Abstract:
The present invention provides a portable pulling apparatus suitable for mounting in an exit pit during installation of a pipeline. A portable pulling apparatus of the invention includes an elongated stake having a lower end portion configured for insertion into the ground and an upper end portion. A winch including a pulling cable is mounted on the upper end portion of the stake by a suitable fixture. The winch can then operate to exert a horizontal pulling force on a cable and is secured against movement when the lower end portion of the stake is inserted into the ground. Such a pulling apparatus can be used in a method of installing an underground pipe according to the invention.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to a portable pulling machine useful in combination with a pneumatic impact ground piercing tool for installing an underground pipeline.  
         BACKGROUND OF THE INVENTION  
         [0002]    Self-propelled pneumatic tools for making small diameter holes through soil are well known. Such tools are used to form holes for pipes or cables beneath roadways without need for digging a trench across the roadway. These tools include, as general components, a torpedo-shaped body having a tapered nose and an open rear end, an air supply hose which enters the rear of the tool and connects it to an air compressor, a piston or striker disposed for reciprocal movement within the tool, and an air distributing mechanism for causing the striker to move rapidly back and forth. The striker impacts against the front wall (anvil) of the interior of the tool body, causing the tool to move violently forward into the soil. The friction between the outside of the tool body and the surrounding soil tends to hold the tool in place as the striker moves back for another blow, resulting in incremental forward movement through the soil. Exhaust passages are provided in the tail assembly of the tool to allow spent compressed air to escape into the atmosphere.  
           [0003]    Most impact ground piercing tools of this type have a valveless air distributing mechanism which utilizes a stepped air inlet. The step of the air inlet is in sliding, sealing contact with a tubular cavity in the rear of the striker. The striker has radial passages through the tubular wall surrounding this cavity, and an outer bearing surface of enlarged diameter at the rear end of the striker. This bearing surface engages the inner surface of the tool body.  
           [0004]    Air fed into the tool enters the cavity in the striker through the air inlet, creating a constant pressure which urges the striker forward. When the striker has moved forward sufficiently far so that the radial passages clear the front end of the step, compressed air enters the space between the striker and the body ahead of the bearing surface at the rear of the striker. Since the cross-sectional area of the front of the striker is greater than the cross-sectional area of its rear cavity, the net force exerted by the compressed air now urges the striker backwards instead of forwards. This generally happens just after the striker has imparted a blow to the anvil at the front of the tool.  
           [0005]    As the striker moves rearwardly, the radial holes pass back over the step and isolate the front chamber of the tool from the compressed air supply. The momentum of the striker carries it rearward until the radial holes clear the rear end of the step. At this time the pressure in the front chamber is relieved because the air therein rushes out through the radial holes and passes through exhaust passages at the rear of the tool into the atmosphere. The pressure in the rear cavity of the striker, which defines a constant pressure chamber together with the stepped air inlet, then causes the striker to move forwardly again, and the cycle is repeated.  
           [0006]    In some prior tools, the air inlet includes a separate air inlet pipe, which is secured to the body by a radial flange having exhaust holes therethrough, and a stepped bushing connected to the air inlet pipe by a flexible hose. These tools have been made reversible by providing a threaded connection between the air inlet sleeve and the surrounding structure which holds the air inlet concentric with the tool body. The threaded connection allows the operator to rotate the air supply hose and thereby displace the stepped air inlet rearwardly relative to the striker. Since the stroke of the striker is determined by the position of the step, i.e., the positions at which the radial holes are uncovered, rearward displacement of the stepped air inlet causes the striker to hit against the tail nut at the rear of the tool instead of the front anvil, driving the tool rearward out of the hole. See, for example, Wentworth et al. U.S. Pat. Nos. 5,025,868 and 5,337,837.  
           [0007]    Expanders are tapered, ring-shaped shells that fit over the tapered nose portion of an earth boring tool in order to widen the hole made by the tool as it passes through the ground. In this manner, a 4-inch diameter tool may be used to make a 6- or 8-inch diameter hole. The tool is often sent through to make an initial bore, and then sent through a second time with the expander in order to widen the existing hole and/or crack an existing pipe. According to a known method, a plastic pipe may be attached to the back of the expander with the above described reversible tool inside the pipe so that the pipe is installed as the tool bores through the soil, with or without additional widening of the bore. The tool body is disposed inside the replacement pipe, and in this arrangement friction between the expander and the soil serves to keep the tool and expander from moving backward during the rearward stroke of the striker.  
           [0008]    Problems are encountered as the tool advances further into the ground and the weight of the pipe being drawn behind the tool grows progressively greater. The ground piercing tool relies on friction with the surrounding soil to prevent it from moving backward during the rearward stroke of the striker the same distance the tool moved forward when the striker made its forward impact. The elasticity of the pipe drawn behind the tool can counteract this frictional force, slowing and eventually stopping the tool.  
           [0009]    To remedy this difficulty, it is known to attach a cable to the front end of the impact ground piercing tool and use a winch to apply a continuous pulling force to the tool in the forward direction. The cable is threaded through the existing pipeline or a pilot hole and serves to keep the tool moving and prevent it from deviating from its proper course. While it is possible to push on the existing pipeline from behind instead of pulling on the ground piercing tool using a cable, the pushing operation is less effective because it increases the chance that the ground piercing tool will deviate from the desired path.  
           [0010]    In most pipe replacement operations, entry and exit pits must be dug at the end of the run. The cable used to pull on the ground piercing tool emerges into the exit pit and must be directed up to the winch, which is generally a large, truck mounted unit with a capacity greatly exceeding the amount of pulling force needed to keep the ground piercing tool moving. Setting up the winch for pulling is a cumbersome operation because the winch cannot readily be placed and secured directly in the exit pit. The present invention addresses this problem.  
           [0011]    Directional boring machines are large, hydraulic rod pushing and pulling systems with the capability of rotating the string of rods (drill string). See, for example, units shown in Malzahn U.S. Pat. Nos. 4,945,999 and 5,070,948, Cherrington U.S. Pat. No. 4,697,775 (RE 33,793), Dunn U.S. Pat. No. 4,953,633 and Deken et al. U.S. Pat. No. 5,242,026. Large directional boring machines generate tremendous reaction forces, and thus it has become standard practice to secure the corners of the machine to the ground with tubular stakes several feet in length. A pneumatic ground piercing tool of the same type used to pull the replacement pipe is fitted on the inside of the tubular stake and used to drive the stake into the ground in a few seconds. Reversing the tool causes the tool to emerge from the ground, leaving the stake intact. The stake has been removed by replacing the tool in the stake, removably securing an insert to the stake in a position behind the tool, and then running the tool in reverse.  
         SUMMARY OF THE INVENTION  
         [0012]    The present invention provides a portable pulling apparatus suitable for mounting in an exit pit. A portable pulling apparatus of the invention includes an elongated stake having a lower end portion configured for insertion into the ground and an upper end portion. A winch including a pulling cable is mounted on the upper end portion of the stake by a suitable fixture. The winch can then operate to exert a horizontal pulling force on a cable and is secured against movement when the lower end portion of the stake is inserted into the ground.  
           [0013]    Such a pulling apparatus can be used in a method of installing an underground pipe according to the invention. Such a method comprises the steps of:  
           [0014]    connecting a pipe to be installed to a ground piercing tool so that the pipe moves forward as the tool moves forward;  
           [0015]    positioning the ground piercing tool for entry into an existing underground opening at a front end of the opening;  
           [0016]    mounting a portable pulling apparatus near a rear end of the existing underground opening, which apparatus includes an elongated stake having a lower end portion configured for insertion into the ground and an upper end portion, a winch, and a fixture that mounts the winch on the upper end portion of the stake, wherein the pulling apparatus is mounted by driving the lower end portion of the stake into the ground;  
           [0017]    feeding a cable from the winch through the underground opening and connecting the cable to the ground piercing tool; and  
           [0018]    operating the ground piercing tool in forward mode to pull the pipe into an existing opening while pulling the tool forward using the winch to pull the cable. Such a method permits long runs of underground pipe to be installed at lesser cost and labor than previously known methods, as described in detail hereafter.  
           [0019]    Other objects, features and advantages of the invention will become apparent from the following detailed description. It should be understood, however, that the detailed description is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0020]    The invention will hereafter be described with reference to the accompanying drawing, wherein like numerals denote like elements, and:  
         [0021]    [0021]FIG. 1 is a lengthwise view, partly in section, illustrating the pipe installation method of the present invention;  
         [0022]    [0022]FIG. 2 is a lengthwise view, partly in section, of an embodiment of the apparatus of the invention shown in use in FIG. 1;  
         [0023]    [0023]FIG. 3 is a top view, with underlying parts shown in phantom, of the mounting device shown in FIG. 2;  
         [0024]    [0024]FIG. 4 is a side view, with underlying parts shown in phantom, of the mounting device shown in FIG. 3;  
         [0025]    [0025]FIG. 5 is a front view, with underlying parts shown in phantom, of the mounting device shown in FIG. 3; and  
         [0026]    [0026]FIG. 6 is lengthwise sectional view of an insert used in the apparatus shown in FIG. 2.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0027]    Referring now to the drawings, FIG. 1 illustrates the method of the invention. A first pneumatic ground piercing tool  10 A includes an elongated tool body  12 A having a tapered nose or head assembly  14 A. The type of tool employed is advantageously one which has a reversing mechanism, so that the tool can be run in reverse to disengage it from an expander as described hereafter. Such reversible tools are shown in Wentworth et al. U.S. Pat. Nos. 5,025,868 and 5,337,837, the contents of which are incorporated by reference herein.  
         [0028]    Ground piercing tool  10 A is provided with an expander  22  including a front, frustoconical section  23 , optionally with external bursting blades, and configured to fit closely onto the tapered nose  14 A of the tool. A pipe  28 , such as a PVC or PE plastic pipe, is inserted inside (or outside) of a rear cylindrical section  24  of expander  22  and is secured to expander  22  by any suitable means, such as screws extending through radial holes in section  24  into pipe  28 . In the alternative, pipe  28  may be connected to tool  10 A by a suitable coupling device in a manner known in the art so that it follows behind tool  10 A, and expander  22  may be omitted. In the latter arrangement, the replacement pipe  28  is connected to the rear end of the impact tool  10 A. A first air hose  29 A connected to an air compressor (not shown) runs through pipe  28  and supplies compressed air to operate tool  10 A.  
         [0029]    According to the method of the invention, pipe  28  is connected to expander  22  in a front (launch) pit  31 . At a rear (exit) pit  32 , a pulling apparatus  33  according to the invention is positioned near an exit opening  34  of an existing pipeline  38 , such as a 4-inch diameter clay pipe, to provide a pulling force on a steel cable  37  which extends in the axial direction through the interior of existing pipeline  38 . Cable  37  may be threaded by hand using a fiberglass rod through pipeline  38  and is attached to an eye  39  provided on the front end of tool  10 A. Cable  37  may comprise a steel cable, chain, rope, or other similar device.  
         [0030]    Pulling apparatus  33  is then operated to provide a continuous pulling force on tool  10 A and the new pipe  28  in a manner described hereafter. Tool  10 A is placed with expander  22  in contact with an entrance opening  41  of the existing pipeline or opening  38 , and then operated in forward mode. Tool  10 A moves progressively through the existing pipeline  38  as shown. Expander  22  bursts (shatters or slits) pipeline  38  while tool  10 A drags the new pipe  28  into position behind expander  22 . For a three inch diameter tool  10 A used to install a four inch pipe, it has been found that the pulling apparatus is often needed to advance the run beyond about  50  feet or so in length. In general, according to a preferred form of the invention, pulling apparatus  33  is used in situations where the entrance and exit openings  41 ,  34  are more than about  50  feet apart. In either case, the pulling force in the lengthwise direction of the pipeline  38  also prevents tool  10 A from going off course.  
         [0031]    [0031]FIGS. 2 through 6 illustrate one form of apparatus  33  according to the invention. Pulling apparatus  33  includes an elongated, tubular steel stake  51 , a winch  52 , and a fixture  53  for mounting winch  52  on an upper end portion of stake  51 . Steel stake  51  has a reduced diameter bottom portion  54 . In the illustrated embodiment, bottom portion  54  is tapered to complement the taper of a nose portion  14 B of a second pneumatic impact tool  10 B used to drive stake  51  into the ground. Stake  51  may have one or more spaced fins  56  (for example, three equiangular fins) provided to help the stake hold its position.  
         [0032]    Winch  52  may be a conventional electric unit or a pneumatic unit such as a Thern model 4771. Winch  52  includes a motor disposed within a housing  61  and a cable winding drum  62  on which cable  37  is wound and unwound during operation. As shown in FIG. 1, winch  52  may be run using the same air hose  29 B used to run the impact tool  10 B by uncoupling hose  29 B from a coupling  11 B and attaching it to winch  52 .  
         [0033]    Fixture  53  is used to mount winch  52  on the upper end of stake  51 . Fixture  53  includes a bracket plate  63  having holes  64  by which winch  52  is mounted to plate  63  by suitable means such as welding or nuts and bolts  66  as shown. Plate  63  is welded to the side of a cylindrical sleeve  67  having an inner diameter slightly greater than the outer diameter of stake  51 , and a pair of gussets  65  may similarly be welded between plate  63  and sleeve  67  to provide the fixture with additional strength. A lid  68  having an annular flange  69  fits closely in the upper end of sleeve  67 . As shown in FIG. 3, lid  68  has a central slot or similar aperture  71  through which an air hose  29 B can pass.  
         [0034]    Stake  51  may be provided with a tubular extension  72  at its upper end to make up a difference in diameter between stake  51  and sleeve  67 . Threads  73  are provided on an inner surface of extension  72  for engagement with a tubular insert  81  as described hereafter. Spacers  74  may be provided on the outside of stake  51  at an upper end portion  76  thereof so that sleeve  67  fits securely onto upper end portion  76  of stake  51 .  
         [0035]    At least one fin  56  acts as an external bracket that extends from upper end portion  76  of stake  51 . A row of spaced holes  77  in fin  56  permit a pulley  78  to be mounted over a range of positions as needed to center cable  37  horizontally within the existing pipeline  38 . Pulley  78  includes a rotatable grooved wheel  79  mounted on a plate  80  which is secured to fin  56  by nut and bolt assemblies  82 . Cable  37  extends downwardly from winch drum  62  and is wound approximately 90° about wheel  79  so that it can extend into the pipeline  38 .  
         [0036]    Apparatus  33  is able to apply a continuous pulling force on tool  10 A which keeps tool  10 A moving forward even over long pipeline runs without the need for a large, truck mounted winch. Installation in the exit pit  32  is carried out by placing tool  10 B into the bottom of stake  51  as shown in FIG. 2 with tapered surfaces in engagement as shown. Winch  52  and fixture  53  may be removed temporarily and remounted once stake  51  has been set.  
         [0037]    Tool  10 B is run in forward mode to drive a lower end portion of stake  51  into the ground a sufficient distance so that stake  51  will remain secure. Tool  10 B may be left in place until it is time to remove stake  51 , and for that purpose slot  71  in lid  68  allows hose  29 B to remain in position. In the alternative, tool  10 B may be run in reverse to disengage nose  14 B from tapered lower end portion  54  and then removed through the top of stake  51 , freeing tool  10 B for other work, such as setting a stake for another run while the current run is in progress. Tools  10 A,  10 B may be of the same or different size and type.  
         [0038]    Once the current run is complete or the need for the additional pulling force supplied by the winch has ended, tool  10 B is replaced at the bottom of stake  51  (if previously removed) and tubular insert  81  is inserted into stake  51  behind tool  10 B. Insert  81  is rotated so that external threads  84  of insert  81  are brought into engagement with threads  73  and a bottom end  83  of insert  81  contacts the back of tool  10 B. Tool  10 B is then run in reverse, and the presence of insert  81  securely attached to stake  51  retracts stake  51  out of the ground together with tool  10 B. Insert  81  is then unscrewed from inside of stake  51  so that tool  10 B can be removed, or insert  10 B may be left in place if the entire assembly will be used at another site a short distance away.  
         [0039]    The method and apparatus of the invention provide considerable flexibility and are particularly advantageous in situations where there is limited space for the exit pit. Where the pipeline must connect to the foundation of a building  90  as shown in FIG. 1, it may be difficult or impossible to use a truck-mounted winch in the exit pit, which may adjoin a cinderblock foundation. The pulling apparatus of the present invention is small in size and can be installed and removed vertically, permitting use in small spaces.  
         [0040]    It will be understood that the foregoing description is of preferred exemplary embodiments of the invention, and that the invention is not limited to the specific forms shown. For example, the method of the invention could be practiced for installation of a cable instead of a pipe, or without attaching the pipe to the ground piercing tool. In the latter case, the pipe can be inserted manually into the expanded pipeline hole after the run is complete. The ground piercing tool can be a directional boring machine or rod pusher which pushes the expander from behind while the apparatus of the invention pulls from the front. These options, however, are not preferred because a string of rods extending down an existing pipeline of greater diameter tend to buckle. These and other modifications may be made in without departing from the scope of the invention as expressed in the appended claims.