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[0001]    This application is a continuation of U.S. patent application Ser. No. 10/837,098, filed Apr. 30, 2004, pending which claims priority of U.S. Provisional Patent Application Ser. No. 60/467,829, filed May 2, 2003. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to replacing horizontal underground pipes and in particular to an improved apparatus and method for simultaneously bursting and expanding an existing pipe while simultaneously pulling a replacement pipe through the bore with a unitary tool. 
       BACKGROUND OF THE INVENTION 
       [0003]    Existing techniques for replacing existing underground horizontal pipe include a method in which a bursting or slitting tool is pulled through the pipe with a cable, rope, chain or similar pulling means. As the tool is pulled through the pipe, it bursts and expands the bore, readying the bore for a replacement pipe. In one variation, the replacement pipe is pulled through the bore in a separate operation using a pulling apparatus connected to the end of the replacement pipe. In another variation the pulling apparatus and replacement pipe are towed behind the bursting apparatus so that the existing pipe is burst and expanded and the replacement pipe is installed in a single pass. In many applications, the replacement pipe is formed from a plastic material such as PVC or HDPE. As is well known, such plastic materials are subject to deformation under load to a greater extent than metals such as steel. 
         [0004]    Systems used in the above described process typically include an expander cone pulled ahead of a separate pipe puller. The expander cone and the pipe puller comprise two separate components that are each loaded with separate forces during the pipe replacement operations. The longitudinal forces or loads produced during pipe replacement using such separate components may be divided and designated as either bursting work, defined as the load to crack the pipe and expand the ground, or pipe friction. Pipe friction is generated when the ground collapses back onto the pipe and adheres to its surface, not unlike clay sticking to a shovel. Normally the bursting load is a significantly larger load than a load resulting from pipe friction. 
         [0005]    The preferred attachment used in pipe puller for pulling HDPE pipe behind a static burst head is of the type known as an expanding taper puller. This system is preferred over other methods because it is easy to install, more or less foolproof and relatively easy to remove from the pipe. To install such a puller, the puller stem is rotated until a male cone is loose from a mating conical bore, located within expanding jaws. The jaws are now in a state of diametrical contraction, and will slip into the plastic pipe. After the jaws are inserted into the pipe, the stem is rotated until the male cone pulls into the mating form of the jaws and pushes the jaws out into the wall of the pipe. Sharp protrusions machined into the profile of the jaw will grip the inside diameter of the pipe. See, for example, Brewis et al. U.S. Pat. No. 5,671,953, Sep. 30, 1997. 
         [0006]    A drawback of existing tapered puller systems is that the load applied by the pulling process typically draws the cone even deeper into the jaws, forcing the jaws deeper into the pliable wall of the plastic pipe. More grip force is produced as the pulling resistance is increased. 
         [0007]    Ideally, a pipe puller design would allow the pipe to stay engaged to the puller jaws even when the tensile load of the pipe is exceeded at which point the pipe will stretch, finally failing and breaking. However, conventional pullers are designed such that the load applied to the forward surface of the pipe puller is passed through the stem to the jaws during the pulling process. If the stem load exceeds the maximum tensile strength of the plastic pipe, the jaws will cause the pliable pipe to extrude and thin out. This extrusion and thinning process can result in the pipe failing before the loading on the pipe exceeds the maximum tensile strength of the pipe. 
         [0008]    Thus, expanding taper pullers have not been successfully used in systems and applications where the force of the bursting operation is transferred to the pipe gripping jaws. Consequently, other fastening systems have been utilized. In one such system, a concentric flange is fused to the leading end of the pipe. A large bolt then secures the flanged end of the pipe to the rear of the burst head or mole. While this system apparently works, it has the disadvantage of requiring the operator to have fusing equipment on site during attachment of the pipe to the head. The fusing process is time consuming, includes the potential of a bad fuse joint, and requires expensive equipment. 
         [0009]    Thus, there exists a need for a tapered cone type pipe pulling system that can be used in a combined unitary static pipe bursting and pulling tool. Other designs have used the travel stop flange on the cone, however these designs have been intended for a very wide range of pipe walls. The replacement pipe used for static pull pipe bursts is nearly always SDR  17  or SDR  21 . These SDR values represent pipes with two very similar wall choices. When used with a pipe of known wall, the design shown here having a predetermined jaw expansion will be capable of bearing both the bursting load and pipe friction load without extruding or overstressing the pipe. 
       SUMMARY OF THE INVENTION 
       [0010]    The invention provides a unitary pipe bursting and pulling tool including a tapered cone pipe puller that limits the magnitude of the load applied to toothed pipe gripping jaws irrespective of the total load placed on the tool. A tapered cone pipe pulling system of the invention limits the axial displacement of the cone to allow the jaws a limited amount of radial displacement. Thus, a replacement pipe may be clamped onto the tool with the deformation of the pipe due to the clamping being limited such that the tensile strength of the pipe is not compromised. In one embodiment, the axial displacement of the cone is limited so that teeth of the pipe gripping jaws penetrate the wall of the replacement pipe to a depth of no more than about 35%, preferably from between 5% and 30%, of the thickness of the replacement pipe wall. 
         [0011]    A pulling apparatus for use in replacing horizontal underground pipes according to one aspect of the invention includes a pipe bursting head having a central lengthwise hole therethrough and a pipe griping mechanism disposed behind the hole. The pipe gripping mechanism includes a plurality of gripping jaws, at least one of the jaws having a pipe gripping tooth extending radially outwardly, and a tapered expander configured to fit between the jaws such that the expander can move forwardly to force the jaws outwardly to engage a replacement pipe. Suitable means are provided for pulling the expander forward relative to the griping jaws in order to pull the pipe bursting head forward. Preferably, a stop mechanism is provided to limit forward travel of the expander and prevent outward radial travel of the jaws after the tooth has been engaged in the wall of the replacement pipe. 
         [0012]    The invention further provides a method for replacement of a pipeline. An elongated pulling device such as a cable is threaded through an existing pipeline, and the pulling device is connected to a pipe bursting and replacement device of the invention. A replacement pipe is connected to the pipe bursting and replacement device by inserting the replacement pipe over the gripping jaws and then pulling the expander forward so that the tooth engages an inner wall of the replacement pipe. The bursting device and replacement pipe are then pulled through the pipeline using the pulling device, whereby the bursting head bursts the existing pipeline and simultaneously pulls the replacement pipeline behind it. The step of engaging the replacement pipe with the tooth (or teeth) may occur during the initial part of the pipe bursting run as the device is positioned at the entry side of the existing pipeline. The pipe pulling machine is positioned at the exit side, such as in a manhole or receiving pit. Unlike in a typical pipe pulling run, the bursting head has a greater diameter than existing pipeline and/or is provided with a blade or other projections for bursting the existing pipeline. These and other aspects of the invention are more fully discussed in the detailed description that follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a perspective view of a tapered burster and pipe pulling apparatus according to the invention; 
           [0014]      FIG. 2  is a partial exploded view of the apparatus of  FIG. 1 ; 
           [0015]      FIG. 3  is top view of the pipe pulling apparatus of  FIG. 1 ; 
           [0016]      FIG. 4  is a cross-sectional view of the pipe expanding and pulling apparatus of  FIG. 3 , taken along line  4 - 4 ; 
           [0017]      FIG. 5  is top perspective view of a pipe expander/slitter incorporating a pipe pulling apparatus according to the invention; 
           [0018]      FIG. 6  is a first cross-sectional view of the pipe slitter of  FIG. 5 , taken along line  6 - 6 ; 
           [0019]      FIG. 7  is a second cross-sectional view of the pipe slitter of  FIG. 5 , taken along line  7 - 7 ; 
           [0020]      FIG. 8  is a cross-sectional view of a unitary pipe bursting and pulling apparatus wherein the expander cone and jaws are configured and applied to a replacement pipe in accordance with the invention; and 
           [0021]      FIG. 9  is a cross-sectional view of a pipe bursting and pulling apparatus wherein the jaws have deformed the replacement pipe there by weakening the pipe. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and are not to delimit the scope of the invention. References to “tapered” or “conical” shapes or surfaces shall be understood to include not only those exact shapes but also similar shapes approximating those shapes. References to “bursting” will be understood to include both shattering of a frangible pipe and slitting of a ductile pipe, the method of the invention being useful for both of these purposes. 
         [0023]    Referring now to  FIGS. 1 through 4 , in a first embodiment, a unitary pipe bursting and pulling apparatus  10  according to the invention is designed to be pulled though a horizontal under ground pipe, bursting and/or expanding the pipe while simultaneously pulling a replacement pipe into the bore. Any conventional pipe pulling machine may be used for this purpose, but a cyclic pipe puller that uses a cable is preferred, such as the PB30 available from Earth Tool Company LLC, described in commonly-assigned copending U.S. Ser. No. 10/352,267, filed Jan. 27, 2003, the contents of which are incorporated by reference herein, or the pullers described in part in Carter et al. U.S. Pat. No. 6,305,880, issued Oct. 23, 2001. Apparatus  10  includes a nose  12  with an eyelet  14  for connecting the apparatus to a cable, rope, chain or rod string for pulling the apparatus through a bore. A cylindrical extension  18  extending rearwardly from end wall  20  of nose  12  includes a rearwardly opening threaded hole  23  for receiving a central stem or shaft  22 . 
         [0024]    Eyelet  14  is adapted for connecting apparatus  10  to a cable, rope, string of rods, chain or similar elongated pulling device. As best illustrated in  FIGS. 2 and 4 , axially extending center shaft  22  is engaged in hole  23  and includes a center threaded section  24  and threaded end portion  26  adapted to receive an end eyelet  30 . End eyelet  30  is designed to receive a rope or cable that is attached to the trailing end of a replacement pipe section (not shown) pulled behind apparatus  10  to aid in pulling the section through a bore during the pipe replacement operation. 
         [0025]    A hollow, generally cylindrical body  32  comprising the bursting head positioned over extension  18  and shaft  22  includes a small diameter forwardly opening annular recess  34 , with a first inner wall  36  and a large diameter rearwardly opening annular recess  38  defining a second inner wall  40 . A tapered inner wall  44  extends between first and second inner walls  36 ,  40 . Inner wall  36  includes a groove  48  for receiving an O-ring  50  to prevent debris from entering between nose  12  and cylindrical body  32 . Inner wall  40  similarly includes a groove  52  for receiving O-ring  56  to seal between inner wall  40  and a pipe (not shown) inserted therein. As illustrated, cylindrical body  32  also includes a conical exterior wall  60  that is rearwardly inclined from the foremost end  64  of the body to a cylindrical outer wall  62  that extends to the rearmost end  66  of body  32 . A bursting ridge or blade  61  configured to create a localized intense pressure against the inside diameter of a pipe to be burst, extends along tapered wall  60  between foremost end  64  of body  32  and cylindrical outer wall  62 . 
         [0026]    As best illustrated in  FIG. 4 , a sleeve  68  includes a front end wall  67 , a rear end wall  71  and central axial opening  69  sized to fit over shaft  22  inside body  32 . Sleeve  68  includes a small diameter forward section  70 , a tapered shoulder  72  configured to abut tapered inner wall  44  and a large diameter rear section  74  with a counterbored recess  80  including an interior end wall  81  formed in rear wall  71  of sleeve  68 . In one embodiment, sleeve  68  is press fitted into body  32  with forward section  70  fitting into annular recess  34  and large diameter rear section positioned in annular recess  38  of body  32 . 
         [0027]    A plurality of semi-cylindrical jaws  84  each having a front wall  85 , an arcuate inner wall  86 , radially extending side walls  88 , an arcuate outer wall  90 , and a tapered end section  82  are arranged in a cylindrical pattern around shaft  22 , forming a cylindrical jaw assembly  92  that extends rearward from sleeve  68 . As illustrated, jaw assembly  92  comprises three jaws  84 , each of which extends approximately 120° circumferentially around shaft  22 . Although as illustrated, three jaws  84  are utilized, jaw assembly  92  may comprise a greater or lesser number of jaws depending upon the specific design and application. Each of jaws  84  includes a plurality of grooves  96  for receiving elastomeric O-rings  98  which hold jaws  84  together around shaft  22 . Jaw assembly  92  and inner wall  40  define an rearwardly opening annular pipe receiving aperture  100 , into which the foremost end of a pipe  104  ( FIG. 8 ) may be inserted. 
         [0028]    Each of jaws  84  also includes a forwardly extending flange  102  configured to fit into counterbored recess  80  and a plurality of serrations  106  formed across arcuate outer wall  90 . As shown in  FIG. 4 , arcuate inner walls  86  of jaws  84  are tapered radially outward in a rearward direction to receive a conical expander  110  having a tapered body  112  with a foremost end  114  inserted between jaws  84  and shaft  22 . Expander  110  includes a central opening  116  with a threaded inner wall  118  adapted to be threadedly engaged with center threaded section  24  of center shaft  22 , a tapered outer wall  120  and travel stop flange  122 . As expander  110  is advanced by threading the expander onto threaded portion  24  of shaft  22 , expander  110  forces jaws  84  radially outward from shaft  22 . In order to allow for outward movement of jaws  84  counterbored recessed  80  is sized such that flanges  102  may move radially outward a limited distance from shaft  22  within the recess. 
         [0029]    To install apparatus  10  on the end of a replacement pipe, the end of the pipe  104  ( FIG. 8 ) is inserted into annular aperture  100  between jaws  84  and inner wall  40 . While body  32  is restrained, eyelet  14  is pulled forward, causing conical expander  110  to engage and push jaws  84  radially outward so that serrations  106  engage and dig into the interior diameter of pipe  104 . Eyelet  14  is then rotated, causing conical expander  110  to be drawn forward on threaded center section  24  of shaft  22 , clamping pipe  104  between jaws  84  and inner wall  40 . Eyelet  14  is rotated until stop flange  122  is abutted against rear walls  87  of jaws  84  and front walls  85  of jaws  84  are pushed against rear wall  71  of sleeve  68 . At this point, conical expander  110  can not be advanced any further forward on shaft  22 , and jaws  84  have consequently been extended radially outward from shaft  22  to the maximum extent possible. A towing cable, rope or chain is attached to eyelet  14  and apparatus  10  is ready to be inserted into an existing pipe to be replaced. 
         [0030]    In accordance with the invention, jaws  84  are sized such that when jaw assembly  92  has been expanded to the maximum extent possible, pipe  104  is clamped between jaws  84  and inner wall  40  with serrations  106  engaged in the inside diameter of a replacement pipe  104 . ( FIG. 8 ) Although pipe  104  is securely clamped, deformation of the pipe is non-existent or limited to a small, predetermined amount corresponding to the maximum radial extension of jaws  84  permitted by stop flange  122 . Preferably, stop flange  122  is configured to limit radial extension of jaws  84  so that penetration of serrations  106  into the wall of replacement pipe  104  is limited to between 5% and 30% of the thickness of the pipe wall. Since jaws  84  have not significantly deformed pipe  104 , the tensile strength of the pipe has not been compromised, and the pipe is much less likely to break as it is pulled behind apparatus  10 . As one skilled in the art will understand, the dimensions of the jaws  84  and tubular wall  40  are selected to match the diameter and thickness of the replacement pipe. Tubular wall  40  is preferred to provide a more secure connection with the replacement pipe, but could be omitted. In such a case, the apparatus would rely entirely on the jaws to hold the replacement pipe. 
         [0031]    In order to fully appreciate this advantage,  FIG. 8  illustrates a unitary pipe bursting and pulling apparatus  124  according to the invention with a plastic replacement pipe  104  clamped in the apparatus. As illustrated, expander  126  is positioned such that stop flange  128  is abutted against jaws  130  which in turn are abutted against expander body  132  such that jaws  130  have reached maximum limit of radial extension permitted by stop flange  128 . In this position, the gripping teeth or serrations  134  of jaws  130  are engaged in the inside diameter of pipe  104 , however, jaws  130  have not dug into or deformed the pliable plastic pipe  104 . Thus, tensile strength of pipe  104  has not been significantly impacted by the clamping action of jaws  130  and the pipe should be capable of being loaded to its maximum tensile strength without failing. 
         [0032]      FIG. 9  illustrates a hypothetical bursting and pulling apparatus  124   a  that does not include the features of the invention. In the apparatus illustrated in  FIG. 9 , the jaws  84   a , expander  126   a  and stop flange  128   a  are not configured to stop the radial extension of jaws  84   a  before pipe  104  is deformed. As illustrated, expander  126   a  has been advanced and jaws  130  expanded outward to the point that the jaws  130   a  have compressed and deformed pipe  104   a , causing the wall of the pipe to become thinner and thus reducing the tensile strength of the pipe. Consequently, when pipe  104   a  is pulled behind apparatus  124   a  in a bore, the pipe is more likely to fail prior as the load on the pipe is increased. 
         [0033]    In order to fully appreciate the difference between apparatus  124  and  124   a , it must be understood that when a plastic pipe, for example a pipe formed from PVC or HDPE, is pulled through a bore, the longitudinal force on the pipe due to friction between the pipe and the bore is large, placing significant longitudinal tensile stress on the pipe. As the tensile stress increases, the wall of the pipe tends to elongate, becoming thinner as the pipe is stretched. If the pipe wall is compressed to the point of deformation between gripping jaws and the inner wall of a puller as illustrated in  FIG. 9 , the pipe is weakened at that location, and the probability of a failure is greater than if the pipe were not compressed. In contrast, pipe  104  clamped in apparatus  124 , while securely clamped in the apparatus is not deformed, and consequently is much less likely to fail. 
         [0034]    Turning now to  FIGS. 5-7 , in an alternate embodiment, a pipe slitter and pulling apparatus  140  according to the invention comprises a yoke  142  with an aperture  144  and pin  146  adapted to connect slitter  140  to a flexible pulling means such as a rope, cable or chain. Yoke  140  includes a stem or shaft like extension  150  having a rear most end  152  with a threaded opening  154  extending axially into end  152 . A threaded center shaft  160 , engaged in opening  154  extends rearward from yoke  142 . As illustrated, center shaft  160  passes through a slitter body  162  that includes a first annular opening  164  within a first inner wall  180  sized to fit over extension  150 . A second, larger diameter annular opening  166  defined by a second inner wall  182  extends rearwardly from first opening  164  with a intermediate wall  168  between first and second openings  164 ,  166 . A conical outer wall  172  extends from the front most end  174  of body  162  to a cylindrical outer wall  178  that extends between conical wall outer wall  172  and the rearmost end  184  of the body. 
         [0035]    As illustrated, a slitter blade  190  is mounted in a longitudinally extending slot  192  in slitter body  162 . Slitter blade  190  is configured and adapted to slit existing pipe in horizontal bore as slitting tool  140  is pulled through the bore with a winch or similar pulling device. As best illustrated in  FIGS. 6 and 7 , slitter blade  190  is secured in slot  192  with a set screw or bolt  196 . Alternatively, slitter blade  190  may be welded in place. 
         [0036]    A plurality of semi-cylindrical jaws  200 , each having a front wall  202 , a tapered arcuate inner wall  204 , radially extending side walls, similar to side walls  88  of jaws  84  of  FIG. 4 , an arcuate outer wall  208 , and a rear end wall  210  are positioned around the circumference of center shaft  160 , forming a cylindrical jaw assembly  212 . Jaw assembly  212  comprises three jaws  200 , arranged in the same fashion as jaws  84  of  FIGS. 2 and 4  each of which extends approximately 120° circumferentially around center shaft. Each of jaws  200  includes a plurality of grooves  216  for receiving O-rings  218  that hold jaws  200  in position around center shaft  160 . Each of jaws  200  also includes a plurality of teeth or serrations  214  extending across the circumference of outer wall  208  of the jaw. As illustrated, jaw assembly  212  and second inner wall  182  form an annular pipe receiving aperture  220  for receiving a pipe  222 . 
         [0037]    Referring to  FIG. 6 , a conical expander  226  is illustrated in a first position wherein the expander is threaded onto center shaft  160  and received between tapered inner walls  204  of jaws  200  and center shaft  160 . Expander  226  includes a threaded annular hole  228 , and an outer wall  230  that is tapered from a stop flange  232  to the narrow forward most end  234  of the expander. As illustrated in  FIG. 6 , apparatus  140  is configured with expander  226  in a loosened position such that the end of pipe  222  can be fitted into annular receiving aperture  220 . To prevent expander  226  from being rotated off of center shaft  160  when the expander is loosened, a retainer pin  161  is treaded into a retainer hole  163  formed at the rear end of shaft  160 . 
         [0038]    After pipe  222  is positioned as illustrated in  FIG. 6 , yoke  142  is pulled in a forward direction, illustrated by the arrow, while slitter body  162  is restrained, causing expander  226  to bear against jaw assembly  212  and force jaws  200  radially outward so that serrations  214  engage the inner diameter of pipe  222 . Center shaft  160  is then rotated by turning yoke  142 , drawing expander  222  forward on the shaft. As expander  226  is drawn forward, the expander forces jaws  200  radially outward causing serrations  214  to penetrate the inside wall of pipe  222 . Center shaft  162  is rotated in this manner until expander  226  and jaws  220  are moved into the position illustrated in  FIG. 7  wherein stop flange  232  has been drawn up against rear end walls  210  of jaws  200  and the front walls  202  of jaws  200  are abutting intermediate wall  168 . In this position, pipe  222  is firmly clamped between jaw assembly  212  and inner wall  182  with serrations  214  engaged in the inner wall of the pipe. When expander  226  has been drawn forward to the position illustrated in  FIG. 7 , the expander cannot be moved further forward; consequently, jaws  200  are at the outer limit of possible radial travel. In a preferred embodiment, when jaws  200  are at the outer limit of possible radial travel, serrations  214  have penetrated to a depth of between 5% and 30% of the thickness of the wall of pipe  222 . Thus, although firmly clamped in this position, the wall of pipe  222  is not compressed to the extent that the wall deforms because the outward movement of jaw assembly  212  has been limited by stop flange  232  of expander  226 . 
         [0039]    In operation, pipe slitter and pulling apparatus  140  is pulled through an existing under ground pipe with a cable, chain or rope secured to yoke  142 . As apparatus  140  moves through the pipe, slitter blade  190  cuts or scores the pipe which is expanded by conical outer wall  172  of slitter body  162 . Simultaneous, apparatus  140  is pulling a replacement pipe  222  through the expanded bore. The friction between replacement pipe  222  and the bore results in a significant tensile loading on the pipe which tends to elongate the pipe, causing the wall of the pipe to stretch and become thinner. This effect is particularly significant at the end of pipe  222  where the pipe is clamped to apparatus  140  as described above. Thus, by insuring pipe  222  is not deformed at the clamped location, apparatus  140  can utilize the available tensile strength of the undeformed pipe without increasing the probability of breaking the pipe. 
         [0040]    While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. The apparatus could, for example, omit the central shaft and instead use a portion of the cable or other pulling device extended through the central hole in the bursting head and secured in any suitable manner, such as by a knot, upset or stop, or by securing the cable with self-actuating cable gripping collets. Although a conically tapered bursting head is preferred, a stepped head could also be used. Various other modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.

Summary:
A pipe bursting and pulling apparatus for use in replacing horizontal underground pipes including a cylindrical body with a tapered forward section including means for attaching one of a cable, rod, rope or chain, the cylindrical body including an annular inner wall defining a longitudinally extending, rearwardly opening recess, a shaft passing through the recess, a plurality of gripping jaws, at least one of the jaws including a pipe gripping tooth extending radially outward relative to a longitudinal axis of the shaft, a tapered expander connected to the shaft and configured to fit between the jaws, the expander forcing the jaws outward to clamp a replacement pipe inserted into the cylindrical body between the jaws and the inner wall when pulled by the shaft, a stop, the stop limiting the forward travel of the expander and preventing outward radial travel of the jaws after the tooth has been engaged in the wall of the replacement pipe whereby the tooth penetrates to a depth of no more than 35% of the thickness of the wall of the replacement pipe.