GB2520301A

GB2520301A - Filter drill rod adapted for cleaning

Info

Publication number: GB2520301A
Application number: GB1320177.7A
Authority: GB
Inventors: John Kosovich
Original assignee: Mincon International Ltd
Current assignee: Mincon International Ltd
Priority date: 2013-11-15
Filing date: 2013-11-15
Publication date: 2015-05-20
Also published as: WO2015071381A2; GB201320177D0; WO2015071381A3

Abstract

The present invention relates to a filter drill rod 3 comprising first 11 and second 12 fluid flow channels, with a filter 17 disposed within said first channel, wherein pressure fluid can flow in either one of said channels and return fluids flows in the opposite channel, for connection to a hydraulic down-the-hole hammer 1, means 2 to selectively place first and second channels in fluid communication with one another and a filter cleaning valve component containing a moveable member 13.

Description

I

FILTER DRILL ROD ADAPTED FOR CLEANING

Field of the Invention

The present invention relates to filter arrangements for hydraulic down-the-hole hammers, and in particular, to a filter drill rod that maybe cleaned in situ.

Backuround to the Invention Particulate contamination is an important issue in all hydraulic systems. High particulate contamination levels are very detrimental to hydraulic system reliability, th longevity and performance. While some contamination is produced internally by all hydraulic systems, most is introduced from the outside environment. With this in mind, system designers and end users go to considerable lengths to stop the ingress of contaminants. However, in spite of their best efforts, contamination is unavoidable in certain circumstances. Whatever its sources, it is very important that contamination is removed from the hydraulic circuit as quickly as possible. This is normally achieved through the use of filtration, it is preferable that the filter that facilitates removal of contamination is placed as close as possible to the contamination sources, so that the contamination passes through as little of the hydraulic circuit as possible.

In a hydraulic down-the-hole hammer rock drilling system, contamination is most likely to be introduced into the hydraulic circuit while in operation during addition or removal of drill rods, known as "rod changing". In an effort to remove this contamination as close as possible to its source, filters are sometimes installed in the drill rods to intercept contaminant particles before they reach the hammer percussion mechanism. This "in-rod" filtration can be arranged in a number of ways, but the most efficient way is to have the filter(s) housed within a dedicated drill rod, which can be removed from the drill string when the filters become clogged and replaced with a new one. Australian PatentNos. AU2010100222 and ATJ2010200944 disclose such a filter drill rod. A drawback of this arrangement is that the filter drill rod must be periodically removed from the system and disassembled in a clean environment, to allow the filter elements therein to be cleaned or changed. As drilling is often conducted in remote locations, away from such workshop facilities, this often represents a significant inconvenience and/or cost.

It is well known that filters that operate by physically arresting contaminate particles can be cleaned by "reverse flushing". That is, if the flow of fluid through a filter element is reversed, the fluid can dislodge particulate matter trapped in the filter media and carry it away in much the same way as it carried it into the filter in the first place.

Thus, an effective cleaning method for a particulate filter is to reverse flush it at flow rates similar to those used in its normal operation. Of course, this reverse flow will carry the particulate to another point in the circuit. However, if another, more easily accessible filter is included in the circuit at a convenient point, this could be used to remove the contaminant from the circuit in a more efficient manner, thereby reducing th the overall maintenance requirement. Hydraulic down-the-hole drilling rigs often include easily accessible, high capacity filters located in the return line that carries the hydraulic fluid back to the storage tank. It is therefore desirable to provide a filter drill rod which allows these filters to be utilised to enable the filters in the drill rod to be cleaned in situ. It is also desirable to provide a cleaning system for attachment to a hydraulic down-the-hole drilling rig to facilitate such a cleaning operation.

Summary of the Invention

According to an aspect of the present invention, there is provided a filter drill rod for a hydraulic down-the-hole hammer, comprising: a first fluid flow channel through the drill rod; and a second fluid flow channel through the drill rod; at least one filter disposed in the first fluid flow channel; wherein the drill rod is configured to permit pressure fluid to flow in the first fluid flow channel and return fluid to flow in the second fluid flow channel, or pressure fluid to flow in the second fluid flow channel and return fluid to flow in the first fluid flow channel.

As used herein, the term "pressure fluid" is intended to indicate fluid that is supplied towards the hammer under pressure, for example, from a drilling rig percussion pump, and the term "return fluid" is intended to indicate fluid that is returned from the hammer or drill string, for example, to a storage tank at the surface.

The filter drill rod may be connectable to the hammer, such that the first fluid flow channel is in fluid communication with a pressure channel of the hammer and the second fluid flow channel is in fluid communication with a return channel of the hammer. The connection may be direct or indirect (with one or more intermediate components between the drill rod and the hammer). During normal drilling operation, the drill rod may be configured to permit pressure fluid to flow in the first fluid flow channel and into the pressure channel of the hammer and return fluid to flow from the return channel of the hammer into the second fluid flow channel. Any contaminant material contained in the pressure fluid is trapped by the filter and prevented from th entering the hammer percussion mechanism. An advantage of the anangcment described above is that if the fluid connections to the drill rod are reversed, fluid is permitted to flow in a reverse direction in the filter drill rod, thereby flushing the filter.

This reverse flow will carry any contaminant material trapped in the filter back towards the hydraulic fluid storage tank at the surface. Hydraulic down-the-hole drilling rigs typically include high capacity filters between the storage tank and the drill string through which the return fluid flows. Any contaminant material flushed from the filter drill rod may be trapped by these high capacity filters. Because these filters are much more easily accessible than the filter in the filter drill rod, they may be removed for cleaning or replacement much more conveniently than the filter in the drill rod.

The drill rod may frirther comprise means for selectively placing the first and second fluid flow channels in fluid communication with one another at a point downstream of the filter, that is, between the filter and the hammer. When fluid connections to the drill rod are reversed to facilitate cleaning of the filter, the first and second fluid flow channels may be placed in fluid communication with one another downstream of the filter, for example, between the filter and the hammer, so that pressure fluid supplied to the second fluid flow channel flows back through the first fluid flow channel, thereby reverse flushing the filter.

The means may comprise: a connection interface for connection of the filter drill rod to a complementary connection interface of a hydraulic down-the-hole hammer, wherein the connection interface is disposed downstream of the filter, for example, between the filter and the hammer; and a member moveably mounted in the connection interface, wherein the member is moveable between a first position, in which the first fluid flow channel is placed in fluid communication with a pressure channel of the hammer and the second fluid flow channel is placed in fluid communication with a return channel of the hammer, and a second position, in which the first and second fluid flow channels are placed in fluid communication with one another.

th The term "downstream" as used herein refers to a location or orientation closer to the percussion mechanism of the hammer.

According to one embodiment of the invention, the member is mounted in the connection interface such that when the filter drill rod is connected to the hammer, the member is moved into the first position. In this embodiment, the member may be mounted in the connection interface such that when the filter drill rod is at least partially disconnected from the hammer, the member is moved into the second position. Ideally, the member is biasedly mounted in the connection interface, wherein the bias is such that when the filter drill rod is at least partially disconnected from the hammer, the member moves into the second position under bias. Thus, cleaning of the filter in the filter drill rod may be facilitated by at least partially disconnecting the filter drill rod from the hammer to allow pressure fluid supplied to the second fluid flow channel to flow back through the first fluid flow channel towards the fluid storage tank, thereby reverse flushing the filter.

In an alternate embodiment of the invention, the means may comprise: a member moveably mounted in the drill rod, wherein the member is moveable between a first position, in which the first fluid flow channel is placed in fluid communication with a pressure channel of the hammer and the second fluid flow channel is placed in fluid communication with a return channel of the hammer, and a second position, in which the first and second fluid flow channels are placed in fluid communication with one another; wherein the member is mounted in the drill rod such that when pressure fluid is supplied to the first fluid flow channel, the member is moved into the first position.

In this embodiment, the member may be mounted in the drill rod such that when pressure fluid is supplied to the second fluid flow channel, the member is moved into the second position. The filter drill rod may further comprise restriction means in the second fluid flow channel downstream of the moveable member, that is, between the moveable member and the hammer, wherein the restriction means is arranged to restrict flow of pressure fluid to the hammer when pressure fluid is supplied to the second fluid th flow channel. In this embodiment, cleaning of the filter in the filter drill rod may be achieved without disconnecting the filter drill rod from the hammer. Instead, the moveable member is arranged so that the pressure exerted on it by the pressure fluid causes it to move between the first and second positions. Thus, by simply reversing the fluid connections to the drill rod, pressure fluid supplied through the second fluid flow channel is allowed to flow back through the first fluid flow channel towards the storage tank, thereby reverse flushing the filter.

In this embodiment, the member may be mounted in the drill rod such that when a pressure differential between the first and second flow channels is below a threshold, that is, when the fluid pressure in the first and second flow channels is substantially equal, the member moves to a third position, in which fluid flow out of the first and second fluid flow channels in a downstream direction, that is, towards the hammer, is restricted or prevented. Thus, Wa seal failure in the hammer is detected, supply of pressure fluid to both the first or second fluid flow channels may be cut off at the drill rig, so that neither channel is supplied with pressurised fluid. The fluid pressure in the two flow channels is therefore substantially equal, so that the moveable member moves into the third, neutral, position, thereby preventing leakage of fluid from either channel into the hole.

According to another aspect of the invention, there is provided a filter cleaning valve component for connection in a drill string of a hydraulic down-the-hole hammer, downstream of a filter drill rod, for example, between the filter drill rod and the hammer, comprising: a first fluid flow channel through the valve component; and a second fluid flow channel through the valve component; wherein the valve component further comprises means for selectively placing the first and second fluid flow channels in fluid communication with one another.

Preferably, the filter cleaning valve component is connectable to the drill string such that the first fluid flow channel is placed in fluid communication with a fluid flow channel of the filter drill rod in which a filter is disposed. The filter cleaning valve component may also be connectable to the hammer, such that the first fluid flow th channel is in fluid communication with a pressure channel of the hammer and the second fluid flow channel is in fluid communication with a return channel of the hammer. During normal drilling operation, pressure fluid flows from the drill string through the first fluid flow channel of the valve component and into the pressure channel of the hammer and return fluid flows from the return channel of the hammer into the second fluid flow channel of the valve component and back through the drill string in the usual manner. To enable cleaning of the filter drill rod, the fluid flow in the drill string may be reversed and the first and second fluid flow channels in the valve component may be placed in fluid communication with one another, so that pressure fluid flows through the second fluid flow channel and back up through the first fluid flow channel to reverse flush the filter in the filter drill rod.

The means may comprise: a connection interface for connection of the valve component to a complementary connection interface of a hydraulic down-the-hole hammer; and a member movcably mounted in the connection interface, wherein the member is moveable between a first position, in which the first fluid flow channel is placed in fluid communication with a pressure channel of the hammer and the second fluid flow channel is placed in fluid communication with a return channel of the hammer, and a second position, in which the first and second fluid flow channels are placed in fluid communication with one another.

According to a first embodiment, the member is mounted in the connection interface such that when the valve component is connected to the hammer, the member is moved into the first position. In this embodiment, the member may be mounted in the connection interface such that when the valve component is at least partially disconnected from the hammer, the member is moved into the second position. The member may be biasedly mounted in the connection interface, wherein the bias is such that when the valve component is at least partially disconnected from the hammer, the member moves into the second position under bias.

In an alternate embodiment of the filter cleaning valve component, the means may comprise: th a member moveably mounted in the valve component, wherein the member is moveable between a first position, in which the first fluid flow channel is placed in fluid communication with a pressure channel of the hammer and the second fluid flow channel is placed in fluid communication with a return channel of the hammer, and a second position, in which the first and second fluid flow channels are placed in fluid communication with one another; wherein the member may be mounted in the valve component such that when pressure fluid is supplied to the first fluid flow channel, the member is moved into the first position.

In this embodiment, the member may be mounted in the valve component such that when pressure fluid is supplied to the second fluid flow channel, the member is moved into the second position. The filter cleaning valve component may further comprise restriction means in the second fluid flow channel downstream of the moveable member, that is, between the moveable member and the hammer, wherein the restriction means is arranged to restrict flow of pressure fluid to the hammer when pressure fluid is supplied to the second fluid flow channel.

In this embodiment, the member may be mounted in the valve component such that when a pressure differential between the first and second flow channels is below a threshold, that is, when the fluid pressure in the first and second flow channels is substantially equal, the member moves to a third position, in which fluid flow out of the first and second fluid flow channels in a downstream direction, that is, towards the hammer, is restricted or prevented. Thus, if a seal failure in the hammer is detected, supply of pressure fluid to both the first or second fluid flow channels may be cut off at the drill rig, so that neither channel is supplied with pressurised fluid.. The pressure in the two flow channels is thus substantially equal, so that the moveable member moves into the third, neutral, position, thereby preventing leakage of fluid from either channel into the hole.

According to another aspect of the invention, there is provided a filter rod cleaning system for a hydraulic down-the-hole hammer, comprising: a filter drill rod as described above; and th optionally, a filter cleaning valve component as described above; and means for selectively supplying pressure fluid to either the first or second fluid flow channel of the filter drill rod.

According to another aspect of the invention, there is provided a valve component for connection in a drill string of a hydraulic down-the-hole hammer, comprising: a first fluid flow channel through the valve component; and a second fluid flow channel through the valve component; and a member moveably mounted in the valve component, such that when a pressure differential between the first and second flow channels is below a threshold, that is, when the fluid pressure in the first and second flow channels is substantially equal, the member moves to a position in which fluid flow out of the first and second fluid flow channels in a downstream direction, that is, towards the hammer, is restricted or prevented.

Brief Description of the Drawings

Figure 1 is a schematic representation of a drilling rig running a hydraulic down-the-hole system including a filter drill rod and a filter cleaning valve component according to the invention; Figure 2 is schematic of a hydraulic circuit illustrating a first embodiment of the invention; Figure 3 is a schematic of a hydraulic circuit illustrating a second embodiment of the invention; Figure 4 is a cross-section of a filter drill rod according to an embodiment of the invention; Figure 5 is two transverse cross-sections of the filter drill rod of Figure 4, taken along lines A-A and B-B respectively; and Figure 6 is a cross-section of a portion of the filter drill rod ofFigurc 4 connected to a hydraulic down-the-hole hammer.

Detailed Description of the DrawinQs

Figure 1 shows a typical drilling rig configured to run a hydraulic down-the-hole JM drilling system. A hydraulic down-the-hole hammer 1 is driven by hydraulic fluid, normally oil, which is pressurised by the rig's percussion pump 7. The pressurised fluid flows as directed by a percussion control valve 6. When hammer operation is not required, the control valve 6 is in the neutral position as shown in Figure 1. In this position, pressure fluid from the percussion pump 7 is directed back to a fluid reservoir or storage tank 9 via a return filter 8. When hammer operation is required, control valve side 6A is energised and the pressurised fluid from pump 7 is directed by the control valve 6 to the pressure line 11. Pressure fluid then travels first through a rotation swivel and then series of drill rods 4 to the hammer 1 to activate it. Interposed between the drifi rods 4 and the hammer 1 are a filter drill rod 3 and a filter cleaning valve 2. In the embodiment shown in Figure I, the filter cleaning valve is provided as a separate component. However, in alternate embodiments, the filter cleaning valve may be incorporated into the filter drill rod 3. The pressure fluid, once exhausted from the percussion mechanism of the hammer 1 becomes low pressure return fluid and travels back to the fluid reservoir 9 via the cleaning valve 2, the filter drill rod 3, the drill rods 4, rotation swivel 5, return line 12 and return filter 8. The drill rods 4, filter drill rod 3 and filter cleaning valve 2 make up the drill string. Each of the drill sfring components and the hammer I includes additional channels to allow a flow of flushing fluid to be carried into thc hole to flush drill cuttings from thc hole.

The filter drill rod 3 comprises a first fluid flow channel, which carries pressure fluid during normal operation of the hammer as described above, and a second fluid flow channel, which carries return fluid back to the reservoir 9 during normal operation of the hammer. The filter drill rod 3 frirther comprises at least one filter element 17 disposed in the first fluid flow channel, which filters pressure fluid on it way to the hammer 1. In this way, any particulate contamination introduced into the drill string when rods 4 are added or removed is prevented from entering the percussion mechanism of hammer 1.

When the filter elements 17 in the filter drill rod 3 become clogged with contaminants, they maybe cleaned by reverse flushing, to allow their continued use. The filter cleaning process is facilitated by the filter cleaning valve 2 as described below. The process is activated by energising side 6B of the percussion control valve 6, to reverse the fluid connections to the drill rods. Thus, pressure fluid from the pump 7, is directed JM into line 12 and down the return channels of the drill rods 4 and into the second fluid flow channels in the filter drill rod 3 and filter cleaning valve 2.

A first embodiment of the invention is shown in greater detail in Figure 2. In this embodiment, the filter cleaning valve component 2 comprises means for selectively placing the first and second fluid flow channels in fluid communication with one another. The means comprises a connection interface for connection of the valve component to a complementary connection interface of a hydraulic down-the-hole hammer, and a member or spool 13 moveably mounted in the connection interface. The spool 13 is moveable between a first position, in which the first fluid flow channel is placed in fluid communication with a pressure channel of the hammer and the second fluid flow channel is placed in fluid communication with a return channel of the hammer, and a second position, as shown, in which the first and second fluid flow channels are placed in fluid communication with one another.

The spool 13 is moved into the first position (in the direction of arrow X) by connection of the filter cleaning valve component 2 to the hammer 1. This is the position the spool takes during normal operation of the hammer I. In this position, the spool allows an unrestricted path for the pressure and return fluid to travel to and from the hammer, respectively. When filter cleaning is required, the drill string is partially unscrewed from the hammer until the spool moves under spring bias to the second position, shown in Figure 2. In this position, the spool connects the first and second fluid flow channels together for unrestricted flow in either direction. Activation of side 6B of the percussion valve 6 at this time creates a reverse flow of fluid through the drill rods 4 and filter drill rod 3 so that pressure fluid flows from the second fluid flow channel in the filter cleaning valve component 2 into the first fluid flow channel and back through the first fluid flow channel and thus the filter elements 17 of the filter drill rod 3, thereby dislodging contaminants from the filter elements 17 (by reverse flushing) and carrying them back towards reservoir 9. Return filter 8 traps these contaminants, thereby preventing them from entering reservoir 9. Because return filter 8 is located at the surface, it is easily accessible for cleaning or replacement.

In this embodiment, the system is manually activated by a drill rig operator via a push th button 10 in the rig's cabin, or similar. When a filter cleaning cycle has been completed, the drill string is retightened onto the hammer 1, thereby moving spool 13 back to the first position for continued drilling. In this manner, the filter drill rod 3 may be used indefinitely, with all cleaning controlled from the rig's cabin and without any manual handling required. This represents a significant reduction in overall maintenance requirement.

This embodiment of the filter cleaning valve may be incorporated into the filter drill rod 3, as shown in Figure 4, without adding significant complexity to the connection valve 16 which allows connection of the filter drill rod to the hammer 1, or detracting from the cffcctivcncss of the filter cleaning process. Alternatively, the filter clcaning valve may be provided as a separate component 2, as shown in Figure 2, which can be maintained independently of the filter drill rod 3.

A second embodiment of the invention is shown in Figure 3. In this embodiment, the spool 14 is mounted in the connection interface of the filter cleaning valve such that when pressure fluid is supplied to the first fluid flow channel, the member is moved into the first position. Thus, when side ÔA of percussion control valve 6 is energised, pressure fluid flows through the first fluid flow channel and energiscs spool 14 on side A, so that the spool moves into the first position. In this position, pressure fluid can flow unrestricted to the hammer 1. Return fluid coming back from the hammer 1 flows through a check valve 15, which is disposed in the second fluid flow channel downstream (i.e. closer to the hammer) of the spool, and into the second fluid flow channel of the filter cleaning valve component 2 and back through the filter drill rod 3, drifi rods 4, rotation swivel 5, lines 12 and back to the reservoir 9 via return filter 8.

When fiher cleaning is required, side 6B of the percussion control valve 6 is energised so that pressure fluid is supplied to line 12 and into the second fluid flow channel in the filter cleaning valve component 2. However, check valve 15 in the second fluid flow channel is arranged to prevent flow of pressure fluid to the hammer 1 and a back pressure develops in the second fluid flow channel of the filter cleaning valve component and the filter drill rod. This back pressure energises side B of spool 14 and th the spool moves to the second position, in which the first and second fluid flow channels are placed in fluid communication with one another. This allows unrestricted flow of fluid back up through the first fluid flow channel of the filter drill rod 3, thereby cleaning contaminants from the filter elements 17 (by reverse flushing) and depositing them in the return filter 8, as described above.

This embodiment of the filter cleaning valve may be activated without partial disconnection from the hammer 1, that is, with all drill string components in their working positions, because the spool 14 is arranged so that the pressure exerted on it by the pressure fluid moves it between the first and second positions. The cleaning process can be instantaneously activated and lends itself to being performed in many short cycles which can be integrated into the overall drilling cycle. For instance, filter cleaning can take place while the rig is tramming between hole locations, or when setting up on a new hole location, or when removing the drill string from a completed hole. Furthermore, the cleaning process may be completely automated, being activated by one of the other rig functions, such as tramming, as described above.

An additional feature of this embodiment is a safety mechanism to prevent fluid loss in the event of a seal failure within the hammer. Should a seal failure in the hammer be detected, control valve 6 may be deactivated so that it returns to its neutral position (shown in Figure 1). This allows spool 14 to return to its neutral position as shown in Figure 3, since pressure fluid is not supplied to either the first or second fluid flow channels in the filter cleaning valve component, and so the pressure differential between the two channels falls below the minimum pressure required to move the spool into either the first or second positions. This, along with the action of check valve 15, prevents any fluid already present in either the pressure or return fluid channels of the drifi string from leaking down and being lost extemally, thereby eliminating the cost and environmental consequences of such a hammer seal failure.

A filter drill rod 3 incorporating a filter cleaning valve 2 according to an embodiment of the invention is shown in Figure 4. The drill rod 3 comprises an external cylindrical outer wear sleeve 24, within which are arranged a series of modular components stacked end to end. The wear sleeve protects the inner components from the drill cuttings that JM pass around the filter drill rod in transit out of the drilled hole. The drill rod 3 has a male connection interface at a first (upper) end and a female connection interface 16 at a second (lower) end. The male connection interface is for connection of the filter drill rod 3 to a female connection interface of a drill rod 4, as shown in Figure 1. The female connection interface 16 is for connection of the filter drill rod to the hammer 1, as shown in Figure 1.

The male connection interface includes a strengthened housing or male tool joint 25 connected to a first (upper) end of wear sleeve 24 by way of an internal thread provided on wear sleeve 24 and an external thread provided on tool joint 25. The female connection interface 16 includes a strengthened housing or female tool joint 26 connected to a second (lower) end of wear sleeve 24 by way of a similar threaded connection. The forces from the two opposing tool joints at opposite ends of the drill rod 3 keep the internal components of the filter drill rod in firm contact with one another.

The filter drill rod comprises a first fluid flow channel 18, 19 and a second fluid flow channel 20 therethrough. Face seals on the contacting ends of the components seal the flow channels that carry fluids through the drill rod. The drill rod also comprises a plurality of filter elements 17, in the form of filter modules, disposed in the first fluid flow channel 18. The number of filter elements 17 within the filter drill rod can be varied by simply adding or subtracting modules and using a long or shorter wear sleeve 24 accordingly.

A spool 13 is moveably mounted in the tool joint 26 in the female connection interface 16. The spool 13 is moveable between a first position (shown in Figure 6), in which the first fluid flow channel 18, 19 is placed in fluid communication with a pressure channel of the hammer 1 and the second fluid flow channel 20 is placed in fluid communication with a return channel of the hammer 1, and a second position (shown in Figure 4), in which the first 18, 19 and second 20 fluid flow channels are placed in fluid communication with one another. The spool is spring-mounted in the connection interface 16 such that when the filter drill rod 3 is connected to the hammer 1, the spool is moved into the first position (as shown in Figure 6) against the bias of the spring.

th When the filter drill rod 3 is at least partially disconnected from the hammer 1, the spool 13 moves into the second position (shown in Figure 4) under bias of the spring.

As shown in Figure 6, under normal drilling operation, the filter drill rod 3 is frilly connected to the hammer I so that the spool 13 is depressed against the spring bias in to the first position, and ports 21 are moved away from return channel 20. SeaLs 31 isolate first fluid flow channel 19 from second fluid flow channel 20. Pressure fluid is supplied from rod 4 into channel 18. It then passes through fitting 22 and into the gallery 23 surrounding the filter elements 17. Drillings 27 in a manifold 28 (as shown in FigureS) allow the fluid to pass between the filter modules which are all arranged as filters in parallel, that is, the fluid may pass through and be filtered by any individual filter. Once the pressure fluid passes through the filter elements 17, it is delivered into channel 19 to pass out through the female connection interface 16 and into the pressure channel of hammer 1. Channel 20 carries return fluid from the hammer 1 through the length of the device. Channels 29 are also provided to allow flushing fluid to be supplied to the cutting face of the hammer.

For filter cleaning, the filter drill rod 3 is at least partially disconnected from the hammer, until spool 13 moves into the second position under spring bias, as shown in Figure 4. In this position, the ports 21 in the spoo1 13 open a path between the second fluid flow channel 20 and the first fluid flow channel 19, so that these channels are placed in fluid communication with one another. Reverse flow of fluid in the drifi rod, activated by side 6B of percussion control valve 6, while the spool is in this position, will clean the filter elements 17 by reverse flushing as described above. In this mode, fluid is delivered from the rig via the rods 4 into second fluid flow channel 20, through ports 21 in spool 13 and into first fluid flow channel 19, back through the filter elements 17, then out of fitting 22 and into channel 1 to be returned to the rig via the rods 4.

The words "comprises/comprising" and the words "having/induding" when used herein with reference to the present invention are used to speci1i the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

th It is appreciated that certain features of the invention, which arc, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

Claims

Claims 1. A filter drill rod for a hydraulic down-the-hole hammer, comprising: a first fluid flow channel through the drill rod; and a second fluid flow channel through the drill rod; at least one filter disposed in the first fluid flow channel; wherein the drill rod is configured to permit pressure fluid to flow in the first fluid flow channel and return fluid to flow in the second fluid flow channel, or pressure fluid to flow in the second fluid flow channel and return fluid to flow in the th first fluid flow channel.
2. A filter drill rod as claimed in claim I, wherein the drill rod further comprises means for sclcctivcly placing the first and second fluid flow channels in fluid communication with one another at a point downstream of the filter.
3. A filter drill rod as claimed in claim 1 or claim 2, wherein the means comprises: a connection interface for connection of the filter drill rod to a complementary connection interface of a hydraulic down-the-hole hammer, wherein the connection interface is disposed downstream of the filter; and a member moveably mounted in the connection interface, wherein the member is moveable between a first position, in which the first fluid flow channel is placed in fluid communication with a pressure channel of the hammer and the second fluid flow channel is placed in fluid communication with a return channel of the hammer, and a second position, in which the first and second fluid flow channels are placed in fluid communication with one anothcr.
4. A filter drill rod as claimed in claim 3, wherein the member is mounted in the connection interface such that when thc tiltcr drill rod is connected to the hammer, the member is moved into the first position.
5. A filter drill rod as claimed in claim 3 or claim 4, wherein the member is mounted in the connection interface such that when the filter drill rod is at least partially disconnected from the hammer, the member is moved into the second position.
6. A filter drill rod as claimed in any of claims 3 to 5, wherein the member is biasedly mounted in the connection interface, wherein the bias is such that when the filter drill rod is at least partially disconnected from the hammer, the member moves into the second position under bias.
7. A filter drill rod as claimed in claim 1 or claim 2, wherein the means comprises: a member moveably mounted in the drill rod, wherein the member is moveable between a first position, in which the first fluid flow channel is placed in fluid th communication with a pressure channel of the hammer and the second fluid flow channel is placed in fluid communication with a return channel of the hammer, and a second position, in which the first and second fluid flow channels are placed in fluid communication with one another; wherein the member is mounted in the drill rod such that when pressure fluid is supplied to the first fluid flow channel, the member is moved into the first position.
8. A ifiter drill rod as claimed in any of claims 1, 2 or 7, wherein the member is mounted in the drill rod such that when pressure fluid is supplied to the second fluid flow channel, the member is moved into the second position.
9. A filter drill rod as claimed in claim 7 or claim 8, further comprising: restriction means in the second fluid flow channel downstream of the moveable member, wherein the restriction means is arranged to restrict flow of pressure fluid to the hammer when pressure fluid is supplied to the second fluid flow channel.
lO.A filter drill rod as claimed in any of claims 7 to 9, wherein the member is mounted in the drill rod such that when a fluid pressure in the first and second flow channels is substantially equal, the member moves to a third position, in which fluid flow out of the first and second fluid flow channels towards the hammer is restricted.
11.A filter cleaning valve component for connection in a drill string of a hydraulic down-the-hole hammer, downstream of a filter drill rod, comprising: a first fluid flow channel through the valve component; and a second fluid flow channel through the valve component; wherein the valve component further comprises means for selectively placing the first and second fluid flow channels in fluid communication with one another.
1 2.A filter cleaning valve component as claimed in claim II, wherein the means comprises: a connection interface for connection of the valve component to a complementary connection interface of a hydraulic down-the-hole hammer; and a member moveably mounted in the connection interface, wherein the member is th movcable between a first position, in which the first fluid flow channel is placed in fluid communication with a pressure channel of the hammer and the second fluid flow channel is placed in fluid communication with a return channel of the hammer, and a second position, in which the first and second fluid flow channels are placed in fluid communication with one another.
13.A filter cleaning valve component as claimed in claim 12, wherein the member is mounted in the connection interface such that when the valve component is connected to the hammer, the member is moved into the first position
1 4.A filter cleaning valve component as claimed in claim 12 or claim 13, wherein the member is mounted in the connection interface such that when the valve component is at least partially disconnected from the hammer, the member is moved into the second position.
15.A filter cleaning valve component as claimed in any of claims 12 to 14, wherein the member is biasedly mounted in the connection interface, wherein the bias is such that when the valve component is at least partially disconnected from the hammer, the member moves into the second position under bias.
1 6.A filter cleaning valve component as claimed in claim 11, wherein the means comprises: a member moveably mounted in the valve component, wherein the member is moveable between a first position, in which the first fluid flow channel is placed in fluid communication with a pressure channel of the hammer and the second fluid flow channel is placed in fluid communication with a return channel of thc hanimcr, and a second position, in which the first and second fluid flow channels are placed in fluid communication with one another; wherein the member is mounted in the valve component such that when pressure fluid is supplied to the first fluid flow channel, the member is moved into the first position.
17.A filter cleaning valve component as claimed in any of claims 11, 12 or 16, wherein 0 the member is mounted in the valve component such that when pressure fluid is supplied to the second fluid flow channel, the member is moved into the second position.
18.A filter cleaning valve component as claimed in claim 16 or claim 17, further comprising: restriction means in the second fluid flow channel downstream of the moveable member, wherein the restriction means is arranged to restrict flow of pressure fluid to the hammer when pressure fluid is supplied to the second fluid flow channel.
1 9.A filter cleaning valve component as claimed in any of claims 16 to 18, wherein the member is mounted in the valve component such that when a fluid pressure in the first and second flow channels is substantially equal, the member moves to a third position, in which fluid flow out of the first and second fluid flow channels towards the hammer is restricted.
20.A filter rod cleaning system for a hydraulic down-the-hole hammer, comprising: a filter drill rod as claimed in claim I; a filter cleaning valve component as claimed in any of claims 11 to 19; and means for selectively supplying pressure fluid to either the first or second fluid flow channel of the filter drill rod.
21.A filter rod cleaning system, comprising: a filter drill rod as claimed in any of claims 2 to 10; and means for selectively supplying pressure fluid to either the first or second fluid flow channel of the filter drill rod.
22.A valve component for connection in a drill string of a hydraulic down-the-hole hammer, comprising: a first fluid flow channel through the valve component; and a second fluid flow channel through the valve component; and a member moveably mounted in the valve component, such that when a fluid in the first and second flow channels is substantially equal, the member moves to a th position in which fluid flow out of the first and second fluid flow channels towards the hammer is restricted.
23.A filter drill rod substantially as hercinbcfore described with reference to and/or as illustrated in any of the accompanying drawings.
24.A filter cleaning valve component substantially as hereinbefore described with reference to and/or as illustrated in any of the accompanying drawings.
25.A filter rod cleaning system for connection in a drill string of a hydraulic down-the-hole hammer downstream of a filter drill rod substantially as hereinbefore described with reference to and/or as illustrated in any of the accompanying drawings.
26.A valve component for connection in a drill string of a hydraulic down-the-hole hammer substantially as hereinbefore described with reference to and/or as illustrated in any of the accompanying drawings.