Abstract:
A tandem rod or cable apparatus for bursting and replacing pipe, which includes a frame, two sets of oppositely-disposed hydraulic cylinders having piston rods, each of which pairs of piston rods are attached to a yoke, with a gripping element provided in each yoke for independently gripping a rod or cable extending through the aligned gripping elements. One end of the rod or cable is attached to a bursting and stored energy head and the other end extends through the gripping elements, typically to a reel (in the case of a cable) for taking up slack in the cable. Advancement of the bursting and stored energy head through a defective pipe to be burst and typical simultaneous replacement with an attached replacement pipe is effected by operation of the two sets of hydraulic cylinders and the corresponding gripping elements to push or pull the rod or pull the cable. In a preferred embodiment a pneumatic hammer is typically seated in the bursting and stored energy head and operates in cooperation with a pair of springs to optimize bursting of the defective pipe as the pneumatic hammer repeatedly strikes the bursting and stored energy head. The combined actions of the rod or cable operating hydraulic cylinders and the hammer cause the bursting and stored energy head to progressively rupture the defective pipe and typically draw the replacement pipe into position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is related to my co-pending application Ser. Nos. 10/021,587, filed Dec. 12, 2001 and Ser. No. 10/234,216, filed Sep. 4, 2002, now U.S. Pat. No. 6,672,802. This application also claims the benefit of and incorporates by reference prior filed U.S. Provisional Application Ser. No. 60/480,699, filed Jun. 24, 2003. 

   SUMMARY OF THE INVENTION 
   This invention includes a new and improved device for replacing a defective underground gas, water, sewer or other utility pipe by progressively cutting and bursting the pipe and typically simultaneously drawing a replacement pipe into position behind the migrating burst point of the pipe being replaced. In a preferred embodiment the apparatus of this invention is characterized by a specially designed rod or cable pulling hydraulic tandem device or apparatus which is typically fitted with two pairs of oppositely-disposed, double-action hydraulic rod or cable driving members or cylinders, each attached to a separate yoke having oppositely-disposed, aligned rod-gripping elements. The rod or cable pulling device is typically vertically or horizontally situated in a manhole or in an excavation at one end of a defective pipe to be replaced. A pull rod or cable is extended through the aligned rod driving gripping members mounted on the rod or cable pulling device yokes and through the defective pipe and is attached in a preferred embodiment to a stored energy housing connected to a tapered bursting head (hereinafter called bursting and stored energy head), typically fitted with multiple blades which initially engage the opposite end of the pipe to be broken. A pneumatic hammer is typically spring-biased in the stored energy housing and a replacement pipe is typically removably attached to the bursting head. In typical operation the aligned gripping elements driven by the oppositely-disposed pairs of rod or cable driving members of the rod or cable pulling device repeatedly and alternately grip, pull (or push, in the case of a rod) and release the pull rod or cable and move to a new gripping position on the pull rod or cable. This action pulls (or pushes) the stored energy head element against the bursting head component and thus, the bursting head against the pipe to be replaced, as the pneumatic hammer repeatedly strikes the bursting and stored energy housing and forces the bursting head against the pipe. 
   The combined pulling or pushing action of the rod or cable pulling device and the driving action of the pneumatic hammer cause the bursting and stored energy head to migrate along the defective pipe and progressively cut and rupture the pipe and simultaneously draw the replacement pipe into position behind the migrating burst point of the old pipe. In a preferred embodiment a pair of springs fitted in the stored energy housing are compressed and biased to store energy and apply the energy against the bursting head element as the rod or cable pulling device pulls or pushes the rod or pulls the cable and moves the bursting and stored energy head. As the hammer strikes the stored energy element against the bursting head, tension released by the springs in the stored energy housing augments the driving action of the hammer and assists the rod or cable pulling device and hammer in forcing the bursting and stored energy head along the pipe. The pneumatic hammer is typically used in combination with the tandem apparatus, typically under circumstances in which valves, concrete encasements, timbers or other significant obstructions are likely to be encountered by the bursting and stored energy head in or around the pipe being split or burst and replaced. When such obstructions are unlikely to be encountered by the bursting and stored energy head, the rod or cable pulling device can be used without the pneumatic hammer to pull or push the pipe bursting and stored energy head along the pipe. The tandem apparatus of this invention can be horizontally oriented, typically in a trench or excavation, for direct pull or push in a substantially horizontal pipe bursting application or vertically positioned in a manhole for horizontal pipe bursting applications using a pulley and pull cable system. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood by reference to the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of a preferred embodiment of the tandem apparatus of this invention, characterized by oppositely-disposed sets of tandem-oriented hydraulic cylinders disposed for pulling or pushing a rod or pulling a cable and forcing a bursting and stored energy head through a defective pipe; 
       FIG. 2  is a top view of the tandem apparatus illustrated in  FIG. 1  disposed in a first rod or cable operating mode; 
       FIG. 3  is a top view of the tandem apparatus illustrated in  FIG. 1  disposed in a second rod or cable operating mode; 
       FIG. 4  is a perspective view of the tandem apparatus illustrated in  FIG. 1  oriented in a vertical configuration above a manhole for pulling a cable attached to a pipe bursting device, wherein the cable is extended into the manhole and then directed horizontally from the manhole to the pipe bursting device by means of a pulley; 
       FIG. 5  is a side sectional view taken along line  5 — 5  of  FIG. 1  of a typical hydraulic cylinder used in the tandem apparatus illustrated in  FIG. 1 , particularly illustrating operation of the hydraulic cylinder; 
       FIG. 6  is a top sectional view taken along line  5 — 5  of  FIG. 1  of the hydraulic cylinder illustrated in  FIG. 5 , more particularly illustrating operation of the hydraulic cylinder; 
       FIG. 7  is a top view of the tandem apparatus illustrated in  FIG. 1 , more particularly illustrating a typical hydraulic pump reservoir and feed and return line system configuration for operating the dual, oppositely-disposed pairs of hydraulic cylinders; 
       FIG. 8  is a top view, partially in section, of a first preferred gripping element for mounting on each one of a pair of yokes attached to each of the oppositely-disposed pairs of hydraulic cylinders illustrated in  FIG. 1 , for gripping the rod or cable during operation of the respective tandem pairs of hydraulic cylinders; 
       FIG. 9  is a sectional view taken along line  9 — 9  of the gripping device illustrated in  FIGS. 8 and 12 ; 
       FIG. 10  is a sectional view taken line along  10 — 10  of the gripping element illustrated in  FIGS. 8 and 12 ; 
       FIG. 11  is a sectional view taken along line  11 — 11  of the gripping element illustrated in  FIGS. 8 and 12 ; 
       FIG. 12  is a top view, partially in section, of an alternative preferred gripping element; and 
       FIG. 13  is a sectional view of a preferred embodiment of the bursting and stored energy head and hammer components of the tandem apparatus of this invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring initially to  FIGS. 1–3  and  5  of the drawings the tandem apparatus of this invention is generally illustrated by reference numeral  1 . The tandem apparatus  1  is characterized by a frame  3 , which is typically shaped by cylinder mounts  6  and end frame members  4 , spanning side frame members  5 , as illustrated. A pair of front rod driving members  11  include a pair of parallel hydraulic cylinders  12 , each having a front end  11   a  and cylinder mount flanges  15 , secured to one of the cylinder mounts  6  of the frame  3 , typically using mount bolts  18 , as illustrated. A pair of rear rod driving members  56  are disposed opposite the front rod driving members  11  in the frame  3  and include a second set of parallel hydraulic cylinders  12 , mounted to the second cylinder mount  6  using additional mount bolts  18 . Each of the four hydraulic cylinders  12  includes a piston  19  ( FIG. 5 ), having a piston rod  20  which extends through the front end  11   a  of the front rod driving members  11  and the rear rod driving members  56 , respectively. The piston rod  20  of the hydraulic cylinders  12  in the front rod driving members  11  are each connected to a common front yoke  84 , which mounts a single gripping element  25 , as further illustrated in  FIG. 1 . Similarly, the piston rods  20  of the hydraulic cylinders  12  in the rear rod driving members  56  are each connected to a common rear yoke  85 , which mounts a second gripping element  25 . It will be appreciated from a consideration of  FIGS. 1–3  that the gripping elements  25  are in alignment to receive a pull rod  40  or a pull cable (not illustrated), as desired. One end of the pull rod  40  is attached to the front end of a bursting and stored energy head  43 , illustrated in phantom in  FIG. 1 . The opposite end of the pull rod  40  extends through aligned rod or cable openings  4   a  in the end frame members  4  ( FIG. 1 ) and through the respective aligned gripping elements  25 . In the case of a pull cable (not illustrated) the free end of the cable may be gathered on a cable take-up drum (not illustrated), as desired. 
   Referring to  FIGS. 2 ,  3  and  8 – 12  of the drawings, the tandem apparatus  1  is illustrated in alternating push or pull configurations. Referring initially to  FIG. 2 , the gripping element  25  which is attached to the front yoke  84  served by the parallel hydraulic cylinders  12  in the dual front rod driving members  11  is illustrated as engaging the pull rod  40 , while the gripping element  25  mounted on the rear yoke  85  and served by the dual, parallel hydraulic cylinders  12  in the rear rod driving members  56 , is released from the pull rod  40 . As the parallel piston rods  20  in each of the hydraulic cylinders  12  of the front rod driving members  11  extend, the pull rod is advanced in the direction of the arrows in  FIG. 2 , throughout the full stroke of the piston rods  20 . When this stroke is complete, the gripping element  25  in the front rod driving members  11  releases its grip from the pull rod  40  and the gripping element  25  in the rear rod driving members  56  grips the pull rod  40 , as the piston rods  20  in the corresponding hydraulic cylinders  12  retract and continue the forward movement of the pull rod or cable  40  in the direction of the arrow, throughout the full stroke of the piston rods  20 , as illustrated in  FIG. 3 . The sequence continues in order to advance the pull rod or cable  40  and pull or push the bursting head (not illustrated) through a pipe to be broken, as hereinafter further described. Sequential gripping of the rod  40  by the respective gripping elements  25  is effected by contact between the unidirectional teeth  27   b  shaped in the respective wedges  27 , as illustrated in  FIGS. 8 and 12  of the drawings. The respective sets of teeth  27   b  grip the rod  40  as each gripping element  25  is forced in the direction of the arrows in sequence by the respective hydraulic cylinders  12  as described above with respect to  FIGS. 2 and 3  of the drawings. The degree of force applied by the teeth  27   b  on the rod  40  is determined by the tension in the gripping element spring  35  ( FIG. 8 ) or the rubber washers  38  ( FIG. 12 ). Reverse non-gripping movement of the respective gripping elements  25  on the pull rod  40  is facilitated since the rod  40  motion is opposite the unidirectional orientation of the respective teeth  27   b  in the corresponding wedges  27  ( FIGS. 2 ,  3 ,  8  and  12 ). 
   Referring now to  FIG. 4  of the drawings it will be appreciated by those skilled in the art that the tandem apparatus  1  illustrated in  FIG. 1  can be vertically oriented for operation in a manhole structure  88 , (illustrated in phantom) typically in the orientation detailed in my U.S. patent application Ser. No. 10/234,216, filed Sep. 4, 2002, now U.S. Pat. No. 6,672,802. Accordingly, the frame  3  can be attached to the vertically-oriented pulley mount  89  (illustrated in phantom) that is inserted in the base or bottom of the manhole structure  88  and the apparatus includes a bottom pulley  93 , secured to the pulley mount  89  at the bottom of the manhole structure  88 . Accordingly, a pull cable  40   a  (illustrated in phantom) extends around the bottom pulley  93 , horizontally to a bursting and stored energy head  43 , also illustrated in phantom, and upwardly, parallel to the pulley mount  89 , through the aligned gripping elements  25 , to a cable drum  89   a  (illustrated in phantom) designed to take up the slack in the pull cable  40   a  during the operation of the vertically-oriented tandem apparatus  1 . A top pulley  95  is fitted to the top end of the pulley mount  89  to align the pull cable  40   a  with the cable drum  89   a , as further illustrated in  FIG. 4 . Accordingly, operation of the tandem apparatus  1  in the manner heretofore described with respect to  FIGS. 2 and 3  and the pull rod  40 , facilitates progressive extension of the pull cable  40   a  upwardly for spooling on the cable drum  89   a  and causes the bursting and stored energy head  43  to extend through and break the pipe  83 . As further heretofore described, a hammer  41  (illustrated in phantom) is used in association with the bursting and stored energy head  43  and the tension in the pull cable  40   a  to advance the bursting and stored energy head  43  through the pipe  83  as the bursting and stored energy head  43  approaches the bottom of the manhole structure  88 . 
   Operation of the tandem apparatus  1  illustrated in  FIGS. 1–4  of the drawings is effected by tandem, selectively alternating or simultaneous operation of the hydraulic cylinders  12  in the manner illustrated in  FIGS. 5–7  of the drawings. Referring initially to  FIGS. 5 and 6 , pressurized hydraulic fluid (not illustrated) is introduced into the fluid chambers  14  of each of the parallel sets of hydraulic cylinders  12  in the front rod-driving members  11  and the rear rod driving members  56 , through the respective front hydraulic fluid port  22  ( FIG. 5 ). The hydraulic fluid applies pressure to the piston  19  to facilitate rearward displacement of the piston  19  in the fluid chamber  14  in the direction of the arrow. This action causes rearward extension of the piston rod  20  through the front end  11   a , sealed by the front end O-rings  11   b , and the end plate  13 , sealed by the end plate O-rings  17 , respectively, in the hydraulic cylinders  12 . Reverse operation of the hydraulic cylinder  12  by entry of the hydraulic fluid into the rear hydraulic cylinder fluid port  22   a  ( FIG. 5 ) effects a reverse movement of the piston  19  and the piston rods  20  in each of the hydraulic cylinders  12 , in operation of the tandem apparatus  1 . As illustrated in  FIG. 7 , the tandem apparatus  1  is typically operated by means of a hydraulic fluid system that includes a hydraulic pump  96   a , that pumps hydraulic fluid from a hydraulic fluid tank  96 , initially through a hydraulic feed line  97 , to the hydraulic cylinders  12  of the front rod driving members  11 , as illustrated in  FIG. 5  and described above. This hydraulic feed effects extension of the corresponding front yoke  84  and associated gripping element  25  in the direction of the arrows. Hydraulic fluid also flows from the front rod driving members  11  hydraulic cylinders  12 , to the dual hydraulic cylinders  12  of the rear rod driving members,  56  to extend the rear yoke  85  and the corresponding gripping element  25  in non-gripping sequence. The fluid then flows back into the hydraulic fluid tank  96  through the hydraulic fluid return line  99 . The hydraulic fluid flow is then reversed to reverse the operation of the tandem apparatus described above. 
   Referring now to  FIGS. 8–11  of the drawings, in a preferred embodiment of the invention the two gripping elements  25  that receive the pull rod  40  or the pull cable  40   a  are each characterized by a cylindrical adaptor housing  26 , having a cone-shaped internal top surface that houses three correspondingly-tapered wedges  27  (illustrated in phantom), each fitted with a set of unidirectional teeth  27   b  and a threaded wedge hole  27   a  in the top thereof, as illustrated in  FIGS. 8 ,  9  and  12 . A mount flange  28  encircles the adaptor housing  26  at the top thereof and a pair of diametrically-opposed mount flange slots  28   a  are provided in the mount flange  28 , for purposes which will be hereinafter described. A rod or cable opening  29  is also provided in the centers of the cone-shaped wedges  27  at the point of convergence of the wedges  27  and the teeth  27   b , as illustrated in  FIG. 9 , for receiving a pull rod  40  or a pull cable  40   a  (illustrated in phantom in  FIGS. 8 and 12 ). The pull rod  40  or pull cable  40   a  also extends through the center of a gripping element spring  35 , interposed between a bottom compression plate  37 , positioned directly above the wedges  27 , and a top compression plate  34 , as further illustrated in  FIG. 8  of the drawings. The top compression plate  34  includes three threaded stabilizing bolts  36 , each having stabilizing bolt nuts  36   a  threaded thereon above the top compression plate  34 , but normally not touching it. The bottom ends of each of the stabilizing bolts  36  are threaded into the corresponding threaded wedge hole  27   a  of a corresponding wedge  27 , as further illustrated in  FIG. 8 . The top compression plate  34  is positioned on top of the gripping element spring  35  by means of two T-bolts  32 , the T-bolt heads  32   c  of which are removably seated in corresponding mount flange slots  28   a , provided in the mount flange  28 . A top nut  32   a , threaded on the upper end of each of the T-bolts  32 , maintains a desired degree of tension in the gripping element spring  35 . A bottom nut  32   b  is also threaded on each of the T-bolts  32 , between the top compression plate  34  and the bottom compression plate  37 , and a washer  33  is welded to each T-bolt  32 , about one-eighth of an inch above the mount flange  28 , to facilitate removal of the T-bolt heads  32   c  from the corresponding mount flange slots  28   a . Accordingly, it will be appreciated from a consideration of  FIG. 8  that a desired degree of tension can be applied to the gripping element spring  35  by adjusting the respective top nuts  32   a  on the corresponding T-bolts  32  and compressing the gripping element spring  35  between the top compression plate  34  and the bottom compression plate  37 . This tension is also applied to the respective wedges  27  disposed beneath the bottom compression plate  37 , to force the wedges  27  inwardly and downwardly along the cone-shaped interior wall of the adaptor housing  26 , and engage the respective teeth  27   b  with the pull cable  40   a.    
   As further illustrated in FIGS.  1  and  8 – 11 , a housing mount  30  is mounted on each of the front yokes  84  and rear yoke  85  and is extended around a corresponding housing flange  31 , attached to the adaptor housing  26 , as illustrated in  FIGS. 8 ,  10  and  11  of the drawings. The housing mount  30  receives the housing flange  31  in a housing mount slot  30   a  and serves to removably secure each gripping element  25  in position on the respective front yoke  84  and rear yoke  85  of the tandem rod and cable pulling apparatus  1 , as further illustrated in  FIG. 1  of the drawings. 
   Referring now to  FIG. 12  of the drawings, in an alternative preferred embodiment of the gripping elements of the tandem apparatus  1 , each gripping element  25  may be constructed using one or more rubber washers  38  interposed between the top compression plate  34  and the bottom compression plate  37 , in place of the gripping element spring  35  illustrated in  FIG. 8 . The purpose of the rubber washers  38 , like the gripping element spring  35 , is to exert pressure on the bottom compression plate  37  and thus, the wedges  27 , by tightening or loosening the respective top nuts  32   a  on the corresponding T-bolts  32 , to exert the desired degree of force on the respective wedges  27 . 
   Referring to  FIG. 13  of the drawings a preferred bursting and stored energy head  43  is illustrated for use in the tandem apparatus  1  of this invention. The bursting and stored energy head  43  includes a cylindrical bursting head housing  43   a , fitted into a wedge sleeve  45 , having an expander or pipe bursting wedge  44  and knives  44   a  on the end thereof. The wedge sleeve  45  is attached to a replacement pipe  82 , typically by means of suitable pipe connectors  46 , such as lag screws, such that the replacement pipe  82  is continuously pulled forward by advancement of the bursting and stored energy head  43 , responsive to the tension applied to the pull rod  40  (or a pull cable, not illustrated), in the manner hereinafter described. An end plate  47  is provided in the forward end of the bursting and stored energy head housing  43  adjacent to the expander wedge  44  and a rubber disc  48  is positioned adjacent to the end plate  47 , as further illustrated in  FIG. 13 . A front plate washer  49  is positioned against the rubber disc  48 , such that the rubber disc  48  is interposed between the end plate  47  and the front plate washer  49  and a rear plate washer  50  is slidably disposed inside the bursting head housing  43   a  and is attached to the extending end of the pull rod  40  (or the pull cable), as the case may require. A front spring  51  is interposed between the rear plate washer  50  and the front plate washer  49  and a spring stop  53   a  is typically secured to the rear plate washer  50  and extends inside the coils of the front spring  51 , to limit the tension applied to the front spring  51  and thus extend the life of the front spring  51 , as the free end of the spring stop  53   a  contacts the front plate washer  49 , upon extreme tensioning of the front spring  51 . 
   As further illustrated in  FIG. 13 , a rear spring  51   a  is positioned in the interior of the bursting and stored energy head housing  43   a , rearwardly of the front spring  51  and is maintained in this position by a rear spring washer  52 , seated on a rear spring rod  51   b  and maintained in position by a nut  42 . The opposite end of the rear spring rod  51   b  is secured to a hammer  41  by means of a hammer pin  41   a , and a rear spring seat  53  receives the opposite end of the rear spring  51   a  from the rear spring washer  52 . A tapered hammer seat  42   a  is shaped in the bursting head housing  43   a  rearwardly of the rear spring seat  53  and corresponds in shape to the tapered end of the hammer  41 , as further illustrated in  FIG. 13 . 
   In operation, and referring again to the drawings, the tandem apparatus  1  is used to pull a bursting and stored energy head  43  through a pipe  83  and break the pipe  83  into pipe fragments  83   a  using a pull rod  40  or a pull cable  40   a , as follows. The pull rod  40  or the pull cable  40   a  is extended through the rod or cable openings  29  of the aligned gripping elements  25 , as illustrated in  FIGS. 1–3  and  12  of the drawings, after extension through the rod or cable openings  4   a  provided in the end frame members  40 , as further illustrated in  FIG. 1 . One end of the pull rod  4  is attached to a bursting and stored energy head  43 , as illustrated in phantom in  FIG. 1  and in  FIG. 13 . In a preferred embodiment of the invention, the pull rod  40  is secured to the bursting and stored energy head  43  illustrated in  FIG. 13  by projecting the pull rod  40  through the center opening located in the expander wedge  44 , and then through corresponding, aligned openings (not illustrated) provided in the end plate  47 , rubber disc  48 , and front plate washer  49 . The pull rod  40  is further extended through the interior of the front spring  51  and the spring stop  53   a  and finally through the rear plate washer  50 , where it is attached by a bolt or any suitable means as further illustrated in  FIG. 13 . Under circumstances where a cable (not illustrated) is used instead of the pull rod  40  for coupling to the bursting and energy head  43 , a segment of the pull rod  40  may be installed on the rear plate washer  50  in the manner described above and the cable attached to the extending end of the pull rod  40  by an I-bolt or other suitable means. When the pull rod  40  is extended through the aligned gripping elements  25  as illustrated in  FIG. 1  of the drawings, the pull rod  40  projects through the rod or cable openings  29  provided in the respective wedges  27  and through either the gripping element spring  35  illustrated in  FIG. 8 , or a corresponding opening (not illustrated) provided in the rubber washers  38 , as illustrated in  FIG. 12 . In each case, the teeth  27   b  of the wedges  27  in each of the gripping elements  25  are pressed against the pull rod  40  by operation of the bias in either the gripping element spring  35  illustrated in  FIG. 8 , or the rubber washers  38 , illustrated in  FIG. 12 . 
   The tandem apparatus  1  illustrated in  FIGS. 1–3  and  FIG. 7  is now ready for operation to pull the bursting and stored energy head  43  through the pipe  83  and locate the replacement pipe  82  in the place of the pipe  83 , as illustrated in  FIG. 13 . Accordingly, the tandem apparatus  1  is operated as heretofore described with respect to  FIGS. 5 ,  6  and  7  to incrementally force the pull rod  40  through the tandem apparatus  1  and pull the bursting and stored energy head  43  through the pipe  83  to break the pipe  83  and replace it with the replacement pipe  82 . 
   Referring again to  FIG. 13  of the drawings, as tension or force is applied to the pull rod  40 , the front spring  51  is compressed in the bursting and stored energy head  43 . Additional force applied to the pull rod  40  also compresses the rubber disc  48 , as the spring stop  53   a  contacts the front plate washer  99  that overlays the rubber disc  48 . This compression causes the rubber disc  48  to enlarge and seal the bursting head housing  43   a  against the intrusion of water and debris in the pipe  83 . While the front spring  51  is so compressed, the hammer  41  is operated to strike the hammer seat  42   a  in the bursting head housing  43   a , using the tension in the rear spring  51   a , which is also compressed as the hammer  41  is withdrawn from the hammer seat  42   a , for striking. Successive hammer strikes, coupled with the forward forces created by the tension in the front spring  51  and the rear spring  51   b , enhance the progress of the bursting and stored energy head  43  through the pipe  83 . 
   It will be appreciated from a consideration of  FIGS. 1–3  of the drawings that under circumstances where a pull rod  40  is used to operate the bursting and stored energy head  43 , the front driving members  11  and the rear driving members  56  can be operated intermittently and alternatively as described above, by engaging one respective set of hydraulic cylinders  12  at a time in the exertion of pressure on the pull rod  40 . In another mode, all hydraulic cylinders  12  can be operated simultaneously in a common pulling direction to exert even greater force on the pull rod  40 , when one of the gripping elements  25  is reversed in the corresponding housing mount  30 . In the latter case, under circumstances where the bursting and stored energy head  43  encounters an exceptionally resistant structure such as a concrete casement, timber, valve or the like, the tandem apparatus  1  can be manipulated to facilitate a common pulling of both the front rod driving members  11  and the rear rod driving members  56  together, with both of the gripping elements  25  engaging the pull rod  40  simultaneously to achieve this result. However, it is understood that while the strength and pulling force on the pull rod  40  is doubled in this configuration, the speed of advancement of the bursting and stored energy head  43  is only half as fast as the advancement in the intermittent and alternative sequence described above. 
   It will be further appreciated by a consideration of  FIGS. 1–3  of the drawings that under circumstances where the pull rod  40  is utilized in the tandem apparatus  1 , the operating end of the pull rod  40  can be attached to the rear of the bursting and stored energy head  43  in any suitable manner, to push the bursting and stored energy head  43  through the pipe  83 , instead of pulling it, as described above. Furthermore, while oppositely-disposed sets of the hydraulic cylinders  12  are preferred for operating the tandem apparatus, additional hydraulic cylinders  12  can be attached to the respective front yoke  84  and rear yoke  85  ( FIG. 1 ), as deemed necessary and convenient. Moreover, while a hydraulic system is preferred as described above, in some applications a pneumatic system may be used, wherein the fluid-operated cylinders are typically operated by air pressure. 
   Accordingly, while the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications may be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.