Technical Field

[0001] The present invention relates generally to a check valve for down-the-hole hammers.

Background Art

[0002] Standard down-the-hole (DTH) hammers on the market today have one inlet for motive fluid (e.g., compressed air, water etc.) at the top of the hammer and the exhaust is usually through the drill bit face in the front. In between the inlet and exhaust, the motive fluid is passed over a combined piston/valve, which in turn creates a piston movement up and down with an impact against the drill bit. This creates a power output. The exhausted fluid in the front of the bit clears the volume between bit and rock from rock debris. The rock debris is then transported by the fluid flow on the outside of the hammer casing along the wall of the bore hole.

[0003] The amount of fluid used is needed primarily to achieve a certain power output from the hammer and/or lifting the rock debris and ground water pouring into the created bore hole. When considering the wear life of the drill bit and the outer casing of the hammer, the amount of fluid used is excessive in relation to what is needed to flush the rock debris. A smaller amount of fluid flow would be beneficial for the wear life of drill bit and hammer casing.

[0004] 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.

[0005] Every time a new drill pipe is added to the drill string, the fluid pressure drops in the drill string, which would allow backpressure from groundwater to push mud, rock debris and/or dirt into the hammer. To prevent this, standard hammers have a check valve function at the inlet of the hammer. With additional exhaust ports near the proximal end, a separate check valve is required for the exhaust flow. Summary of Invention

[0006] An objective of the present invention is to provide an improved check valve solution which facilitates handling flow of motive and exhaust fluid through the back head of a DTH hammer. The device is described in the appended claims.

[0007] According to a first aspect of the present disclosure, there is provided a check valve for use with a down-the-hole, DTH, hammer to control flow of a motive fluid, said check valve comprising: at least one through-going first internal passage defining a first flow path for the motive fluid; and at least one through-going second internal passage defining a second flow path for an exhaust fluid, separate from the first flow path.

[0008] By means of the first and second flow paths, the check valve is configured to control separate and simultaneous flows of motive and exhaust fluid.

[0009] In one embodiment, the check valve comprises a cylindrical body, wherein the at least one first internal passage comprises an axial conduit extending in a substantially axial direction from a first end to a second end of the cylindrical body and, and a tubular stem extending in an axial direction from the second end of the cylindrical body, wherein an internal cavity defined by the tubular stem extends into but not through the cylindrical body, wherein the cylindrical body further comprises at least one second conduit extending in a substantially radial direction from the cavity to an outer surface of the cylindrical body such that the cavity and the at least one second conduit together form the second internal passage. In this configuration, the check valve may be realised in a single component, thereby reducing complexity and cost of manufacture as well as increasing service life due to fewer moving parts and reduced wear. Additionally, the check valve allows for a more effective sealing solution.

[0010] In one embodiment, the outer surface of the cylindrical body comprises an annular recess aligned with the orifice of the at least one second conduit. The annular recess allows distribution of the exhaust fluid along the circumference of the cylindrical body to facilitate fluid communication with evacuation ports at any angular position arranged e.g. in the back head of a DTH hammer. [0011] In one embodiment, the cylindrical body comprises first and second annular seals seated in first and second annular grooves arranged on the outer surface of the cylindrical body adjacent to and on opposite sides of the annular recess. The annular seals ensure fluid tight sealing at the interface between the DTH hammer and the check valve in an open position.

[0012] In one embodiment, the cylindrical body further comprises a third annular seal seated in a third annular groove arranged on the outer surface of the cylindrical body adjacent to the second end of the cylindrical body such that the second annular groove is substantially equidistant from the first and third annular grooves, respectively. The additional seal provides fluid tight sealing at the interface between the DTH hammer and the check valve in a closed position.

[0013] The check valve according to any one of the preceding claims, wherein the cylindrical body comprises an elevated portion protruding from the first end of the cylindrical body. The elevated portion may extend into a supply port of the DTH hammer in a closed position of the check valve to block supply of motive fluid.

[0014] In one embodiment, the cylindrical body comprises a fourth annular seal seated in a fourth annular groove arranged on the elevated portion. The fourth seal provides fluid tight sealing at the interface between the supply port of the DTH hammer and the check valve in the closed position.

[0015] In one embodiment, the annular seals are X-rings. X-rings provide improved sealing and increased service life in reciprocating applications compared to other types of gaskets such as O-rings, due to reduced running and breakout friction and reduced risk of spiraling.

[0016] In one embodiment, the tubular stem is coaxial with a longitudinal axis of the cylindrical body. The coaxial configuration provides rotational symmetry of the check valve for facilitating manufacture and optimal operation in a DTH hammer.

[0017] In one embodiment, the at least one first conduit is arranged offset from a longitudinal axis of the cylindrical body. The offset, eccentric configuration of the first conduit(s) provides optimal use of space and distribution of material thickness in the cylindrical body to separate the first and second flow paths in an effective, balanced manner.

[0018] In one embodiment, a cross-section of the at least one first conduit has an arcuate shape. The arcuate shape enables adapting and increasing the cross-sectional area of the first conduit, e.g. in combination with a coaxial tubular stem.

[0019] In one embodiment, the cylindrical body comprises two first conduits arranged substantially diametrically opposite to each other. In one embodiment, the cylindrical body comprises two second conduits arranged substantially diametrically opposite to each other. Two oppositely arranged passages increases the available cross-sectional area and balances distribution of fluid flow through the check valve.

[0020] In a second aspect of the present disclosure, there is provided a DTH hammer configured for operation under the influence of motive fluid, the DTH hammer comprising: a housing; a back head connected to the housing; an actuator configured to be operated by motive fluid; and a check valve according to the first aspect arranged in the back head and arranged in fluid communication with an actuator drive flow path to control supply of motive fluid to the actuator drive flow path through the at least one first flow path. The check valve is further arranged in fluid communication with an actuator exhaust flow path and configured to receive an exhaust fluid and to control evacuation of exhaust fluid from the actuator exhaust flow path through the at least one second flow path.

[0021] In one embodiment, the back head comprises at least one motive fluid supply port and at least one exhaust fluid evacuation port separated from the at least one motive fluid supply port, wherein the check valve is configured to be displaced between a first, closed position wherein the at least one motive fluid supply port and the at least one exhaust fluid evacuation port are blocked by the cylindrical body of the check valve, and a second, open position, wherein the first and second flow paths are in fluid communication with the motive fluid supply port and the at least one exhaust fluid evacuation port, respectively, to allow simultaneous supply of motive fluid and evacuation of exhaust fluid through the back head. [0022] In one embodiment, the at least one exhaust fluid evacuation port comprises a first opening configured for communication with the recess and/or the orifice of the at least one second conduit, and a second opening configured for communication with an exterior of the back head. The two openings may be aligned with each other, representing a substantially straight evacuation port. Alternatively, the evacuation port may be formed by a non-straight passageway between the two openings.

[0023] In one embodiment, an inner surface of the back head comprises two annular raised portions arranged adjacent to the first opening of the at least one exhaust fluid evacuation port, distal and proximal thereto. The annular raised portion ensures optimal sealing contact between the inner surface of the back head and the annular seals in the closed and open positions of the check valve. At the same time, the sliding contact between the annular seals and the inner surface of the back head during travel between the respective end positions is reduced or even eliminated. Thereby the service life of the annular seals is increased due to reduced wear. The reduced friction during travel also serves to reduce the required force to close the check valve, thereby ensuring reliability of the function of the check valve. Finally, any debris caught between the seals, inner surface and cylindrical body in the closed position will be flushed out in the open position.

Brief Description of Drawings

[0024] The invention 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

Fig. 2a is a perspective view of a check valve according to one embodiment of the present disclosure.

Fig. 2b is a plan end view of the check valve of Fig. 2a.

Figs. 2c and 2d are cross-sectional views taken along sections A-A and B-B of the check valve in Fig. 2b.

Figs. 3a and 3b are cross-sectional views taken along sections A-A and B-B, respectively of the check valve arranged in a back head of a DTH hammer in a closed position. Figs. 4a and 4b are cross-sectional views taken along sections A-A and B-B, respectively of the check valve arranged in a back head of a DTH hammer in an open position.

Figs. 5a-5c are close-up cross-sectional views of the check valve arranged in a back head of a DTH hammer in closed, open and intermediate positions, respectively.

Fig. 6a and 6b are perspective and cross-sectional views of an alternative check valve of the present disclosure.

Figs. 7a-7c are perspective and cross-sectional views of an alternative check valve of the present disclosure.

Figs. 8a-8e are perspective and cross-sectional views of an alternative check valve of the present disclosure.

Description of Embodiments

[0025] In the following, a detailed description of device according to the invention 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 invention. 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.

[0026] In the present application, 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. [0027] For the sake of simplicity and consistency in this specification, the term ‘axial’ refers to a direction parallel to a central axis of a DTH hammer as illustrated in the drawings. 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.

[0028] 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.

[0029] 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.

[0030] Referring now to Fig. 1, there is shown an exemplary DTH hammer 1 comprising a housing 4 with a back head 2 at a first, proximal end and a drill bit 3 at a second, distal end. The back head 2 comprises a threaded conical portion 5 for connection with drill pipes of a drill string (not shown) and supply of motive fluid. Further, the back head 2 comprises a flat recess 6, known as a key grip, as well as evacuation ports 8 for an exhaust fluid, as will be further explained below. In the context of the present disclosure, the term ‘exhaust fluid evacuation port’ is interpreted as an opening or passageway of any shape suitable for the intended purpose, namely to convey exhaust fluid from the inside to the outside of the housing 4. Inside the housing 4, there is arranged an actuator (not shown) configured to be operated by motive fluid supplied through the back head 2 in a reciprocating motion to impact the drill bit 3. The motive fluid is then evacuated from the housing 4 as exhaust fluid, partially through the drill bit 3 at the distal end to flush out the debris from drilling, and partially through the evacuation ports 8 at the proximal end.

[0031] Referring now to Figs. 2a-2d, there is shown a check valve 10 according to one embodiment of the present disclosure. Fig. 2a shows the check valve 10 in a perspective view. Fig. 2b is an end view of the proximal end 12 of the check valve 10 as seen from above, and Figs. 2c and 2d are cross-sectional views taken along lines A-A and B-B in Fig. 2b, respectively.

[0032] The check valve 10 comprises a cylindrical body 11 extending between a first, proximal end 12 and a second, distal end 13. A tubular stem 15 extends in a distal direction from the second end 13 of the cylindrical body 11. The cylindrical body 11 comprises at least one through-going first internal passage in the form of a first conduit 14 extending from the proximal end 12 to the distal end 13. The first conduit 14 defines a first flow path for motive fluid through the check valve 10. As may be seen in the embodiment shown in Figs. 2a-2b, the cylindrical body 11 comprises two first conduits 14 arranged diametrically opposite to each other and offset from a longitudinal axis X of the check valve 10 to distribute the flow of motive fluid in a balanced manner. The first conduits 14 may be arcuate in shape extending along a circular arc as shown in Fig. 2b to increase the cross- sectional area within the available material space of the cylindrical body 11. However, the number, shape and positioning of first conduits 14 may be varied within the scope of the present disclosure.

[0033] The tubular stem 15 delimits an internal cavity 16 which extends into and terminates inside the cylindrical body 11, i.e., the cavity 16 is not through-going. The cylindrical body 11 further comprises at least one second conduit 17, extending in a substantially radial direction from the cavity 16 and terminating in an orifice 20 on an outer surface 18 of the cylindrical body 11. Together, the cavity 16 and the second conduit 17 form a second internal passage, defining a second flow path for exhaust fluid through the check valve 10. The first and second flow paths are separate from each other such that flows of motive fluid and exhaust fluid are not mixed. [0034] In one embodiment, the tubular stem 15 is coaxial with the longitudinal axis X to provide a rotationally symmetrical check valve 10, thus facilitating manufacture and ensuring optimal operation in a DTH hammer. Further, the cylindrical body 11 may comprise two second conduits 17 arranged substantially diametrically opposite to each other to distribute the flow of exhaust fluid in a balanced manner.

[0035] The outer surface 18 of the cylindrical body 11 may further comprise an annular recess 19 along the circumference which is aligned with the orifice 20 of the second conduit 17. The recess 19 allows exhaust fluid exiting the orifice 20 to flow along the circumference of the cylindrical body 11 such that the flow of exhaust fluid may be distributed and evacuated from any of the evacuation ports 8 in the back head 2. The diameter of the orifice 20 is smaller than or equal to the width of the recess 19. In one embodiment, the second conduit 17 has a circular cross-section which corresponds to the diameter of the orifice 20. Further, the diameter of the orifice 20 and/or the width of the recess 19 substantially correspond to the diameter of the evacuation ports 8 in the back head 2, such that the flow of exhaust fluid from the second conduit 17 through the evacuation ports 8 is facilitated when the recess 19/orifice 20 is aligned therewith.

[0036] In some embodiments, an exhaust fluid evacuation port 8 of the back head 2 may comprise a first opening configured for communication with the recess 19 and/or the orifice 20 of the at least one second conduit 17, and a second opening configured for communication with an exterior of the back head 2. In some embodiments, the first and second openings of the evacuation port 8 may at least partly overlap. In some embodiments as illustrated in Figs. 1 and 3-5, the exhaust fluid evacuation port 8 may comprise one opening configured for communication with the recess 19 and/or the orifice 20 of the at least one second conduit 17 and also communication with an exterior of the back head 2.

[0037] Further, the outer surface 18 of the cylindrical body 11 may be provided with annular grooves 31, 32, 33 along the circumference serving as seats for corresponding annular seals 21, 22, 23. First and second annular seals 21, 22 are seated in first and second annular grooves 31, 32 arranged adjacent to the recess 19 on opposite sides thereof. A third annular seal 23 is seated in a third annular groove 33 arranged adjacent to the second end 13 of the cylindrical body. The annular grooves 31, 32, 33 are arranged such that the second groove 32 is substantially equidistant from both the first and third annular grooves 31, 33, respectively. The annular seals 21, 22, 23 provide fluid-tight sealing between the check valve 10 and the back head 2 as will be further explained below.

[0038] The cylindrical body 11 further comprises an elevated portion 25 which protrudes from the first end 12 of the cylindrical body 11. As may be seen in Figs. 2c and 2d, the cavity 16 may terminate in the elevated portion 25 such that that the diameter of the elevated portion 25 is substantially equal to the diameter of the tubular stem 15. A fourth annular groove 34 is arranged on the elevated portion 25 and serves as a seat for a fourth annular seal 24.

[0039] In one embodiment, the annular seals 21, 22, 23, 24 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.

[0040] Referring now to Figs. 3a-3b and 4a-4b, the function of the check valve 10 in a DTH hammer 1 will be explained in more detail. The check valve 10 is arranged in the back head 2 of the DTH hammer to control the flow of motive fluid and exhaust fluid. In Figs. 3a and 3b, the check valve 10 is shown in a first, closed position. As may be seen, the distal end of the tubular stem 15 extends into an opening 43 of a distributor 40 which is arranged in a fixed position inside the housing 4. A biasing member, here in the form of a resilient spring 26 arranged on the outside of the tubular stem 15, is provided between the check valve 10 and the distributor 40 to bias the check valve 10 in a proximal direction towards the closed position.

[0041] In the closed position, the elevated portion 25 of the cylindrical body 11 extends into a supply port 7 of the back head 2 to block the opening thereof. The fourth annular seal 24 on the elevated portion 25 provides a fluid tight seal with the inner wall of the supply port 7 such that no motive fluid may enter or exit the housing 4 of the DTH hammer 1 in the closed position of the check valve 10. At the same time, the orifice 20 of the second conduit 17 in the cylindrical body 11 is in a proximal position out of alignment with the evacuation ports 8. The second and third annular seals 22, 23 provide a fluid tight seal with the inner wall of the back head 2 such that no exhaust fluid may exit from the housing 4. Additionally, no fluid or debris present outside the housing 4 may enter into the housing through the evacuation ports 8. [0042] Turning now to Figs. 4a and 4b, the check valve 10 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 5, pushes on the elevated portion 25 to displace the check valve 10 in a distal direction against the bias of the spring 26. The tubular stem 15 bottoms out as the distal end reaches the bottom of the opening 43.

[0043] In the open position, the elevated portion 25 no longer extends into the supply port 7, thereby allowing the motive fluid to flow through the first conduits 14 of the cylindrical body 11 and further into an actuator drive flow path inside the housing 4, here defined by one or more conduits 41 arranged in the distributor 40 and holes 42 of an inner cylinder 60 arranged between the housing 4 and the distributor 40. The conduits 41 may be distributed about the circumference of the distributor 40 and terminate in an annular groove 45 formed in the outer surface of the distributor 40. The flow of motive fluid is illustrated by the downwardly directed arrows. The motive fluid acts on an actuator (not shown) to impart reciprocating motion thereon to impact on a drill bit 3 and thus operate the DTH hammer 1.

[0044] After the motive fluid has performed its action on the actuator, it is exhausted from the housing 4 as exhaust fluid. As explained above, part of the exhaust fluid is evacuated through the drill bit 3 to clear away the debris from the drilling. The remaining part of the exhaust fluid is evacuated through an actuator exhaust flow path which is arranged in fluid communication with the second flow path defined by the cavity 16 and the second conduit 17. The cavity 43 of the distributor 40 is part of the second flow path through the distributor 40 and defined by having a larger diameter than the remaining part 44, thus providing an abutment or shoulder for stopping the distal travel of the tubular stem 15. The exhaust fluid flows through the second flow path of the distributor 40 and further into the cavity 16, the second conduit 17 and out through the evacuation ports 8 via the orifice 20. The flow of exhaust fluid is illustrated by the upwardly directed arrows.

[0045] As such, the check valve 10 of the present disclosure allows simultaneous but separate supply of motive fluid and evacuation of exhaust fluid through the back head 2 by means of one single component. This greatly reduces the complexity and cost of manufacture of the check valve as well as increasing service life due to fewer moving parts and reduced wear. [0046] Referring now to Figs. 5a-5c, there is shown close-up views of the interface between the outer surface 18 of the cylindrical body 11 and the inner surface of the back head 2. As previously mentioned, the annular seals 21, 22, 23 may be constituted by X- rings which present two smaller contact surfaces on the top and bottom, in contrast to a comparatively larger single contact surface of a standard O-ring on the top and bottom. As may be seen in Figs. 5a-5c, the inner surface of the back head 2 comprises two annular raised portions 35, 36 adjacent to and on opposite sides of the evacuation port 8, i.e. on the proximal and distal side, respectively. The distance between the raised portions 35, 36 substantially corresponds to the distance between the first and second annular grooves 31, 32, as well as the distance between the second and third annular grooves 32, 33, wherein the first, second and third annular seals 21, 22, 23 are seated.

[0047] In some embodiments not shown here, the exhaust fluid evacuation port 8 of the back head 2 may comprise a first opening configured for communication with the recess 19 and/or the orifice 20 of the at least one second conduit 17, and a second opening configured for communication with an exterior of the back head 2, wherein an inner surface of the back head 2 comprises two annular raised portions 35, 36 arranged adjacent to the first opening of the at least one exhaust fluid evacuation port 8, distal and proximal thereto.

[0048] In the closed position of the check valve 10 illustrated in Fig. 5a, the second and third seals 22, 23 are positioned on the proximal and distal side of the evacuation port 8, respectively, and in contact with the respective raised portions 35, 36 to provide a fluid tight seal. The second and third seals 22, 23 thus prevent flow of motive or exhaust fluid out of the housing 4, and flow of external fluid and debris into the housing 4.

[0049] In the open position of the check valve 10 illustrated in Fig. 5b, the first and second seals 21, 22 are positioned on the proximal and distal side of the evacuation port 8, respectively, and in contact with the respective raised portions 35, 36 to provide a fluid tight seal. The first and second seals 21, 22 thus prevent flow of motive or exhaust fluid between the first and second flow paths defined by the first conduit 14, and the cavity 16 and second conduit 17, respectively. [0050] Referring now to Fig. 5c, there is shown the check valve 10 in an intermediate position between the closed and open positions. In the intermediate position, the annular seals 21, 22, 23 are not aligned with the raised portions 35, 36 and thus, there is a small gap between the inner surface of the back head 2 and the annular seals 21, 22, 23. As a result, the sliding contact between the annular seals 21, 22, 23 and the inner surface of the back head 2 during travel of the check valve 10 between the respective end positions is reduced or even eliminated. Thereby the service life of the annular seals 21, 22, 23 is increased due to reduced wear. The reduced friction during travel also serves to reduce the required force to close the check valve 10 by the biasing member, thereby ensuring reliability of the function of the check valve 10. Finally, any debris caught between the annular seals21, 22, 23, inner surface of the back head 2 and cylindrical body 11 in the closed position, will be flushed out in the open position.

[0051] The pressure of the motive fluid and exhaust fluid during travel of the check valve 10 from the open position to the closed position is higher than the backpressure of any external fluid in the bore hole, giving rise to a negligible leak flow in the gap and out through the evacuation ports 8. As such, entry of external debris or fluid into the housing 4 through the evacuation ports 8 will be suppressed, i.e., the gap does not affect normal operation of the DTH hammer 1.

[0052] In some embodiments, the negligible leak flow in the gap may be completely blocked by an extra check valve arranged at each of the evacuation ports 8, wherein the extra check valve may be of any type for the intended use.

[0053] Referring now to Figs. 6a and 6b, there is shown an alternative check valve 100 in a perspective view and a cross-sectional view of the proximal end of the DTH hammer 1, respectively. The check valve 100 differs from the check valve 10 only in that the cylindrical body 110 has a smaller length along the longitudinal axis such that in the closed position shown in Fig. 3a and 3c, the cylindrical body 110 does not cover the evacuation ports 80. Instead, there is provided an additional component in the form of an external sleeve 120 arranged on the outer surface of the back head 50 and biased distally toward a closed position by means of a second biasing member 125 in the form of a spring. The spring 125 is arranged between the external sleeve 120 and the distal end of a drill pipe 9 connected to the back head 50. In operation, the pressure of the exhaust fluid in the evacuation ports 80 acts on the external sleeve 120 to push it in the proximal direction and thereby open the evacuation ports 80 to allow egress of exhaust fluid. To this end, the evacuation ports 80 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 120 may be combined with the embodiment of Figs. 2a-2d and also other embodiments described below to provide an additional safeguard against ingress of external fluid and debris.

[0054] The check valve 100 allows simultaneous but separate supply of motive fluid and evacuation of exhaust fluid through the back head 50 by means of two components, the cylindrical body 110 and the external sleeve 120. This solution reduces the material required for the cylindrical body and provides a separate blocking of the evacuation ports 80.

[0055] Referring now to Figs. 7a -7c, there is shown another alternative check valve assembly 400 and distributor 300. Fig. 7a illustrates the check valve assembly 400 and distributor 300 in a perspective view, whereas Figs. 7b and 7c show close-up cross- sectional views of the proximal end of the DTH hammer 1 with the check valve assembly 400 in the open position, wherein the section in Fig 7b is rotated 90 degrees about the longitudinal axis in relation to the section in Fig. 7c. The distributor 300 differs from the distributor 40 in that the distributor body 310 extends further in the proximal direction such that internal 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. A tubular stem 46 extends distally from the distributor body 310 defining a distributor bore 360 terminating in the cavity 370.

[0056] 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 7. 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 the proximal end 411 of the cylindrical body 410 to ensure a fluid tight seal against the back head 150. 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 150 to the axial conduits 320 of the distributor 300 via the annular groove 380 and the holes 43, and further into the intermediate space 47 between the inner cylinder 60 and the housing 4.

[0057] The cylindrical body 410 further comprises one or more lateral openings (not shown). The lateral openings 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 180 in the back head 150 formed e.g. by one or more axially oriented channels milled in the back head 150. 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 150, for instance through gaps in the thread profiles. In the closed position of the check valve assembly 400, the lateral openings are no longer aligned with the radial conduits 375, thus blocking passage of the exhaust fluid.

[0058] The check valve assembly 400 allows simultaneous but separate supply of motive fluid and evacuation of exhaust fluid through the back head 150 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 150 for accommodating the check valve assembly 400, thereby facilitating manufacture, in addition to increasing service life due to fewer moving parts and reduced wear.

[0059] Referring now to Figs. 8a-8c, there is shown another alternative check valve assembly 500. Fig. 8a illustrates the check valve assembly 500 in a perspective view, whereas Figs. 8b and 8c show close-up cross-sectional views of the proximal end of the DTH hammer 1 with the check valve assembly 500 in the open position, wherein the section in Fig. 8b is rotated 90 degrees about the longitudinal axis in relation to the section in Fig. 8c.

[0060] The check valve assembly 500 is similar to the check valve assembly 400 of Figs. 7a-7c 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 50. 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 50. The proximal end of the lateral slots 522 are in fluid communication with the evacuation ports 80 of the back head 50. Together, the central conduit 521, the lateral slots 522 and the evacuation ports 80 form the second internal passage defining the second flow path for the exhaust fluid.

[0061] Similar to the check valve of Figs. 6a and 6b, an external sleeve 120 is provided to close the evacuation ports 80. 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 50 to the axial conduits 41 of the distributor 40 and further into the intermediate space 47 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

[0062] The check valve assembly 500 allows simultaneous but separate supply of motive fluid and evacuation of exhaust fluid through the back head 50 by means of three components, the cylindrical body 510, the second valve member 520 and the external sleeve 120. 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 80.

[0063] Referring now to Figs. 8d and 8e, there is shown another alternative check valve assembly 600. Figs. 8d and 8e show close-up cross-sectional views of the proximal end of the DTH hammer 1 with the check valve assembly 600 in the open position, wherein the section in Fig. 8d is rotated 90 degrees about the longitudinal axis in relation to the section in Fig. 8e.

[0064] The check valve assembly 600 is similar to the check valve assembly 500 comprising a cylindrical body 610 and a second valve member 620, but differs therefrom in that it 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 4. 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.

[0065] The check valve assembly 600 allows simultaneous but separate supply of motive fluid and evacuation of exhaust fluid through the back head 50 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.

[0066] Embodiments of a check valve for a DTH hammer according to the present disclosure has been described. However, the person skilled in the art realises that this can be varied within the scope of the appended claims without departing from the inventive idea. [0067] 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.