes  30  of the bottom connection  31  of the pumping tree  4 .  
         [0059]    It is to be noted that in this previously described embodiment:  
         [0060]    the body means  2  forms part of the bottom flanged connection  31  of an integral pumping tree  4 ; and  
         [0061]    the axial centerlines  14 ,  13  of each associated shaft  26  and cylindrical member  16  are offset and the two elements are connected by a T-shaped head  25  and slot  28  arrangement, whereby the elements are tied together and move as a unit axially, but the threaded shaft  26  (which generates the lineal locking force) can rotate without turning the cylindrical member  16  (which will be locked with the vertical rod  8 ).  
         [0062]    In operation, each gland tube  21  can be screwed in, to compress its packing  23  and provide a seal around the unthreaded inner end  29  of the contained shaft  26 . To lock the polished rod  8 , the shafts  26  are advanced inwardly, biasing the locking members  16  into firm contact with the polished rod  8 .  
         [0063]    In a variant, the inner end portions of the polished rod locking members  16  can pivot to align with the polished rod  8 , to thereby prevent damage to the rod&#39;s surface.  
         [0064]    When the B.O.P. rams are closed about the polished rod  8 , the latter can be tilted slightly. If the polished rod cylindrical members  16  are rigidly fixed and perpendicular to the axis of the bore  3 , they can damage the tilted polished rod.  
         [0065]    In this alternative assembly, shown in FIGS. 10 and 11, each cylindrical member  16  is formed in two parts, an inner part  16   a  and an outer part  16   b . The parts  16   a ,  16   b  are connected so that they move together axially as a unit, but inner part  16   a  can pivot slightly to self-align with the polished rod  8 . More particularly the inner part  16   a  has a spherical nose  40  which is received in a spherical cavity  41  formed in the inner end of outer part  16   b . There is a slight clearance  31  between the cylindrical member parts  16   a ,  16   b . A horizontal bolt  43  holds the parts  16   a ,  16   b  together while allowing part  16   a  to pivot when it is fully inserted into the vertical bore  3  and has cleared the inner surface  32  of the tree side wall  33 . To prevent the inner part  16   a  getting separated should the bolt  43  break, it has a short thread  44  which can be threaded past a short thread  45  formed by the outer part  16   b . The shaft  26  has a centerline  46  and the cylindrical member  16  has a centerline  47 , which centerlines are offset one from the other.  
         [0066]    O-rings  101  are mounted around each cylindrical outer part  16   b , for sealing against the adjacent inside surface  65  of the radial opening  9  in which the part is contained. It will be noted that the gland assembly  20  in this embodiment does not contain packing.  
         [0067]    The PRL assembly  1  has been described in terms of a body means  2  which is provided by two partial segments of the bottom connection  31 , positioned between pairs of bolt holes  48  as shown in FIGS. 4, 5 and  18 . This design is useful when the radial openings  9  are of relatively small diameter, as are the contained components. When it is desirable to use components of greater diameter, then the body means  2  involves a complete transverse layer of the tree  4 , as shown in FIG. 6.  
         [0068]    The PRL assembly  1  comprises a leverage assembly  51  which is designed with the following concept in mind:  
         [0069]    the shafts  26  can be hand turned with a wrench to bring the cylindrical member end faces  19  into firm contact with the polished rod  8 —this is referred to as “hand tightening” the locking members  50 ;  
         [0070]    the leverage assembly  51  can then be used to apply a much greater rotational torque to one of the shafts  26  to thereby increase the frictional force with which the end faces  19  secure the polished rod  8 .  
         [0071]    The leverage assembly  51  is illustrated in FIGS. 12, 13 and  14 . It comprises a post  52  affixed to the tree  4 . The post  52  extends outwardly in parallel with the adjacent shaft  26 . A sleeve  53  is rotatably mounted on the outer end of the post  52 . The sleeve  53  can turn on the post  52 . The sleeve  53  forms a through-hole  69 . A horizontal, externally threaded swing bolt  54  extends through the through-hole  69 . At its inner end the swing bolt  54  has an annular head  55 . A nut  56  is screwed onto the outer end  57  of the swing bolt  54 . The nut  56  abuts the sleeve  53 . An arm  58  extends between the swing bolt&#39;s annular head  55  and the shaft  26 . The arm  58  has a hollow box-like section as shown in FIG. 12. At its lower end, the arm  58  has a transverse hexagonal opening  59 . A hexagonal nut  60  is fixed on the shaft&#39;s outer end  27 . When the arm  58  is added to the leverage assembly  51 , its lower end opening  59  receives the shaft nut  60  and the arm  58  engages the nut  60 , so that they will turn together. At its upper end, the arm  58  has a second transverse opening  61 . A bolt  62  extends through the arm upper opening  61  and through the opening  63  of the swing bolt annular head  55 . A nut  64  locks the bolt  62  in place, to effect a pivoting connection between the upper end of the vertical arm  58  and the inner end of the horizontal swing bolt  54 .  
         [0072]    From the foregoing, it will be appreciated:  
         [0073]    that the swing bolt nut  56  can be turned to cause the swing bolt  54  to linearly retract to the right (having reference to FIG. 14), thereby applying a powerful pull on the bolt  62  linking the arm  58  and swing bolt  54 ; and  
         [0074]    this bias or pull applied to the upper end of the arm  58  applies powerful torque to the shaft nut  60 , causing the shaft  26  to advance to linearly bias the cylindrical member  16  into tight frictional engagement with the polished rod  8 .  
         [0075]    In another embodiment shown in FIGS.  15 - 17 , the PRL assembly  1  comprises relatively long and short gland members  20   a ,  20   b . One cylindrical member  16   c  is longer than the other cylindrical member  16   d . One gland assembly  20   a  is relatively longer than the other gland assembly  20   b . The gland assembly  20   a  forms a longer cavity  70   a  for accommodating the cylindrical member  16   c  in the retracted or open position shown in FIG. 15. The gland assembly  20   b  forms a cavity  70   b  which is adapted to accommodate the cylindrical member  16   d  in the ‘blind’ position shown in FIG. 17, thereby enabling the cylindrical member  16   c  to cover or extend across the vertical bore  3 . The cylindrical member  16   c  carries a suitable seal  68  for sealing the vertical bore  3  and the radial openings  9 .  
         [0076]    From the foregoing it will be understood that the body means  2  and the locking members  50  co-operate to enable one cylindrical member  16   c  to extend transversely across the vertical bore  3  to close and seal it.

Summary:
The assembly functions to clamp onto and frictionally engage the polished rod of a well&#39;s rod string, with sufficient force to suspend the string from the wellhead. The assembly comprises an annular body forming opposed, radial, internally threaded side openings extending from its outer circumferential surface to its central vertical bore. An externally threaded locking member is positioned in each side opening and protrudes externally. The locking members can be manually threaded inwardly to engage the polished rod. An external leverage assembly is anchored to the body and engages one of the locking members. This leverage assembly can be manually turned to tighten the locking member against the polished rod with powerful axial force to provide enhanced gripping.