EP1809853A2

EP1809853A2 - Underground piercing tool

Info

Publication number: EP1809853A2
Application number: EP05816992A
Authority: EP
Inventors: Duane Preston; Michael Grabnic; Dan Marsalek
Original assignee: Allied Construction Products LLC
Current assignee: Allied Construction Products LLC
Priority date: 2004-10-25
Filing date: 2005-10-20
Publication date: 2007-07-25
Also published as: WO2006047386A3; CA2585264A1; WO2006047386A2

Abstract

A pneumatically operated underground piercing tool 10 that includes an elongate cylindrical body (12) carrying an anvil (14) at one end and and a striker (16) slidably received within a chamber (25) defined by the body (12) and captured therein by an end cap (20). A valve assembly (22) controls the communication of pressurized air to and from the body (12) and is operator adjustable in order to produce forward or rearward movement of the piercing tool (10).

Description

UNDERGROUND PIERCING TOOL

Technical Field

The present invention relates generally to underground boring and, in particular, to an improved fluid pressure operated piercing tool.

Background Art

Pneumatically operated, underground piercing tools are commonly used to install wire, conduit and tubing under a roadway, sidewalk, etc. The use of these devices reduces the need for excavating or trenching and, hence, provide a cost effective method for installing utility lines, cable, etc. in developed areas. This type of tool eliminates the need for excavating through hard landscape items that obstruct the path of the line or conduit being installed. An example of this type of piercing tool is fully disclosed in U.S. Patent No. 4,662,457 which is hereby incorporated by reference. As fully explained in that patent, a striker mechanism which is operated by pressurized air, either repeatedly impacts an anvil mounted at the nose of the tool in order to move the tool forwardry, or repeatedly impacts an abutment located at the rear of the tool in order to move the piercing tool rearwardly, i.e., to withdraw the tool from the bore hole. U.S. Patent Nos. 3,865,200 and 5,465,797 illustrate other examples of piercing tools that have other types of striking elements i.e. percussion tips located at a forward end of the tool.

The piercing tool disclosed in the '457 patent has enjoyed commercial success. However, it has become desirable to improve the reliability and life of these types of tools, and to reduce and simplify maintenance. In the type of tool to which this invention pertains, the various components that make up the tool assembly are connected together using threaded connections. The threaded connections facilitate both assembly during the manufacture of the tool and facilitate disassembly when the tool requires maintenance. It has been found, however, that these threaded connections can be a source of failαre during operation of the tool. These threaded connections experience substantial impact loads as the internal striker repeatedly strikes either the anvil or the rear abutment. These failures can be further precipitated by operating the tool at higher than recommeαded air pressures and/or operating the tool outside its intended parameters. It is, therefore, desirable to provide a tool of this type that can be manufactured at reduced cost, but with improved reliability while at the same time facilitating Its maintenance and repair.

Disclosure of Invention

The present invention provides a new and improved underground piercing tool assembly that includes strengthened component interconnections while facilitating disassembly of the tool in order to perform maintenance and repair.

In the preferred and illustrated embodiment, a fluid pressure operated underground piercing tool is disclosed that includes an elongate cylindrical body that carries an anvil at one end. A striker is slidably received in a chamber defined by the cylindrical body. An end cap is threadedly received by another end of the body, such that the end cap captures the striker within the body chamber. A valve assembly for controlling the communication of pressurized fluid, i.e., pressurized air, to the body is provided that is operator adjustable in order to produce forward or rearward movement of the underground piercing tool. In accordance with the invention, the threaded engagement between the cylindrical body and the end cap is of a tapered thread configuration. In a more preferred embodiment, the threaded engagement is provided by tapered buttress threads formed on the cylindrical body and end cap.

In a more preferred embodiment, a female tapered thread is formed on the other end of the cylindrical body whereas a complementally configured male tapered, thread is formed on the end cap.

According to a feature of the invention, the striker may define a plurality of balancing grooves which aid in the uniform distribution of pressurized fluid, i. e., air around the striker. According to another feature of the invention, an end wall of the striker may define at least one recess which inhibits pressurized fluid from being trapped between the striker and the end cap when the striker is reciprocating within the body.

According to another feature of the invention, the striker defines at least one radial port that is oblong or slot-like in shape. In the preferred configuration, a long dimension of the port is parallel to an axis or a centerline of the striker. With this configuration, a strengthened region of the striker where the port is defined is provided without sacrificing port area.

According to another feature of the invention, the piercing tool may include a tail adaptor that is coupled to the end cap using tapered thread configurations formed on the end cap and tail adaptor. According to still another feature of the invention, an exhaust bushing which supports the valve assembly in its operative position is received by the end cap and secured in its operative position by the tail adaptor. In accordance with this feature of the invention, the thread configurations formed on the tail adaptor end cap are complementally formed tapered buttress threads.

Additional features of the invention will become apparent and a fuller understanding obtained by reading the following detailed description made in connection with the accompanying drawings.

Brief Description of Drawings

Figure 1 is an exploded view of a piercing tool constructed in accordance with the preferred embodiment of the invention;

Figure IA is an exploded view of a valve assembly forming part of the tool shown in Figure 1,

Figure 2 is a sectional view of the piercing tool shown in Figure 1;

Figure 3 is an enlarged, fragmentary sectional view of the piercing tool shown in Figure 2;

Figure 4 is another fragmentary, sectional view of the piercing tool shown in Figure 2 with certain components shown in alternate positions;

Figure 5 is an enlarged sectional view of a portion of the piercing tool;

Figure 6 is a sectional view of an end cap forming part of trie piercing tool shown in Figure 1 ;

Figure 7 is an enlarged fragmentary, sectional view of the end cap shown in Figure 6; Figure 8 is a sectional view of a tail adaptor forming part of the piercing tool;;

Figure 9 is an elevational view of the tail adaptor shown in Figure S ;

Figures 1 OA-I OC illustrate the various operating positions of a detent mechanism forming part of the valve assembly shown in Figure IA;

Figure 11 is a fragmentary, sectional view of a spherical joint forming part of the present invention; and,

Figure 12 is a perspective view of a guide member forming part of the present invention.

Best Mode for Carrying Out the Invention

Figure 1 is an exploded view of an underground piercing tool 10 constructed in accordance with a preferred embodiment of the invention. The piercing tool 10 includes an elongate, cylindrically shaped, hollow body 12 having a tapered nose 12 a. An anvil 14 is pressed into the nose 12a of the body 12 using known pressing methods. When pressed in position, a portion of the anvil 14 extends forwardly of the nose 12a.

A striker 16 is reciprocally movable within the body 12 and is captured within the body 12 by an end cap 20 having an externally threaded segment 20a that is threadedly received by an internally threaded body section 12b. The threaded segment 20a is preferably tapered as best seen in Figure 7. In operation, and as is conventional, the striker 16 either repeatedly strikes the anvil 14 in order to move the piercing tool 10 forward or repeatedly strikes the end cap 20 to move the piercing tool 10 in a reverse direction.

A valve assembly 22 including a control spool 22a is used to control the direction of movement of the piercing tool 10. When assembled, the spool 22a extends into and is received by a bore 32 defined by the striker 16. Referring also to Figures 2 and 3, the valve assembly 22 carries a bushing 24 at its rear end that includes a plurality of air flow passages 24a (shown best in Figure 3). As is conventional, movement in the striker 16 is produced by the application of air pressure, hi particular and as will be explained, the valve assembly 22 is connected a supply hose or conduit 26 shown in Figures lOA-C. The supply hose 26 delivers air under pressure from an air pressure source (not shown) to the valve assembly 22. Ultimately the pressurized air is communicated to a striker pressure chamber or cavity 25 and elsewhere and depending on the mode of operation, causes the striker 16 to move the piercing tool forward by repeatedly strilcing the anvil 14 or producing reverse movement in the piercing tool 10 by repeatedly striking the end cap 20.

According to a feature of the invention, the striker includes a plurality of balancing grooves 27. The grooves aid in the uniform distribution of air around the striker 16 and it is believed will tend to center the striker 16 within the body 12, i.e. maintain a more uniform radial clearance between the striker 16 and the body 12. In addition, the grooves 27 tend to more uniformly distribute lubrication around the striker. In general, lubrication, i.e., oil is entrained in the air supply and is delivered along with the air to the boring tool.

According to another feature of the invention, a pair of arcuate recesses 29 are formed on a right end "wall (as viewed in Figure 1) of the striker 16. The recesses 29 prevent air from being trapped between the striker 16 and the end cap 20 as the striker reciprocates within the tool body 12. Without these recesses 29, any trapped air would hinder movement of ttie striker 16 and reduce performance of the tool.

As will be explained, the mode of operation for the piercing tool, i.e., whether it is moving forwardly or rearwardly is determined by the positioning of the valve spool 22a within the body 12. The right end (as viewed if Figure 1) of the valve assembly 22 is secured within the end cap 20 by a tail adaptor 28. In particular, the bushing 24 is suitably secured to the right end of the valve assembly 22. As will be detailed below, the bushing 24 is captured, between the end cap 20 and the tail adaptor 28 which includes an externally threaded segment 28a that is threadedly received by an internally threaded segment 20b defined h>y the end cap 20. The valve assembly 22 includes a. detent mechanism, indicated generally by the reference character 30, which determines the distance to which the spool 22a extends into the tool body 12 and, hence, the operational mode (i.e., forward or reverse) of the piercing tool 10. The overall operation of a piercing tool of the type disclosed in Figure 1, is fully explained in U.S. Patent No. 4,662,457 which is hereby incorporated by reference. Referring to Figures 2 and 3, the longitudinal position of the valve spool 22a, within the tool body 12, determines the direction of movement for the piercing tool 10. As seen best in Figure 3, the spool 22a is slidably received within the blind bore 32 defined by the striker 16. The pressure chamber 25 is defined by the blind end of the bore 32 and an end face 37 of the control spool 22a.

As seen best in Figure 3, a rear portion of the striker 16 includes a larger diameter portion 16b near its right end (as viewed in Figure 3) that sealingly engages a cylindrical bore 34 defined by the body 12. The diameter of the striker portion 1 6c to the left of the sealing region 16b has a reduced diameter and defines a gap G between the outside of the striker portion 16c and the inside bore 34 of the body 12. The gap G forms a passage which enables air to flow around the striker 16 and into a reverse pressure chamber 36 defined by the left end (as viewed in Figure 2) of the body bore 34 and the forward end of the striker 16. As should be apparent, when air pressure is communicated to the chamber 36, it creates a force on the striker 16 urging it away from the anvil 14.

Referring, in particular, to Figure 3, the valve spool 22a is shown in a position in which it produces forward motion in the piercing tool, i.e., in a position at which it causes the striker 16 to repeatedly strike the anvil 14 to generate an impact force that tends to move the piercing tool towards the left as viewed in Figure 2. In the position shown in Figure 3, air pressure in the front chamber 36 is being exhausted via the gap G and a plurality of radial ports 38 formed in the striker 16. In particular, the air pressure in the chamber 36 travels through the radial ports 38 and is exhausted out the rear of the piercing tool via the exhaust passages 24a formed in the bushing 24.

In the preferred and illustrated embodiment, and referring also to Figure 1, two radial ports 38 are formed in the striker 16 and are oblong or slot-like in shape. In the illustrated construction, the long dimension of the slot is parallel to an axis or centerline 40 (shown in Figure 3). With this preferred construction, the cross sectional area of the port is increased over that of a port that is circular and this increased cross section area is obtained without weakening the striker wall in the vicinity of the ports as is the case with strikers that utilize three or more circular ports that define a total port cross section that is equal to the port cross section defined by the elongate ports 38 of trie present invention. It was found in the prior art that the port area on the striker is susceptible to failure, since the material removed to form the ports weakens the wall of the striker in the vicinity of the ports.

During tool operation, air under pressure is at all times communicated to the chamber 25 via a central passage 39 defined in the valve assembly 22 (shown in Figure 4). In the preferred embodiment, the passage is coextensive with trie centerline 40 of the valve assembly 22. Air communicated to the chamber 25 urges the striker 16 towards the left as view in Figure 3 i.e., towards the anvil 14. Ultimately, a front surface 16d of the striker 16 strikes a base surface 14a of the anvil 14 with a significant impact force which urges the overall piercing tool 10 towards the left as viewed in Figure 2. During leftward movement of the striker 16, the radial ports travel along the outer surface of the valve spool 22a.

With the valve spool 22a in the position shown in Figure 3, as the striker 16 impacts (or just before the striker impacts the anvil 14), the radial ports 38 move beyond the front end face 37 of the control spool 22a and, hence, communicate the pressure chamber 25 with the gap G. In this position, air pressure in the chamber 25 is communicated to the chamber 36 thus creating a force on the striker 16 in opposition to the force created by the air pressure in the chamber 25. The cavity/bore 32 is sized such that an internal effective pressure area defined by the chamber 25 is less than the effective pressure area defined by the front end of the striker 16 so that a net reversing force is created on the striker 16 tending to move the striker rearwardly, i.e., towards the right as view in Figure 3.

By the proper positioning of the control spool 22a and the radial ports 38, the net reversing force is generated on the stiiker just before or just after the striker 16 strikes the anvil 14. The pressure in the front chamber 36 causes the striker 16 to move rearwardly until the radial ports 38 move past a rear edge 42 of the spool 22a (this position is shown in Figure 3) so that the pressurized air in the front chamber 36 can be exhausted through the bushing 24, thus depressurizing the front chamber 36 and causing the striker 16 to reverse direction due to the pressure in the chamber 25 which is now substantially unopposed by a reduced pressure in the front chamber 36. As should ^"be apparent, with the valve spool 22a in the position shown, a reciprocating motion will be produced in the striker 16 "which will cause the striker to repeatedly strike the anvil 14 in order to move the tool in the forward direction.

To produce reverse motion in the piercing tool 10, the control spool 22a is moved rightwardly as viewed in Figure 3 to the position shown in Figure 4 In effect, by moving the control spool 22a rightwardly, the position of the striker 16 at which the radial ports 38 are exposed, changes. With the valve spool 22a in the position shown in Figure 4, the radial ports 38 move beyond the rear edge 42 of the valve spool 22a just before an end face 44 the striker 16 strikes an end surface 46 defined by the end cap 20. Conversely, the radial ports 38 are moved beyond the front end face 37 of the valve spool 22a well before the front end face 16d of the striker 16 impacts the anvil 14. As a consequence, when the control piston or spool 22a is in the position shown in Figure 4, the striker 16 repeatedly impacts the end surface 46 of the end cap 20 in order to move the piercing tool 10 rearwardly, i.e., towards the right as viewed in Figure 4 (and does not strike the anvil 14).

Turning now to Figures 5- 7, features of the invention are shown in detail. In the preferred embodiment, the threaded engagement between the end cap 20 and the tool body is provided by a tapered buttress thread indicated by the reference character 50 and including an internal thread segment 50a machined into the body segment 12b and a mating external thread segment 50b machined into the end cap segment 20a. The thread 50 transfers the reverse, impacting force generated by the striker 16 (as it strikes the end surface 46), to the body 12. In particular, during reverse operation, a radial end face 44 of the striker 16 repeatedly strikes a radial end surface 46 defined by the end cap 20. This impact force is transferred to the body 12 via the buttress threads 50.

According to this feature of the invention, an end face 56 of the piercing tool body 12 abuttably engages a radial surface 58 defined by the end cap 20. With this construction, the impact forces are more uniformly distributed ajnd a positive stop is defined between the end cap 20 and the body 12 when the end cap is threaded into the body. More importantly, by using a tapered thread, balanced engagement sections indicated generally by the reference characters 60, 62 are defined greatly reducing stress risers that could cause failure in the connection. In addition, a counter recess 64 is defined around the end surface 46 of the end cap 20 to further control the direction of the impact forces exerted by the striker 16 on the end cap 20. Finally relieved sections 66, 68 defined by the threaded segment of the body 12, as well as relieve sections 70, 72 defined by the end cap 20 substantially reduce stress risers. The use of the disclosed tapered thread also facilitates assembly and disassembly of the tool. In the illustrated embodiment, a 12 pitch American National Standard 7deg./45deg. buttress thread is illustrated which has been found to provide good performance in this type of application. The illustrated thread has a taper in the range of 1.5 inches per foot. With the disclosed construction, the end cap to body engagement is provided by 19 threads, but due to the tapered configuration, it requires only 9 turns to assemble. This greatly facilitates maintenance of the piercing tool.

It should be noted that other tapers may also provide satisfactory results and are contemplated by the invention. It should also be noted that other non-buttress type thread profiles may also provide satisfactory results and are contemplated by the present invention. The invention should not be limited to the illustrated thread profile.

In the preferred embodiment and referring also to Figures 8 and 9, the tail adaptor 28 is held to the end cap 20 by a similar thread configuration. A_s seen in Figure 5, a tapered buttress thread indicated generally by the reference character 75 secures the tail adaptor 28 to the end cap 20. The tail adaptor includes an external thread 75a and the end cap 20 includes a mating internal thread 75b. In this preferred embodiment, the end cap 20 defines a radial end face 76 which abuttably engages a radial surface 78 defined by the adaptor 28. This engagement provides a positive stop between the end cap 20 and tail adaptor 28; there is not an interference type thread engagement as found in the prior art. The tail adaptor 28 includes a radial locating or clamping surface 80 which secures the exhaust bushing 24 and, hence, the valve assembly in its operative position. As seen best in Figures 5 and 6, the bushing 24 is received by the end cap 20 in a uniform diameter portion 82. One side of the bushing 24 abuts a radial locating surface 84 (seen best in Figure 7) defined by the end cap 20 and is secured in the illustrated position by the tail adaptor 28 which abuts the opposite side of the bushing 24 aaid clamps the bushing in position, between the end cap radial surface 84 and the clamping surface 80 defined by the tail adaptor 28. With the disclosed construction, maintenance of the bushing and/or valve assembly is greatly facilitated. The use of the buttress thread 75 provides a reliable engagement while allowing easy disassembly. Removal of the tail adaptor 28 allows the bushing 24 and associated valve assembly to be easily pulled from the piercing tool body 12 for maintenance or replacement.

According to another feature of the invention, curvilinear, tapered surfaces 94, 96 are provided by both the end cap 20 and tail adaptor 28, respectively for promoting smooth air flow to and through the bushing 24 and improving the flow characteristics of the air being exhausted by the tool, thus improving its efficiency.

The end cap 20 includes relieved sections 90, 92 (see Figures 5 and 6) on either side of the threaded segment 75b. Similarly, relieved areas 98, 1 00 are also formed on the tail adaptor 28 on either side of the threaded segment 75a in order to reduce stress risers. As seen best in Figures 6, 7 and 9, both the end cap 20 and the tail adaptor 28 include at least a pair of spaced apart flats 104, 106, respectively, that are engageable by a suitable tool such as a wrench. The flats 104, 106 facilitate the assembly and disassembly of the tool and in particular the installation and removal of the end cap 20 and tail adaptor 28.

An example of a detent mechanism 30 for adjusting the position of the valve spool 22a is fully illustrated and explained in U.S. Patent No. 4,662,457. The detent mechanism of the tool shown in Figures 1-4 is functionally similar to the mechanism shown in the '457 patent, but differs in details. Referring to Figures IA and Figures 10A- C, the detent mechanism 30 includes interlocking, relatively ro taxable finger and guide members 110, 112 which determine the distance between the control piston 22a and the bushing 24. In the illustrated embodiment, a biasing spring 48 urges the control spool 22a away from the bushing 24. When air pressure is not being supplied to the piercing tool 10, this biasing spring 48 moves the control spool 22a away from the bushing 24, i.e., to a maximum separation permitted by the detent mechanism 30 (the position shown in Figure 10A). When air pressure is applied to the piercing tool, the pressure in the chamber 25 exerts a force on the front face 37 of the control spool 22a moving it towards the bushing 24 until the finger and guide members 110, 112 of the detent mechanism 30 engage and prevent further rearward movement in the control spool 22a.

The finger and guide members define two different operating positions depending on the relative rotational positions of the finger member and the guide member (these positions are shown in Figure 1OB and 10C). In one relative position, the application of air pressure moves the control spool 22a to the position shown in Figure 3 whereas in another relative rotational position of the finger portions, the control spool 22a moves to the position shown in Figure 4.

The relative position of the finger and guide members 110, 112 is changed by depressurizing the piercing tool 10 to allow the biasing spring 48 to move the control spool 22a to its extreme outer position(i.e. to a position that is spaced further from the bushing 24, thus disengaging and separating the finger and guide members forming part of the detent mechanism 30 (Figure 10A). The conduit 26 is rotated in order to rotate the finger member 110 through a predetermined angle i. e. 120° witli respect to the guide member 112. The change in relative position of the finger and guide members changes the distance to which the control spool 22a is allowed to move towards the right (as viewed in Figure 3 and 4) when air pressure is restored.

Referring, in particular, to Figure IA, the valve assembly 22 includes a support shaft or valve stem 116 which defines a through passage 116a through which air under pressure is delivered from the conduit 26 (shown in Figures 1 OA-C) to the pressure chamber 25 (shown in Figure 3). In the illustrated embodiment, the right end of the valve stem 116 (as viewed in Figure IA) includes a threaded segment 116d and threadedly receives a fitting or conduit adapter 22b. In the illustrated embodiment, the conduit 26 is connected to the stem 116 via the adapter 22b.

The control spool 22a is secured to the end of the support 116 via a spherical joint (indicated generally by the reference character 118) which includes a spherical shaped end 116b formed in the support shaft 116. Details of the spherical joint 118 are shown in Figure 11. In particular, the spherical end 116b of the stem 116 is inserted into an elastomeric socket member 119. The stem 116 with the socket member 119 installed, is then inserted into a bore 117 forming part of the spool 22a. Once inserted, an internal snap ring 115 is installed which is received by a snap ring groove 117a formed in the bore 117. The snap ring 115 maintains the socket 119 and engaged spherical end 116b in the spool 22a.

The finger member 1 10 is received by the support shaft and includes engagement structure to prevent relative rotation between the shaft 1 16 and the finger member 110. In the illustrated embodiment, the shaft or stem 116 (as seen best in Figure IA) includes a pair of flats 121 (only one flat is shown). Referring to Figure 12, the finger member 110 includes an internal bore 110a that includes complementally shaped flat surfaces 110b that are engageable with the flats 121 formed on the valve stem 116.

The guide member 112 includes an enlarged, uniform diameter knurled portion 122 which is sized to be tightly received by a through bore 124 formed in the bushing 24. The engagement between the enlarged, uniform diameter portion knurled 122 with the bore 124 inhibits relative rotation between these two components.

The guide member 112 defines a through bore 1Z6 which is sized to slidably receive a uniform diameter, tubular segment 116c of the support rod 116. Clearance is provided between the tubular segment 116c and the bore 126 to permit the support shaft 116 to both slide longitudinally and rotate with respect to the guide member 112. As seen best in Figure 1OA, the fitting/connector 22b secured to the right end of the valve stem 116 inhibits the valve stem 116 from being pulled through the guide member 112 to which the bushing 24 is mounted.

Referring now to Figures 10a- 10c, the finger member 110 includes a longitudinally extending tongue portion 130. The guide member 112 defines two longitudinally spaced slot segments 132, 134, either of which are sized to receive the tongue 130.

As indicated above, the conduit fitting 22b is secured to the outer end of the support shaft or stem 116. With this construction, rotation of the supply conduit 26 (which is attached to the fitting 22b) produces rotation in the finger member 110 relative to the guide member 112. Rotating the finger member 110 with respect to the guide member 112 will cause the tongue 130 of the finger rn ember to engage the slot 132 or the slot 134 depending on the direction of rotation and will thus determine whether the piercing tool 10 moves forward or backward.

Figure 1OA represents the positions the finger member 110 and the guide member 112 assume when the tool 10 is depressurized and the biasing spring 48 (not shown in Figures 10A- 10C) acts to urge the members 1 10, 1 12 apart. Figure 1OB shows the relationship between the finger portion 110 and the guide member 112 when the tool is pressurized and in a forward mode. In this mode, the valve spool 22a, as seen in Figure 3, is spaced further from the bushing 24 since the tongue 130 is engaging the slot 132.

In Figure 1OC, the tongue 130 is engaging the slot segment 134 which allows the control spool 22a to move to the position shown in Figure 4, when the tool 10 is pressurized. As is apparent when comparing Figure 1 OB and 1OC, the control spool 22a is substantially closer to the bushing 24 when the tongue 130 engages the slot segment 134. In this position, the tool 10 moves rearwardly. Although the invention has been described with a certain degree of particularity, it should be understood that those skilled in the art can make various changes to it without departing from the spirit or the scope of the invention as hereinafter claimed.

Claims

1. A fluid pressure operated underground piercing tool, comprising: a) an elongate cylindrical body having a striking element at one end; b) a striker slidably received within a chamber defined by said cylindrical body; c) an end cap threadedly engaged with another end of said body, said end cap capturing said striker within said body chamber; d) a valve assembly for controlling the communication of pressurized fluid to said body and for controlling the discharge of pressurized fluid from said body, said valve assembly being operator adjustable in order to produce forward or rearward movement of said underground piercing tool; and e) said threaded engagement between said cylindrical body and said end cap being of a tapered thread configuration.

2. The piercing tool of claim 1, wherein said threaded engagement between said cylindrical body and said end cap is a tapered buttress thread.

3. The piercing tool of claim 1, wherein a female tapered thread is formed on said other end of said cylindrical body and a complementally configured male tapered thread is formed on said end cap.

4. The piercing tool of claim 1, wherein the pressurized fluid for operating the tool is pressurized air.

5. A fluid pressure operated underground piercing tool, comprising: a) an elongate cylindrical body having a striking element at one end; b) a striker slidably received within a chamber defined by said cylindrical body; c) an end cap threadedly engaged with another end of said body, said end cap capturing said striker within said body chamber; d) a valve assembly for controlling the communication of pressurized fluid to said body and for controlling the discharge of pressurized fluid from said body, said valve assembly being operator adjustable in order to produce forward or rearward movement of said underground piercing tool; and e) said striker defining a plurality of balancing grooves which aid in the uniform distribution of pressurized fluid around the striker.

6. The piercing tool of claim 5, wherein an end wall of said striker defines at least one recess which inhibits pressurized fluid from being trapped between the striker and said end cap when said striker is reciprocating within the body.

7. The piercing tool of claim 1, wherein said striker defines at least one radial port that is oblong in shape and in which the long dimension of the port is parallel to an axis of, or centerline of the striker.

8. The piercing tool of claim 1, further comprising a tail adaptor coupled to said end cap, the coupling between said tail adaptor and said end cap being provided by the coengagement of tapered thread configurations formed on said end cap and tail adaptor.

9. The piercing tool of claim 8, further including an exhaust bushing for mounting said valve assembly in its operative position, said exhaust bushing being received by said end cap and secured in its operative position by said tail adaptor.

10. The piercing tool of claim 8, wherein said thread configurations formed on said tail adaptor and end cap are tapered buttress threads.

L 5

11. The piercing tool of claim. 5, wherein the pressurized fluid for operating the tool is pressurized air.

12. A pneumatically operated underground piercing tool, comprising: a) an elongate cylindrical body having striking element at one end; b) a striker slidably received within a chamber defined by said cylindrical body; c) an end cap threadedly engaged with another end of said body, said end cap capturing said striker within said body chamber; d) a valve assembly for controlling the communication of pressurized air to said body and for controlling the discharge of pressurized air from said body, said valve assembly being operator adjustable in order to produce forward or rearward movement of said underground piercing tool; and, e) said threaded engagement between said cylindrical body and said end cap being of a tapered buttress thread configuration; f) said striker defining a plurality of balancing grooves which aid in the uniform distribution of pressurized air around said striker.

13. The piercing tool of claim 1 wherein said striking element is an anvil.

14. The piercing tool of claim 5 wherein said striking element is an anvil.

15. A fluid pressure operated underground piercing tool, comprising: a) a cylindrical body; b) a striker slidably received within a chamber defined by said cylindrical body; c) a valve assembly for controlling the communication of pressurized fluid to said body and for controlling the discharge of pressurized fluid from said body, said valve assembly being operator adjustable in order to produce forward or rearward movement of said underground piercing tool; d) said valve assembly including a detent mechanism comprising first and second relatively rotatable members and a control spool secured to a,n end of a spool support forming part of said valve assembly; e) said spool support defining structure engageable by complementally formed structure on one of said members, such that said engagement permits relative slidiag movement between said spool support and said member while inhibiting relative rotation between said spool support and said member.

16. The piercing tool of claim 15 further including means for biasing said one member into engagement with said structure on said spool support.

17. The piercing tool of claim 16 wherein said means for biasing comprises a spring that urges said one member into operative engagement with said structure on said spool support.

18. The apparatus of claim 15 wherein said structure formed on said spool support comprises at least one flat formed on an outside surface of said spool support and said complementally formed structure comprises a flat defined by an internal bore formed in said one member.

19. The piercing tool of claim 15 wherein one of said members comprises a finger member and other of said members comprises a guide member.

20. The piercing tool of claim 15 wherein said structure formed on said spool support comprises a pair of flats and said structure formed on said one member comprises coinplemental flats formed on an inside bore defined by said one member.

21. The piercing tool of claim 15 wherein said valve support includes a spherical end held in an elastomeric socket which is received by a bore defined by said control spool and said socket held in said control spool bore by a retaining element, said spherical joint permitting angular movement in said valve spool to facilitate alignment of said valve spool with a spool receiving bore defined in said striker.

22. A fluid pressure operated underground piercing tool, comprising: a) an elongate cylindrical body having a striking element at one end; b) a striker slidably received within a chamber defined by said cylindrical body; c) a valve assembly for controlling the communication of pressurized fluid to said body and for controlling the discharge of pressurized fluid from, said body, said valve assembly including a valve spool, a valve spool support and a socket structure for coupling said valve spool to said valve spool support, said socket structure comprising: i) a spherical element formed on one end said of said spool support; ii) an elastomeric socket adapted to receive said spherical element; iii) a bore defined by said valve spool adapted to receive said socket; and, iv) a retaining element for maintaining said socket within said receiving bore defined by said spool.

23. The piercing tool of claim 22 wherein said retaining element comprises a snap ring, said coupling between said valve spool and said valve spool support permitting relative angular movement between said valve spool and said spool support.

24. The piercing tool of claim 1 , wherein said threaded engagement b etween said cylindrical body and said end cap is a buttress thread with a taper of substantially 1.5 inches per foot.

25. The piercing tool of claim 1 , wherein said threaded engagement b etween said cylindrical body and said end cap is a 12 pitch American National Standard 7deg./45deg. buttress thread.