WO2006008723A2

WO2006008723A2 - A down-the-hole hammer

Info

Publication number: WO2006008723A2
Application number: PCT/IE2005/000063
Authority: WO
Inventors: Joseph Purcell
Original assignee: Minroc Technical Promotions Limited
Priority date: 2004-07-16
Filing date: 2005-06-07
Publication date: 2006-01-26
Also published as: WO2006008723A3; IES20040482A2

Abstract

A down-the-hole hammer is described. It comprises an external cylindrical outer wear sleeve (10), an inner cylinder (9) mounted co-axially within the outer wear sleeve (10), a sliding piston (11) mounted for reciprocating movement within the inner cylinder (9) and the outer wear sleeve (10), to strike a hammer bit (40) mounted at the lower end of the outer wear sleeve (10) and an elongate cylindrical air distributor (3) positioned within the hammer assembly. The lower end of the air distributor (3) is positioned substantially concentrically within the upper end of the inner cylinder (9). A shoulder (38) on the air distributor (3) engages the underside of a complementary shoulder (15) on the inner cylinder (9). The top end of the outer wear sleeve (10) is screw-threadably engaged with the lower part of an annular locking member (1), and the top end of the inner cylinder (9) abuts the lower end of the locking member (1) such that the inner cylinder is rigidly mounted in the drill assembly relative to the outer wear sleeve (10) by means of a locking engagement between the air distributor (3) and the-locking member (1).

Description

"A DOWN-THE-HOLE HAMMER"

Technical Field of the Invention

The present invention relates to "down-the-hole" hammers or fluid-operated percussion drill tools operated by a supply of compressed air.

Background to the Invention Some designs of conventional down-the-hole hammers and fluid-operated percussion drill tools comprise an external cylinder or outer wear sleeve, within which is mounted an inner cylinder which in turn engages with a backhead assembly. A sliding reciprocating piston co-operates with the inner cylinder and backhead assembly, which when air pressure is supplied through the backhead assembly, acts with a percussive effect on a drill bit retained within a chuck on the- outer wear sleeve.

In down-the-hole hammers the energy created is in part dependent on the cross sectional area of the reciprocating piston. This is because the force is determined by the formula P x A (where P = air pressure and A = cross sectional area of the piston). In most modern down-the-hole hammers the piston is a sliding valve, which reciprocates between a strike position on a bit and a top of stroke position. The length and timing of the stroke is determined by the supply and exhaust of air to a lift chamber and top pressure chamber.

hi known conventional arrangements, the inner cylinder is effectively suspended within the outer wear sleeve by means of a compressible retaining ring, such as a circlip, which has to be slid up the inner cylinder so as to seat against a shoulder or lip at one end thereof, being compressed when the inner cylinder is dropped down within the outer wear sleeve, and then expanding outwardly into a groove or shoulder formed on the inner diameter of the outer wear sleeve with a snap action. When in this position, the circlip seats within the groove and abuts against the lip of the inner cylinder, by which the inner cylinder is suspended within the outer wear sleeve. EP1004744A, of the same applicant, discloses a segmented ring mounting for retaining the inner cylinder within the outer wear sleeve in a fluid-operated percussion drill tool, such as a down-the-hole hammer.

The retaining ring seats the smaller diameter inner cylinder within the larger diameter outer wear sleeve. The outer wear sleeve is formed with a groove cut on its inside diameter, or a shoulder for seating the retaining ring against a lip of the inner cylinder. The ring is capable of radial compression and expansion so as to expand radially into the seating groove or shoulder for retaining the components one within the other in use. The retaining ring comprises at least three segments, which when touching end to end form a complete circle, and an expansible O-ring, for holding the segments together but allowing the segments to expand radially and move apart by sufficient amount so as to seat the segments in the groove or against the shoulder.

The inner cylinder of EP 1004744 A. is integral to the porting_of. the hammer. In the system the piston runs on the inner diameter of the inner cylinder and also on the inner diameter of the outer wear sleeve. It is essential that the fit between the outer diameter of the inner cylinder and the bore of the outerwear sleeve be a tight/close fit to ensure optimum alignment of the two bores. This means that the clearance and hence the efficiency of the hammer is optimised because the operation of the hammer relies on a partial seal between the piston and the top and bottom chambers, i.e. the tighter the clearance the greater the energy (within reason). In the seating ring system of EP1004744A effective operation relies on a difference in wear sleeve bore diameter above and below the seating ring groove. This means the usable diameter for the piston, and thus the energy, is reduced. This is because the inner diameter of the wear sleeve above the seating ring has to be larger than below to ensure that the seating ring is located in position. This results in an effective reduction in the cross-sectional diameter of the piston, which reduces the force on the piston.

Other manufacturers have in the past made the inner cylinder as part of a threaded component which screws into the outer wear sleeve. The disadvantage of this is that the hammer wears externally and in many cases it is rebuilt by replacing all external components. This would obviously be extremely expensive in the above scenario. There is also the issue of the clearance which would be necessary, between the external diameter of the inner cylinder portion and the bore of the wear sleeve, to allow the component to screw into the wear sleeve. As will be explained below the clearance needs to be minimised to optimise the concentricity of the inner cylinder bore and the wear sleeve bore.

hi other known prior art percussion hammers the inner cylinder is mounted within the outer wear sleeve by means of a compressible retaining ring, such as a circlip, which is expanded outwardly to seat into the groove or shoulder formed on the inner diameter of the outer wear sleeve.

The outer wear sleeve of down-the-hole hammers is subject to very strong abrasive forces when in use causing significant wear of, and removal of metal from, the outer sleeve. This weakens the outer wear sleeve to the point where it has to be replaced. In the prior art hammers described the provision of circumferential seating grooves for circlips, seating rings and the like, in the inner face of the wear sleeve reduce the wear thickness of the outer sleeve. This means that the outer wear sleeve has to be replaced more quickly than would be the case if the wear sleeve contained no more grooves.

In other prior art down-the-hole hammers (e.g. those having a seating ring) the inner cylinder is located on a shoulder provided by a groove in the wear sleeve. It is then locked in position by the application of torque at the backhead, which locks down on a compression ring or the like. The result is that there is a significant locking force which acts between the shoulder and the threads of the wear sleeve. The possibility that this force could cause distortion on the wear sleeve will increase as the external wear on the wear sleeve outer diameter increases.

Another type of locking system relies on a collet type system (e.g. WO9967065 Azuko). This system applies not only a force down a shoulder on the wear sleeve but also an outward force on the wear sleeve. Again the effect of these forces increases as the wear sleeve wears. In summary, the disadvantages of the prior art systems are as follows.

Where a seating ring is used this results in:

• a reduction of the available piston cross-section due to shoulder requirements for the seating ring;

• a reduction of wear sleeve cross-section due to the requirement to provide a seating ring groove;

• high locking forces required on the seating ring shoulder of the wear sleeve.

Where a compressible/expandable circlip is used this results in:

• a reduction of the wear sleeve cross-section due to the requirement to provide a seating ring groove; • high locking forces required on the seating ring shoulder of the wear sleeve.

Where an integral inner cylinder and threaded component is used, this results in:

• a requirement for clearance between the inner cylinder and the wear sleeve resulting in concentricity problems;

• it is expensive to rebuild.

WO2004/031530, of the same applicant, successfully addresses the problems of the prior art outlined above. However, the preferred embodiment set out in that application includes an elongate cylindrical air distributor positioned within the hammer assembly, such that an abutment on the inner cylinder engages a complementary abutment on the air distributor. It has now been found advantageous to achieve a simpler construction involving fewer parts which is more easily assembled, and in which the distributor is of shorter length. Furthermore, in the embodiments described in WO2004/03530, the locking components lie flush with the outer wear sleeve and may thus be subjected to wear in use. Therefore, when the exterior of the drill tool becomes worn and requires replacement, the locking mechanism must be disassembled and certain parts of it replaced. Object of the Invention

It is an object of the invention to provide a down-the-hole hammer, or other fluid operated percussion drill tool, having means for rigidly mounting the inner cylinder in the outer wear sleeve while still maximising the bore of the wear sleeve. It is a further object of the invention to overcome the above-identified problems with prior art arrangements.

Summary of the Invention

The present invention provides a fluid-operated percussion drill tool, in particular a down-the-hole hammer, comprising an external cylindrical outer wear sleeve, an inner cylinder mounted co-axially within the outer wear sleeve, a sliding piston mounted for reciprocating movement within the inner cylinder and the outer wear sleeve, to strike a hammer bit mounted at the lower end of the outet-wear sleeve, characterised in that the inner cylinder is rigidly mounted and held in the drill tool assembly relative to the outer wear sleeve by means of a locking engagement between a complementary engagement means and a locking means.

In a preferred embodiment of the invention, the inner cylinder has an abutment which in the assembled tool is clamped between the complementary engagement means and the locking means, and the inner cylinder is rigidly mounted and held in the drill tool assembly relative to the outer wear sleeve by means of a locking engagement between the complementary engagement means and the locking means.

Preferably, a cylindrical air distributor is positioned within the tool assembly, and in the assembled tool an abutment on the inner cylinder engages with a complementary abutment on the air distributor and locking means connected to the outer wear sleeve is provided to clamp the abutment on the inner cylinder between the abutment on the air distributor and the locking means, and the inner cylinder is rigidly mounted and held in the drill tool assembly relative to the outer wear sleeve by means of a locking engagement between the cylindrical air distributor and the locking means. Preferably, the locking means is connected to the outer wear sleeve by means of a screw-thread arrangement.

According to a preferred feature of the invention, the locking means comprises an annular member fitted concentrically around the air distributor within the outer wear sleeve and the annular member is provided with a plurality of upwardly inclined through-holes arranged at an angle to the longitudinal axis of the drill tool, and the air distributor is provided with a corresponding plurality of stops arranged perpendicular to the direction of the through-holes such that fastening means inserted into the through- holes engage the stops so as to provide a locking engagement between the air distributor and the annular member.

This locking arrangement provides an upward locking force between the air distributor and the locking means, that is, the air distributor is pulled upwards towards the locking means. The angle at which the through-holes are inclined- to the vertical determines what proportion of the locking force is applied in a vertical direction. The more acute the angle of incline, the greater the component of the locking force in the vertical direction. Correspondingly, the closer to horizontal the through-holes become, the less force is applied in the vertical direction. Preferably, the through-holes are arranged at an acute angle, for example, an angle of between 40° and 80° to the longitudinal axis of the drill tool. Ideally, the through-holes are arranged at an angle of 50° to the longitudinal axis of the drill tool, that is, at 40° to the horizontal.

Ideally, the through-holes are internally threaded and the fastening means comprises a fastening screw threadably inserted into each through-hole such that the fastening screws engage the corresponding stops. The fastening screws maybe grub screws or set screws.

Preferably, the stops comprise angled recesses defined within the air distributor, having substantially planar end surfaces arranged perpendicular to the direction of the through-holes, such that in the assembled tool the fastening means inserted into the through-holes enter the angled recesses and engage the end surfaces of said recesses so as to provide a locking engagement between the air distributor and the annular member. The arrangement described above represents a number of improvements over the identified prior art. A first advantage of the present arrangement is that it has relatively few components and may be more easily and straightforwardly assembled than prior art devices. A further advantage is that the air distributor is significantly shorter than that of the prior art arrangement and is thus more easily manufactured. Furthermore, the locking member, air distributor and inner cylinder may be sub-assembled and need not be disassembled unless one of these parts requires servicing. The subassembly may later be easily screw-fitted to the outer wear sleeve.

According to a further preferred feature of the invention, an additional wear sleeve is positioned concentrically around locking means such that when the tool is in use, the additional wear sleeve protects the locking means from external wear. Ideally, the additional wear sleeve is provided with a plurality of grooves, and the locking means is provided with a plurality of flats, such that when the tool is asserfibled the grooves interoperate with the flats so as to prevent rotational motion of the additional wear sleeve relative to the locking means.

A further advantage of the present arrangement and of the additional wear sleeve is that the elements which lock the inner cylinder in place are not exposed to external wear as in prior art arrangements. In the event of the hammer requiring rebuilding due to external wear, the outer components, that is, the outer wear sleeve, additional wear sleeve and hammer bit chuck, may be replaced, while retaining the sub-assembled inner components which have not been exposed to external wear.

Accordingly to an optional feature of the invention, the locking means is formed with a central cavity, and in the assembled tool a check valve and a check valve seat are inserted into cavity such that when the valve is in the closed position, its upper surface is seated on the lower end of the check valve seat. Preferably, the check valve seat is secured within the cavity by means of a screw thread arrangement. The cavity may be formed with a shoulder at its upper end and an O-ring seal may be provided on said shoulder such that the check valve seat is seated on the O-ring seal. The check valve may occasionally need to be serviced or replaced. An advantage of this feature is that this can be achieved by simply removing the check valve seat, and the check valve (and spring) can be tipped out through the cavity in the locking means.

Brief Description of the Drawings

Figure 1 is a sectional side elevation of a preferred embodiment of a down-the-hole hammer of the invention, showing the piston in the strike position;

Figure 2 is a sectional side elevation of the hammer of Figure 1, showing the piston in the top of stroke position;

Figure 3 is a sectional side elevation of the top part of the hammer of Figure 1 to a larger scale; ^* - -

Figure 4 is a cross-sectional plan view of the down-the-hole hammer of Figure 1, on the line E-E of Figure 2;

Figure 5 is a cross-sectional plan view of the down-the-hole hammer of Figure 1, on the line G-G of Figure 2;

Figure 6 is a cross-sectional plan view of the down-the-hole hammer of Figure 1, on the line H-H of Figure 2;

Figure 7 is a perspective view of the air distributor of the down-the-hole hammer of Figure 1;

Figure 8 is a perspective view of the air distributor of Figure 6, showing the position of grub screws in the assembled tool;

Figure 9 is a perspective view of the air distributor of Figure 6, showing its position within the inner cylinder in the assembled tool; Figure 10 is a perspective view of the air distributor and inner cylinder of Figure 8, showing their position relative to the grub screws, locking means and additional wear sleeve in the assembled tool; and

Figure 11 is a perspective view of the locking means and the additional wear sleeve of the down-the-hole hammer of Figure 1.

Detailed Description of the Drawings

Referring to Figures 1, 2 and 3 of the drawings, a preferred embodiment of a down-the-hole hammer of the invention comprises an external cylindrical outer wear sleeve 10. An inner cylinder 9 is mounted co-axially within the outer wear sleeve 10. A sliding piston 11 is mounted for reciprocating movement within the inner cylinder 9 and the outer wear sleeve 10, to strike a hammer bit 36 mounted for sliding movement in a chuck 41 located at the forward end of the outer wear sleeve 10, in well known manner. ^ - -

Referring now to Figure 3, at the back end of the hammer, an annular locking member 1 is mounted on an annular air distributor 3 by means of a locking engagement, which will be further described below. Air distributor 3 is fitted concentrically through inner cylinder 9 and when assembled an outwardly-directed annular flange 38 on the lower end of air distributor 3 abuts the underside of an inwardly-directed annular shoulder 15 in inner cylinder 9. The top end 14 of inner cylinder 9, above the shoulder 15, in turn abuts the lower end 54 of the annular locking member 1. The annular locking member 1 has a lower part, which fits within the top end of the wear sleeve 10, and is screw-threadably engaged with the inner wall of the wear sleeve 10, by means of screw threads 39. Annular locking member 1 is provided with an annular flange 52 against which the top annular rim of the outer wear sleeve 10 abuts, and is locked in place when the locking member 1 is fully engaged with the wear sleeve 10. The inner cylinder 9 is thus effectively locked between a flange 52 (between locking member 1 and outer wear sleeve 10) and shoulder 15 (between air distributor 3 and inner cylinder 9). Shoulder 15 maybe tapered if required.

Stated differently, the inner cylinder 9, at its upper end, has an inwardly extending annular shoulder or flange 14 which is rigidly held between the shoulder 15 and the lower end 54 of the annular locking member 1 when the annular locking member has been screwed into position in the top end of the wear sleeve 10, and has been lockedly engaged with the air distributor. When the annular locking member 1 is lockedly engaged with the top of the air-distributor 3, this acts to pull the air-distributor 3 upwardly against the shoulder 15, and in turn pulls the inner cylinder 9 upwardly against the shoulder 54. The whole assembly then locks down on flange 52.

The locking engagement between air distributor 3 and annular locking member 1 will now be described in more detail with reference to Figures 3, 7, 8 and 10. As shown in Figure 3, the annular locking member 1 is fitted concentrically around air distributor 3 within outer wear sleeve 10. The annular member 1 is provided with a plurality of upwardly inclined through-holes 24 arranged at an angle to the longitudinal axis of the drill tool. In the embodiment shown, the through-holes 24 are internally threaded. The air distributor 3 is provided with a corresponding plurality of stops 21. In the illustrated embodiment, the stops comprise angled recesses 53 defined

3, having substantially planar end surfaces 21 arranged perpendicular to the direction of the through-holes 24. A fastening screw 12 is threadably inserted into each through- hole 24, so that it enters the corresponding angled recess 53 in the air distributor 3. The fastening screws 12 then engage the end surfaces 21 of the recesses 53 so as to provide a locking engagement between the air distributor 3 and the annular member 1. In the embodiment shown", the fastening screws 12 are grub screws.

To ensure maximum alignment between the inner cylinder 9 and the wear sleeve 10 the fit must be as close to size for size as possible. Due to tolerance restrictions this means that the fit could be a very close sliding fit, a size for size fit, or a slight interference fit. The efficiency of the hammer is partly dependent upon the clearance between the piston 11 and the wear sleeve 10, because the sliding contact between the piston 11 and the inner diameter of the wear sleeve 10 acts as a pneumatic seal. The clearance between these parts is of the order of 0.1 mm. It will be appreciated that the piston 11 is running in the bore of the wear sleeve 10 at the lower end of its stroke (see Fig. 1) and runs in the bore of the inner cylinder 9 at the top of the stroke (see Fig. 2). Again the clearance is of the order of 0.1 mm. It is also important to ensure that the bore of the inner cylinder 9 is concentric with the bore of the outer wear sleeve 10, and that there is no sideways (i.e. radial) movement. This is achieved by having the inner cylinder 9 as a very snug, or interference, fit within the bore of the outer sleeve 10.

The tolerance on the bore of the outer wear sleeve 10 relative to the piston 11 is about 20 microns and a tolerance of about 10 microns in the outer diameter of the inner cylinder 9, relative to the outer diameter of the piston 11. The clearance between these parts should be in the range of 0.11 mm and 0.14 mm. If the clearance is greater than about 0.14 mm there is a loss of efficiency of the hammer because compressed air bypasses the piston.

As mentioned above, the annular locking member 1 is screw-threadably engaged with the top of wear sleeve 10 by means of screw threads 39 (see Fig. 2) which are cut into the inner face of the wear sleeve 10. The axial depth of cut of the screw thread 39 is kept to a minimum to minimise the stress on the wear sleeve. When considering the axial depth of screw -thread 39 it is important to note that as the diameter of the hammer increases (hammer models are generally denoted by the nominal size which they are designed to drill e.g. 3", 4", 5", 6", 8" etc.) the minimum thread depth would increase. In the case of 3" and 4" hammers the minimum depth could be in the range of 1.0 to 1.4 mm. On the larger sizes, e.g. 8", this minimum depth could be in the range of 1.6mm to 2.0mm.

In a preferred method of assembly of the hammer, the bottom end of the hammer is assembled first. The hammer is then placed upright. The piston 11 is placed into the wear sleeve 10. The inner cylinder 9 is placed over the air distributor 3 such that shoulder 15 abuts flange 38. Annular locking member 1 is then placed over air distributor 3 such that through-holes 24 and recesses 53 are aligned. Fastening screws 12 are then threadably inserted into through-holes 24 so that they enter recesses 53 and engage end surfaces 21 so as to provide a locking engagement between air distributor 3 and locking member 1. This in turn forces the lower end 54 of locking member 1 against the flange 14, thus locking the inner cylinder in place between the air distributor 3 and the locking member 1. This sub-assembly should not need to be disassembled unless it is required to service one of the parts involved. The additional wear sleeve 20 is then mounted on locking member 1 and is prevented from rotating relative to the locking member by means of interoperating grooves 22 and flats 23. The entire sub- assembly is then inserted into the outer wear sleeve 10 and locking member 1 is screwed into the outer wear sleeve 10 such that flange 52 engages the upper end of the outer wear sleeve. There are other ways of assembling the hammer but the above method has been found to be convenient.

The drill tool also includes a check valve assembly as shown in Figure 3. Locking member 1 is formed with a central cavity 55 having an upper opening 56. Air distributor 3 is also formed with a central cavity 57, which in the assembled tool is coaxial with cavity 55. The check valve arrangement is assembled by dropping spring 5 into cavity 57 in air distributor 3 through opening 56 in the upper end of locking member 1. Check valve 4 is then inserted into cavity 57 in air distributor 3. A check valve seat 13 is then inserted through opening 56 in locking member 1 and secured to the locking member by a thread engagement 27. Cavity 55 in locking member 1 is formed with a shoulder 58 at its upper end. An O-ring seal 28 is provided on shoulder 58 and when screwed in place, the check valve seat is seated on the O-ring seal 28. The whole check valve assembly is held in place by an internal circlip 16. Check valve 4 is shown in the open position in the accompanying drawings. However, in the closed position, the valve 4 is seated on check valve seat 13. If the check valve needs to be serviced or replaced, the check valve seat may simply be removed, and the check valve and spring can be tipped out through the cavity 55 in the locking means.

The operation of the hammer is as follows. Referring to Fig. 3, compressed air is supplied through top locking member 1 and forces check valve 4 open by pushing down on a compression spring 5. The compressed air is then supplied through longitudinal chambers formed between locking member 1 and air distributor 3 by means of 4 grooves 25 machined in air distributor 3 (see Figs. 4, 6 and 7). From there the compressed air passes down through ports 19 in inner cylinder 9 and into the segmentally-shaped chambers 61 between the inner cylinder 9 and the wear sleeve 10. From here the air is supplied through ports 21 in the inner cylinder 9.

When the piston 11 is in the strike position (Fig 1), air is supplied from the ports 21 into the chamber 59 between the piston 11 and the wear sleeve 10. From here it is supplied through the channels 28 and 29 in the piston 11 to undercut 30 and into lift chamber 31.

At the back end of the piston, in a top chamber 32, air is free to exhaust through piston bore 33 and bit bores 34 and 35 to atmosphere. As a result a pressure differential exists between the lift chamber 31 and the top chamber 32 and the piston lifts to the top of stroke position (Fig. 2).

In this position air is cut-off from entering chamber 31, and air can exhaust from chamber 31 through bit bores 34 and 35 to atmosphere. Pressurised air is supplied from ports 21 to a chamber 59 between piston 11 and inner cylinder 9. From here it is supplied though channels 28 in piston 11 to undercut 60 in inner cylinder 9 to top chamber 32 which is prevented from exhausting by probe 6 which is in piston bore 33. As there is now a pressure differential between chambers 31 and 32 the piston is driven down to strike the bit 36 and the cycle repeats itself. - -- ~

In this embodiment, the air distributor 3 and the probe 6 are all in one piece, which improves the strength of the assembly.

From the foregoing, it will be apparent that numerous modifications and variations can be effected without departing from the true spirit and scope of the novel concept of the present invention. It will be appreciated that the present disclosure is intended to set forth the exemplifications of the invention which are not intended to limit the invention to the specific embodiments illustrated. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.

Where technical features mentioned in any claim are followed by reference signs, these reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs. The words "comprises/comprising" and the words "having/including" when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claims

1. A fluid-operated percussion drill tool, in particular a down-the-hole hammer, comprising an external cylindrical outer wear sleeve (10), an inner cylinder (9) mounted co-axially within the outer wear sleeve (10), a sliding piston (11) mounted for reciprocating movement within the inner cylinder (9) and the outer wear sleeve (10), to strike a hammer bit (36) mounted at the lower end of the outer wear sleeve (10), characterised in that the inner cylinder (9) is rigidly mounted and held in the drill tool assembly relative to the outer wear sleeve (10) by means of a locking engagement between a complementary engagement means (3) and a locking means

(D-

2. A fluid-operated percussion drill tool as claimed in claim 1, characterised in that the inner cylinder (9) has an abutment (15) which in the assembled tool is clamped between the complementary engagement means (3) and the locking-means (1), and the inner cylinder (9) is rigidly mounted and held in the drill tool assembly relative to the outer wear sleeve (10) by means of a locking engagement between the complementary engagement means (3) and the locking means (1).

3. A fluid-operated percussion drill tool as claimed in any preceding claim, characterised in that a cylindrical air distributor (3) is positioned within the tool assembly, and in the assembled tool an abutment (15) on the inner cylinder (9) engages with a complementary abutment (38) on the air distributor (3) and locking means (1) connected to the outer wear sleeve (10) is provided to clamp the abutment on the inner cylinder (15) between the abutment (38) on the air distributor (3) and the locking means (1), and the inner cylinder (9) is rigidly mounted and held in the drill tool assembly relative to the outerwear sleeve (10) by means of a locking engagement between the cylindrical air distributor (3) and the locking means (1).

4. A fluid-operated percussion drill tool as claimed in claim 3, characterised in that the locking means comprises an annular member (1) fitted concentrically around air distributor (3) within outer wear sleeve (10) and the annular member (1) is provided with a plurality of upwardly inclined through-holes (24) arranged at an angle to the longitudinal axis of the drill tool, and the air distributor (3) is provided with a corresponding plurality of stops (21) arranged perpendicular to the direction of the through-holes (24) such that fastening means (12) inserted into the through-holes (24) engage the stops (21) so as to provide a locking engagement between the air distributor (3) and the annular member (1).

5. A fluid-operated percussion drill tool as claimed in claim 4, characterised in that the through-holes (24) are internally threaded and the fastening means comprises a fastening screw (12) threadably inserted into each through-hole (24) such that the fastening screws (12) engage the corresponding stops (21).

6. A fluid-operated percussion drill tool as claimed in claim 5, characterised in that the fastenings screws (12) are grub screws or set screws.

7. A fluid-operated percussion drill tool as claimed in any one of claims 4, 5 or 6, characterised in that the stops comprise angled recesses (53) defined within air distributor (3), having substantially planar end surfaces (21) arranged perpendicular to the direction of the through-holes, such that in the assembled tool the fastening means (12) inserted into through-holes (24) enter angled recesses (53) and engage end surfaces (21) of said recesses so as to provide a locking engagement between the air distributor (3) and the annular member (1).

8. A fluid-operated percussion drill tool as claimed in any preceding claim, characterised in that an additional wear sleeve (20) is positioned concentrically around locking means (1) such that when the tool is in use, the additional wear sleeve

(20) protects locking means (1) from external wear.

9. A fluid-operated percussion drill tool as claimed in claim 8, characterised in that the additional wear sleeve (20) is provided with a plurality of grooves (22), and locking means (1) is provided with a plurality of flats (23), such that when the tool is assembled grooves (22) interoperate with flats (23) so as to prevent rotational motion of the additional wear sleeve (20) relative to locking means (1).

10. A fluid-operated percussion drill tool as claimed in any preceding claim, characterised in that locking means (1) is formed with a central cavity (55), and in the assembled tool a check valve (4) and a check valve seat (13) are inserted into cavity (55) such that when the valve (4) is in the closed position, its upper surface is ^; seated on the lower end of the check valve seat (13).