AU2015203009A1

AU2015203009A1 - Arrangement and method for feeding flushing fluid

Info

Publication number: AU2015203009A1
Application number: AU2015203009A
Authority: AU
Inventors: Tatu Miikkulainen
Original assignee: Sandvik Mining and Construction Oy
Current assignee: Sandvik Mining and Construction Oy
Priority date: 2014-06-13
Filing date: 2015-06-05
Publication date: 2016-01-07
Anticipated expiration: 2035-06-05
Also published as: US20150361743A1; EP2955319A1; AU2015203009B2; WO2015192151A2; WO2015192151A3

Abstract

Abstract of the disclosure The invention relates to a flushing system and a method of controlling feeding of flushing fluid. The flushing system (14) comprises a pump unit (15) for feeding pressurized flushing fluid to a feed duct (16) connected to a rock drill ing machine (5). Flow rate of the flushing fluid to be fed is controlled by controlling pumping of the flushing fluid. The flow rate is determined by means of one or more sensing device. (Figure 2) 6474222 1 (GHMatters) P99912.AU JENNIFER

Description

1 Arrangement and method for feeding flushing fluid Background of the invention The invention relates to a flushing system of a drilling unit. The flush ing system comprises a pump unit for feeding pressurized flushing fluid needed 5 in drilling. The flushing system further comprises means for conveying the flush ing fluid and means for controlling feeding of the flushing fluid. The invention further relates to a method of controlling feeding of flushing fluid in a flushing system of a rock drilling rig. The field of the invention is defined more specifically in the pream 10 bles of the independent claims. In mines and at other work sites, rock drilling machines are used for drilling bore holes into rock surfaces. The rock drilling machine comprises a ro tating device for rotating a drilling tool during drilling. Flushing systems have been developed for feeding flushing fluid through the tool to the drill bit and fur 15 ther to the bottom of the drill hole. In some solutions flow of flushing fluid is ad justed by means of adjusting valves, which are designed especially for the pur pose. However, these known flushing systems have some drawbacks. Some known solutions are disclosed in documents US-2012/048620-Al, WO 03/071096-Al, GB-1437442-A, WO-2007/122288-Al, WO-2007/138170-Al 20 and WO-2004/065761 -Al. Brief description of the invention An object of the invention is to provide a novel and improved flushing system and a method of controlling feeding of flushing fluid of a rock drilling unit. 25 The flushing system according to the invention is characterized by characterized features of independent apparatus claim. The method according to the invention is characterized by features of independent method claim. An idea of the disclosed solution is that flushing fluid is fed from a 30 pump unit to a drilling unit for flushing drilling cuttings away from a bore hole 6474222 1 (GHMatters) P99912.AUJENNIFER 2 being drilled. Flow rate flowing to the drilling unit is adjusted by controlling pumping of the flushing fluid. An advantage of the disclosed solution is that adjustable needle valves or corresponding adjusting elements are not needed in the flushing sys 5 tem. Instead, the needed adjustments may be executed by controlling the pumping. The flushing flow may be adjusted accurately and the operation of the system is easy to control. The disclosed solution may allow a simple and relia ble configuration to be utilized in the flushing system. According to an embodiment, a feed duct of the flushing system is 10 provided with one or more valves. The valve is without any adjusting means allowing adjusting the flow being fed through the valve. Thus, the valve is on/off -type having only two positions, namely an open position and a closed position. This type of valve is easy to control, reliable and inexpensive. According to an embodiment, the flushing system comprises at least 15 a first feed duct and a second feed duct, which are operationally parallel relative to each other. The first feed duct is provided with a first valve and a first throttle. Correspondingly, the second feed duct is provided with a second valve and a second throttle. The first throttle and the second throttle both have orifices, which differ in size. Further, the first valve and the second valve are inde 20 pendently controllable, whereby the valves may be opened and closed sepa rately and simultaneously. The control unit is configured to control opening and closing of the first valve and the second valve according to the operation of the drilling unit. In this embodiment flushing flow may be directed through one or more suitable valves by controlling opening and closing of simple on/off -valves 25 arranged in the feed ducts. The system is simple and requires no expensive components. It should be noted that the number of the parallel feed ducts may be three, four or even more, and the feed ducts are provided with the disclosed valves, throttles and differing orifice sizes. According to an embodiment, the flushing system comprises two or 30 more parallel feed ducts provided with valves. The valves are operationally par allel and have flow paths which are different in size. Flow rate of the flushing system is adjusted by controlling a pump. Flushing fluid flow is directed through 6474222 1 (GHMatters) P99912.AUJENNIFER 3 the two or more valves so, that opening and closing of valves is controlled in response to magnitude of the supplied volume flow of the pump unit. According to an embodiment, at least one feed duct of the flushing system is provided with a control valve and a throttle. The throttle is an integrat 5 ed element of the valve. Thus, the throttle is a constructive part of the structure of the valve whereby no separate throttle element or device is needed. The structure may then be compact. According to an embodiment, at least one feed duct of the flushing system is provided with a control valve and means for throttling flow of the feed 10 duct. The valve may comprise a control element, such as a control spindle, which may be moved in order to influence to flow through the valve. The control element may be moved between closing and opening positions. Further, one or more preset intermediate positions may be determined for the control element so that when the control element is at the intermediate positions, different throt 15 tling is achieved. Thus, instead of several valves, different preset throttling may be achieved by means of a single valve. The control element may comprise one intermediate position whereby two different throttling may be achieved, for ex ample. According to an embodiment, at least one feed duct of the flushing 20 system is provided with a control valve and a throttle. The throttle is a separate element relative to the valve. Thus, the valve and the throttle may both be sim ple standard hydraulic components. Valves and throttles having different prop erties may be combined in order to find a desired combination. According to an embodiment, flow rate determination is performed by 25 means of a pressure difference measurement. Thus, at least one feed duct of the flushing system is provided with means for throttling flow of the feed duct. At least one throttle may be arranged in the at least one feed duct, wherein the throttle causes a pressure drop. Pressure drop over the throttling is sensed or measured and this data is used for determining flow rate in the observed feed 30 duct. The produced data may be transmitted to a control unit of the flushing sys tem. The pressure difference measurement is a reliable measuring principle and 6474222 1 (GHMatters) P99912.AUJENNIFER 4 requires no expensive measuring devices. Pressure sensors are durable and easily mountable. According to an embodiment, the flushing system comprises at least one first pressure sensing device for detecting pressure of the flushing fluid act 5 ing before the throttle, and correspondingly at least one second pressure sens ing device for detecting pressure of the flushing fluid acting after the throttle. The sensed pressure data is transmitted to a control unit of the flushing system. The control unit is configured to determine a pressure difference caused by the throttle in the feed duct. The control unit is further configured to determine the 10 flow rate of the flushing fluid on the basis of the detected pressure difference. The produced data on the flow rate may be utilized for controlling a pump of the flushing system in order to control the flow rate of the flushing fluid. According to an embodiment, the flow rate is determined by means of one or more flow meters. The produced data is utilized for controlling a pump 15 of the flushing system. In this embodiment at least one feed duct of the flushing system is provided with at least one flow meter for determining the flow rate of the flushing fluid. According to an embodiment, produced flow rate of a feed duct is ad justed by adjusting operating speed of the pump. The pump may be driven by 20 an electrical motor. Operating speed of the pump is adjusted in order to adjust the produced flow of the flushing fluid. Rotational speed of the electric motor may be adjusted by means of an adjusting device. According to an embodiment, produced flow rate of a feed duct is ad justed by adjusting operating speed of the pump. The pump is driven by an 25 electrical motor and the speed of the motor is adjusted by means of a frequency converter. The frequency converter allows an accurate control of rotational speed. Further, the frequency converter is a reliable component. According to an embodiment, produced flow rate of a feed duct is ad justed by adjusting operating speed of the pump. The pump is driven by means 30 of a hydraulic motor. According to an embodiment, the pump of the flushing system is a pump provided with fixed displacement, such as a centrifugal pump or a gear 6474222 1 (GHMatters) P99912.AUJENNIFER 5 pump. The produced pressure of the pump is adjusted by adjusting rotational speed of the pump. The pump with fixed displacement has simple and durable structure and is inexpensive and easy to control. According to an embodiment, the pump is a variable displacement 5 pump allowing flow rate of the flushing fluid to be varied. Displacement capacity i.e. amount of fluid may be varied by adjusting pumping elements of the pump. According to an embodiment, the flushing system is provided with an air-mist flushing feature. Then the flushing system may comprise one or more compressors for producing compressed air for the flushing. The system further 10 comprises a water pump arranged to produce pressurized water for the flush ing. The produced pressurized flushing water and the pressurized flushing air may be mixed in a feed duct in order to produce air-mist. The flushing system comprises a control unit, which is configured to control the operation of the compressor and the water pump. The air-mist flushing system may be an op 15 tional system, which may be used when needed. Thus, in the optional system the flushing may be executed using liquid flushing or air-mist flushing depending on flushing need. The water pump may be arranged to produce needed water flows for the normal liquid flushing and the air-mist flushing. Further, when the flushing system comprises both flushing types, there may be two feed ducts or 20 lines, which are dimensioned for different flow rates. Thus, the system may comprise a liquid flushing feed duct to be utilized in liquid flushing and having a greater cross section as compared to an air-mist flushing feed duct. In the liquid flushing a great amount of flushing fluid is typically used and in the air-mist flushing the flow rate may be substantially smaller. Ac 25 cording to an embodiment, the flushing system is provided with an air-mist flushing feature. The system comprises a compressor for producing needed pressurized air flow. Operational speed of the compressor may be controlled by means of a control unit. The compressor may be driven by an electrical motor and rotation speed of the electrical motor is controlled. The speed of the electri 30 cal motor may be controlled by means of a frequency converter in order to ad just production of the compressed air. An advantage of this solution is that the compressor may be controlled accurately and by using reliable control system. 6474222 1 (GHMatters) P99912.AUJENNIFER 6 According to an embodiment, the flushing system is provided with an air-mist flushing feature. The system comprises a compressor for producing needed pressurized air flow. The compressor may be driven by a hydraulic mo tor and rotation speed of the motor is controlled by means of a control unit. 5 According to an embodiment, the flushing system comprises one or more control units for controlling feed of the flushing fluid. The control unit may comprise one or more processing devices for implementing the control. The control unit may be provided with one or more predetermined control principles for the operation of the flushing system. The control principle may be stored in 10 memory storage of the control unit or it may be retrieved from an external data source. The control unit is configured to determine control parameters in the processing device on the basis of the received sensing data and the control principle. The sensing data may be received from one or more sensing devices arranged to measure and detect properties of the fed flushing fluid. The prede 15 termined control principle may be configured to control feeding of the flushing fluid by utilizing a flow control principle, which is disclosed in this patent applica tion. Another control principle may be configured to monitor drilling procedure on the basis of the sensed data. Further still, an alternative control principle may be configured to detect failures in the flushing system. 20 According to an embodiment, the flushing system comprises a con trol unit and one or more control principles to be executed in the control unit. An optional control principle may be designed to detect clogging of flushing fluid apertures of a drill bit of a drilling tool. The drill bit may be provided with several narrow fluid channels into which rock material may enter during drilling and 25 cause the apertures to clog. The clogging causes sudden increase in flow re sistance, since the flushing fluid is not escaping the drill bit. Then the flow of flushing fluid decreases and pressure in the feed duct increases. The control unit may then detect that the clogging occurs. The clogging may be detected by monitoring the flow and pressure prevailing in the feed duct. 30 According to an embodiment, the flushing system comprises a con trol unit and one or more control principles to be executed in the control unit. An optional control principle may be designed to detect cracks and cavities in the 6474222 1 (GHMatters) P99912.AUJENNIFER 7 material being drilled. Pressure in the feed duct may decrease suddenly when a drill bit of drilling tool enters a cavity. That is because the flushing fluid may then escape freely from the drill bit to a space surrounding the drill bit instead of flow ing to a narrow space between the drilling tool and the drilled bore hole. When 5 the drilling tool enters the cavity in the rock material flow resistance of the flush ing fluid decreases. Also, when the drilled rock material has cracks or is frag mented, the flushing fluid may flow to voids in the rock material, whereby the flow resistance of the flushing fluid may decrease. Then the flow of flushing fluid increases and pressure in the feed duct decreases. The control unit may then 10 detect the change in the drilling conditions. The system may monitor the flow and pressure prevailing in the feed duct. According to an embodiment, pressure of the flushing fluid is set as high as possible. A maximum pressure rate is defined by a structure of a drilling machine. One or more pressure sensors or pressure sensing devices may be 15 utilized to detect pressure of the flushing fluid acting in the drilling machine. The maximum pressure rate tolerated by the drilling machine is known by the control unit, whereby the control unit may control the pump unit to produce a pressure close to the predefined maximum pressure. Flushing of drilling cuttings may be improved by using as high pressure as possible. In addition to pressure, also 20 flow of the flushing fluid may be increased, whereby total flushing capacity is increased. According to an embodiment, the flushing fluid is water. According to an embodiment, the rock drilling machine of the drilling unit is a down-the-hole (DTH) drilling machine comprising a rotating unit and a 25 percussion unit arranged at opposite ends of a tool. The disclosed flushing sys tem and method may be applied in DTH -drilling. According to an embodiment, the rock drilling machine of the drilling unit is a rotary drilling machine comprising a rotating unit. The rotary drilling ma chine is without any percussion device. The disclosed flushing system and 30 method may be applied in rotary drilling. According to an embodiment, the rock drilling machine of the drilling unit is a top hammer drilling machine comprising a rotating device and a per 6474222 1 (GHMatters) P99912.AUJENNIFER 8 cussion device located at a rear end of the tool. The disclosed flushing system and method may be applied in rotary drilling. According to an embodiment, the disclosed flushing system is utilized in surface drilling. 5 According to an embodiment, the disclosed flushing system is utilized in underground drilling. The above-disclosed embodiments can be combined in order to form suitable solutions provided with necessary features disclosed. Brief description of the figures 10 Some embodiments are described in more detail in the accompany ing drawings, in which Figure 1 is a schematic side view of a rock drilling rig provided with a drilling unit and a flushing system, Figure 2 is a schematic diagram of a flushing system, 15 Figure 3 is a schematic diagram of a flushing system provided with means for an air-mist flushing in addition to normal liquid flushing, and Figure 4 is a schematic graph showing different control situations of a flushing system. For the sake of clarity, the figures show some embodiments of the 20 disclosed solution in a simplified manner. In the figures, like reference numerals identify like elements. Detailed description of some embodiments Figure 1 shows a rock drilling rig 1, which comprises a movable car rier 2 and a drilling boom 3 connected movably to the carrier 2. At a distal end 25 of the boom 3 is a drilling unit 4, which comprises a drilling machine 5. The drill ing machine 5 may comprise a shank 6 at a front end of the rock drilling ma chine 5 for connecting a tool 7. The tool 7 may comprise one or more drill rods 8 and a drill bit 9 located at a distal end of the tool 7. The tool 7 may comprise a flushing channel leading to the drill bit 9. The drilling machine 5 further compris 30 es a rotating device 10 for rotating the shank 6 and the tool 7 connected to the shank 6. The drilling machine 5 may also be provided with a percussion device 6474222 1 (GHMatters) P99912.AUJENNIFER 9 for generating impact pulses to the tool 7. The drilling unit 4 may further com prise a feed beam 11 on which the drilling machine 5 may be supported. The drilling machine 5 may be moved on the feed beam 11 by means of a feed de vice 12. 5 At a drilling site, one or more drill holes 13 are drilled with the drilling unit 4. The drill holes 13 may be drilled in a vertical direction, as shown in Fig ure 1, or in a horizontal direction. During drilling rock material is detached by means of the drill bit 9. Produced drilling cuttings needs to be removed from the drill hole 13. Therefore the rock drilling rig 1 is provided with a flushing system 10 14, which comprises a pump unit 15 for feeding pressurized flushing fluid by means of a feed duct or hose 16 to the drilling machine 5. The drilling machine 5 may comprise a flushing housing around the shank 6 so that the flushing fluid may enter to a longitudinal flushing channel of the tool 7. Thus, the flushing fluid may flow through the tool 7 towards the drill bit 9. The drill bit 9 is provided with 15 flushing apertures allowing the flushing fluid to finally escape from of the drill bit 9. In the drill hole 13 the flushing fluid pushes the drilling cuttings towards a mouth of the drill hole 13. During drilling a need for flushing may vary because of executed drilling efficiency or rock material being drilled, for example. Amount of flushing may be adjusted accurately and fast when using flushing system dis 20 closed in this patent application. Figure 2 discloses in a simplified manner a flushing system 14 com prising a pump unit 15, a valve 17, a flow meter F, a feed duct 16 and a control unit CU. The pump unit 15 comprises a power device 18, which is arranged to drive a pump 19 for producing pressurized flushing fluid flow to the feed duct 25 16. The valve 17 is arranged in the feed duct 16 for controlling feeding of the flushing fluid. The valve 17 may be on/off type allowing only opening and clos ing the feed duct 16. The valve 17 is opened when the flushing fluid is fed, and closed when no need for flushing exists. Flow rate of the flushing fluid may be sensed by means of the flow meter F and the sensing data may be transmitted 30 to the control unit CU. Based on the received sensing data the control unit CU may control pumping of the flushing fluid. The power device 18 may be a hy draulic motor connected to a hydraulic system 20. The pumping unit 15 may 6474222 1 (GHMatters) P99912.AUJENNIFER 10 comprise an adjusting device 21 allowing rotational speed of the hydraulic mo tor and the pump 19 to be adjusted. The control unit CU may control the adjust ing device 21 and the valve 17. Alternatively, the power device 18 may an elec trical motor and the adjusting device 21 may be a frequency converter. Further, 5 the feed duct 16 may be provided with an optional pressure sensing device P for detecting prevailing pressure of the feed duct 16. The pressure sensing data may also be transmitted to the control unit CU. Thanks to the pressure sensing data, it is possible to set the pressure of the flushing fluid as high as tolerated by the drilling unit 4. The pressure data may also utilized for detecting changes 10 in the rock material being drilled. Figure 3 discloses a flushing system 14, which is provided with a liq uid flushing system and an air-mist flushing system. The air-mist system com prises a compressor 22, which may be driven by means of a power device 23, such as an electrical motor. Supply of pressurized air may be adjusted by 15 means of an adjusting device 24, which may be a frequency converter, for ex ample. The produced air flow of the compressor 22 may be conveyed through an air feed duct 25 to a feed duct 16 wherein the air mixes with the flushing flu id. In the air-mist flushing amount of flushing fluid is smaller than in a normal liquid flushing. A control unit CU may control opening and closing of an air valve 20 17C, adjusting device 24 and a small sized valve 17A of a feed duct 16a in or der to produce desired air-mist flushing. In Figure 3 the flushing fluid system 14 comprises two parallel feed ducts 16a and 16b, which are provided with control valves 17A and 17B. The control valves 17A and 17B may have orifices which have mutually different 25 size. The control valve 17A may be utilized in air-mist flushing as disclosed above. The control valve 17B may be utilized in liquid flushing alone or in com bination with the control valve 17A. The valves 17A and 17B may be opened and closed according to the produced flow, whereby different operational com binations of the valves may be utilized for scaling the flow path in response to 30 the supplied flow. The control valves 17A and 17B may be provide with throttles 25a and 25b, or alternatively the throttles may be individual components ar ranged in parallel feed ducts 16a and 16b. The control valves 17A and 17B may 6474222 1 (GHMatters) P99912.AUJENNIFER 11 be on/off type valves since adjusting of the flushing system is based on adjust ment of the pump unit 15. In Figure 3 flow rate determination is based on a pressure difference measurement utilizing pressure sensors P1 and P2. Thus, the feed duct 16 is 5 provided with means for throttling flow of the feed duct. The throttle 25a, 25b causes a pressure drop. Pressure drop over the throttling is sensed or meas ured by means of pressure sensors P1, P2 and this data is used for determining flow rate in the feed duct 16. The adjusting device 21 may be controlled on the basis of the detected flow rate. The control unit CU also selects opening and 10 closing of valves 17A and 17B according to the need. Control principles, algo rithms and an additional data may be input to control unit by means of a user interface UI. The flushing system 14 may also differ from the one disclosed in Fig ure 3. In an alternative solution more than two operationally parallel feed duct 15 portions and valves may be utilized. Further, the flow rate may be detected by means of a flow meter instead of pressure difference measurement. The pump unit 15 may also be hydraulically driven as it is shown in Figure 2. Figure 4 illustrates three different scales of flows. Reference is made to the flushing system of Figure 3 comprising valves 17A and 17B in the feed 20 duct. A lowermost curve A relates to a situation when only valve 17A is open, curve in the middle relates to a situation when only valve 17B open, and further an uppermost curve A + B shows a situation when both valves 17A and 17B are open. Depending on the flow rate the control unit opens and closes the valves 17A and 17B. 25 The drawings and the related description are only intended to illus trate the idea of the invention. In its details, the invention may vary within the scope of the claims. In the claims which follow and in the preceding description of the in vention, except where the context requires otherwise due to express language 30 or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. 6474222 1 (GHMatters) P99912.AUJENNIFER 12 It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. 5 6474222 1 (GHMatters) P99912.AUJENNIFER

Claims

1. A flushing system of a drilling unit, wherein the drilling unit (4) comprises a drilling machine (5) and a tool (7) connectable to the drilling machine (5); 5 and the flushing system (14) comprising: a pump unit (15) for feeding pressurized flushing fluid, wherein the pump unit (15) comprises a pump (19) and a power device (18) for driving the pump (19); at least one feed duct (16) for feeding the pressurized flushing fluid 10 from the pump (19) to the drilling machine (5); at least one valve (17) in the feed duct (16) for controlling flow of the flushing fluid conveyed to the drilling machine (5); at least one sensing device arranged to measure at least one proper ty of the fed flushing fluid; 15 at least one control unit (CU) for controlling the feed of the flushing fluid in response to a sensing data received from the at least one sensing de vice; and wherein the pump unit (15) is a variable flow rate pump unit (15) provided with adjusting means allowing flow rate of the flushing fluid to be varied; and 20 the control unit (CU) is configured to determine flow rate of the flush ing fluid on the basis of the received sensing data, and the control unit (CU) is further configured to control the flow rate of the fed flushing fluid by adjusting the pressure supplied by the pump (19); cha racte rized in that 25 the flushing system (14) comprises at least a first feed duct (16a) and a second feed duct (16b), which are operationally parallel relative to each other; the first feed duct (16a) is provided with a first valve (17A) and a first throttle (25a); the second feed duct (16b) is provided with a second valve (17B) and 30 a second throttle (25b); the first throttle (25a) and the second throttle (25b) have orifices, which differ in size; 6474222 1 (GHMatters) P99912.AUJENNIFER 14 the first valve (17A) and the second valve (17B) are independently controllable; and the control unit (CU) is configured to control opening and closing of the first valve (17A) and the second valve (17B) according to the operation of 5 the drilling unit (4).

2. The flushing system as claimed in claim 1, c h a r a c t e r i z e d in that the valve (17) is of on/off -type without adjusting means. 10

3. The flushing system as claimed in claim 1 or 2, c h a r a c t e r ized in that the throttle (25a, 25b) is an integrated element of the valve (17A, 17B). 15

4. The flushing system as claimed in any one of the preceding claims 1 -3, characterized in that the throttle (25a, 25b) is a separate element relative to the valve (17A, 17B). 20

5. The flushing system as claimed in any one of the preceding claims 1 to4, characterized in that at least one throttle (25a, 25b) is arranged in the at least one feed duct (16a, 16b), wherein the throttle (25a, 25b) causes a pressure drop; 25 the flushing system (14) comprises at least one first pressure sensing device (P1) for detecting pressure of the flushing fluid acting before the throttle (25a, 25b); the flushing system (14) comprises at least one second pressure sensing device (P2) for detecting pressure of the flushing fluid acting after the 30 throttle (25a, 25b); the sensed pressure data is transmitted to the control unit (CU); 6474222 1 (GHMatters) P99912.AUJENNIFER 15 the control unit (CU) is configured to determine a pressure difference caused by the throttle (25a, 25b); and the control unit (CU) is further configured to determine the flow rate of the flushing fluid on the basis of the detected pressure difference. 5

6. The flushing system as claimed in any one of the preceding claims 1 to4, characterized in that the at least one feed duct (16) is provided with at least one flow me ter (F) for determining the flow rate of the flushing fluid. 10

7. The flushing system as claimed in any one of the preceding claims 1 to6, characterized in that the pump (19) is driven by an electrical motor; operating speed of the pump (19) is adjusted in order to adjust the 15 produced flow of the flushing fluid; and rotational speed of the electric motor is adjusted by means of an ad justing device (21).

8. The flushing system as claimed in claim 7, c h a r a c t e r i z e d in 20 that the pump (19) is a fixed displacement pump; and the supplied pressure of the pump is adjusted by adjusting rotational speed of the pump (19). 25

9. The flushing system as claimed in claim 7 or 8, c h a r a c t e r ized in that the adjusting device (21) is a frequency converter.

10. The flushing system as claimed in any one of the preceding 30 claims 1 to9, characterized in that at least one pressure sensing device (P) is arranged to detect pres sure of the flushing fluid acting in the drilling machine (5); 6474222 1 (GHMatters) P99912.AUJENNIFER 16 the pressure of the flushing fluid is adjusted by adjusting the pump (19); a maximum pressure rate tolerated by the drilling machine (5) is set to the control unit (CU); and 5 the control unit (CU) is arranged to control the pump unit (15) to sup ply a pressure close to the predefined maximum pressure.

11. The flushing system as claimed in any one of the preceding claims 1 to 10, characterized inthat 10 the flushing system (14) is provided with an air-mist flushing system; the flushing system (14) comprises at least one compressor (22) for supplying compressed air for the flushing; the pump (19) is a water pump arranged to supply pressurized water for the flushing; 15 the supplied pressurized flushing water and the pressurized flushing air are mixed in the feed duct (16), whereby air-mist is produced; and the control unit (CU) is arranged to control the operation of the com pressor (22). 20

12. The flushing system as claimed in claim 11, c h a r a c t e r i z e d in that the compressor (22) is driven by a second electrical motor (23); and operational speed of the second electrical motor (23) is controlled by means of a second frequency converter (24) in order to adjust flow rate of the 25 compressed air.

13. A method of controlling feeding of flushing fluid of a flushing sys tem of a rock drilling unit, which flushing system is in accordance with inde pendent apparatus claim 1, 30 the rock drilling unit (4) comprising a drilling machine (5) and a tool connectable to the drilling machine (5); and the method comprises: 6474222 1 (GHMatters) P99912.AUJENNIFER 17 pressurizing flushing fluid by means of at least one pump unit (15) and conveying the pressurized flushing fluid to the drilling machine (5) through at least one feed duct (16); controlling the feeding of the flushing fluid by means of at least one 5 valve (17) arranged in the feed duct (16); monitoring the fed flushing fluid by means of at least one sensing de vice; and controlling flow rate of the flushing fluid according to the monitoring; characterized by 10 controlling flow rate of the flushing fluid by adjusting pressure sup plied by the pump unit (15); directing the flushing fluid through at least two valves (17A, 17B) be ing operationally parallel and having flow paths which are different in size; and selecting opening and closing of the at least two valves (1 7A, 17B) in 15 response to magnitude of the supplied volume flow of the pump unit (15). 6474222 1 (GHMatters) P99912.AUJENNIFER