Flap valve for percussion drill tools

Abstract

The present invention relates to a flap valve for a percussion drill tool. The valve has a first side that can engage a flat surface of an element of the percussion drill tool to alternately close first and second fluid flow paths of the percussion drill tool. The flat surface has first and second holes that are in fluid communication with the first and second fluid flow paths, respectively. The first side of the flap valve has first and second flat surface portions and a first curved tip intermediate the first and second flat surface portions. The flap valve is pivotable about the first curved tip between a first position in which the first flat surface portion of the flap valve is in sealing contact with the flat surface to close the first hole and a second position in which the second flat surface portion of the flap valve is in sealing contact with the flat surface to close the second hole.

Description

[Technical Field]

[0001] The present invention relates to fluid-operated percussion drilling tools, and more particularly to a flap valve for controlling air distribution in pneumatic drilling tools. [Background technology]

[0002] Down-the-hole hammer and fluid-operated percussion drilling tools of conventional design, such as that shown in Figure 1, typically include an outer or outer wear sleeve 2 having an inner barrel 21 mounted therein which in turn engages a backhead assembly 3. A sliding reciprocating piston 1 cooperates with the inner barrel 21 and backhead assembly 3 when air pressure is supplied through the backhead assembly, causing the piston to impart an impact action to a drill bit 13 held in a chuck 22 on the outer wear sleeve.

[0003] Compressed air is alternately supplied from the back head 3 to the upper and lower chambers 11, 12, causing the piston to reciprocate. This can be accomplished using a planar flap valve 4 and an air distributor 16, as shown in Figure 1, which has an upper surface 5 with three flat surfaces 6, 7, and 8. Flat surfaces 7 and 8 are angled downward relative to a central plane 6. One side 9 of the distributor supplies air to the upper chamber 11 above the piston, and the other side 10 of the distributor assembly supplies air to the lower chamber 12 below the piston. The flap valve 4 is shown in its neutral position in Figure 1 and is positioned to pivot around the edge of the central plane 6 of the air distributor. When the flap valve is pivoted to one side 9, it contacts the flat surface 8, thereby sealing the distributor hole(s) 14 so that air is directed through one or more holes 15 on the other side 10 of the distributor assembly, into a channel 24 between the wear sleeve 2 and the inner barrel 21, and out from under the piston, pressurizing the lower chamber 12 and thereby moving the piston upward and away from the bit 13. At this point in the cycle, the upper chamber 11 vents through the piston bore 18 and the bit bore 23. As the piston moves upward, the piston bore 18 engages and seals against the air distributor extension 17, so that the upper chamber can no longer vent through the piston bore. The upper chamber 11 also decreases in volume as the piston moves upward, resulting in an increase in pressure within the upper chamber. When the piston reaches a point where the piston nose 19 moves out of sealing engagement with the aligner 20, the lower chamber 12 begins to vent through the bit bore 23, resulting in a decrease in pressure within the lower chamber. When the pressure in the lower chamber falls below the pressure in the upper chamber, the pressure difference causes the flap valve 4 to switch position, contacting the flat surface 7 and sealing the hole 15 in the air distributor 16. Air then flows through the hole 14 on the other side 9 of the distributor assembly, further pressurizing the upper chamber and thereby allowing the piston to be forced back down towards the drill bit.As the piston moves downward, piston nose 19 moves back into sealing engagement with aligner 20, so that the lower chamber can no longer vent through bit bore 23, and dispenser extension 17 moves out of engagement with piston bore 18, so that the upper chamber begins to vent again. Thus, the volume of the lower chamber decreases, and the pressure in the lower chamber begins to increase again, and the cycle begins again. Thus, the flap valve "flaps" or rocks back and forth around the edge of flat surface 6, alternately contacting dispenser flat surfaces 7 and 8.

[0004] While this type of configuration is useful due to its simplicity, it has several drawbacks. Specifically, flap valves tend to fail due to fatigue when the operating pressure exceeds an upper threshold due to the repeated application of higher forces to the valve. Flap valves also have a relatively short lifespan. Because the valve oscillation is not smooth, the valve is subjected to relatively high stresses. Therefore, it is desirable to provide a flap valve configuration that can extend its lifespan and operate over a wider range of pressures. Summary of the Invention

[0005] According to one aspect of the present invention, a flap valve for a percussion drill tool comprises: a first side surface engageable with a flat surface of the element of the percussion drill tool to alternately close first and second fluid flow paths of the percussion drill tool, the flat surface comprising first and second holes in fluid communication with the first and second fluid flow paths, respectively; The first side of the flap valve has a first planar portion and a second planar portion and a first curved tip intermediate the first and second planar portions, and the flap valve has a first side that is pivotable about the first curved tip between a first position in which the first planar portion of the flap valve is in sealing contact with the planar surface to close the first hole and a second position in which the second planar portion of the flap valve is in sealing contact with the planar surface of the dispensing device to close the second hole.

[0006] Preferably, the first planar portion, the second planar portion, and the first curved tip are arranged to form a single continuous surface without any edges, corners, or discontinuities between them. An advantage of this configuration is that the flap valve rotates (or swings or pivots) around the curved tip of the valve, thereby allowing for smoother operation than existing configurations. This, in turn, reduces stress on the valve, thereby extending the life of the valve and increasing its ability to withstand higher operating pressures.

[0007] In one embodiment, the plane is a flat proximal (or rear or upper) surface of an intermediate plate disposed proximal to (or rearward or above) the fluid distribution device of the percussion drill tool. In other embodiments, the plane may be integrally formed with the fluid distribution device to form the flat proximal (or rear or upper) surface of the fluid distribution device of the percussion drill tool. The flap valve assembly may include a flap valve, an intermediate plate, and / or a fluid distribution device.

[0008] The first curved tip of the flap valve preferably has a radius of curvature between 10 mm and 10,000 mm. The radius of curvature of the first curved tip can be selected to tailor the performance of the valve. For example, a larger radius of curvature of the first curved tip can result in improved high-power, low-frequency performance, while a smaller radius of curvature can result in improved performance at low power consumption and high frequencies. In certain applications, a radius of curvature of approximately 500 mm can be particularly advantageous.

[0009] The first curved tip is positioned between the first and second planar portions so that the angle between them is greater than 180°. When the flap valve moves from the first or second position to the neutral position (halfway between the first and second positions), the flap valve moves through a stroke angle. The angle between the first and second planar portions is twice the value of 180° plus the stroke angle. Generally, the larger the stroke angle, the more responsive the valve is, which increases the operating frequency but reduces power. In contrast, a smaller stroke angle may not provide enough flow area on the "open" side of the dispenser to allow enough air to be supplied to the chamber, which may lead to premature switching of the valve due to the pressure difference across the valve. Therefore, an appropriate stroke angle must be selected to effectively operate the valve. Preferably, the stroke angle is between 1 and 10°. Ideally, the stroke angle is about 3°, and as the flap valve swings up and down, it represents an angle of about 6°.

[0010] In one embodiment, the curved tip is located along the centerline of the valve so that the first and second planar portions of the first side of the flap valve are equal in length, and the operation of the valve in this embodiment is symmetrical.

[0011] In another embodiment, the curved tip is offset from the centerline of the valve so that the first and second planar portions are different lengths. The offset biases the valve into contact with the planar surface because the longer planar portion of the valve, due to its larger surface area, generates increased force from the pressurized fluid on the larger portion. In this embodiment, the valve can still pivot around the curved tip so that the smaller planar portion of the valve contacts the planar surface, but the larger side is initially closed. A pressure differential between the upper and lower chambers of the percussion drill tool, which are respectively connectable to the first and second fluid flow paths, flips or rocks the valve during use. When the areas of the first and second fluid holes are the same, a higher pressure is required to flip the valve when the larger planar portion is in contact with the dispensing device, thereby biasing the larger portion closed. The position of the tip relative to the centerline of the flap valve affects the degree to which the valve is biased in one direction.

[0012] In some embodiments, the second side of the flap valve opposite the first side is flat. However, in other embodiments, the second side of the flap valve includes a third flat portion, a fourth flat portion, and a second curved tip intermediate the third and fourth flat portions. Thus, the flap valve can be reversed so that the second side of the valve is engageable with the flat portion to alternately close the first and second fluid flow paths of the percussion drill tool. In this configuration, the flap valve is pivotable about the second curved tip between a third position in which the third flat portion of the flap valve is in sealing contact with the flat portion to close the first hole, and a fourth position in which the fourth flat portion of the flap valve is in sealing contact with the flat portion to close the second hole.

[0013] In certain embodiments, the radius of curvature of the first curved tip is the same as the radius of curvature of the second curved tip, which allows the flap valve to be reversed to extend the life of the valve.

[0014] However, in other embodiments, the radius of curvature of the first curved tip is different from the radius of curvature of the second curved tip. This allows each side of the flap valve to have different operating characteristics. As mentioned above, the radius of curvature can be used to adjust the performance of the valve. By providing two different radii of curvature on the same valve, the operator can adjust the performance of the hammer by switching the flap valve to the other side.

[0015] Each of the first and second curved tips may be located on the centerline of the flap valve or may be offset from the flap valve. One tip may be located on the centerline of the flap valve and the other may be offset from the flap valve, or both tips may be offset from the centerline by the same or different amounts and in the same or different directions. This allows the direction in which the valve is biased and / or the degree to which the valve is biased in one direction to be selected by selecting the appropriate side of the valve.

[0016] Preferably, the flap valve is made from sheet steel. In other embodiments, the valve may be made from an engineering plastic material.

[0017] According to a second aspect of the present invention, there is provided a flap valve assembly including the above-described flap valve, wherein the first and second ends of the flap valve have a convex profile, and the flap valve guide has at least one internal recess dimensioned to receive the flap valve and inhibit lateral movement of the flap valve as the valve pivots between the first and second positions. In one embodiment, the flap valve guide includes a pair of internal recesses, each dimensioned to receive one end of the flap valve. Preferably, each internal recess includes a sloped inner surface configured to cooperate with the convex end of the flap valve to inhibit lateral movement of the flap valve.

[0018] An advantage of the flap valve guide is that it inhibits lateral movement of the flap valve as it pivots from the first position to the second position.

[0019] According to another aspect of the present invention, there is provided a down-the-hole hammer further comprising an outer wear sleeve, a sliding piston adapted to reciprocate within the outer wear sleeve and strike a percussion bit of a drill bit assembly located at a forward end of the outer wear sleeve, and a flap valve or flap valve assembly as described above, configured to control the flow of air to cause the piston to reciprocate. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a longitudinal cross-sectional view of a percussion drill tool including a conventional flap valve arrangement. [Figure 2] 1 is a perspective view of a flap valve according to the present invention; [Figure 3] 1 is a cross-sectional side view of a flap valve according to a first embodiment of the present invention shown in use with an intermediate plate of a percussion drill tool. [Figure 4] FIG. 4 is a top perspective view of the configuration of FIG. 3. [Figure 5] FIG. 4 is a side view of the arrangement of FIG. 3 showing the flap valve in a first position. [Figure 6A] FIG. 4 is a side view of a flap valve according to a second embodiment of the present invention. [Figure 6B] FIG. 6B is a top view of the flap valve of FIG. 6A. [Figure 7] FIG. 10 is a side view of a flap valve according to a third embodiment of the present invention. [Figure 8] FIG. 4 is a cross-sectional view of a flap valve assembly according to a second embodiment of the present invention. [Figure 9] 1 is a longitudinal cross-sectional view of a down-the-hole hammer including a flap valve assembly according to the present invention; FIG. DETAILED DESCRIPTION OF THE INVENTION

[0021] A flap valve 100 according to a first embodiment of the present invention is shown in Figure 2. The valve comprises a first side surface 101 engageable with a planar surface 102 of an intermediate base plate 103 of a percussion drill tool to alternately close first and second fluid flow paths of the percussion drill tool, as shown in Figures 3 and 4. The planar surface 102 comprises first and second holes 104, 105 in fluid communication with the first and second fluid flow paths, respectively.

[0022] The first side 101 of the flap valve 100 includes a first planar portion 106, a second planar portion 107, and a first curved tip 108 intermediate the first and second planar portions. As shown, the first planar portion, the second planar portion, and the first curved tip form a single continuous surface without any edges, corners, or discontinuities between them. Because the curved tip 108 is located along the centerline 109 of the valve, the first and second planar portions 106, 107 of the first side 101 of the flap valve are equal in length. Therefore, the operation of the valve in this embodiment is symmetrical.

[0023] 5 shows the flap valve 100 in a first position, with a first planar portion 106 of the flap valve in sealing contact with the planar surface 102 to close the first hole 104. The valve is pivotable about a first curved tip 108 from the first position to a second position, with a second planar portion 107 of the flap valve in sealing contact with the planar surface 102 to close the second hole 105.

[0024] 2 to 5, the flap valve has a tip radius of 500 mm. In other embodiments, the radius of curvature of the first curved tip portion may be 10 mm to 10,000 mm.

[0025] In the embodiment shown in Figures 2-5, the angle between the first and second planar portions is approximately 186°. As the flap valve 100 moves from the first position shown in Figure 5 to the neutral position shown in Figure 3, it travels a stroke angle of approximately 3°. Thus, as the flap valve oscillates, it subtends an angle of approximately 6°.

[0026] A flap valve 200 according to another embodiment of the present invention is shown in Figures 6A and 6B. In this embodiment, a first curved tip 208 is offset from the centerline of the valve, resulting in first and second planar portions 206, 207 having different lengths L1 and L2, as shown in Figure 6A. The use of the offset biases the larger planar portion 206 of the valve into contact with the planar surface due to its larger surface area and increased force generated by the fluid pressure of the pressurized fluid supplied by the longer side backhead assembly (indicated by the arrow). In this embodiment, the valve is still able to pivot about the curved tip 208 so that the smaller planar portion of the valve contacts the planar surface, but the larger portion is initially closed.

[0027] A flap valve 300 according to a third embodiment of the present invention is shown in FIG. 7. The flap valve 300 comprises a first side 301 including a first planar portion 306 and a second planar portion 307 joined by a first curved tip 308. The flap valve further comprises a second side 310 opposite the first side 301. The second side 310 comprises a third planar portion 311, a fourth planar portion 312, and a second curved tip 313 intermediate the third and fourth planar portions. Thus, the flap valve 310 may be reversed such that the second side of the valve is engageable with the planar surface 102 to alternately close the first and second fluid flow paths of the percussion drilling tool.

[0028] In the embodiment shown in Figure 7, the radius of curvature of the first curved tip 308 is the same as the radius of curvature of the second curved tip 313. This allows the flap valve to be reversed to extend the life of the valve. In an alternative embodiment, the radius of curvature of the first curved tip 308 may be different from the radius of curvature of the second curved tip 313. Providing two different radii of curvature on the same valve allows the operator to adjust the performance of the hammer by switching the flap valve to the other side.

[0029] 7, the first curved tip 308 is located on the centerline of the flap valve, and the second curved tip 313 is offset from it. This allows the degree to which the valve is biased in one direction to be selected by selecting the appropriate side of the valve. In alternative embodiments, both tips may be located on the centerline of the flap valve, or each may be offset from the centerline by the same or different amounts.

[0030] A flap valve assembly according to one embodiment of the present invention is shown in FIG. 8. Assembly 820 includes a flap valve 800 similar to that described above with reference to FIGS. 2-5, having a first side 801 with first and second planar portions 806 and 807, and a first curved tip 808. In this embodiment, each end 821, 822 of the flap valve has a convex profile. The assembly further includes a flap valve guide 823 having a pair of internal recesses 824, each sized to receive one end of the flap valve 800. Each internal recess has a sloped inner surface 825, 826 at its end that is configured to cooperate with the convex ends 821, 822 of the flap valve to restrict lateral movement of the flap valve as the valve pivots between its first and second positions.

[0031] 9 shows a down-the-hole hammer with a flap valve assembly 920 according to one embodiment of the present invention. The tool 900 includes a piston 1 mounted for reciprocation within an outer wear sleeve 2. When air is supplied through a backhead assembly 3, the piston impacts a drill bit 13 at the forward end of the wear sleeve.

[0032] Compressed air is alternately supplied from the back head 3 to the upper and lower chambers 11, 12, causing the piston to reciprocate. This is accomplished using a flap valve assembly 920, which includes a flap valve 900 having a first side 901 engageable with a flat surface 902 of an intermediate base plate 903 to alternately close the first and second fluid flow paths 17, 18 of the percussion drill tool. The flat surface 902 includes first and second holes 904, 905 in fluid communication with the first and second fluid flow paths, respectively. The first side 901 of the flap valve 900 includes a first flat portion 906, a second flat portion 907, and a first curved tip 908 intermediate the first and second flat portions. As shown, the first flat portion, the second flat portion, and the first curved tip form a single continuous surface without intermediate edges, corners, or discontinuities. The first and second planar portions 906, 907 of the first side 901 of the flap valve 900 are equal in length such that the curved tip 908 lies along the centerline of the valve and hammer. The valve 900 is pivotable about the first curved tip 908 between a first position in which the first planar portion 906 of the flap valve is in sealing contact with the planar surface 902 to close the first hole 904, and a second position in which the second planar portion 907 of the flap valve is in sealing contact with the planar surface 902 to close the second hole 905.

[0033] Each end 921, 922 of the flap valve has a convex profile. The assembly 920 further includes a flap valve guide 923 having a pair of internal recesses 924 sized to receive the flap valve 900. Each internal recess includes an inclined inner surface 925, 926 at its end configured to cooperate with the convex ends 921, 922 of the flap valve to inhibit lateral movement of the flap valve as the valve pivots between the first and second positions.

[0034] An intermediate base plate 903 is positioned above the air distribution device 16. In other embodiments, the plate 903 may be formed integrally with the air distribution device 16. One side 9 of the air distribution device supplies air to an upper chamber 11 above the piston, and the other side 10 of the distribution device supplies air to a lower chamber 12 below the piston. The flap valve 900, shown in a neutral position in FIG. 9 , is positioned to pivot about its first curved tip 908, as described above. When the flap valve is pivoted to one side 9, a first flat portion 906 of the flap valve makes sealing contact with the flat surface 902, closing the first hole 904. As a result, air is forced through holes 905 on the other side 10 of the base plate, into channels in the wall of the wear sleeve 2, and out from under the piston, pressurizing the lower chamber 12 and thereby moving the piston upward and away from the bit 13. The upper chamber 11 is open to exhaust via a flow passage 927. As the piston moves upward, the flow passage 928 is opened, allowing the lower chamber to vent. At the same time, the flow passage 927 for venting the upper chamber 11 is sealed by the piston, thus increasing the pressure in the upper chamber as its volume decreases. When the pressure in the lower chamber falls below the pressure in the upper chamber, the pressure difference causes the flap valve 903 to switch positions so that the second planar portion 907 makes sealing contact with the planar surface 902, sealing the hole 905 in the base plate 903. Air then flows through the hole 904 on the other side of the base plate 9 through the air distribution device, further pressurizing the upper chamber and thereby forcing the piston downward toward the drill bit. As the piston moves downward, the pressure in the upper chamber decreases, and the pressure in the lower chamber begins to increase again, restarting the cycle. Thus, the flap valve continuously and smoothly rocks back and forth around the first curved tip 908, alternately bringing the first and second planar portions 906 and 907 into contact with the base plate 903. Lateral movement of the flap valve 900 is constrained by a guide 923 .

[0035] The terms "comprise" and "have / include" as used in connection with the present invention are used to specify certain features, values, methods or elements and do not exclude the presence or addition of other features, values, methods or elements or combinations thereof.

[0036] It should be noted that several features of the invention that are, for brevity, described in separate embodiments may also be combined in a single embodiment. Conversely, various features of the invention that are, for brevity, described in a single embodiment may also be provided separately or in any suitable subcombination.

Claims

1. A flap valve assembly, comprising: a flap valve for a percussion drill tool, comprising: a first side engageable with a flat surface of an element of the percussion drill tool to alternately close first and second fluid flow paths of the percussion drill tool, the flat surface comprising first and second holes in fluid communication with the first and second fluid flow paths, the first side of the flap valve comprising first and second flat surface portions and a first curved tip intermediate the first and second flat surface portions, the flap valve pivotable about the first curved tip between a first position in which the first flat surface portion of the flap valve is in sealing contact with the flat surface to close the first hole, and a second position in which the second flat surface portion of the flap valve is in sealing contact with the flat surface to close the second hole, the first and second ends of the flap valve having convex profiles; a flap valve guide having at least one internal recess sized to receive the flap valve, the at least one internal recess having a sloped inner surface at an end thereof, the sloped inner surface configured to cooperate with a first end or a second end of the flap valve to inhibit lateral movement of the flap valve as the flap valve pivots between the first position and the second position; Flap valve assembly.

2. The flap valve assembly of claim 1 , wherein the first curved tip is directly intermediate the first planar portion and the second planar portion.

3. 3. The flap valve assembly of claim 1 or 2, wherein the first planar portion, the second planar portion, and the curved tip are arranged to form a single continuous surface.

4. The flap valve assembly of claim 3 , wherein the single continuous surface has no edges, corners, or discontinuities formed between the first planar portion, the second planar portion, and the curved tip.

5. The flap valve assembly of claim 1, wherein the first curved tip has a radius of curvature in the range of 10 mm to 10,000 mm.

6. 2. The flap valve assembly of claim 1, wherein the first and second planar portions of the first side of the flap valve are equal in length such that the first curved tip lies along a centerline of the valve.

7. A flap valve assembly according to any one of claims 1 to 5, wherein the curved tip is offset from a centreline of the valve such that the first and second planar portions are of different lengths.

8. A flap valve assembly as described in claim 1, wherein the flap valve guide has a pair of inner recesses, each inner recess being dimensioned to receive one end of the flap valve.

9. A down-the-hole hammer comprising an outer wear sleeve which is an outer tube, and a sliding piston adapted to reciprocate within said outer wear sleeve and strike a percussion bit of a drill bit assembly located at the front end of said outer wear sleeve, and further comprising a flap valve assembly as described in any one of claims 1 to 8, configured to control the flow of air to cause the reciprocating movement of said piston.

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