Technical Field

[0001] The present disclosure relates generally to a down-the-hole hammer driven by a motive fluid, more specifically to a down-the-hole hammer comprising means for handling flow of motive fluid and exhaust fluid therethrough.

Background Art

[0002] The two most common methods for drilling rock involve either quasi-static loading of rock as used in rotary drilling, or high intensity impact loading as used in down- the-hole (DTH) drilling. DTH applications include a hammer assembly having a piston or actuator that reciprocates within the drill casing and applies a cyclical impact on an anvil. The anvil is typically part of or directly connected to the drill bit so that impact forces of the piston striking the anvil are transferred through the drill bit into the rock being drilled. The piston typically reciprocates in response to motive fluid (e.g., compressed air), alternatingly raising and lowering the piston. The motive fluid is typically exhausted from the drill through the drill bit after actuating the hammer assembly, then referred to as exhaust fluid to differentiate from the motive fluid which enters the DTH hammer. The exhaust fluid exits through the drill bit to clear cuttings and other debris from around the drill bit and carry such debris up out of the hole or bore being drilled on the outside of the hammer casing. Hybrid rock drills (called percussive assist rotary drills or PARD) that utilize a DTH hammer assembly to impact a rotary drill bit are also known, and also have a flow of exhaust fluid through the drill bit.

[0003] When the exhaust fluid exits through the drill bit, it flows over an exterior surface of the drill bit (“flows over” and variations thereof meaning in this specification that the motive fluid flows across and in contact with the drill bit exterior surface) and up the bore being drilled. In known DTH hammer assemblies having reverse circulation configurations, the exhaust fluid actually exits above the drill bit, flows down over the drill bit exterior, and then flows up through the center of the drill bit, hammer, and drill pipe or drill string to the surface. In this specification, the term “through the bit” and “bit exhaust” are intended to include exhaust fluid that flows over the drill bit exterior surface, whether flowing out of the bit and up the bore or flowing in a reverse circulation direction. [0004] In the present disclosure, the terms “down-the-hole hammer”, “hammer”, and “hammer assembly” refer to a drilling arrangement using the impact forces of a reciprocating piston or other moving actuator, whether such drilling arrangement is present in a DTH application, a PARD arrangement, or another arrangement, and regardless of whether the drilling arrangement includes a standard bit, drag bit, rotary bit, or another cutting surface.

[0005] In general, a certain amount of motive fluid is needed to achieve the desired power output from the hammer as well as for lifting the rock debris and ground water pouring into the created bore hole. However, considering the wear on the drill bit and the outer casing of the hammer, the supply of motive fluid often exceeds what is needed to flush the rock debris from the drill bit. It would therefore be beneficial to reduce the amount of exhaust fluid passing over the drill bit.

[0006] WO 2010/093685 A2 discloses a DTH hammer wherein at least a portion of the actuator flow portion of the motive fluid is exhausted through the proximal end of the drill, above the drill bit such that it does not flow over the drill bit's exterior surface.

[0007] During operation of DTH hammers, as the length of the bore hole increases, new drill pipes are added to the drill string. Every time a new drill pipe is added, the supply of motive fluid is momentarily interrupted and the pressure drops in the drill string. This allows backpressure from groundwater to push mud, rock debris and/or dirt into the DTH hammer. To combat this, standard DTH hammers have a check valve function near the inlet for motive fluid into the hammer. With additional exhaust ports near the proximal end, a separate check valve is required for the exhaust flow.

[0008] Hence, there is a need for an improved DTH hammer which reduces the complexity of the check valve compared to known solutions to optimise fluid flow through the back head.

Summary

[0009] An objective of the present disclosure is therefore to provide an improved DTH hammer which reduces the complexity of the check valve and optimises fluid flow through the back head. The DTH hammer is described in the appended claims. [0010] According to a first aspect of the present disclosure, there is provided a down- the-hole, DTH, hammer configured for operation under the influence of motive fluid, the DTH hammer comprising: a housing extending between a first end and a second end along a longitudinal axis of the DTH hammer; a back head connected to the first end of the housing and comprising at least one supply port for motive fluid and at least one evacuation port for exhaust fluid, separate from each other; an actuator configured to be operated by motive fluid; and a check valve assembly arranged in the back head in fluid communication with the at least one supply port and an actuator drive flow path to control supply of motive fluid to the actuator drive flow path. The check valve assembly is further arranged in fluid communication with the at least one evacuation port and an actuator exhaust flow path to control evacuation of exhaust fluid from the actuator exhaust flow path. In a first, open position, the check valve assembly is configured to enable simultaneous flow of motive fluid from the at least one motive fluid supply port to the actuator drive flow path and flow of exhaust fluid from the actuator exhaust flow path to the at least one exhaust fluid evacuation port, wherein the flows of motive fluid and exhaust fluid are separated from each other.

[0011] By separating the simultaneous flows of the motive fluid and the exhaust fluid in the check valve assembly, the DTH hammer according to the present disclosure facilitates controlling the flows through the back head by means of one single valve arrangement with reduced complexity and cost of manufacture. Additionally the service life is increased due to fewer moving parts and reduced wear.

[0012] In one embodiment, in a second, closed position, the check valve assembly is further configured to simultaneously block flow of motive fluid through the at least one motive fluid supply port and flow of exhaust fluid through the at least one exhaust fluid evacuation port. With the single valve arrangement, a simple and quick solution for blocking the flows of both motive and exhaust fluid is achieved.

[0013] In one embodiment, the check valve assembly comprises at least one biasing member arranged to bias the check valve assembly toward the second, closed position, and wherein the check valve assembly is arranged to be displaced to the first, open position by the pressure of motive fluid delivered to the back head through the at least one motive fluid supply port. The biasing member ensures that the DTH hammer remains closed until requisite operation conditions are achieved, to prevent ingress of external fluid and debris into the housing.

[0014] In one embodiment, the check valve comprises two biasing members, wherein a first biasing member is arranged to bias the check valve assembly to block the at least one supply port, and a second biasing member is arranged to bias the check valve assembly to block the at least one evacuation port. Preferably, the second biasing member is arranged on an external surface of the back head and configured to bias an external sleeve to block the at least one evacuation port. By means of the two biasing members, individual control of closing and opening of the supply port and the evacuation port is achieved. The external sleeve provides an effective and simple solution for closing the evacuation port.

[0015] In one embodiment, the at least one evacuation port is oriented in a substantially radial direction of the DTH hammer, a substantially axial direction of the DTH hammer, and/or a combination thereof. The orientation of the evacuation port may thus be adapted to available space and material thickness in the back head.

[0016] In one embodiment, the check valve assembly comprises at least two separate flow paths, for the motive fluid and the exhaust fluid, respectively. The two separate flow paths ensure separation of the flows of motive and exhaust fluid.

[0017] In one embodiment, at least one first flow path for the motive fluid is defined by an internal space delimited by the back head and the check valve assembly and in fluid communication with the at least one supply port in the first, open position of the check valve assembly. By letting the motive fluid pass on an outside portion of the check valve, a simple solution for providing the first flow path is achieved.

[0018] Alternatively, at least one first flow path for the motive fluid is defined by a first internal passage in the check valve assembly arranged to be placed in fluid communication with the at least one supply port in the first, open position of the check valve assembly. The first internal passage allows controlling the flow of motive fluid through the check valve assembly in an effective manner.

[0019] In one embodiment, at least one second flow path for the exhaust fluid is defined by a second internal passage in the check valve assembly arranged to be placed in fluid communication with the at least one evacuation port in the first, open position of the check valve assembly. The second internal passage allows controlling the flow of exhaust fluid through the check valve assembly in an effective manner.

[0020] In one embodiment, the DTH hammer further comprising a tubular member with a closed first end and having at least one lateral opening adjacent the first end, wherein the tubular member is movably arranged in a central conduit of the second internal passage between a first, open position in which flow of exhaust fluid through the second internal passage is enabled, and a second, closed position in which flow of exhaust fluid through the second internal passage is blocked. The tubular member provides a simple solution for closing the second internal passage to block flow of exhaust fluid.

Brief Description of Drawings

[0021] The disclosure is now described, by way of example, with reference to the accompanying drawings, in which:

Fig. l is a perspective view of a down-the-hole (DTH) hammer according to one embodiment of the present disclosure.

Fig. 2 is an exploded view of the DTH hammer shown in Fig. 1.

Fig. 3 is a cross-sectional view of the DTH hammer shown in Figs. 1 and 2.

Fig. 4 is a perspective view of a check valve assembly according to one embodiment of the present disclosure.

Figs. 5a-5d are cross-sectional views of the proximal end of the DTH hammer shown in Fig. 3 with the check valve assembly according to Fig. 4 in closed and open positions, respectively.

Fig. 6 is a perspective view of a check valve assembly according to an other embodiment of the present disclosure.

Figs. 7a-7d are cross-sectional views of the proximal end of the DTH hammer with a check valve assembly according to Fig. 6 in closed and open positions, respectively. Fig. 8 is a perspective view of a check valve assembly according to an other embodiment of the present disclosure.

Figs. 9a-9d are cross-sectional views of the proximal end of the DTH hammer with a check valve assembly according to Fig. 8 in closed and open positions, respectively.

Fig. 10 is a perspective view of a check valve assembly according to an other embodiment of the present disclosure.

Figs. 1 la-1 Id are cross-sectional views of the proximal end of the DTH hammer with a check valve assembly according to Fig. 10 in closed and open positions, respectively.

Figs. 12a-12d are cross-sectional views of the proximal end of the DTH hammer with an alternative check valve assembly according to Fig. 10 in closed and open positions, respectively.

Description of Embodiments

[0022] In the following, a detailed description of a DTH hammer according to the present disclosure is presented. In the drawing figures, like reference numerals designate identical or corresponding elements throughout the several figures. It will be appreciated that these figures are for illustration only and do not in any way restrict the scope of the present disclosure. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of ‘including’, ‘comprising’, or ‘having’ and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms ‘mounted’, ‘connected’, '‘supported’, and '‘coupled’ and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, ‘connected’ and ‘coupled’ are not restricted to physical or mechanical connections or couplings.

[0023] In the present disclosure, the terms “down-the-hole hammer”, “hammer”, and “hammer assembly” refer to a drilling arrangement using the impact forces of a reciprocating piston or other moving actuator, whether such drilling arrangement is present in a DTH application, a PARD arrangement, or another arrangement, and regardless of whether the drilling arrangement includes a standard bit, drag bit, rotary bit, or another cutting surface.

[0024] For the sake of simplicity and consistency in this specification, the term ‘axial’ refers to a direction parallel to a central longitudinal axis of a DTH hammer as illustrated in the drawings. The term ‘radial’ refers to a direction perpendicular to the axis of the DTH hammer. All the main elements of the hammer discussed below are generally ring-shaped or cylindrical and therefore all have inner and outer surfaces. The term ‘inner surface’ refers to the surface facing toward the central axis or generally toward the inside of the hammer and the term ‘outer surface’ refers to the surface facing away from the central axis or generally away from the inside of the hammer. All elements also have first and second ends which, using the convention of the illustrated embodiment, may be referred to as ‘proximal’ and ‘distal’ ends with respect to the typical operating orientation of the hammer in relation to the operator.

[0025] In the context of the present disclosure, the term ‘flow path’ should be understood as the way or course followed by a fluid through the DTH hammer. A flow path does not necessarily constitute a physical structure of the DTH hammer, the term instead being used as a general description of how the fluid flows through the DTH hammer. A flow path may be defined by an internal passage in the DTH hammer or any component thereof which delimits the boundaries of the flow path and thereby constitutes a physical structure of the DTH hammer. An internal passage may in turn be subdivided into one or more sections, thus comprising conduits, channels, bores and/or openings which together form the internal passage.

[0026] In the context of the present disclosure, motive fluid is a fluid that is supplied to the DTH hammer to actuate a piston of the hammer, whereas exhaust fluid is a fluid that is evacuated from the DTH hammer after having acted on the piston.

[0027] Fig. 1 shows a down-the-hole (DTH) hammer 1 according to one embodiment of the present disclosure in a perspective view. Figs. 2 and 3 are exploded and cross- sectional views of the DTH hammer 1 and illustrate the following basic components: a back head 10, a check valve assembly 20, a distributor 30, a cylinder 40, a piston or actuator 50, an exhaust tube 60, a shank adapter 70, an outer sleeve or housing 80, a chuck 90, and a drill bit 100. Operation of the DTH hammer 1 will now be briefly explained with reference to Figs. 2 and 3.

[0028] Referring now to Fig. 2, the housing 80 extends between a first end 81 and a second end 82 and is arranged to accommodate the other components of the DTH hammer 1 therein. To this end, the back head 10 is fixedly arranged to the first end 81, and the chuck 90 is fixedly arranged to the second end 82. The shank adapter 70 extends between a first end 71 and a second end 72 which is attached to the drill bit 100. In other embodiments, the shank adapter 70 and drill bit 100 may be integrally formed in one piece. When mounted, the shank adapter 70 passes through the chuck 90. A washer or retaining ring 75 is provided between the chuck 90 and the housing 80 to retain the shank adapter 70 and drill bit 100. The washer 75 engages a first splined portion 73 adjacent the first end 71 and restricts distal movement of the shank adapter 70 in a flush position of the DTH hammer 1, i.e., when the drill bit 100 is not in contact with rock to be drilled.

[0029] The inner cylinder 40 extends between a first end 41 and a second end 42 and is fixedly arranged inside the housing 80 such that an intermediate space 45 (cf. Fig. 5a) is formed between the housing 80 and the inner cylinder 40. Further, the inner cylinder 40 comprises at least one first through-going hole 43 adjacent the first end 41 and at least one second through-going hole 44 adjacent the second end 42.

[0030] The distributor 30 comprises a cylindrical body 31 having at least one through- going axial conduit 32 (cf. Fig. 4c) therein extending in a distal direction from a first end 33 of the cylindrical body 31, substantially parallel to a longitudinal axis of the distributor 30. The distributor 30 further comprises a tubular stem 34 comprising a central distributor bore 36 extending in a distal direction from the body 31. The distributor bore 36 is separate from the axial conduit 32. The distributor 30 may comprise a plurality of axial conduits 32 distributed about the circumference and terminating in an annular groove 38 formed in the outer surface of the cylindrical body 31.

[0031] The distributor 30 is fixedly arranged between the back head 10 and the first end 41 of the inner cylinder 40 and extends partially into the first end 41 of the inner cylinder 40 such that the axial conduit 32 is in fluid communication with the intermediate space 45 through the first hole 43 in the inner cylinder 40. [0032] The actuator is in the form of a piston 50 extending between a first end 51 and a second end 52 and comprises a central piston bore 53. The piston 50 is arranged to reciprocate in an axial direction inside the housing 80 to impact on the distally arranged drill bit 100, the first end 51 of the piston 50 extending partially into the second end 42 of the inner cylinder 40.

[0033] An internal space of the inner cylinder 40 defines a drive chamber 46 proximal to the piston 50 and an internal space of the housing 80 defines a return chamber 85 distal to the piston 50. As may be seen in Fig. 3, the tubular stem 34 of the distributor 30 extends into the drive chamber 46, placing the distributor bore 36 in fluid communication therewith.

[0034] The drill bit 100 comprises a central drill bit bore 101 which is aligned with and in fluid communication with a central bore 74 of the shank adapter 70. The exhaust tube 60 is seated in the central bore 74 of the shank adapter 70 and extends from the first end 71 in a proximal direction. The drill bit bore 101, the central bore 74 of the shank adapter 70 and the exhaust tube 60 together form a bit exhaust path for exhaust fluid to flush debris from the external face of the drill bit 100. In the context of the present disclosure, motive fluid is the fluid that is supplied to the DTH hammer 1 to actuate the piston 50, whereas exhaust fluid is the fluid that is evacuated from the DTH hammer 1 after acting on the piston 50, as will be explained further below.

[0035] As noted above, the piston 50 is arranged to reciprocate inside the housing 80 when motive fluid is supplied through a drill string (not shown) attached to the back head 10. This reciprocating motion periodically places the intermediate space 45 in fluid communication with the drive chamber 46 and the return chamber 85, respectively, through the at least one second hole 44 in the inner cylinder 42. The periodic fluid communication between the intermediate space 45 and the drive chamber 46 and the return chamber 85, respectively, causes motive fluid to be supplied from the intermediate space 45 to the drive chamber 46 and return chamber 85 in alternating fashion, to cause the piston 50 to reciprocate in a distal and a proximal direction, respectively.

[0036] At the same time, reciprocation of the piston 50 in the housing 80 periodically places the piston bore 53 in fluid communication with the return chamber 46 and the drive chamber 85, respectively. The periodic fluid communication between the piston bore 53 and the return chamber 85 and the drive chamber 46 causes exhaust fluid to be exhausted from the return chamber 85 and the drive chamber 46 in alternating fashion, distally through the exhaust tube 60, shank adapter bore 74 and drill bit bore 101, and/or proximally through the distributor bore 36.

[0037] The piston 50 comprises a first flared portion 55 adjacent the first end 51 having an outer diameter substantially corresponding to the inner diameter of the inner cylinder 40, and a second flared portion 56 adjacent the second end 52 having an outer diameter substantially corresponding to the inner diameter of the housing 80. The drive chamber 46 is defined by a section of the inner cylinder 40 having an inner diameter greater than the outer diameter of the first flared portion 55. The return chamber 85 is defined by a section of the housing 80 having an inner diameter greater than the outer diameter of the second flared portion 56.

[0038] Displacement of the piston 50 in a proximal direction at least temporarily places the drive chamber 46 in fluid communication with the intermediate space 45 when the first flared portion 55 of the piston 50 fully extends into the drive chamber 46.

Contrarily, displacement of the piston 50 in a distal direction at least temporarily places the return chamber 85 in fluid communication with the intermediate space 45 when the second flared portion 56 of the piston 50 fully extends into the return chamber 85.

[0039] Concomitantly, the displacement of the piston 50 in the proximal direction at least temporarily cuts off fluid communication between the drive chamber 46 and the piston bore 53, while placing the return chamber 85 in fluid communication with the piston bore 53. Additionally, the displacement of the piston 50 in the distal direction at least temporarily cuts off fluid communication between the return chamber 85 and the piston bore 53, while placing the drive chamber 46 in fluid communication with the piston bore 53.

[0040] In one embodiment, the piston bore 53 comprises a first narrow section 57 adjacent the first end 51 of the piston 50 having a diameter substantially corresponding to the diameter of the tubular stem 34 of the distributor 30, and a second narrow section 58 adjacent the second end 52 of the piston 50 having a diameter substantially corresponding to the diameter of the exhaust tube 60. The reciprocating motion of the piston 50 in the proximal direction at least temporarily cuts off fluid communication between the drive chamber 46 and the piston bore 53 when the tubular stem 34 of the distributor 30 extends into the first narrow section 57. Contrarily, the reciprocating motion of the piston 50 in the distal direction at least temporarily cuts off fluid communication between the return chamber 85 and the piston bore 53 when the exhaust tube 60 extends into the second narrow section 58 (as shown in Fig. 3).

[0041] By means of the reciprocating motion of the piston 50, the actuator drive flow path of the motive fluid to actuate the piston 50 in the drive stroke and return stroke is kept separated from the actuator exhaust flow path of the exhaust fluid for evacuation.

[0042] In one embodiment (not shown), the piston bore 53 comprises a first section extending from the first end 51 of the piston 50 and a second section extending from the second end 52, wherein the first and second sections are not in fluid communication with each other. In other words, the piston bore 53 is not through-going. As a result, the exhaust fluid from the return chamber 85 will only be evacuated in the distal direction through the exhaust tube 60, shank adapter bore 74 and drill bit bore 101, whereas the exhaust fluid from the drive chamber 46 will only be evacuated in the proximal direction through the distributor bore 36. By varying the length of the first and second sections, it is possible to control the amount of exhaust fluid being evacuated in the respective directions.

Alternatively, other aspects such as the dimensions of the drive chamber 46 and the return chamber 85 may be varied to achieve the same purpose.

[0043] Referring now to Figs. 4 and 5a-5d, there is shown a check valve assembly 20 according to one embodiment of the present disclosure. Fig. 4 illustrates the check valve assembly 20 in a perspective view, whereas Figs. 5a-5d show close-up cross-sectional views of the proximal end of the DTH hammer 1 with the check valve assembly 20 in the closed and open positions, wherein the sections in Figs. 5a and 5b are rotated 90 degrees about the longitudinal axis in relation to the sections in Figs. 5c and 5d.

[0044] The check valve assembly 20 is arranged in an internal space of the back head

10 proximal to the distributor 30. The back head 10 comprises a threaded conical portion

11 for connection with drill pipes 5 of a drill string (shown partially e.g. in Fig. 7a) and supply of motive fluid through a proximal opening called the supply port 12. Further, the back head 10 comprises a flat recess 13, known as a key grip, as well as one or more evacuation ports 14 for an exhaust fluid, as will be further explained below.

[0045] The check valve assembly 20 is configured to control simultaneous flow of motive fluid and exhaust fluid, respectively, into and out of the housing 80 in such a way that the flow of motive fluid is separated from the flow of exhaust fluid. To this end, the check valve assembly 20 comprises a cylindrical body 21 extending between a first, proximal end 22 and a second, distal end 23. A tubular stem 25 extends in a distal direction from the second end 23 of the cylindrical body 21. The cylindrical body 21 comprises at least one through-going first internal passage in the form of an axial conduit 24 extending from the proximal end 22 to the distal end 23. The axial conduit 24 forms a first internal passage in the check valve assembly 20, defining a first flow path for motive fluid through the check valve assembly 20. As may be seen in in Figs. 4c and 5d, the cylindrical body 21 comprises two axial conduits 24 arranged diametrically opposite to each other and offset from a longitudinal axis X of the check valve assembly 20 to distribute the flow of motive fluid in a balanced manner. The axial conduits 24 may be arcuate in shape extending along a circular arc to increase the cross-sectional area within the available material space of the cylindrical body 21. However, the number, shape and positioning of axial conduits 24 may be varied within the scope of the present disclosure.

[0046] The tubular stem 25 delimits an internal cavity 26 which extends into and terminates inside the cylindrical body 21, i.e., the cavity 26 is not through-going. The cylindrical body 21 further comprises at least one radial conduit 27, extending laterally in a substantially radial direction from the cavity 26 and terminating in an orifice on an outer surface 28 of the cylindrical body 21. Together, the cavity 26 and the radial conduit 27 form a second internal passage which defines a second flow path for exhaust fluid through the check valve assembly 20. The first and second flow paths are separate from each other such that flows of motive fluid and exhaust fluid are not mixed.

[0047] In one embodiment, the tubular stem 25 is coaxial with the longitudinal axis X to provide a rotationally symmetrical check valve assembly 20, thus facilitating manufacture and ensuring optimal operation in a DTH hammer. Further, the cylindrical body 21 may comprise two radial conduits 27 arranged substantially diametrically opposite to each other to distribute the flow of exhaust fluid in a balanced manner.

[0048] The outer surface 28 of the cylindrical body 21 may further comprise an annular recess 29 along the circumference which is aligned with the orifice of the radial conduit 27. The recess 29 allows exhaust fluid exiting the orifice to flow along the circumference of the cylindrical body 21 such that the flow of exhaust fluid may be distributed and evacuated from any of the evacuation ports 14 in the back head 10. The diameter of the orifice is smaller than or equal to the width of the recess 29. In one embodiment, the radial conduit 27 has a circular cross-section which corresponds to the diameter of the orifice. Further, the diameter of the orifice and/or the width of the recess 29 substantially correspond to the diameter of the evacuation ports 14 in the back head 10, such that the flow of exhaust fluid from the radial conduit 27 through the evacuation ports 14 is facilitated when the recess 29 (and orifice) is aligned therewith.

[0049] Further, the outer surface 28 of the cylindrical body 21 may be provided with annular grooves along the circumference serving as seats for corresponding annular seals. First and second annular seals are seated in first and second annular grooves arranged adjacent to the recess 29 on opposite sides thereof. A third annular seal is seated in a third annular groove arranged adjacent to the second end 23 of the cylindrical body. The annular grooves are arranged such that the second groove is substantially equidistant from both the first and third annular grooves, respectively. The annular seals provide fluid-tight sealing between the check valve assembly 20 and the back head 10 as will be further explained below.

[0050] The cylindrical body 21 further comprises an elevated portion 250 which protrudes from the first end 22 of the cylindrical body 21. As may be seen in Figs. 5a-5d, the cavity 26 may terminate in the elevated portion 250 such that that the diameter of the elevated portion 250 is substantially equal to the diameter of the tubular stem 25. A fourth annular groove is arranged on the elevated portion 250 and serves as a seat for a fourth annular seal. [0051] In one embodiment, the annular seals are X-rings. However, other types of annular seals such as O-rings with a circular cross-section, square rings with square profiles, flat gaskets or packings may also be used.

[0052] The function of the check valve assembly 20 in a DTH hammer 1 will now be explained in more detail. The check valve assembly 20 is arranged in the back head 10 of the DTH hammer to control the flow of motive fluid and exhaust fluid. In Figs. 5a and 5c, the check valve assembly 20 is shown in a first, closed position. As may be seen, the distal end of the tubular stem 25 extends into a cavity 37 of the distributor 30. A biasing member, here in the form of a resilient spring 35 arranged on the outside of the tubular stem 25 and abutting against a shoulder 240, is provided between the check valve assembly 20 and the distributor 30 to bias the check valve assembly 20 in a proximal direction towards the closed position.

[0053] In the closed position, the elevated portion 250 of the cylindrical body 21 extends into a supply port 12 of the back head 10 to block the opening thereof. The fourth annular seal 24 on the elevated portion 250 provides a fluid tight seal with the inner wall of the supply port 12 such that no motive fluid may enter into the housing 80 of the DTH hammer 1. At the same time, the orifice of the radial conduit 27 in the cylindrical body 21 is in a proximal position out of alignment with the evacuation ports 14. The second and third annular seals provide a fluid tight seal with the inner wall of the back head 10 such that no exhaust fluid may exit from the housing 80. Additionally, no fluid or debris present outside the housing 80 may enter into the housing through the evacuation ports 14.

[0054] Turning now to Figs. 5b and 5d, the check valve assembly 20 is shown in a second, open position, wherein the fluid pressure of motive fluid, supplied through a drill string (not shown) connected to the DTH hammer 1 by means of the threads 11, pushes on the elevated portion 250 to displace the check valve assembly 20 in a distal direction against the bias of the spring 35. The tubular stem 25 bottoms out as the distal end reaches the bottom of the cavity 37.

[0055] In the open position, the elevated portion 250 no longer extends into the supply port 12, thereby allowing the motive fluid to flow through the axial conduits 24 of the cylindrical body 21 and further into an actuator drive flow path inside the housing 80, here defined by one or more canals 41 and holes 42 arranged in the distributor 30. The flow of motive fluid is illustrated by the downwardly directed arrows. The motive fluid acts on the piston 50 to impart reciprocating motion thereon to impact on the drill bit 100 and thus operate the DTH hammer 1 as explained above.

[0056] After the motive fluid has performed its action on the piston 50, it is exhausted from the housing 80 as exhaust fluid. As explained above, part of the exhaust fluid is evacuated distally through the drill bit 100 to clear away the debris from the drilling. The remaining part of the exhaust fluid is evacuated proximally through the distributor bore 36 which is arranged in fluid communication with the second flow path defined by the cavity 26 and the radial conduit 27. The cavity 37 of the distributor 30 is part of the distributor bore 36 and defined by having a larger diameter than the remaining part, thus providing an abutment or shoulder for stopping the distal travel of the tubular stem 25. The exhaust fluid flows through the distributor bore 36 and further into the cavity 26, the radial conduit 27 and out through the evacuation ports 14 via the orifice. The flow of exhaust fluid is illustrated by the upwardly directed arrows.

[0057] As such, the check valve assembly 20 allows simultaneous but separate supply of motive fluid and evacuation of exhaust fluid through the back head 10 by means of one single component. This greatly reduces the complexity and cost of manufacture of the check valve assembly 20 as well as increasing service life due to fewer moving parts and reduced wear.

[0058] Referring now to Figs. 6 and 7a-7d, there is shown an other embodiment of a check valve assembly 200. Fig. 6 illustrates the check valve assembly 200 in a perspective view, whereas Figs. 7a-7d show close-up cross-sectional views of the proximal end of the DTH hammer 1 with the check valve assembly 200 in the closed and open positions, wherein the sections in Figs. 7a and 7b are rotated 90 degrees about the longitudinal axis in relation to the sections in Figs. 7c and 7d.

[0059] The check valve assembly 200 differs from the check valve assembly 20 only in that the cylindrical body 210 has a smaller length along the longitudinal axis such that in the closed position shown in Fig. 7a and 7c, the cylindrical body 210 does not cover the evacuation ports 14. Instead, there is provided an additional component of the check valve assembly 200 in the form of an external sleeve 220 arranged on the outer surface of the back head 10 and biased distally toward a closed position by means of a second biasing member 225 in the form of a spring. The spring 225 is arranged between the external sleeve 220 and the distal end of a drill pipe 5 connected to the back head 10. In operation, the pressure of the exhaust fluid in the evacuation ports 14 acts on the external sleeve 220 to push it in the proximal direction and thereby open the evacuation ports 14 to allow egress of exhaust fluid. To this end, the evacuation ports 14 are oriented in a proximal direction, i.e. at a non-perpendicular angle to the longitudinal axis of the DTH hammer 1. It should be understood that the external sleeve 220 may be combined with the embodiment of Figs. 5a-5d and also other embodiments described below to provide an additional safeguard against ingress of external fluid and debris.

[0060] The check valve assembly 200 allows simultaneous but separate supply of motive fluid and evacuation of exhaust fluid through the back head 10 by means of two components, the cylindrical body 210 and the external sleeve 220. This solution reduces the material required for the cylindrical body and provides a separate blocking of the evacuation ports 14.

[0061] Referring now to Fig. 8 and 9a-9d, there is shown an other embodiment of a check valve assembly 400 and distributor 300. Fig. 8 illustrates the distributor 300 and the check valve assembly 400 in a perspective view, whereas Figs. 9a-9d show close-up cross- sectional views of the proximal end of the DTH hammer 1 with the check valve assembly 400 in the closed and open positions, wherein the sections in Figs. 9a and 9b are rotated 90 degrees about the longitudinal axis in relation to the sections in Figs. 9c and 9d.

[0062] The distributor 300 differs from the distributor 30 in that the distributor body 310 extends further in the proximal direction such that the cavity 370 is arranged to receive substantially the whole length of the check valve assembly 400 in the open position. The distributor 300 comprises one or more axial conduits 320 distributed about the circumference and terminating in an annular groove 380 formed in the outer surface of the distributor body 310.

[0063] Further, the distributor body 310 comprises one or more radial conduits 375 extending laterally in a substantially radial direction from the wider cavity 370 and terminating in an orifice on an outer surface of the distributor body 310. The radial conduit 375 is in fluid communication with the distributor bore 360 through the wider cavity 370. The check valve assembly 400 is in the form of a cylindrical body 410 closed at a first end 411 facing towards the supply port 12. A biasing member 350 in the form of a resilient spring is arranged inside the cylindrical body 410 and urges the check valve assembly 400 towards the closed position. A gasket 405 may be arranged at a proximal end of the cylindrical body 410 to ensure a fluid tight seal against the back head 110. When motive fluid is supplied through the supply port, the fluid pressure displaces the cylindrical body 410 in the distal direction, allowing passage of motive fluid on the outside of the cylindrical body 410 through the internal space of the back head 10 to the axial conduits 320 of the distributor 300 via the annular groove 380 and the holes 43, and further into the intermediate space 45 as explained above.

[0064] The cylindrical body 410 further comprises one or more lateral openings 420. The lateral openings 420 are configured to be in alignment with the radial conduits 375 of the distributor 300 when the check valve assembly 400 is in the open position to allow flow of exhaust fluid from the distributor bore 360 to the radial conduits 375. The distributor 300 may also comprise an annular groove 385 formed inside the cavity 370 and in alignment with the radial conduits 375 to distribute the flow of exhaust fluid around the circumference of the cylindrical body 410 of the check valve 400. The radial conduits 375 are in turn in fluid communication with evacuation ports 140 in the back head 110 formed e.g. by one or more axially oriented channels milled in the back head 110. In other embodiments (not shown), the exhaust fluid may pass from the radial conduits 375 via a space between the housing 80 and the back head 110, for instance through gaps in the thread profiles. In the closed position of the check valve assembly 400, the lateral openings 420 are no longer aligned with the radial conduits 375, thus blocking passage of the exhaust fluid.

[0065] The check valve assembly 400 allows simultaneous but separate supply of motive fluid and evacuation of exhaust fluid through the back head 10 by means of a single component, the cylindrical body 410 co-operating with the modified distributor 300. This solution greatly reduces the space required inside the back head 110 for accommodating the check valve assembly 400, thereby facilitating manufacture, in addition to increasing service life due to fewer moving parts and reduced wear.

[0066] Referring now to Fig. 10 and 1 la-1 Id, there is shown an other embodiment of a check valve assembly 500. Fig. 10 illustrates the check valve assembly 500 in a perspective view, whereas Figs. 1 la-1 Id show close-up cross-sectional views of the proximal end of the DTH hammer 1 with the check valve assembly 500 in the closed and open positions, wherein the sections in Figs. I la and 1 lb are rotated 90 degrees about the longitudinal axis in relation to the sections in Figs. 11c and l id.

[0067] The check valve assembly 500 is similar to the embodiment of Figs. 8 and 9a- 9d in that it comprises a cylindrical body 510 with an internally arranged biasing member which urges the check valve assembly in the proximal direction toward the closed position. A gasket 505 may be arranged at a proximal end of the cylindrical body 410 to ensure a fluid tight seal against the back head 110. However, the cylindrical body 510 is seated in a second valve member 520 which in turn is seated in the cavity 37 of the distributor 30. The second valve member 520 comprises a central conduit 521 in fluid communication with the distributor bore 36 and diametrically opposed lateral slots 522 on an outer surface of the second valve member 520. The lateral slots 522 are in fluid communication with the central conduit 521 via through-going openings 523 near a distal end of the slots 522. The walls 524 delimiting the lateral slots 522 on the outer surface of the second valve member 520 have a thickness chosen such that the outer diameter of the second valve member 520 substantially corresponds to the inner diameter of the back head 10. The proximal end of the lateral slots 522 are in fluid communication with the evacuation ports 14 of the back head 10. Together, the central conduit 521, the lateral slots 522 and the evacuation ports 14 form the second internal passage defining the second flow path for the exhaust fluid.

[0068] Similar to the embodiment of Figs. 7a-7d, an external sleeve 220 is provided to close the evacuation ports 14. In the open position of the check valve assembly 500, the motive fluid flows on the outside of the cylindrical body 510 and the second valve member 520 through the internal space of the back head 10 to the axial conduits 32 of the distributor 30 and further into the intermediate space 45 as explained above, thus forming the first internal passage defining the first flow path for the motive fluid. The first flow path is separated from the second flow path by means of the walls 524 delimiting the lateral slots 522

[0069] The check valve assembly 500 allows simultaneous but separate supply of motive fluid and evacuation of exhaust fluid through the back head 10 by means of three components, the cylindrical body 510, the second valve member 520 and the external sleeve 220. This solution simplifies the configuration of the exhaust fluid path, reduces wear due to fewer moving parts and provides a separate blocking of the evacuation ports 14.

[0070] Referring now to Figs. 12a-12d, there is shown an other embodiment of a check valve assembly 600. Figs. 12a-12d show close-up cross-sectional views of the proximal end of the DTH hammer 1 with the check valve assembly 600 in the closed and open positions, wherein the sections in Figs. 12a and 12b are rotated 90 degrees about the longitudinal axis in relation to the sections in Figs. 12c and 12d.

[0071] The check valve assembly 600 is similar to the check valve assembly 500 comprising a cylindrical body 610 and a second valve member 620 having the same features denoted by ‘6’ as the first digit instead of ‘5’, but differs therefrom in that it further comprises a tubular member 630 movably arranged inside the central conduit 621. The tubular member 630 is closed at a first end and comprises one or more lateral openings 635. In the closed position of the check valve assembly 600, the tubular member 630 is in a distal position at the bottom of the central conduit 621, e.g. by the effect of gravity. In this position, the lateral openings 635 are not aligned with the lateral slots 622 and there is no flow of exhaust fluid. Likewise, the closed first end of the tubular member 630 blocks external fluid from entering into the housing 80. In the open position of the check valve assembly 600, the pressure of the exhaust fluid pushes the tubular member 630 in the proximal direction such that the exhaust fluid may flow through the central conduit 621 and lateral slots 622 of the second valve member 620 and out through the evacuation ports 14.

[0072] The check valve assembly 600 allows simultaneous but separate supply of motive fluid and evacuation of exhaust fluid through the back head 10 by means of three components, the cylindrical body 610, the second valve member 620 and the tubular member 630. This solution simplifies the configuration of the exhaust fluid path, reduces wear due to fewer moving parts and provides a separate closure of the central conduit 621.

[0073] Embodiments of a DTH hammer according to the present disclosure has been described. However, the person skilled in the art realizes that this can be varied within the scope of the appended claims without departing from the inventive idea.

[0074] All the described alternative embodiments above or parts of an embodiment can be freely combined without departing from the inventive idea as long as the combination is not contradictory.