A closing member assembly for a check valve of a DTH hammer, a check valve and a DTH hammer
The closing member assembly with adjustable choke members in the DTH hammer addresses the need for easy bypass flow adjustment, reducing disassembly and improving operational efficiency.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- ROBIT OYJ
- Filing Date
- 2025-11-10
- Publication Date
- 2026-05-21
Smart Images
Figure FI2025060076_21052026_PF_FP_ABST
Abstract
Description
[0001] A CLOSING MEMBER ASSEMBLY FOR A CHECK VALVE OF A DTH HAMMER, A CHECK VALVE AND A DTH HAMMER FIELD OF THE DISCLOSURE
[0002] The present disclosure relates to percussive rock drilling and more particularly to DTH (down-the-hole) -hammers used in percussive rock drilling. The present disclosure further concerns a check valve assembly used in such a DTH hammer, and a closing member for such a check valve assembly.
[0003] BACKGROUND OF THE DISCLOSURE
[0004] In percussive rock drilling, a pressurized motive fluid is used to operate a percussion device, commonly referred to as hammer, to impart impacts to a drill bit acting against a bottom of the drill hole. Particularly in DTH-drilling, the hammer is located, as the name suggests, at the bottom of the hole with the drill bit, and is preceded in an uphole direction by the remaining drill string, which couples the hammer and drill bit to the drill rig atop. In operation, the drill bit impacts the bottom of the hole and crushes the ground thereby generating crushed particles, typically referred to as drill cuttings. To prevent the cuttings from forming a layer between the bottom of the hole and the drill bit, it needs to be removed. To this end, the pressurized motive fluid is commonly exhausted from the hammer, often via flushing channels of the drill bit, to the face surface of the drill bit. The flushing flow then runs over the face of the drill bit and exhausts upwardly along the periphery of the drill hole.
[0005] To ensure efficient flushing of the drill cuttings, a portion of the pressurized motive fluid is often directed to bypass a working cylinder of the piston, so as to provide a continuous flushing flow to the face of the drill bit. Multiple factors, including characteristics of the drill rig, hammer, drill bit and the borehole, determine a suitable portion of the pressurized motive fluid to be bypassed. Hence, it is generally desirable to provide a way for customizing the bypass portion to suit the prevailing conditions and circumstances. Typical arrangements for allowing adjustment of the bypass ratio require substantial dismantling of the DTH hammer.
[0006] Moreover, to prevent impurities from travelling upwards in the drill string when provision of the pressurized motive fluid is interrupted, a DTH hammer is typically coupled with a check valve, which is configured to close when the provision of the pressurized motive fluid is interrupted, and respectively, to open when the pressurized motive fluid is introduced into the DTH-hammer. BRIEF DESCRIPTION OF THE DISCLOSURE
[0007] An object of the present disclosure is to provide arrangements, which allow for eased adjustment of the bypass flow.
[0008] The object of the disclosure is achieved by a closing member assembly for a check valve of a DTH hammer, a check valve and a DTH hammer, which are characterized by what is stated in the independent claims. The preferred embodiments of the disclosure are disclosed in the dependent claims.
[0009] The disclosure is based on the idea of the provision of bypass flow adjustment in connection with a closing member of a check valve. As the check valve is typically provided under a backhead of the DTH-hammer - which can be accessed simply by removing the backhead, the amount of disassembly required for bypass flow adjustment is substantially reduced in comparison conventional arrangements.
[0010] In a first aspect of the present disclosure, a closing member assembly for a check valve is provided. The assembly comprises a closing member, in turn, comprising a head portion and a stem portion protruding from the head portion.
[0011] The head portion defines a closure zone for engaging, in a closed configuration, against a valve seat of the check valve so as to interrupt flow through the valve seat past the closure zone. The stem portion is configured to be receivable within a valve guide of the check valve so as to guide the closing member between an open configuration and the closed configuration. Preferably, the stem portion protrudes in a down-stream direction from the head portion (i.e. in the direction of intended flow of the motive fluid).
[0012] The closing member further defines a bypass duct extending between a first position on an outer surface of the closure member downstream of the closure zone and an internal space of the stem portion. That is, the bypass duct runs from an outside of the closing member to an inside thereof.
[0013] The closing member assembly further comprises a choke member for restricting flow through the bypass duct.
[0014] Such a configuration allows bypass flow adjustment of the associated DTH hammer by removing or replacing the choke member to another one with different choke characteristics, or even by replacing the closing member to another one with different choke characteristics.
[0015] In an embodiment according to the first aspect of the disclosure, the closing member further comprises an annular groove at the first position. Moreover, the choke member is suitably provided as an annular choke ring received within the annular groove and at least partially blocking an opening of the bypass duct at the first position.
[0016] Such an arrangement allows for adjustment of the bypass flow by removing or replacing the choke rings to ones with different coverage of the opening of the bypass duct at the first position.
[0017] Preferably, but not necessarily, the closing member comprises a further bypass duct extending between a further position on the outer surface of closure member downstream of the closure zone and an internal space of the stem portion. That is, a further bypass duct extending between the outside and the inside of the closing member may be provided. In such a configuration, the further position of the further bypass duct is arranged axially spaced from the first position of the first bypass duct. Moreover, the closing member assembly comprises a further choke member for restricting flow through the further bypass duct.
[0018] Such an arrangement allows for greater adjustability, as the multiple bypass ducts can be adjusted separately.
[0019] Most suitably, the bypass duct has a cross-sectional flow area different from that of the further bypass duct, thereby allowing more versatile bypass flow adjustment.
[0020] Advantageously, the closing member assembly comprises a further annular groove at the further position, and the further choke member is suitably provided as a further annular choke ring received within the further annular groove and at least partially blocking an opening of the further bypass duct at the further position.
[0021] Preferably but not necessarily, the choke ring is elastically deformable so as to be removable from the annular groove.
[0022] Preferably, but not necessarily, the further choke ring is elastically deformable so as to be removable from the further annular groove.
[0023] The provision of an elastically deformable choke ring facilitates the removal and replacement of the choke ring form the associated annular groove.
[0024] In another embodiment of the present disclosure, the choke ring comprises an orifice extending radially therethrough. Advantageously, such a choke ring is selectively rotatable to a first choked circumferential position, in which the orifice is aligned with the opening at the first position of the bypass duct. Such an arrangement provides for an alternative way of facilitating bypass flow adjustment, in which the choke ring does not necessarily need to be removed or replaced, but adjustment can be achieved by rotation of the choke ring about the closing member. Most suitably, the closing member comprises a further bypass duct extending between a further position on the outer surface of closure member downstream of the closure zone and an internal space of the stem portion. In this arrangement, the further position of the further bypass duct is arranged circumferentially spaced from the first position of the first bypass duct.
[0025] Moreover, the choke ring is selectively rotatable to a further choked circumferential position, in which the orifice is aligned with the opening at the further position of the further bypass duct. Advantageously, the opening of the bypass duct at the first position and the opening of the further bypass duct at the further position are of different sizes.
[0026] Such an arrangement allows for greater adjustability of the bypass flow, while encompassing the advantages associated to the rotatable choke ring.
[0027] Furthermore, where multiple bypass ducts are provided, they are most suitably provided equally spaced apart along the circumference of the closing member, so as to maximize the distance between adjacent bypass ducts and to minimize associated stress concentrations. For example, where two bypass ducts are provided, they can be positioned on opposite sides of the closing member
[0028] Preferably, but not necessarily, the choke ring is selectively rotatable to a blocked circumferential position, in which the choke ring prevents fluid communication into the internal space of the stem portion through an outer surface of the closing member.
[0029] Preferably, but not necessarily, the choke ring comprises a stud on an inner surface thereof. Moreover, the annular groove comprises one or more recesses configured to receive the stud so as to engage the choke ring in a circumferential position.
[0030] For example, for each bypass duct, a corresponding recess could be provided on an opposing side of the closing member, thereby allowing the bypass duct and the corresponding recess to be provided with a drilling operation extending through the closing member.
[0031] In an alternative example, the stud could be configured to engage with an opening of a bypass duct. In such an arrangement, the recess corresponding to a bypass duct could be provided as the opening of another bypass duct, thereby eliminating the need for providing a separate recess. It should be noted that the first aspect encompasses any combination of two or more embodiments, or variants thereof, as discussed above.
[0032] According to a second aspect of the present disclosure, a check valve is provided. The check valve comprises a valve seat, a closing member and a valve guide. Particularly, the closing member is one according to the first aspect of the present disclosure.
[0033] The closing member is biased against the valve seat for selectively allowing or interrupting fluid communication through the valve seat. The valve guide has a space for at least partially receiving the closing member so as to define a path of movement thereof towards and away from the valve seat.
[0034] Most suitably, the bypass duct is or bypass ducts are in fluid communication with the space of the valve guide for at least partially receiving the closing member.
[0035] According to a third aspect of the present disclosure, a DTH (down-the-hole) hammer for percussive rock drilling is provided. In the context of the present disclosure, the term DTH hammer is used to describe a percussion device for rock drilling, which is intended to be operated within the borehole (as opposed to percussion devices operated outside the borehole). Particularly, the term DTH hammer encompasses both conventional DTH hammer as well as RC (reverse circulation) hammers). The DTH hammer according to the third aspect of the present disclosure comprises a wear sleeve and a backhead attached to an uphole end of the wear sleeve for attaching the hammer to a drill string. The DTH hammer further comprises a chuck attached to a downhole end of the wear sleeve for receiving and retaining a drill bit. Moreover, the DTH hammer is provided with a piston arranged within the wear sleeve and configured to reciprocate upon provision of a motive fluid flow through the backhead so as to impart percussive impacts upon a drill bit received within the chuck.
[0036] Particularly, the DTH hammer comprises a check valve according to the second aspect of the disclosure. The DTH hammer further comprises a bypass channel for conducting a portion of the motive fluid flow to a central flushing channel of the drill bit regardless of the position of the piston. Notably, the bypass duct of the check valve is coupled in fluid communication with the bypass channel of the hammer.
[0037] Preferably, but not necessarily, the check valve is arranged upstream of the piston (i.e. with respect to the intended flow direction of the motive fluid. Most suitably, the bypass channel runs through the piston.
[0038] Preferably, but not necessarily, the valve seat is formed on the backhead. This ensures that the closing member of the check valve can be readily accessed by simply removing the backhead from the wear sleeve. With easy access to the closing member, bypass flow adjustments are greatly facilitated
[0039] BRIEF DESCRIPTION OF THE DRAWINGS
[0040] In the following, the disclosure will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which:
[0041] Fig. 1 illustrates a cut view of a closing member assembly according to an embodiment of the aspect of the disclosure;
[0042] Fig. 2 illustrates a cut view of a closing member assembly according to another embodiment of the aspect of the disclosure;
[0043] Fig. 3a illustrates a perspective view of the closing member of Fig. 2;
[0044] Fig 3b illustrates a perspective view of the choke member of Fig. 2, and
[0045] Fig. 4 illustrate a cut view of a DTH hammer according to the present disclosure. DETAILED DESCRIPTION OF THE DISCLOSURE
[0046] Fig. 1 illustrates a closing member assembly, shown as a cut view along a longitudinal central plane of closing member 1 according to an embodiment of the present disclosure. In the illustrated embodiment, the closing member 1 comprises a cylindrical body constituting a head portion 2 and a stem portion 3 protruding longitudinally from the head portion 2. A conical area of the head portion 2 constitutes a closure zone 2a intended to abut against a valve seat of an associated check valve (valve seat and check valve not illustrated in Fig. 1).
[0047] The closing member 1 comprises a bypass duct 4 extending between an outside of the closing member 1 and an internal space 3a of the stem portion 3. Notably, the bypass duct 4 is provided at a first position 4a downstream of the closure zone 2a (i.e., in a direction towards the stem portion 3. Particularly, the closing member 1 further comprises an annular groove 1 a in which an external opening of the bypass duct 4 resides. Depicted by a broken circular line, a choke member 5 is received within the annular groove 1 a, thereby blocking the opening of the bypass duct 4 and obstructing flow into the bypass duct 4. The choke member 5 can be provided as a resilient ring, such as an O-ring, which allows for efficient sealing, as well as easy removal and replacement thereof for adjusting the bypass flow.
[0048] The embodiment depicted in Fig. 1 also comprises a further bypass duct 6 extending between an outside of the closing member 1 and an internal space 3a of the stem portion 3. Notably, the further bypass duct 6 is provided at a second position 6a downstream of the closure zone 2a (i.e. , in a direction towards the stem portion 3. The closing member 1 of Fig. 1 additionally comprises a further annular groove 1b in which an external opening of the further bypass duct 6 resides. A further choke member 7 is received within the further annular groove 1b, thereby blocking the opening of the further bypass duct 6 and obstructing flow into the further bypass duct 6. For example, the further choke member 7 can be provided as a resilient ring, such as an O-ring, which allows for efficient sealing as well as easy removal and replacement for adjusting the bypass flow.
[0049] Moreover, in the embodiment of Fig. 1 , the first position 4a and the second position 6a are spaced apart from each other in the longitudinal direction of the closing member 1. While the embodiment illustrated in Fig. 1 shows a configuration in which the annular grooves 1a, 1b, and respectively the bypass duct 4 and further bypass duct 6, are immediately adjacent to each other, it is noted that they may equally well be distanced apart from each other.
[0050] Notably, each of the bypass duct 4 and the further bypass duct 6 can be provided with or without a respective choke member 5, 7. As the bypass duct 4 and the further bypass duct 6 are of different cross-section flow areas, the closing member of Fig. 1 allows for four configurations having distinct bypass flow characteristics.
[0051] It is additionally noted that the present disclosure also encompasses embodiments with only a single bypass duct (and suitably a respective annular groove), or with additional further bypass duct(s) (and suitably respective annular grooves). Moreover, the provision of choke members of the kind obstructing the external opening of an associated bypass duct only partially may easily be envisaged,
[0052] Fig. 2 illustrates a closing member assembly, shown as a cut view along a longitudinal central plane of closing member 1 according to another embodiment of the present disclosure. In a similar manner as to the arrangement of Fig. 1 , the closing member has a cylindrical body defining a head portion 2 with a closure zone 2a, and a stem portion 3 protruding from the stem portion 3. However, the closing member 1 of Fig. 2 comprises a single annular groove 1a, at which the bypass duct 4 and the further bypass duct 6 are respectively positioned at a first position 4a and a further position 6a being circumferentially spaced apart from each other.
[0053] Moreover, the embodiment depicted in Fig. 2 comprises a choke member 5 provided as an annular ring received within the annular groove 1a and having an orifice 5a. Notably, the choke member 5 can be rotated about the closing member 1 so as to selectively align the orifice 5a with the bypass duct 4, further bypass duct 6, or a blank portion of the outer surface of the closing member. While not assigned with a reference numeral, Fig. 2 shows exemplary positions additional further bypass ducts extending into the internal space 3a of the stem portion 3.
[0054] Moreover, in the configuration illustrated in Fig. 2, the choke member 5 is rotated into a position in which the orifice 5a is aligned with the bypass duct 4, thereby allowing fluid communication therethrough. Correspondingly, the further bypass duct 6 is aligned with a blank portion of the choke member 5, thereby interrupting fluid communication through the further bypass duct. It is also possible to provide a configuration, in which the choke member 5 interrupts fluid communication through multiple, or all bypass ducts.
[0055] Again, as the bypass duct 4 and bypass duct 6 are of different cross-sectional flow areas, bypass flow can be adjusted by rotating the choke member 5 so as to align the orifice 5a with a bypass duct providing the most suitable bypass flow characteristics.
[0056] Moreover, differing from the arrangement of Fig. 2, a closing member assembly can be provided with multiple annular grooves, each with a respective annular ring having an orifice, which can selectively be aligned with none, one or multiple bypass ducts associated to the respective annular groove.
[0057] Fig. 3a and Fig. 3b illustrate perspective views of the closing member 1 and choke member 5 of the closing member assembly of Fig. 2. That is, Fig. 3a shows the closing member without the choke member 5, whereas a Fig. 3b shows the choke member 5 without the closing member 1.
[0058] As can readily be seen from Fig. 3a, in addition to the bypass duct 4 provided at the first position 4a, multiple further bypass ducts 6 can be provided at respective further positions 5a. Notably, multiple bypass ducts 4, 6 can be provided in a single annular groove.
[0059] Fig 3b illustrates a stud 5b provided on an inner surface of the chocking member 5 provided as an annular ring. The stud 5b can engage with a corresponding recess provided on the closing member so as to provide secure the choking member 5a in the desired rotational position. For example, such recess can be provided as separate recesses. Alternatively, or in addition such recess can be provided as a bypass duct extending through the wall of the stem portion 3. Preferably, a hole constituting a recess positioned opposite to a corresponding bypass duct, which enables both openings to be made with a single drilling operation.
[0060] Fig. 4 illustrates a DTH hammer according to an embodiment of the present disclosure as seen as a cut view along a longitudinal central plane. While depicted in Fig. 4 for illustrative purposes, a drill bit 17 and a drill string 16 preceding the DTH hammer 11 are not generally considered to form a part of the hammer itself. That being said, it is obvious that the DTH hammer 11 is intended to be operatively coupled with both the preceding drill string 16 and the drill bit 17, as discussed in more detail below.
[0061] In the embodiment illustrate in Fig. 4, the DTH hammer 11 comprises a wear sleeve 12. A backhead 13 is detachably attached (e.g., with a threaded coupling) to the up-hole end of the wear sleeve 12 and allows the DTH hammer 11 to be coupled to the preceding drill string 16. The DTH hammer 11 further comprises a chuck 14 detachably attached (e.g., with a threaded coupling) to the down-hole end of the wear sleeve 12 and allows the drill bit to be attached to the DTH hammer 11. Moreover, a piston 15 is arranged within the wear sleeve 12 and is configured to reciprocate upon introduction of a pressurized motive fluid into the DTH hammer 11 , so as impart percussive impacts on the drill bit 17.
[0062] Furthermore, the DTH hammer 11 comprises a check valve 10, which in the embodiment of Fig. 4 is arranged upstream of the piston 15. The checkvalve 10 comprises a valve seat 8 constituted, in this embodiment, as a surface on the backhead 13. The check valve also comprises a closing member assembly according to a first aspect of the present disclosure, and a valve guide 9. The stem portion 3 of the closing member 1 is received in the valve guide 9 so as to guide the closing member assembly along a translational path towards and away from the valve seat 8. The closing member assembly is biased towards the valve seat 8, such that the closure zone 2a of the closing member 1 abuts the valve seat 8, when the provision of pressurized motive fluid to the DTH hammer 11 is interrupted. The DTH hammer 11 further defines a bypass channel 11a into which a portion of the pressurized motive fluid is introduced via the bypass duct 4, and where applicable, also via further bypass duct(s) 6. The bypass channel 11 a is arranged to conduct the portion of the pressurized motive fluid to a front face of the drill bit 17 via a central flushing channel 17a thereof, regardless of the position of the piston 15.
[0063] In the particular embodiment of Fig. 4 the bypass channel 11a extends to the valve guide 8, and is arranged in fluid communication with the internal space 3a of the stem portion 3. The flow path then runs through the piston 15 and into the central flushing channel 17a of the drill bit.
[0064] LIST OF REFERENCE NUMERALS
[0065] 1 closing member
[0066] 1a annular groove 1b further annular groove
[0067] 2 head portion
[0068] 2a closure zone
[0069] 3 stem portion
[0070] 3a internal space of stem portion 4 bypass duct
[0071] 4a first position
[0072] 5 choke member, choke ring 5a orifice
[0073] 5b stud
[0074] 6 further bypass duct
[0075] 6a further position
[0076] 7 further choke member
[0077] 8 valve seat
[0078] 9 valve guide
[0079] 10 check valve
[0080] 11 DTH hammer
[0081] 11a bypass channel
[0082] 12 wear sleeve
[0083] 13 backhead
[0084] 14 chuck
[0085] 15 piston
[0086] 16 drill string
[0087] 17 drill bit
[0088] 17a central flushing channel
Claims
CLAIMS1 . A closing member assembly for a check valve, comprising a closing member (1) having:- a head portion (2) defining a closure zone (2a) for engaging, in a closed configuration, against a valve seat (8) of the check valve so as to interrupt flow through the valve seat (8) past the closure zone (2a), anda stem portion (3) protruding from the head portion (2), the stem portion (3) being configured to be receivable within a valve guide (9) of the check valve so as to guide the closing member (1) between an open configuration and the closed configuration,wherein the closing member (1 ) further defines a bypass duct (4) extending between a first position (4a) on an outer surface of the closure member downstream of the closure zone and an internal space (3a) of the stem portion (3), andwherein the closing member assembly further comprises a choke member (5) for restricting flow through the bypass duct (4)characterized in that the closing member (1) further comprises an annular groove (1 a) at the first position (4a), andwherein the choke member is provided as an annular choke ring (5) received within the annular groove (1a) and at least partially blocking an opening of the bypass duct (4) at the first position (4a).
2. The closing member assembly according to claim 1 , characterized in that the closing member (1) comprises a further bypass duct (6) extending between a further position (6a) on the outer surface of closure member (1) downstream of the closure zone (2a) and an internal space (3a) of the stem portion (3),wherein the further position (6a) of the further bypass duct (6) is arranged axially spaced from the first position (4a) of the first bypass duct (4), andwherein the closing member assembly comprises a further choke member (7) for restricting flow through the further bypass duct (6).
3. The closing member assembly according to claim 2, characterized in that the closing member (1) comprises a further annular groove (1b) at the further position (6a), and wherein the further choke member is provided as a further annular choke ring (7) received within the further annular groove (1b) and at least partially blocking an opening of the further bypass duct (6) at the further position (6a).
4. The closing member assembly according to any of the preceding claims 1-3, characterized in that the choke ring (5) is elastically deformable so as to be removable from the annular groove (1 a).
5. The closing member assembly according to any of the preceding claims 2-4, characterized in that the further choke ring (7) is elastically deformable so as to be removable from the further annular groove (1b).
6. The closing member assembly according to claim 1 , characterized in that the choke ring (5) comprises an orifice (5a) extending radially therethrough, andwherein the choke ring (5) is selectively rotatable to a first choked circumferential position, in which the orifice (5a) is aligned with the opening at the first position (4a) of the bypass duct (4).
7. The closing member assembly according to claim 6, characterized in that the closing member (1) comprises a further bypass duct (6) extending between a further position (6a) on the outer surface of closure member (1) downstream of the closure zone (2a) and an internal space (3a) of the stem portion (3),wherein the further position (6a) of the further bypass duct (6) is arranged circumferentially spaced from the first position (4a) of the first bypass duct (4), wherein the choke ring (5) is selectively rotatable to a further choked circumferential position, in which the orifice (5a) is aligned with the opening at the further position (6a) of the further bypass duct (6), andwherein the opening of the bypass duct (4) at the first position (4a) and the opening of the further bypass duct (6) at the further position (6a) are of different sizes.
8. The closing member assembly according to claim 6 or 7, characterized in that the choke ring (5) is selectively rotatable to a blocked circumferential position, in which the choke ring (5) prevents fluid communication into the internal space (3a) of the stem portion through an outer surface of the closing member (1).
9. The closing member assembly according to any of the preceding claims 6 - 8, characterized in that the choke ring (5) comprises a stud (5b) on an inner surface thereof, andwherein the annular groove (1a) comprises one or more recesses configured to receive the stud (5b) so as to engage the choke ring (5) in a circumferential position.
10. A check valve (10), comprising a valve seat (8), a closing member (1 ) biased against the valve seat (8) for selectively allowing or interrupting fluid communication through the valve seat (8) and a valve guide (9) having a space for at least partially receiving the closing member (1) so as to define a path of movement thereof towards and away from the valve seat (8), characterized in that the closing member (1 ) according to any of the preceding claims 1-9.
11. The check valve (10) according to claim 10, characterized in that the bypass duct (4) is in fluid communication with the space of the valve guide (9) for at least partially receiving the closing member (1).
12. A DTH (down-the-hole) hammer (11) for percussive rock drilling, comprising- a wear sleeve (12),- a backhead (13) attached to an uphole end of the wear sleeve (12) for attaching the hammer to a drill string (16),- a chuck (14) attached to a downhole end of the wear sleeve (12) for receiving and retaining a drill bit (17), and- and piston (15) arranged within the wear sleeve (12) and configured to reciprocate upon provision of a motive fluid flow through the backhead (13) so as to impart percussive impacts upon a drill bit (17) received within the chuck (14), characterized in that the hammer (11) comprises a check valve (10) according to claim 10 or 11 ,wherein the hammer (11) further comprises a bypass channel (11a) for conducting a portion of the motive fluid flow to a central flushing channel (17a) of the drill bit (17) regardless of the position of the piston (15), andwherein the bypass duct (4) of the check valve (10) is coupled in fluid communication with the bypass channel (11 a) of the hammer (11).
13. The DTH hammer (11) according to claim 12, characterized in that the check valve (10) is arranged upstream of the piston (15), and wherein the bypass channel (11a) runs through the piston (15).
14. The DTH hammer (11) according to claim 12 or 13, characterized in that the valve seat (8) is formed on the backhead (13).