FIELD OF THE INVENTION 
       [0001]    The invention relates generally to systems for use in the trenchless removal of underground pipe, and more particularly, to systems which use hydraulic cylinders as the cable puling device. 
       BACKGROUND OF THE INVENTION 
       [0002]    The underground location of water and sewer lines, as well as electrical conduits, makes their replacement difficult. This is particularly so where additional infrastructure has been developed around or on the previously built underground lines or conduits. Often such lines were installed via open trenches years ago and now they cannot be easily re-excavated. Over the years, new developments, such as roads, parking lots, buildings, or landscaping have been placed over the surface of the old lines, thus making re-excavation impossible or unacceptably costly. 
         [0003]    Numerous methods have been developed over the years to address the problem of how to replace worn out water and sewer lines without excavating the lines. Typically, such methods will replace the older iron or steel lines with a new line made from a flexible plastic material. One such method, of which this invention is an improvement, is called pipe bursting. 
         [0004]    Pipe bursting methods for replacing old, typically metal, water, sewer, or electrical conduit lines make use of a conical shaped mole that is pulled through an existing pipe. The mole is shaped such that it is smaller than the inside diameter of the old pipe at one end of the mole and larger than the inside diameter of the pipe at the other end of the mole, and thus, the mole causes the original pipe to be burst or fractured upon the mole being pulled through the pipe. The original pipe is burst outward radially. Typically, attached to the back of the mole is a length of flexible replacement piping which is drawn into the space formerly occupied by the burst pipe and therefore takes the place of the original. Thus, the new pipe replaces the old pipe without excavating along the entire length of the pipe being replaced. Excavation is required typically only at the ends of the pipe to be replaced. 
         [0005]    The basic components of prior art pipe bursting systems include a mole, a length of cable engageable to the mole, a cable pulling device, and a mounting structure for supporting the cable pulling device against an opening through which the mole is to be pulled. In order to pull a mole through an iron pipe, pulling force on the order of 15-75 tons may be required. To provide sufficient pulling force, many prior art pipe bursting processes have used winches of various types. U.S. Pat. No. 5,328,297 to Handford is one example of such a device. However, winches of sufficient size to generate 75 tons of pulling force typically weigh several tons themselves and are frequently mounted on trucks or are attached to other large excavation devices. In some applications, space limitations prevent the use of a winch as the source of pulling force. 
         [0006]    Due to the relatively large size of a winch suitable for pulling a mole through an iron or steel pipe, efforts have been made to find smaller devices capable of generating the necessary pulling force. These devices typically make use of the high force that can be generated by relatively compact hydraulic cylinders. Such devices are exemplified by U.S. Pat. No. 6,305,880 to Carter et al (“the Carter patent”). The Carter patent uses a pair of single acting hydraulic cylinders as the cable pulling device. The cylinders are are sufficiently small that the puller, along with a pulling frame, can be used by one or two operators and represents an improvement in the art over a winch based system. 
         [0007]    The pulling device of the Carter patent however, nevertheless suffers from certain drawbacks. One drawback of the Carter device is that because the device uses single acting hydraulic cylinders, it has a relatively slow cycle time. Another drawback of the Carter device is that to prevent the cable from rebounding back into the pipe to be burst, the device requires additional hardware to hold the pulling cable stationary while the hydraulic cylinders make their return stroke. 
         [0008]    Accordingly, there persists a need in the in art of trenchless pipe replacement for an improved cable pulling device that does not suffer the aforementioned drawbacks. Preferably, such a device would be smaller than the prior art winch-type devices, yet have a substantially faster cycle time than prior art hydraulic devices. A faster acting device would be more cost efficient for contractors and thus would reduce the time and cost of trenchless pipe replacement work. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention comprises an improved cable puller for the trenchless replacement of underground pipes including water, sewer, and electrical conduits. The cable puller of the present invention improves upon prior art hydraulic cable pullers. Unlike the single-acting pullers of the prior art which pull only on their outward stroke and do little, or no, useful work on their inward or recovery stoke, the present invention cable puller pulls continuously on the cable on both the device&#39;s outward and inward strokes and therefore doubles the speed at which a mole may be pulled through a pipe to be burst. Moreover, because the device pulls the cable on both its inward and outward strokes, the present invention puller has no need for a mechanism to hold the cable stationary during the return stroke as is required by the prior art. Such a device however, may be provided with the present invention puller for added safety. 
         [0010]    The present invention double acting cable puller comprises a cylinder body which houses four hydraulic cylinders. The cylinder body has a forward end and an aft end. One pair of hydraulic cylinders operates in tandem on the forward end of the cylinder body and another pair of cylinders operates in tandem on the opposite, aft end of the cylinder body. Each of the hydraulic cylinders houses one double acting piston and piston rod, and each cylinder has its own inlet and outlet ports for hydraulic fluid. For each set of paired forward and aft cylinders, the cylinder rods are attached to a puller, and each puller has a set of jaws for engaging the pulling cable. 
         [0011]    In operation the present invention cable puller is securely attached to a pulling base designed for use with the puller. During phase I in the operation cycle, pressurized hydraulic fluid is directed into each of the paired cylinders so that pressure bears on the outward faces of the pistons (the faces opposite the rods) causing both the forward and aft pullers to travel outward away from the cylinder body until the cylinders&#39; maximum length of travel has been reached. During this phase, the aft puller&#39;s jaws engages the cable so that the cable is displaced (i.e. the mole is pulled through the pipe to be burst) as the aft puller travels away from the cylinder body. During this phase, the forward puller&#39;s jaws are not engaged with the cable and therefore the cable simply passes freely through the forward jaws. 
         [0012]    During phase II of the present invention cable puller&#39;s operation, pressurized hydraulic fluid is redirected into the cylinders so pressure bears upon the outward faces (i.e. the faces on the same side as the rods) so that both pullers travel inward towards the cylinder body. During this phase, the two pullers have alternated tasks: the forward puller&#39;s jaws are now engaged the cable and now pull the cable through the pipe to be burst, while the aft puller&#39;s jaws have released the cable, allowing cable to pass freely between them. The cycle repeats continuously until the mole is pulled through the length of pipe to be burst. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  shows a typical prior art system for trenchless pipe replacement using hydraulic cylinders as the force for pulling a mole attached to a cable through a pipe to be burst. 
           [0014]      FIG. 2  shows the cable puller assembly of the present invention mounted on a pulling base configured to receive the cable puller. 
           [0015]      FIG. 3  shows the cable puller assembly of the present invention, removed from the pulling base, with the pullers shown in their retracted position. 
           [0016]      FIG. 4  shows the cable puller assembly of  FIG. 3  with the pullers in their extended position. 
           [0017]      FIG. 5  shows an exploded view of the cable puller assembly of the present invention. 
           [0018]      FIG. 6  shows an exploded view of a puller of a cable puller of the cable puller assembly of the present invention. 
           [0019]      FIG. 7  shows a perspective view of the cable puller assembly of the present invention, indicating the direction of cable movement when the pullers are in their extended position and beginning a retraction stroke. 
           [0020]      FIG. 8  shows a perspective view of the cable puller assembly of the present invention, indicating the direction of cable movement when the pullers are in their retracted position and beginning an extension stroke. 
           [0021]      FIG. 9  shows the present invention cable puller installed in an excavation, pulling a mole and new replacement pipe through a pipe to be burst. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    With reference to  FIG. 1 , it has long been known in the art that an old pipe  1 , i.e. water, sewer, or electrical conduit, can be replaced by pulling a mole  2  via a cable  3  through the pipe to be burst  1 , and thereby bursting the pipe in a radially outward direction. Typically, a length of flexible plastic pipe  4  is drawn through the burst pipe  1  and thereby takes the place of the burst pipe  1 . Prior art systems require a means for generating the pulling force on the cable  1  and this means has typically been supplied by winches (not shown) or by a hydraulic cylinder-based cable puller  5 . Hydraulic cylinder-based cable pulling systems further require a pulling frame  6  that faces an opening in the pipe to be burst  1  through which the cable  3  may be drawn. Such systems further require a source of pressurized hydraulic fluid  7  and at least one operator  8 . As noted in the background section, prior art systems pull the cable only on their outward stroke. 
         [0023]    Referring to  FIG. 2 , the present invention improves upon the prior art by providing a double-acting hydraulic cable puller  10 , where both the inward and outward strokes of the cable puller, pull the cable  3  through the pipe to be burst  1 . With reference to  FIG. 2 , the double acting cable puller  10  of the present invention is shown attached to a pulling base  12 . For purposes of description, the puller  10  has a forward end and an aft end as indicated in  FIG. 2 , a right hand side and a left hand side as indicated in  FIG. 3 . 
         [0024]    Referring now to  FIGS. 3-5 , the cable puller of the present invention comprises a cylinder body  12  which houses four hydraulic cylinders, two opposed cylinders  24  and  26  are located in a right hand pressure tube  14  and two opposed cylinders  20  and  22  are in a left hand pressure tube  16 . Each of the pressure tubes  14  and  16  features an internal wall  18  (see  FIG. 5 ) in the center of the tubes. The internal wall  18  functions to split each tube ( 14 ,  16 ) into the opposed, independently acting hydraulic cylinders. Therefore, pressure tube  14  on the left hand side includes opposed hydraulic cylinders  20  and  22 , while pressure tube  16  on the right hand side includes opposed hydraulic cylinders  24  and  26 . 
         [0025]    Referring now to  FIGS. 4 and 5 , the forward hydraulic cylinders  20  and  26  feature pistons  28 , piston rods  30 , seals  32  and end caps  34 . Each rod  30  features an end portion  40  which extends beyond the end cap  34 . The end portions  40  of the piston rods  30  are internally threaded to accept cap screws  37 . The end portion  40  of each piston  30  mates in a slip fit within holes  42  bored through a forward puller  36 . Included in the bores  42  of the forward puller  36  are steps  44  (see  FIG. 6 ) which allow the piston rods  30  to be drawn up tightly, or rigidly attached to, the aft puller  36  via the cap screws  37 . 
         [0026]    With continued reference to  FIGS. 4 and 5 , similar to the forward hydraulic cylinders  20  and  26  of the present invention cable puller  10 , the aft hydraulic cylinders  22  and  24  also feature pistons  46 , piston rods  48 , seals  50  and end caps  52 . Each rod  48  also features an end portion  54  which extends beyond the end cap  52 . The end portions  54  of the piston rods  48  are internally threaded to accept cap screws  60 . The end portion  54  of each piston rod  48  mates in a slip fit within holes  58  bored through an aft puller  56 . Included in the bores  58  of the aft puller  56  are steps  44  (see  FIG. 6 ) which allow the piston rods  48  to be drawn up tightly, or rigidly attached to, the aft puller  57  via the cap screws  60 . 
         [0027]    With continued reference to  FIGS. 3 through 5 , the forward hydraulic cylinders  20  and  26  are larger and have a shorter stroke than the aft cylinders  22  and  24 . This is necessary so that the forward and aft pullers  36  and  56  will reach their maximum points of extension and retraction at the same time. The forward and aft pullers can only reach their maximum points of extension and retraction at the same time if both the forward pair of cylinders and the aft pair of cylinders receive an equal volume of hydraulic fluid on their forward and return strokes. Consequently, the pistons  28 , rods  30 , seals  32  and end caps  34  of the forward hydraulic cylinders  20  and  26  are larger than the corresponding pistons  46 , rods  48 , seals  50  and end caps  52  of the aft hydraulic cylinders  22  and  24 , in order to accomplish this goal. 
         [0028]    As noted, two double-acting forward,  20  and  26 , and aft  22  and  24 , pairs of cylinders are responsible for the actuation of the cable puller  10 . The forward cylinders ( 20  and  26 ) control the forward puller  36 , while the aft pair of cylinders ( 22  and  24 ) control the aft puller  56 . Pressurized hydraulic fluid is forced into each of the forward ( 20  and  26 ) and aft ( 22  and  24 ) cylinder pairs on the appropriate side of their pistons to cause simultaneous extension or retraction of the forward and aft pullers  36  and  56 . To cause the cylinders to extend, fluid is forced against the outward piston faces  29  (i.e. the faces opposite the rods). To cause the cylinders to retract, fluid is forced against the inward piston faces  31  (i.e. the faces on the same side as the rods). 
         [0029]    An operational constraint is that each of the forward ( 22  and  26 ) and aft ( 22  and  24 ) cylinder pairs must receive an equal volume of fluid. Receiving an equal volume of fluid is required because the cylinder pairs are opposed, i.e. one pair will receive fluid against the open-face side  29  of their pistons while at the same time the other pair will receive fluid against the side of their pistons to which the cylinder rod attaches  31 . Essentially, during any given phase in the cable puller&#39;s operation, one pair of cylinders will have its volume consumed by fluid only, and the other pair will have its volume consumed both by fluid and the cylinder&#39;s rods. This constraint dictates that the cylinder pairs must be dimensionally different. Specifically, the cylinder pairs must differ in cylinder diameter, rod diameter, and travel distance. For any particular size of cable puller, the above parameters must be adjusted to achieve an equal volume of fluid in each cylinder pair. 
         [0030]    Referring now to  FIGS. 3-5  and particularly  FIG. 6 , the pullers  36  and  56  of the present invention cable puller  10  will be described. The pullers are identical in function and are essentially identical in physical structure with the exception that bores  42  and  58  of the forward and aft pullers are sized differently to correspond to the differently sized piston rods to which they mate. That is, the bores  42  of the forward puller  36  are sized to mate with the rods  30  of the forward cylinders  20  and  26 , while the bores  58  of the aft puller  48  are sized to mate with the rods  48  of the aft cylinders  22  and  24 , the rods of the forward and after cylinders being of different sizes. In all other respects, the forward and aft pullers are identical. 
         [0031]    Each of the forward and aft pullers feature sliding jaws  62 . Each jaw  62  includes serrations  72 . The serrations  72  are designed to grasp or clamp onto the pulling cable  3  (see  FIG. 1 ). Each jaw  62  has a V-shaped surface  74 . The V-shaped surface of the jaws  62  slidably mate with V-shaped surfaces  76  of the centrally located V-section  78  on the puller  36 ,  56 . The sliding interaction of V-shaped surfaces  74  of the jaws  62  with the mating V-shaped surfaces on the puller  36 ,  56  are such that when the puller moves in a direction opposite to that of the narrow portion of the V-section  78 , the jaws  62  clamp down on the cable  3  and pull the cable in the direction of the puller. Likewise, when the puller  36 ,  56  moves in the same direction of the narrow portion of the V-section  78 , the jaws do not clamp down on the cable, but rather remain loose and thereby, the cable passes freely through the jaws. 
         [0032]    To allow for easy insertion of the pulling cable  3 , each puller has a cable access door  64  which is hinged to the puller(s)  36 ,  56 . The hinge is fixedly held in place on one side by a hinge pin  68  which includes a groove  80 . To retain the hinge pin  68  in place, a roll pin  66  passes through groove  80  in pin  68  and passes partially into a hole  82  formed into the puller(s)  35 ,  56 . On an opposite side, the cable access door is held in place by a ball-lock-pin  70 . The ball-lock pin  70  allows the cable door to be readily opened to accept a pulling cable, and just as easily closed. This feature of the present invention cable puller  10  is desirable because it creates a closed cable path through the puller and therefore increases the puller&#39;s safety over prior art devices which may allow a cable under tension to slip out of the puller in the event an operator were to lose control of the device. 
         [0033]    Ball-lock-pin  70  actuated cable doors  64  equipped with cable jaws  62  are located on both the forward  36  and aft  56  cable pullers. Optionally, a stationary puller  84  is may be located on the cylinder body  12 . The optional stationary puller is a safety mechanism and only activates to prevent cable rebound in the event one of the puller assemblies  36 ,  56  fails. 
       Operation of the Cable Puller of the Present Invention 
       [0034]    With reference to  FIG. 9 , prior to beginning operation, if necessary, excavations are made at each end of the pipe to be burst  1 . A pulling cable  3  is then run the full length the pipe to be burst  1 . A mole  2  having an eyelet or other means for cable attachment at one end, of which many prior art designs exist, is connected at the eyelet end to the pulling cable  3 . Replacement piping  4  is attached to the other end of the mole  2 . The present invention cable puller  10  is than attached a pulling base  11  specifically designed for use with the new puller. The new cable puller  10  is then connected to a source of pressurized hydraulic fluid  7 . (Sources of pressurized hydraulic fluid are well known to those of skill in the art.) The ball-lock-pins  70  are pulled which allows the cable doors  64  to be opened and the cable to be pulled to be inserted into the present invention cable puller  10 . (See  FIGS. 5-8 .) 
         [0035]    Referring to  FIGS. 3-4  and  7 - 8 , during phase I in the operation cycle, pressurized hydraulic fluid is directed into the forward ( 20  and  26 ) and aft ( 22  and  24 ) cylinders so that both pullers travel outwardly away from the cylinder body  12  until the cylinders&#39; maximum travel point has been reached. (See  FIGS. 4 and 7 .) During this phase, aft puller&#39;s  56  jaw set  62  engages the cable  3  so that the cable is displaced (i.e. pulled through the pipe to be burst) as the aft puller  56  travels away from the cylinder body  12 . At this time, the forward puller&#39;s  36  jaws are not engaged with the cable  3  and therefore the cable simply passes freely through the forward puller&#39;s jaws  62 . 
         [0036]    During phase II of the cable puller&#39;s  10  operation, pressurized hydraulic fluid is redirected into the cylinders ( 20  and  26 ) and ( 22  and  24 ) so that both pullers ( 36  and  56 ) travel inwardly towards the cylinder body  12 . (See  FIGS. 3 and 8 .) During this phase the two pullers have alternated tasks, the forward puller&#39;s jaws have engaged the cable and now pull the cable  3  through the pipe to be burst  1 , while the aft puller&#39;s jaws have released the cable and cable passes freely between them. The cycle repeats continuously until the mole  2  is pulled through the length of pipe to be burst  1 . 
         [0037]    The foregoing detailed description and appended drawings are intended as a description of the presently preferred embodiment of the invention and are not intended to represent the only forms in which the present invention may be constructed and/or utilized. Those skilled in the art will understand that modifications and alternative embodiments of the present invention, which do not depart from the spirit and scope of the foregoing specification and drawings, and of the claims appended below, are possible and practical. It is intended that the claims cover all such modifications and alternative embodiments.
The present invention comprises an improved cable puller assembly for use in the trenchless replacement of underground pipes including water, sewer and electrical conduits. The improved cable puller assembly utilizes a cylinder body comprising four double acting hydraulic cylinders set up in pairs of two, i.e. Two forward cylinders and two aft cylinders. The cable pullers are configured to move inwardly and outwardly from the cylinder body and feature the ability to pull a cable through a pipe on both their inward and outward strokes.