US Classes175/21, Fluid passage to exterior of drive point173/91, Selective axial direction of impact173/1, PROCESSES173/200, Hammer head driven by pulsating fluid pressure29/428, Assembling or joining175/19BORING WITHOUT EARTH REMOVAL (I.E., COMPACTING EARTH FORMATION)
Attorney, Agent or Firm
International ClassesE21B 11/02
FIELD OF INVENTION
This invention relates to improved percussive tunnelling or "ram-boring" machines. It is particularly related to an improved reversible operation of such machines.
Trenchless technologies are all means for laying services carried by pipes or cables within underground boreholes or tunnels through the soil; as opposed to excavating trenches from the surface downwards by conventional digging means in which to lay them. Such traditional trenches thereafter have to be refilled and surface damage repaired.
This invention belongs to a sub-category of the various trenchless technologies; specifically percussive tunnelling or "ram-boring" machines, which are generically known within the industry as "moles". Moles are mostly used for the production of underground boreholes, by directly boring the required diameter hole through the earth using repeated impacts to drive and compress the soil in its path forwards and outwards. They achieve this ram-boring action by transferring momentum to a piercing head and outer body from an internal piston, which reciprocates axially within the cylindrical body of the machine. The reciprocating motion of the piston is usually driven, and momentum imparted thereto, by the complex through-flow of compressed air and the oscillating pressure differentials created around the piston thereby.
Boreholes are typically created for commercially useful purposes, including but not limited to the laying of pipes or cables carrying utilities such as water, gas, electricity, fibre-optics, communications and data services. Laying such services using moles provides a commercially and practically valuable ability without disrupting the surface of the ground and structures above. Services can be laid beneath buildings, roads and other structures without damage or disturbance thereto. For example, a busy road can function as normal while services are being concurrently laid beneath it.
There are many competing mole designs. The basic features of all modern moles comprise a conical piercing head, a cylindrical body, containing a longitudinally reciprocating piston of high mass, and internal anvils at the ends of the body, onto which this piston imparts momentum by impacting repetitively onto either the front or the rear anvil. The anvils are the features, which receive the momentum from the striker piston and transmit it to the head and body of the machine. A direction switching "reverse mechanism" governs the axial positioning of the control valve. This mechanism thereby effects changes in the direction of operation between forward and reverse modes. Moles are normally powered by compressed air, although it may be possible to use other fluids and or power sources. Of all the technical problems surmounted in the art direction switching or "reverse mechanisms" have probably posed the most intractable problems of all. The art discloses a series of advances over the last century, but each advance has in turn also tended to bring new technical problems to the fore.
Engineers have struggled for many years with the technical conundrum of designing reverse mechanisms, which are easy to operate, easy to maintain, and robust enough to withstand the extremely harsh pulsating, percussive impactions and underground operating conditions. Earlier designs such as disclosed in patent documents GB2134152 and U.S. Pat. No. 4,662,457 involve undesirable operations such as shutting off the compressed air supply before switching from forward to reverse. This permits the damaging ingress of water, sludge and particulate soil debris via the air exhaust ports and leads to accelerated wear and tear, and sometimes even to blockages and or jamming which may prevent the restart of reciprocation of the piston. Such faults force operators to either dig-up the mole or if this was impractical or uneconomic to abandon it where it is.
However, others such as EP0388627 and U.S. Pat. No. 5,086,848 solved this problem with reverse mechanisms capable of being switched from forward to reverse with the piston still reciprocating. This was achieved by shifting the stroke action of the live piston along axially inside the cylindrical body to impart momentum to the rear anvil of the machine with the compressed air supply still switched on. Therefore the reciprocating piston's action is not interrupted and therefore does not need to be restarted. Consequently, the incidence of harmful ingress of water, sludge and particulate soil debris and their damaging effects is greatly reduced. This approach introduced other problems. In particular such "air-on" reverse mechanisms as disclosed in patent documents EP0388627 and U.S. Pat. No. 5,086,848 have, over time been observed to have their own problematic durability and maintenance issues, which when their components fail can and do lead to an inability to change direction. In particular the use of a helical spring which is continually loaded so as to provide forward bias to assist switching from reverse into forward mode and simultaneously also loaded by torsion (or twisting), even when the machine is not in use is in this combination particularly wearing on the spring. So that it eventually causes the spring to become deformed permanently, by wear so as to either become ineffective or to break under load. Both kinds of failure can render it impossible to change the direction of operation, and consequently for the machine to become stuck in a feckless position of neutrality leaving the piston stroke somewhere in between its two modes of operation. Thereby giving rise to such moles becoming stuck underground, sometimes up-against an obstacle and unable to change direction and hence unable to be reversed back out. Consequently, either having to be dug out using traditional means or where this is not possible to be practically irrecoverable or abandoned deemed uneconomic to recover. In turn, even where such failing moles can be recovered, such mechanical failures necessitate repairs that require the extensive disassembly of the majority of the machine to remove and strip down the reverse mechanism. This is difficult to carry out in the field and is widely regarded as a specialist task; which is mostly carried out by mole manufacturers or their agents.
Patents EP388627 and U.S. Pat. No. 5,086,848 disclose an air-on reverse mechanism where the key role is played by a pre-loaded spring held in compression and torsion. The torsion of the spring acts to provide rotational bias on the control sleeve (also referred to as the valve, or control valve) and inter-engaging rotation and axial stops to lock the mechanism against axial loads into its forward and rearward positions of operation. The same spring also acts in compression longitudinally to bias the control sleeve to its forward operating position. However, careful analysis of these patents and machines manufactured according to EP388627 reveals that they are limited to and by the control sleeve being acted upon both axially and torsionally in conjunction with the guide tube having rotation stops for locking and unlocking it in the axial direction relative to the guide sleeve. EP388627 particularly defines a helical spring mounted in a torsional pre-stressed state to not rotate and therefore provide the torsion. It employs this non-rotatably held spring to provide both axial and torsional bias. That mechanism enables the operator to actuate it by turning the air hose against the torsional spring by approximately 90° (or a "quarter turn") to disengage its rotation stop(s) and axial locking, thereby allowing the air pressure on the control sleeve to push it axially rearwards to the reverse operating position stop. Whereupon the torsional loading of the spring urges the mechanism to turn back into an axial lock on to rotation stop(s) and to retain it there.
Another persistent technical problem arises where a mole encounters a partial obstruction between a relatively soft and hard or resilient object in its path. This can lead to the partial obstruction subjecting the passing mole to side loads. This sheer loading to the mole body can cause skewing and or tight spot(s) along the reciprocating stroke of the piston within the body, and in turn of the inner bore of the piston which reciprocates over and along the "control valve" (or as it is otherwise known within the art the "control sleeve"). This skewing can cause one or other or both of these features to be pressed so hard against the other as to increase the friction between them and thereby arrest or jam the piston stroke. U.S. Pat. No. 5,148,878 also identifies manufacturing irregularities as a source of similar jamming problems. It discloses the use of an elastic bush "advantageously arranged between the control sleeve (i.e. the control valve) and the guide tube". According to that invention, the control sleeve and the spring are also anchored non-rotatably to each other.
However, this approach in the art remains only a partial solution to this type of jamming problem. This is because the spring being constantly loaded with varying levels of torsion is constantly reacting thereto by leveraging a resulting force proportionate to its torsional load onto an off-centre radial feature on the supply tube at the rear of the control valve. Thereby producing an undesirable skewing force vector. This biases and deflects the axis of the control valve away from the axis of the bore of the piston, which reciprocates over the length of the valve, and within the main cylinder of the body of the machine. This unfortunate mechanical side effect produces increased friction on one side of the control sleeve and the internal bore of the striker piston. These problems are endemic to such axially and torsionally loaded spring biased reverse mechanism designs. Wear analysis of used control valves (or sleeves) and their mating piston bores typically reveals excessive wear to one side of the control valve (or sleeve), and increased wear within the piston bore, both of which reduce component and product service lifespan.
Further problems in the art arise from the tendency of moles to vibrate their mating components apart from each other, so that threaded joints will shake loose and unscrew during normal operation. Solutions to this problem have involved the addition of more complex bolting systems and or the use of glues to bind mating threaded sections. Thereby rendering the fixing to be semi-permanent and excessively resistant to disassembly, usually requiring return to the manufacturers or their agents for stripping down and maintenance involving specialist expertise, tools and heating to neutralise the bonding and or to burn-off the glue. The net result of which is to make even basic maintenance of such moles expensive and difficult.
OBJECTS OF THE INVENTION
To create a superior mole, capable of being reversed under power with a live piston stroke, with improved reliability and recoverability in cases of component failure and or where impassable obstacles are encountered.
To better ensure that in the event of mechanical failure of the helical spring means that the reverse mechanism "fails-safe" is still capable of being switched into its rearward reverse operating position, and can there be locked axially so as to be capable of being retained and operated in reverse mode to effect salvage.
To render the reversing mechanism itself to be easier and cheaper to disassemble, maintain and or repair; furthermore to reduce the need to do the same.
In particular an object of the invention is to achieve one or more of the above objects or to at least ameliorate the problems the prior art such as the endemic problems resulting from the use of concurrent axial and torsional loading of helical spring means internally within the control assembly and reverse mechanism. Thereby to assist in one or more of: (a) reducing the overall loads acting on the forward biasing longitudinal helical spring means; (b) eliminating torsional loading of the same; (c) reducing the incidence of shearing or skewing of the control valve relative to the axis of the machine; (d) reducing the incidence of jamming arising due to shearing or skewing force vectors within the machine (which would otherwise cause increased friction and or arrest of the piston stroke); (e) reducing rates of wear to (i) the helical spring means, (ii) the control valve, (iii) striker piston bore, (iv) striker piston rings, and (v) the cylinder of the machine body, thereby leading to improved service life for those components. All of which should contribute to reducing the cost to the operator or owner of the mole and thereby confer economic benefits, and help to increase use of this less disruptive and more environmentally friendly "trenchless" method of laying services underground.
SUMMARY OF THE INVENTION
In accordance with the invention, there is provided a reversible pneumatic underground percussive ram-boring machine of the type having a reciprocating striker piston within a cylindrical body. Wherein the striker piston imparts momentum, which determines and drives the direction of action of the machine at the end of its stroke to either the front or the rear internal anvil; and the striker piston stroke is controlled in so doing by the longitudinal position of a valve element within the device.
Wherein the longitudinal position of the valve element can be locked and unlocked axially and circumferentially by manual rotation of features on the air supply tube against rotary indexing location and spring means to create an elastically stressed state therein until the desired index points are reached and engaged. Whereupon the interacting members seat their mating features and the elastically stressed spring means returns to its natural and relatively unstressed state.
From operation in forward mode the direction of action of a machine can have a live or even a stalled piston stroke capable of being switched into reverse mode by rotation of the supply hose through a predetermined arc to unlock the control valve thereby making it free to traverse in the axial plane. Whereupon the valve element is capable of being biased by air pressure to traverse axially rearwards into its reverse operating position. Thereafter the valve element can be locked in position by further manual turning of the air supply hose and thereby to align and re-seat inter-engaging indexing features of the air supply tube and corresponding rotary indexing location and spring means. This is an air-on reverse mechanism enabling switching from forward to reverse with a live piston stroke.
From a static state with no active compressed air supply or alternatively with reduced air pressure or reduced air flow the machine can be switched from reverse back into forward mode by manual rotation of the supply hose through a predetermined arc to unlock the control valve thereby making it free to traverse in the axial plane. Whereupon the valve element is capable of being biased by helical spring means acting longitudinally to traverse axially forwards into its forward operating position. Thereafter the valve element can be locked in position by further manual turning of the air supply hose so as to re-seat inter-engaging indexing features of the air supply tube and corresponding rotary indexing location and spring means.
The inter-engaging indexing features of the air supply tube can comprise rotary indexing location and spring means in the form of an approximately circular flexing spring means, or an encapsulated spring means within an outer housing means or collar capable of providing a gripping or bite like clamping action onto the air supply tube. Having smoothly inter-engaging features with mating profiles on their interacting surfaces, such features corresponding with the rotary timing of axial locking means. So that modest manually applied rotary forces are sufficient to disengage the rotary indexing location and spring means and again create an elastically stressed state therein, until the desired index points are reached. Whereupon the interacting members seat their mating features and the elastically stressed spring means returns again to its natural and relatively unstressed state where this once more locks the mechanism into its alternate operating position.
According to the invention, this reverse mechanism can include an elongated control valve member, which facilitates and controls the flow in the incoming compressed air. Having one end with means for connecting to a pneumatic hose for supplying compressed air and manipulating said valve member; a surrounding striker piston and cylindrical outer body. Having at the front end a first connector for connection to a percussion impact head and at the other end the aforesaid connection means for connection to a compressed air supply. The assembly provides flow paths to facilitate the flow of compressed air therethrough. The aforesaid connecting air supply tube having at least part of an inter-engaging means for guiding and restricting the movement of said control valve within supporting and guide means to two longitudinally spaced locations. With an optional longitudinal compression means or helical spring means to bias the control valve towards a forward position of maximum extension within the body of the mole. An inter-engagement of the rotary indexing location and spring means with the air supply tube; whereby manual turning of the air supply hose through a predetermined arc thereby unlocks the control valve in the axial plane to facilitate longitudinal movement to permit shifting of the stroke of the striker piston therewith. Thereby to provide means for reversing the direction of the machine's ram-boring action.
From operation in forward direction, the reverse mechanism is capable of being actuated by manually turning the air supply hose (as described above). The flow of compressed air through the machine acts to create a pressure differential which in turn is utilised to drive the control valve's traverse longitudinally rearwards to its rearward setting, corresponding to the reverse mode of operation. This biasing action of the compressed air acting on the control valve is capable of being used to drive the control valve rearwards longitudinally and may be damped by the (optional) helical spring or longitudinally acting spring means as it traverses. The longitudinal position of the valve member can thus be shifted to provide for reversing the direction of the ram-boring action of the machine therein having a live piston stroke, which shifts therewith and without interruption of the compressed air supply therethrough.
The rotary indexing location and spring means can take the form of a "C" shaped circlip-like indexing, clamping and locking spring means resembling a circlip or collar; having one or more hump-like features protruding inwards from its inner profile. This engages with corresponding mating rotary indexing and locking grooves, recesses flats or similar features along the outer diameter of the air supply tube which runs through the centre along and around the axis of the machine, inside the rear housing assembly and anvil bore.
In another form, the rotary indexing location and spring means can be comprised of an annular structure having on its inner profile a captured protruding feature, such as a pin, cam or cylindrical roller bearing or ball bearing that is urged inwards by resilient spring means. This protrusion engages with and seats into corresponding rotary indexing and locking grooves, recesses flats or similar features along the outer circumference of the air supply tube, which runs through the centre along and around the axis of the machine inside the rear housing assembly and anvil bore.
Furthermore, the hump-like resilient protrusion may alternatively be located on the outer diameter of the air supply tube which runs through the centre and along the axis of the machine inside the rear housing assembly and anvil bore to engage locking grooves or recesses within the inner diameter of a circumferential element.
In the circlip-like version of the invention, the rotary indexing and locking grooves or other features correspond with the desired longitudinal and rotary traverses of one or more guide means. The same are usually comprised of one or more lugs, or followers, which run within one or more motion defining contoured slots or an arrangement of stops or alternate combinations of the features and functionalities thereof, correspondingly and cooperating between the air supply tube and the rear housing assembly and anvil bore.
It can be seen that these features are required to be interoperable each with the other but their configuration can be swapped so that they take male or female forms relative to their mating counterparts.
The mole is positively locked into its operating positions by the locating and clamping action of the circumferential rotary indexing location and spring means which, or parts of which, are elastically deformed when the air supply tube is rotated against the resilient protrusions thereon or alternatively indentations therein. This deforms within its elastic range to permit the rotation until engaging with the next corresponding features or groove(s). At this point, the stored kinetic energy in the flexing or compressing action of the circumferential spring or other elastic means acts to drive its hump-like protrusion(s) to seat into the corresponding mating groove(s) or other arrangement of equivalent features.
Furthermore, the circumferential rotary indexing location and spring means or other deformable elastic means is conveniently located at the rear of the machine within the conical rear housing. This is consequently provides for this key component to be capable of being easily and quickly replaced, either during routine maintenance or to effect emergency repair in the field. This does not require the reverse mechanism as a whole to be removed from the assembled machine nor for the same to be stripped down. Rather replacement of the circumferential rotary indexing location and spring means can be achieved in a labour saving manner requiring only removal of the rear conical housing to permit access in order to permit removal and replacement of the same.
It can be seen that the invention provides a superior air-on reversible mole that minimises constructional and vibration problems, reduces frictional wear, is free from the adverse integral non-longitudinal force vectors or skewing of the control valve, such as that which arises from torsional loading thereof in the prior art. Thereby more readily provides a more reliable and longer lasting air-on reverse mechanism for a pneumatic underground percussion-excavating device. It also provides easier maintenance, reduced operating costs and increased recoverability in cases of component failure or impassable obstructions.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention can be more readily understood an example comprising a specific preferred embodiment of the invention referred to herein as the "Reliable Rapid Reversible Mole" (or "RRRM") is described below by way of illustration only with reference to the drawings wherein:
FIG. 1 (A) provides a perspective view of an encapsulated RRRM in accordance with a specific preferred embodiment of the invention with its conical rear housing removed; (B) is a cross sectional view of the same more fully assembled and having its conical rear housing in place.
FIG. 2 is an exploded disengaged perspective view of the RRRM in its forward operating position and with its conical rear housing detached.
FIG. 3 is an exploded engaged perspective view of the RRRM in its engaged position with the conical rear housing attached and illustrating the locations of mating threaded sections in particular.
FIG. 4(A) is a perspective view of the rear of an assembled RRRM and (B) a cross sectional view including the rear piston chamber, the control valve, the ball joint between it and the air supply tube, the helical spring and guide means.
FIG. 5 is an enlarged view of the circumferential rotary indexing spring and locking or clamping means in their "C" shaped circlip-like form with mating features engaged with its corresponding counterparts on the outer surface of air supply tube.
DETAILED DESCRIPTION OF A SPECIFIC EMBODIMENT OF THE INVENTION
Referring to the drawings there is shown a RRRM comprised of a superior mole incorporating a superior air-on reverse mechanism; one specific embodiment of which is depicted in FIGS. 1 to 5 hereto.
As shown in the drawings, the mole includes an external cylinder (15) which at one end includes a connection to an air supply hose (10) that connects to an air supply tube (5) that fits within the cylinder (15) and connects at the other end to the control valve (16) by means of a rotatable ball joint as shown in FIG. 4 and fits within the reciprocating mass striker piston rear chamber (14) with bearings that allow for free sliding within the cylinder (15). A spring means (11) engages between the reciprocating the mass striker piston rear chamber (14) and the anvil (6). The conical rear housing (12) covers the connection of the anvil (6) to the air supply hose (10).
The control valve (16) governs the reciprocating stroke of the piston. A direction switching "reverse mechanism" governs the axial positioning of the control valve. This works by displacement of the stroke of the reciprocating piston between forward and rearward operating positions, so as to set it's impaction at either end of its stroke thereby imparting momentum to either the front or rear anvil, i.e. to forward or reverse ram-boring action. This mechanism thereby effects changes in the direction of operation between forward and reverse modes powered by the compressed air, although it may be possible to use other fluids and or power sources.
The benefits of the RRM in its various potential embodiments are that it is easier to maintain and to repair, less prone to reverse mechanism failures including both total and partial failures, and is less prone to accidental reversal and or dropping out of its mode of operation into a feckless or neutral state which is neither forward nor reverse.
These benefits of the invention are achieved in this preferred embodiment known as the RRRM by the use of a "C" shaped circlip-like rotary indexing and locking spring means ("the Circlip") (1). This has one or more hump-like features or tabs (2) protruding inwards, from its inner profile (3). This feature engages with corresponding rotary indexing and locking grooves or recesses (4) along the outer diameter of the air supply tube (5), which runs through the centre of the reverse mechanism assembly and along the axis of the machine inside the rear housing and anvil (6).
The rotary indexing and locking grooves (4) correspond to and cooperate with the guide and support means that define the longitudinal traverses and rotary timing of one or more lugs or followers (7) which run within a motion defining contoured slot (8) correspondingly and cooperating between the air supply tube and the rear housing and anvil bore (6). These key features are required to be interoperable each with the other but their configuration can be swapped so that they could take male or female forms relative to their mating counterparts.
The length of the contoured slot (i.e. the distance between points marked 9) determines the length of longitudinal travel of the control valve within the direction switching mechanism between its two operating positions. At the ends of the contoured slot are circular or rotary slots into which the lug(s) or follower(s) can be turned. The angular timing of the ends of the predefined radial arks about the axis of the machine of this turning motion corresponds with the points at which the hump-like feature or tab (2) locates, is biased into, seats and thereby interlocks with the locking grooves (4) on the air supply tube (5).
This configuration allows the mole to be positively locked into its operating positions by the clamping bite-like action of the circlip-like rotary indexing and spring means (1) which disengages when the air supply tube (5) is rotated against the hump-like feature or tab (2) thereon. Whereupon it deforms to open wider within its elastic range so as to permit the rotation wherein the hump-like feature or tab (2) allows outer diameter of the air supply tube (5) to slide around in contact with the hump-like feature (2) as it is rotated until the next corresponding groove(s) (4) are engaged with. At this point the stored energy in the flexing spring action of the Circlip acts to drive its mating hump-like feature or tab into the groove (4). The depth to which these features interact and the strength of the spring means is calculated to provide sufficient force to urge them to seat each other and to retain that operating position. However, they also have to permit turning of the air supply tube (5) with an appropriate amount of force for intentional direction switching by rotation against each other effected by the operator turning the air supply hose (10), which is attached to and drives the air supply tube (5).
The specific embodiment disclosed includes an optional spring means (11) for also urging the controller assembly back into its forward operating position as shown in FIG. 2. This spring acts only longitudinally in compression and is not critical to the ability to switch the machine into reverse mode, nor to the ability to lock the mole into reverse mode and thereby facilitate recovery of the mole. Whereas otherwise in the prior art where a similar helical spring also acts torsionally to retain forward or reverse modes, failure of such springs can render the mole irrecoverable, due to inability to reset, and or to retain operation of the machine in its reverse mode. This ability is essential to reverse backwards along and out of its borehole when confronted by an insurmountable obstacle.
As the helical spring means of the RRRM acts only longitudinally and is not at all torsionally loaded or stressed it consequently suffers from less wear and (all other things being equal) the RRRM spring should last longer before requiring replacement or failing in service.
Furthermore, the Circlip (1) is conveniently located at the rear of the machine within the conical rear housing (12). In FIGS. 2 and 5 it can be seen that the Circlip (1) is located on the outside of the assembled reverse mechanism at the rear (6) thereof. Thereby rendering it amenable to easy replacement in the event of its failure or during routine maintenance.
Due to the extreme percussive nature of their operation moles can and do vibrate their mating components apart from each other. To combat this tendency the current state of the art moles either use a positive bolted locking system, such as according to that disclosed by U.S. Pat. No. 5,025,868. Another option is a glue-based system on some or on all of the vibration critical points (13), at both the front and rear of the assembled machine.
This embodiment of the RRRM is also superior in terms of its novel elastically sprung interference fit based vibration proof locking system. Affording benefits of ease and simplicity comparable to those of the glued prior art during assembly; but without the associated difficulties during disassembly. Thereby providing for easier and cheaper repairs, maintenance and servicing.
This advance over the prior art being achieved by the incorporation of slots or other means for permitting insertion and accommodation of malleable, compressible and moderately resilient and elastic insert means. Thereby producing a vibration proof, locking interference fit thereof with the key mating screw-threaded joints. The same being comprised of one or more pieces of a material such as nylon but not limited thereto. The accommodating features and inserts being situated within at least one of any two threaded sections being joined. Therein being deformed permanently and elastically during the screwing together of the mating parts being joined and fixed thereby as illustrated in FIG. 3 hereto at some or all joining locations (13) of FIGS. 1, 2 and 3. Such deformation being comprised of a rough mix of the threads cutting mating threads into the inserts and also compressing them elastically, producing an elastically sprung interference fit between the threads and the deformed inserts. Thereby creating a high frictional co-efficient of a magnitude capable of locking the mating components sufficiently to enable the joining to resist the vibrations inherent in the ram-boring action of the machine. Yet also permitting their intentional disassembly without excessive difficulty.
Furthermore the RRRM provides superior resistance to adverse shear or side loading conditions, which can cause moles to jam, or suffer excessive wear, or both of them. Such conditions may arise when a mole is subjected to adverse skewing or loading from the side, and or due to the wear, which occurs within the reciprocating mass striker piston rear chamber (14) and the cylinder (15) or component irregularities howsoever arising. FIG. 4 depicts the invention in the form of the RRRM equipped with a ball and socket joint interposed as joining means between the forward end of the air supply tube (5) and the control valve (16). This ball and socket joint provides greater flexibility and self-centering for the inter-engaging cylinders of the machine. Thereby permitting them the freedom of movement to find their own optimal or "best fit" path as they reciprocate within and over each other. The ball and socket joint employed in the RRRM also provides modest damping characteristics derived from spring means resulting from the characteristics of the material of which it is made; this is a resilient polymer plastic or Nylon material. This increased flexibility and damping means provides reduced susceptibility to component fatigue resulting from axial loading shocks inherent in moles, reduced incidence of jamming and reduced wear during skewing and side load shear situations, and or provides greater tolerance of irregularities howsoever arising whether during manufacturing processes or through wear.
It should be understood that the above description of the RRRM is one which describes a specific preferred embodiment of the invention and is in fact reproduced from drawings of a fully functioning production mole. It is included here only by way of and for the purposes illustration. It is not to be construed as limiting or confining the scope of the invention thereto. Persons skilled in the art without any inventiveness would understand variants of this invention including but not limited to the ability to swap around some male and female features thereof and otherwise to transpose key integers into alternate forms or locations, while still conforming to the invention. Consequently, all such variants are intended to be included within the scope of this invention.