Abstract:
A thrust apparatus for a rod string. The apparatus has a stationary frame, a thrust frame with a rod gripper, two hydraulic cylinders and two rams in fluid communication with the hydraulic cylinders. During low-load operations, the hydraulic cylinders act alone, providing the load to the grippers to pull or push the rod string. When higher loads are required, a check valve is activated, allowing fluid from the hydraulic cylinders to activate the rams. The rams provide additional force to the grippers, and may be activated without mechanical or significant hydraulic changes to the apparatus.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of provisional patent application Ser. No. 61/779,474, filed on Mar. 13, 2013, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The present invention relates generally to a hydraulically actuated pipe-bursting apparatus. 
     BACKGROUND 
     Threaded pipe or rod strings are used in horizontal installations for trenchless technology applications, particularly pipe bursting. High tensile loads are applied to pipe strings which pull bursting tooling through existing pipelines to facilitate replacement with a new product pipe. During push-out, the process of assembling the rod string from individual rods and pushing the assembled string through an existing host pipe takes a modest amount of thrust. During pullback, the portion of the process wherein the pipe is cracked and the surrounding soil is expanded, the load will be higher than during push-out. Variation in job size, host pipe material and adjacent soils all affect the maximum tensile load applied to the rod string. 
     To produce the tensile and thrust loads on the rod string, multiple hydraulic cylinders are often used as they provide an efficient means for producing large loads. These cylinders are part of a downhole device used to thrust, pull, assemble and disassemble said rod string. Further, these cylinders are actuated by hydraulics delivered by a hydraulic pump, most often turned by a gasoline or diesel engine. 
     SUMMARY 
     The present invention is directed to an apparatus for pulling and pushing a rod string. The apparatus comprises a stationary frame, a thrust frame, a hydraulic cylinder, and a ram. The thrust frame comprises a gripper engageable with the rod string. The hydraulic cylinder comprises an extendable rod attached at a first end to the thrust frame and at a second end to the stationary frame. The hydraulic cylinder provides extension force between the thrust frame and the stationary frame. The ram is attached at a first end to the thrust frame and is not attached to the stationary frame. The ram comprises an extendable ram rod at a second end. The ram is in fluid communication with the hydraulic cylinder in a first condition is not in fluid communication with the hydraulic cylinder in a second condition. The extendable ram rod provides extension force between the thrust frame and the stationary frame when in the first condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a pipe bursting operation. 
         FIG. 2  is a perspective view of a rod pushing/pulling machine incorporating hydraulic thrust cylinders and hydraulic rams. 
         FIG. 3  is a perspective view of the primary thrusting/pulling mechanism on a pipe bursting machine with the cylinders and rams extended. 
         FIG. 4  is a partial schematic and a partial section view of thrusting rams and cylinders. 
     
    
    
     DESCRIPTION 
       FIG. 1  shows a rod pushing/pulling machine generally referred to herein as a thrust unit  10  intended for pipe bursting. The thrust unit  10  is connected to a rod string  12  for pushing into an existing pipe  14  and pulling back a pipe splitter  16  and a new pipe  18 . The rod string  12  may be threaded, or may be hooked together from rod sections by turning or fitting pipe sections together. One skilled in the art will appreciate that the process of pushing the rod  12  into the existing pipe  14  will require less thrust than pulling back the splitter  16  and new pipe  18  for pipe bursting purposes. 
     With reference now to  FIG. 2 , a detailed view of the thrust unit  10  is shown with the rod string  12  removed for clarity. The thrust unit  10  comprises a rail  26 , a thrust frame  28 , a gripper  30 , two cylinders  32 , two rams  34 , a rod spinner  35  and a stationary frame  36 . The thrust frame  28  is movable along the rail  26  relative to the stationary frame  36 . The thrust frame  28  supports the gripper  30 , the two cylinders  32 , two rams  34  and rod spinner  35 . As shown, the thrust frame  28  comprises wheels  38  for interaction with the rail  26 . One of ordinary skill will appreciate that rack-and-pinion, pulley, or other systems are appropriate for movement of the thrust frame  28  relative to the stationary frame  36 . Further, the thrust unit  10  may be operable with different numbers of cylinders  32  and rams  34 . Two cylinders  32  and rams  34  are chosen for convenience in the figures and are not limiting on this invention. 
     The gripper  30  may comprise collets, jaws, or any other gripping mechanism suitable for producing gripping forces for pulling and pushing the rod string. As shown, the gripper  30  comprises a slip bowl. The gripper  30  travels toward and away from the stationary frame  36  as the thrust frame  28  moves along the rail  26 . The cylinders  32  are connected on a first end to the gripper  30  and on a second end to the stationary frame  36 . Each cylinder  32  comprises a cylinder rod  40 . The cylinder rods  40  are movable between a retracted and extended position in response to flow of hydraulic fluid to and from the cylinders  32 . As shown, cylinder rods  40  of the cylinders  32  are in the extended position. The cylinders  32  expand and retract to increase or decrease the distance between the stationary frame  36  and the thrust frame  28 , causing the grippers  30  to push out or pull back the rod string. As shown, the cylinders  32  are diagonally disposed about the gripper  30  and therefore the rod string. 
     With continued reference to  FIG. 2 , the rams  34  provide additional pull back load when the thrust of cylinders  32  alone is insufficient. The rams  34  comprise a contact surface or thrust nose  42  for contacting the stationary frame  36 . As shown, the thrust nose  42  is a rounded nose, though a flat end or other configuration may be used. The rams  34  are hydraulically actuated and mechanically retracted cylinders moveable between a retracted and extended position in response to the flow of hydraulic fluid. The rams  34  are attached at a first end to the thrust frame  28  but not attached to the stationary frame  36 . 
     The rams  34  are further adjustable between an activated and inactive condition. When in the activated condition, the rams  34  will extend and retract in concert with the cylinders  32 . When extended, the thrust nose  42  of the rams  34  will contact the stationary frame  36  to provide hydraulic thrust to the grippers  30 , additive of that provided by the cylinders  32 . When in the inactive condition, the rams  34  do not extend and retract. One of ordinary skill will appreciate that it is desirable to have the cylinder rod  40  of the cylinders  32  and the thrust nose  42  of the rams  34  in the direction of the existing pipe  14  ( FIG. 1 ) so that “pulling” forces on the rod string  12  ( FIG. 1 ) receive the force associated with expanding the cylinders and rams. 
     The rod spinner  35  threads on or off sections of the rod string  12  ( FIG. 1 ) to make up or break out the rod string ( FIG. 1 ) during pushing or pulling operations. The rod spinner  35  may alternatively connect sections of the rod string without threading, if unthreaded sections are utilized. A rod support frame  43  travels with the thrust frame  28  and maintains alignment between a rod section about to be added or a newly removed rod section. 
     The stationary frame  36  is a stationary reaction plate to allow the extension of the cylinders  32  to cause the thrust frame  28  to pull or push the rod string. The stationary frame  28  comprises a central aperture  44  and jacks  46 . The rod string  12  ( FIG. 1 ) travels through the central aperture and through the grippers  30  of the thrust frame  28 . Jacks  46  may be utilized to stabilize the stationary frame  36  to the ground such that the operation of the thrust unit  10  does not cause excessive movement in the stationary frame. 
     With reference now to  FIG. 3 , the thrust unit  10  is shown without the stationary frame  36  and track rail  26 . The cylinders  32  comprise the cylinder rods  40 , a cylinder body  48 , a rod boss  50 , and hydraulic fluid outlet port  52 . The rod boss  50  comprises a stationary frame connection  54 , a retraction port  56 , and an extension port  58 . The stationary frame connection  54 , as shown, is a threaded connection between the cylinder rod  40  of the cylinder  32  and the stationary frame  36  ( FIG. 2 ). Other connections between the rod boss  50  and the reaction plate are known in the art and anticipated alternatives thereof. The retraction port  56  provides a location for inserting hydraulic fluid into the cylinders  32  such that the cylinder rods  40  are forced to retract into the cylinder body  48 . The extension port  58  provides a location for inserting hydraulic fluid into the cylinders  32  such that the cylinder rods are forced to extract from the cylinder body  48 . The hydraulic fluid outlet port  52  delivers pressurized hydraulic fluid from the cylinder body  48  of the hydraulic cylinders  32  to the rams  34 . 
     The rams  34  comprise an inlet port  60 , a recess  62 , and a ram rod  64 . As shown in  FIG. 3 , the rams  34  are in the activated condition. As shown, the ram rod  64  is fully extended such that the thrust nose  42  contacts the reaction plate  34  ( FIG. 2 ). Inlet port  60  communicates with recess  62  to create a cavity for a pilot operated check valve (not shown) which permits the rams  34  to be toggled between the activated condition and the inactive condition at the direction of an operator. 
     In operation, as shown in  FIG. 3 , hydraulic fluid has entered the extension port  58  causing the rod  40  to extend from the cylinder body  48 . Fluid leaves the cylinder  32  via hydraulic fluid outlet port  52  and enters the rams  34  through inlet port  60 . Because the rams  34  are extended, it is apparent that the pilot operated check valve within the recess  62  is open, allowing the ram rod  64  to extend. As all hydraulic components are in actuation, maximum load is achieved, though the cost of full load is that the thrust unit  10  may operate at lower extension speed than if just the two cylinders  32  are actuated alone. The rams  34  may be placed in the inactive condition by closing the check valve within the recess  62  causing fluid to bypass the rams. Such a condition as shown in  FIG. 2 . 
     With continued reference to  FIG. 3 , ram rods  64  retract when hydraulic fluid is provided to the retraction port  56  of the hydraulic cylinders  32 . Fluid provided to the retraction port  56  causes the rod  40  to retract into the cylinder body  48 , forcing the thrust frame  28  and stationary frame  36  together. The stationary frame  36  ( FIG. 2 ) contacts the contact surface  42  of the ram rods  64 , causing the rams  34  to mechanically retract and hydraulic fluid to leave the rams  34  through the inlet port  60 . 
     With reference to  FIG. 4 , the cylinders  32  and rams  34  are shown in cross-section with a diagrammatic representation of a hydraulic control system  100 . Extension port  58  communicates through piston passage  102  with piston volume  104 . Retraction port  56  communicates through rod passage  106  with rod volume  108 . The cylinder body  48  is attached to the rod  40  of the cylinders  32  at a gland  110 . When hydraulic fluid is provided at retraction port  56 , the volume of the rod volume  108  expands, causing the rod  40  to retract. Likewise, when hydraulic fluid is provided at extension port  58 , the volume of the piston volume  104  increases, causing the rod  40  to extend. Pressure is provided to the gland  110 , which comprises various elastic seals to facilitate pressurization of the hydraulic cylinder  32 . 
     The hydraulic control system  100  comprises a pump  112 , a fluid supply system  114 , at least one hydraulic fluid tank  116  and a pilot valve system  118 . The pump  112  pressurizes hydraulic fluid in the tank  116  such that it is forced into the hydraulic control system  100  for operating the thrust tool  10 . The fluid supply system comprises a first hose  120 , a second hose  122 , and a cylinder control valve  124 . The first hose  120  provides fluid to the retraction port  56 . The second hose  122  provides fluid to the extension port  58 . The cylinder control valve toggles between providing pressurized fluid to the hoses  120 ,  122  so that expansion and retraction of the cylinders  32  may be alternated. 
     The pilot valve system  118  comprises a check valve  130 , a fluid pilot hose  132 , and a fluid valve  134 . Hydraulic fluid outlet port  52  connects via fluid hoses to the check valve  120 . The check valve  130  may be integrally located within the ram  34  or located outside the rain as shown in  FIG. 4 . Pilot pressure to produce an open check valve  130  condition and therefore an activated ram  34  condition is provided through the fluid pilot hose  132 . Fluid valve  134  controls pilot pressure within the check valve  130  such that the rams  34  may be toggled between an inactive and an activated condition. When in the activated position, hydraulic fluid will enter the ram through inlet port  60 , causing extension of the ram rod  64 , and will exit the ram through the inlet port upon retraction of the cylinders  32 . When in the inactive position, hydraulic fluid will not enter the ram  34 . However, when in the inactive position, check valve  130  will allow hydraulic fluid to pass out of the rams  34  into the hydraulic cylinder  32  when the rams are mechanically retracted. Fluid valve  134  may be manually or electrically manipulated by an operator to place the rams  34  in the activated or the inactive condition as desired for operation of the thrust unit  10 . Additionally, fluid valve  134  may be manipulated by signals from a load sensor (not shown) that indicates that less thrust is acceptable, or that more thrust is required for operation of the thrust unit  10 . 
     Various modifications can be made in the design and operation of the present invention without departing from the spirit thereof. Thus, while the principle preferred construction and modes of operation of the invention have been explained in what is now considered to represent its best embodiments, which have been illustrated and described, it should be understood that the invention may be practiced otherwise than as specifically illustrated and described.