VALVE^AND^METHOD^FOR^MANUFACTURING^A^CLOSURE^MEMBER BACKGROUND^OF^THE^INVENTION^ FIELD^OF^THE^INVENTION^ [0001]^This invention relates to a valve with a closure member. DESCRIPTION^OF^PRIOR^ART [0002]^In industrial processes in which highly pressurized fluids are conveyed over piping systems, it is known to use different wear-reducing methods in order to minimize the deteriorating effect caused on the piping systems by said fluids. Such methods include, for example, applying layers of wear-resistant materials on the surfaces of the piping and valves exposed to the fluids in these systems. However, such methods may only extend the lifetime of the piping system components to a limited extent, while also increasing the cost of the components. [0003]^Operating conditions particularly challenging for these piping systems involve pressurized liquids that undergo a rapid transformation to a gaseous state as a result of pressure drops within the piping system. Such conditions are encountered in, for example, processes related to hydrometallurgy, in which abrasive particles may also be embedded within the liquid. In such conditions, the combination of cavitation and fluid erosion may be a major cause of equipment failures and operation delays, especially when the impacted areas of the piping system are located in expensive components or large segments of the system. Therefore, it is desirable to direct the deteriorating influence of the fluid flow to relatively inexpensive and easily replaceable areas of the piping system, as well as to provide operating conditions with minimized fluid-induced wear. SUMMARY^OF^THE^INVENTION [0004]^An object of the present invention is to alleviate the above- mentioned drawback and to provide a solution allowing for longer replacement intervals of the structural parts of a piping system and more cost-efficient maintenance. This object is achieved with a valve according to independent claim 1 and a method according to independent claim 12. [0005]^By utilizing a valve closure member having a flow channel comprising a first bore and a second bore, it is possible to obtain a structure which enables a prolonged lifetime and more cost-efficient maintenance of the piping system. [0006]^Preferred embodiments of the invention are disclosed in the dependent claims. BRIEF^DESCRIPTION^OF^DRAWINGS [0007]^ In the following the present invention will be described in closer detail by way of example and with reference to the attached drawing, in which [0008]^Figure 1 illustrates a cross-cut section of a first embodiment of a valve as seen from above. DESCRIPTION^OF^AT^LEAST^ONE^EMBODIMENT [0009]^Figure 1 illustrates a cross-cut section of a first embodiment of a valve, as seen from above. As can be seen from this example, the valve 1 comprises a closure member 2 which is arranged in the valve rotatably around an axis of rotation 13. In Figure 1, the axis of rotation 13 of the closure member 2 extends in the direction of viewing, or in other words, the figure illustrates the valve 1 as seen from the direction of the axis of rotation 13. In the illustrated arrangement, the closure member 2 can be moved by rotation between a fully closed position, wherein the closure member 2 prevents flow through the valve 1, and a fully open position, wherein the closure member 2 allows flow through the valve 1. The closure member 2 comprises an inlet opening 3 and an outlet opening 4, and a flow channel 5 providing a flow path from the inlet opening 3 to the outlet opening 4. In other words, the flow channel 5 extends through the closure member 3 between the inlet opening 3 and the outlet opening 4. Furthermore, the flow channel 5 comprises a first bore 6 having a first center axis 7 and a second bore 8 having a second center axis 9. In said example, the flow channel 5 is formed by the first 6 and the second bore 8 as a result of the first bore 6 extending from the inlet opening 3 and the second bore 8 extending from the outlet opening 4, and said bores intersecting within the closure member 2. [0010]^ In the example of Figure 1, the first center axis 7 and the second center axis 9 are non-coaxially arranged to form an angle with each other to turn a direction of the flow channel 5 at an interface between the first bore 6 and the second bore 8. In said example, the first center axis 7 and the second center axis 9 also extend along a common plane which is perpendicular to the axis of rotation 9 are oriented to be non-parallel with each other on a common plane, said plane being perpendicular to the axis of rotation 13 of the closure member 2. In other embodiments of the valve 1, however, the first 7 and the second center axis 9 can also be arranged non-coaxially with each other along multiple planes, in other words so that they extend along separate planes that form an angle with each other. [0011]^In the example of Figure 1, the second bore 8 is also oriented so that the flow channel 5 is directed towards a center axis 10 of the valve 1 at the side of the outlet opening 4 in the fully open position of the valve. In other words, the second bore 8 is arranged to direct a flow of a fluid passing through the closure member 2 towards the middle section of the valve 1 at the side of the outlet opening 4. Said arrangement causes the fluid flow to be directed away from the walls of a fluid conveying structure, such as a pipe, located at the outlet side of the valve 1, allowing the fluid conveying structure to be less impacted by the pressure of the fluid flow. In this context, the center axis 10 of the valve 1 is defined by the middle axis of the fluid conveying channel around the closure member 2. [0012]^In the example of Figure 1, a first step 11 and a second step 12 are provided at the interface between the first bore 6 and the second bore 8. In said example, the first and the second step are formed at said interface as a result of the first bore 6 and the second bore 8 being arranged non-coaxially and forming an angle at their intersection, thereby creating a discontinuity to the flow channel 5 at the interface. In the example of Figure 1, the first bore 6 and the second bore 8 are also arranged to overlap at the interface area, causing the first step 11 and the second step 12 to be formed at different locations along the length of the flow channel 5. In this context, overlapping of the first bore 6 and the second bore 8 means that their individual volumes, as defined by their individually formed inner surfaces, are partially overlapping. In other words, in said arrangement the location of the first step 11 along the length of the flow channel 5 is defined by the depth of the first bore 6 within the closure member 2, as measured from the inlet opening 3, and the location of the second step 12 along the length of the flow channel 5 is defined by the depth of the second bore 8 within the closure member 2, as measured from the outlet opening 4. [0013]^ In the example of Figure 1, the first step 11 and the second step 12 extend along the opposing sides of the flow channel surface. In other words, the first 11 and the second step 12 follow the curvature of the flow channel surface on the opposing sides of the longitudinal middle section of the flow channel 5, as seen from the direction of the axis of rotation 13 of the closure member 2. Furthermore, the first step 11 extends in a direction parallel to the first center axis 7 and the second step 12 extends in a direction parallel to the second center axis 9. Such a form of the first 11 and the second step 12 can be obtained as a result of, for example, manufacturing of the first 6 and the second bore 8 by drilling, wherein the orientation of the first 11 and the second step 12 is defined by the shape of the drill bit used for the drilling. Furthermore, in the example of Figure 1, the first step 11 defines a corner 19 opening towards the inlet opening 3, and the second step 12 defines a corner 20 opening towards the outlet opening 4. In other words, the corner 19 defined by the first step 11 is formed at the end of the first bore 6 at the interface between the first bore 6 and the second bore 8, and forms a location where the flow channel surface turns towards the middle section of the flow channel 5, as viewed in the flow direction. Similarly, the corner 20 defined by the second step 12 is formed at the beginning of the second bore 8, and forms a location where the flow channel surface turns away from the middle section of the flow channel, as viewed in the flow direction. [0014]^With a flow channel 5 arrangement as described, the behavior and direction of the fluid flow within the flow channel 5 can be affected. That is, with the arrangement of the first 7 and the second center axis 9 combined with the arrangement of the first 11 and the second step 12 as described, the direction of the fluid flow can be further turned along the length of the flow channel 5, so that a flow leaving from the outlet opening 4 is significantly directed towards the middle section of the valve 1. In other words, said arrangement of the first 11 and the second step 12 enable flow conditions within the flow channel 5 due to which the flow leaving from the outlet opening 4 is directed towards the middle section of the valve 1 more steeply than in an arrangement in which the flow direction was not influenced by the first 11 and the second step 12. Said arrangement is particularly beneficial when small opening angles of the closure member 2 are used, wherein the second bore 8 is only partially open to the outside of the closure member 2 and is generally oriented towards the walls of the fluid conveying structure at the outlet side of the valve 1. In a valve according to the example of Figure 1, a fluid flow is arranged to assume an essentially S-shaped pattern within the flow channel 5, wherein the first curve of the pattern is defined by the first step 11. [0015]^ In relation to pressurized liquids that undergo a rapid transformation to a gaseous state as a result of pressure drops within the piping system, it is desirable to avoid formation of areas within the flow channel 5 in which such pressure drops are possible. That is, such transformations of a fluid from liquid to gas are typically associated with cavitation-induced damage on fluid conveying structures, which can be further accelerated by the associated deformation of the flow channel surface. These areas are typically formed when the flow cross section area within the flow channel is increased along the length of the flow channel. In the example of Figure 1, fluid pressure within the flow channel 5 is regulated by dimensioning of the flow channel 5 so that the inlet opening 3 has an opening area that is greater than the opening area of the outlet opening 4. With such arrangement, it is ensured that fluid pressure within the flow channel 5 is at a higher level at the outlet opening 4 than at the inlet opening 3, thereby decreasing the risk of cavitation-induced damage as described within the flow channel 5. To further decrease said risk, the first bore 6 of the closure member 2 of Figure 1 has a conical shape that widens towards the inlet opening 3, creating a flow-throttling effect along the length of the first bore 6. At the same time, the second bore 8 has been arranged in a cylindrical shape, wherein the diameter of the second bore 8 does not exceed the diameter of the first bore 6. [0016]^ In the example of Figure 1, the flow channel 5 further comprises a third bore 14 having a third center axis 15, wherein the third center axis 15 is non-coaxially arranged with the first 7 and the second center axis 9 to form an angle with the first 7 and the second center axis 9. In other words, the third center axis 15 is oriented to be non-parallel with the first 7 and the second center axis 9 on the plane perpendicular to the axis of rotation 13 of the closure member 2. In other embodiments of the valve 1, however, the first 7, the second 9 and the third center axis 15 may also be arranged non-coaxially with each other along multiple planes, in other words so that they extend along separate planes, each of which may form an angle with the other planes. Furthermore, in said example the second center axis 9 is oriented between the first center axis 7 and the third center axis 15 along the common plane perpendicular to the axis of rotation 13 of the closure member 2, and none of the first center axis 7, the second center axis 9 and the third center axis 15 is parallel to the center axis 10 of the valve 1 in the fully open position. In said fully open position, the center axis 10 of the valve 1 is also oriented between the first center axis 7 and the second center axis 9 along said common plane. [0017]^Similarly to the second bore 8, the third bore 14 according to the example of Figure 1 is oriented so that the flow channel 5 is directed towards the center axis 10 of the valve 1 at the side of the outlet opening 4 in the fully open position of the valve 1. More precisely, the third bore 14 is arranged to direct a flow of a fluid passing through the closure member 2 towards the middle section of the valve 1 in an angle that is more steep than the angle enabled singularly by the second bore 8. In said example, only one side of the flow channel 5 along the length of the third bore 14 is defined by the third bore 14, whereas the other side of the flow channel 5 in this area is defined by the second bore 8. Furthermore, in said example the flow channel 5 surface in the vicinity of the outlet opening 4 is defined only by the second bore 8, in other words the second bore 8 and the third bore 14 are arranged to fully overlap in this area. Furthermore, a third step 16 is provided at the interface between the second bore 8 and the third bore 14 extending along the flow channel surface. In said example, the third step 16 is formed at said interface as a result of the second bore 8 and the third bore 14 being arranged non- coaxially and forming an angle at their intersection, thereby creating a discontinuity to the flow channel 5 at the interface. In the example of Figure 1, the second bore 8 and the third bore 14 are also arranged to overlap along the length of the flow channel 5, and the third step 16 is formed at the location where the third bore 14 protrudes from the flow channel surface defined by the second bore 8, as viewed in the flow direction. [0018]^In the example of Figure 1, the valve 1 further comprises an inlet shoulder 17 arranged to decrease the flow crosscut area towards the closure member 2 at the side of the inlet opening 3. Similarly, the valve 1 of said example also comprises an outlet shoulder 18 arranged to decrease the flow crosscut area towards the closure member 2 at the side of the outlet opening 4. In other words, the inlet shoulder 17 has been arranged to produce a progressive flow-throttling effect to the fluid flow arriving to the flow channel 5 at the side of the inlet opening 3, thereby progressively increasing the fluid pressure in this area. On the other hand, the outlet shoulder 18 has been arranged to allow the flow crosscut area to progressively increase after the fluid flow has passed the outlet opening 4. In said example, the inlet shoulder 17 and the outlet shoulder 18 have been arranged symmetrically to the fluid conveying channel around the closure member 2, and the outlet shoulder 18 is first contacted by the fluid flow arriving from the outlet opening 4 when the closure member 2 is moved from the fully closed position towards the fully open position. In said arrangement, the outlet shoulder 18 also contributes to protecting the fluid conveying structure at the outlet side of the valve 1 from the pressure of the fluid flow and to directing the fluid flow passing through the closure member 2 towards the middle section of the valve 1. In different embodiments of the valve 1, the inlet shoulder 17 and the outlet shoulder 18 may be implemented as integral parts of the valve 1, or as separate structural elements in which case they may also be replaced as needed independently of the other structural elements of the valve 1. [0019]^Furthermore in the example of Figure 1, the inlet opening 3 has been arranged to be in fluid communication with the outside of the closure member 2 in the fully closed position of the valve 1. In other words, the inlet opening 3 is at least partially open to the fluid conveying channel in the fully closed position to allow fluid to enter the flow channel 5, as illustrated in Figure 1. In this arrangement, the fluid flow through the flow channel 5 is only prevented by the outlet opening 4, which in the fully closed position of the valve 1 is completely closed to the fluid conveying channel on the outlet side of the valve. With said arrangement, the fluid content and pressure can be kept constantly uniform over the flow channel 5 and the fluid conveying channel at the inlet side of the valve 1, as opposed to an arrangement in which the flow channel 5 is only filled with a fluid in the open position of the valve 1. Said arrangement enables pressure shocks caused by pressure nonuniformity over the flow channel 5 and the fluid conveying channel at the inlet side of the valve 1 to be avoided, said nonuniformity causing a pressurized fluid flow entering a flow channel to impact the flow channel surfaces in a conventional ball valve arrangement. [0020]^In the example of Figure 1, the inlet opening 3 and the outlet opening 4 are also positioned to allow flow through the valve 1 only when the closure member 2 is rotated from the fully closed position towards the fully open position by at least 10°. In other words, the outlet opening 4 is arranged to remain fully closed to the fluid conveying channel on the outlet side of the valve 1 until the closure member 2 has been rotated around the axis of rotation 13 by at least 10°. Said arrangement allows the closure member 2 to be re-adjusted to accommodate possible wear of the flow channel 5 or the outlet shoulder 18 caused by the fluid flow, said wear typically causing a gradual widening of the angle range in which a closure member allows flow through a valve in a ball valve structure. Said re- adjustment can take place by, for example, rotating the closure member 2 further around the axis of rotation 13 towards the fully closed position until a desired rate of fluid flow has been achieved, or by rotating the closure member 2 from the fully open position in a direction opposite of the initial direction towards the fully closed position, to achieve a closed arrangement of the flow channel 5 mirroring the initial arrangement. With said arrangement, the replacement intervals of the valve 1 or the closure member 2 in a piping system can be extended. [0021]^A closure member according to the example of Figure 1 can be manufactured by first providing the first bore 6 having the first center axis 7 to the closure member 2, and by then providing the second bore 8 having the second center axis 9 to form the flow channel 5. The closure member 2 prior to said processing steps comprises a solid object with outer dimensions corresponding to the desired dimensioning of the finished closure member 2. In praxis, the first bore 6 can be provided by, for example, drilling the closure member 2 on the side of the desired location of the inlet opening 3, and the second bore 8 can then be provided by drilling the closure member 2 on the side of the desired location of the outlet opening 4 until the second bore 8 forms a connection with the first bore 6. Thereby a flow channel 5 comprising the first bore 6 and the second bore 8 is formed, wherein the first center axis 7 and the second center axis 9 are non-coaxially arranged to form an angle with each other. Furthermore, to achieve a structure according to the example of Figure 1, the third bore 14 having the third center axis 15 is provided to the closure member 2, wherein the third center axis 15 is non- coaxially arranged with the first 7 and the second center axis 9 to form an angle with the first 7 and the second center axis 9. In praxis, the third bore 14 can be provided by, for example, drilling the closure member 2 on the side of the outlet opening 4, the drill bit entering the closure member 2 through the outlet opening 4 formed by the second bore 8. [0022]^ In some embodiments of the valve 1, the first bore 6, the second bore 8 and the third bore 14 can also be manufactured by, for example, additive manufacturing, in which case they can be formed in the closure member 2 directly during the manufacture of the closure member 2 though an additive manufacturing process. In some embodiments of the valve 1, the closure member can also comprise several flow channels 5, wherein each or some of the flow channels 5 may comprise the first bore 6 and the second bore 8 as described. Furthermore, each or some of said flow channels 5 may also comprise the third bore 14 as described independently of each other. Also, in some embodiments of the valve 1, the flow channel 5 or flow channels 5 may comprise any number of bores in addition to the first, the second and the third bore, to achieve a desired shape and orientation of the fluid flow passing through the flow channel 5. [0023]^ It is to be understood that the above description and the accompanying figures are only intended to illustrate the present invention. It will be obvious to a person skilled in the art that the invention can be varied and modified without departing from the scope of the invention.