Abstract
An impeller structure for a centrifugal pump that can feed both fibrous suspensions and water into a headbox of a fibrous web machine. The centrifugal pump utilizing the impeller structure pumps stock for both liquid-laid and foam-laid paper, tissue or board making applications and pumps water or other dilution fluid into a headbox circulation. In general, the impeller of the present invention is especially suitable for all such pumping tasks in the production of fibrous webs that a pulseless or low-pulse impeller is needed.
Claims
1. An impeller of a centrifugal headbox feed pump, the impeller comprising: a shroud with a front face and a circumference; a plurality of long working vanes on the front face; and a plurality of shorter intermediate working vanes on the front face between the long working vanes, the shorter intermediate working vanes having a leading edge and a foot part thereof, wherein the shorter intermediate working vanes have a leading edge with an angle of inclination, a foot length (Lfs) and an edge length (Les), the long working vanes having a leading edge with an angle of inclination, the angles of inclination of the leading edges of the long and shorter working vanes having a difference of 20 to 45 degrees, the foot length (Lfs) of the shorter intermediate working vane being between 1.2* Les and 3.0* Les and at least one of a plurality of openings for gas discharge arranged through the shroud within a circumference formed by the foot parts of the leading edges of the shorter intermediate working vanes and of a plurality of balancing openings arranged through the shroud within a circumference formed by the foot parts of the leading edges of the long working vanes.
2. The impeller as recited in claim 1, wherein the long working vanes have a foot length (Lfl), and the edge length (Les) of the shorter intermediate working vane being between 0.3* Lfl and 0.5* Lfl.
3. The impeller as recited in claim 1, wherein the angle inclination of the leading edge of the shorter intermediate working vanes is 45-70 degrees with the front face of the shroud.
4. The impeller as recited in claim 1, wherein a number of the shorter intermediate working vanes is the same or a multitude of a number of long working vanes.
5. The impeller as recited in claim 1, wherein intermediate shorter vanes divide a radially outer part of each vane passage between the long working vanes into two or more equally sized smaller vane passages.
6. The impeller as recited in claim 1, further comprising rear vanes arranged on a rear face of the shroud.
7. The impeller as recited in claim 6, wherein a number and length of the rear vanes correspond to those of the long and shorter working vanes on the front face of the shroud.
8. The impeller as recited in claim 6, wherein the rear vanes are positioned on the rear face of the shroud opposite the long and shorter working vanes on the front face of the shroud.
9. The impeller as recited in claim 6, wherein the long and shorter working vanes have an average thickness (S) and that the leading or the trailing edges of the working vanes are provided with a rounding (R1).
10. The impeller as recited in claim 9, wherein the rounding (R1) has a radius between *S and *S.
11. The impeller as recited in claim 1, wherein the gas discharge openings are provided with a rounding (R2).
12. The impeller as recited in claim 11, wherein the shroud has a thickness (T) and the rounding (R2) has a radius between *T and *T.
13. The impeller as recited in claim 1, wherein the balancing openings are provided with a rounding (R2).
14. The impeller as recited in claim 13, wherein the shroud has a thickness (T) and the rounding(R2) has a radius between *T and *T.
15. A centrifugal headbox feed pump comprising the impeller of claim 1.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Referring now to the attached drawings which form a part of this original disclosure.
(2) FIG. 1 illustrates a perspective view of the impeller in accordance with a first preferred embodiment of the present invention,
(3) FIG. 2 illustrates schematically a cross-section of the impeller in accordance with the first preferred embodiment of the present invention along line A-A of FIG. 4,
(4) FIG. 3 illustrates schematically a partial cross-section of the impeller in accordance with the preferred embodiments of the present invention along line B-B of FIG. 4,
(5) FIG. 4 illustrates schematically a partial cross-section of the impeller in accordance with the first preferred embodiment of the present invention along line C-C of FIG. 3,
(6) FIG. 5 illustrates schematically a partial cross-section of the impeller in accordance with a second preferred embodiment of the present invention along line C - C of FIG. 3,
(7) FIG. 6 illustrates schematically a partial cross-section of the impeller in accordance with a third preferred embodiment of the present invention along line C - C of FIG. 3, and
(8) FIG. 7 illustrates schematically a partial cross-section of the impeller in accordance with a fourth embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
(9) FIG. 1 illustrates a perspective view and FIG. 2 a cross-sectional view along line A-A of FIG. 4 of the impeller in accordance with a preferred embodiment of the present invention. The impeller 10 is a semi-open impeller having a rear plate or shroud 12 with a hub 14 and longer working vanes 16 and at least one intermediate or shorter working vane 18 in each vane passage between the longer working vanes 16 at the front side of the shroud 12, i.e. at the face 20 of the shroud 12 facing the pump inlet (not shown). The shroud 12 preferably, but not necessarily includes rear vanes 22 at the rear face 24 of the shroud 12. In a further variation of the present invention the rear face 24 includes as many rear vanes 22 as there are working vanes 16 and 18 on the front face 20 of the shroud, the rear vanes 22 being positioned opposite the working vanes 16 and 18 and having, preferably but not necessarily, the same length as the working vanes 16 and 18. The shroud 12 has an outer circumference 26 up to which the working vanes 16 and 18, i.e. both longer and shorter ones, preferably, but not necessarily, extend. Naturally, also the rear vanes 22 extend to the outer circumference 26 in the manner of the working vanes 16 and 18. In a still further variation of the present invention a prerequisite for the optimal operation of the impeller of the invention is that both the longer working vanes and the shorter intermediate working vanes extend up to the same circumference and have the same vane shape and orientation at their outer edges. The longer working vanes 16 extend towards the inlet channel (not shown) of the pump housing such that the outer (in relation to the shroud 12) tips of the leading edges of the longer working vanes are at a small spacing from the annular borderline between the pump inlet channel and the pump volute. In other words, the outer tips of the leading edges of the longer working vanes 16 have substantially the same diameter as the inlet channel of the pump housing.
(10) FIG. 3 illustrates schematically a partial cross-section of the impeller in accordance with preferred embodiments of the present invention, the cross-section being taken along line B-B of FIG. 4. FIG. 3 illustrates in more detail the shape of the intermediate or shorter working vane 18. In other words, the working vane 18 has a leading edge 30 (the edge of the working vane 18 closest to the axis A of the impeller 10, i.e. the edge of the intermediate or shorter working vane 18 receiving the fluid flow), a front edge 32 facing the front wall of the pump casing (not shown), i.e. the edge 32 of the working vane 18 opposite to the foot part 34 of the working vane where the working vane 18 joins to the front face 20 of the impeller shroud 12, and a trailing edge 36. The trailing edge 36 of the shorter intermediate working vanes 18 is of its dimensioning and orientation identical with the trailing edge of the longer working vanes 16. The front edge 32 of the shorter intermediate working vanes 18 is identical with the corresponding part of the front edge of the longer working vanes 16. Also, the angle of tilt (angle between the centreline plane of the working vane and the front face of the shroud in a plane running parallel with the axis A of the impeller via the point of cross section of the centreline plane and the front surface of the shroud and at right angles to the line drawn on the front surface of the shroud to the point of cross section of the centreline plane and the front surface of the shroud as a tangent of the centreline plane) of the shorter working vane is the same as that of the longer working vane for the entire length of the shorter working vane. In other words, even if the angle of tilt of the vanes may change along the length of the vanes, the angles of tilt of the shorter and longer vanes are equal in each particular radial position of measurement. Thus, the shorter intermediate working vanes 18 are, in all respects, identical to the longer working vanes 16 except for the fact that an inner part i.e. a part radially closer to the axis A thereof is missing. Here in FIG. 3, it has been shown, as a preferred embodiment of the present invention, that the leading edge 30 of the shorter intermediate working vane 18 is inclined, i.e. it forms a sharp angle with the front face 20 of the shroud. The inclination angle is between 45 and 70 degrees. The inclination angle is an angle between the leading edge 30 of the shorter intermediate working vane 18 and an imaginary line drawn on the front face 20 of the shroud 12 and being a tangent to the centreline plane of the shorter intermediate working vane 18 at the point of intersection between the leading edge 30 and the front face 20 of the shroud 12. By inclining the leading edge 30 of the shorter intermediate working vane 18 the pressure wave created by the leading edge 30 is made to advance such that the direction of the pressure wave front (direction of, for instance, a single peak of a wave, being parallel with the leading edge 30 of the shorter intermediate working vane 18) is not parallel with the trailing edge 36 of the shorter intermediate working vane 18 but at an angle thereto. Now that such a wave front leaves the trailing edge 36 it enters the flow having a wave front based on the longer working vane 16. As the wave front direction of the longer working vanes 16 is based on the direction of the leading edges of the longer working vanes 16 (substantially perpendicular to both the flow of the fluid entering the vane passages and the front face 20 of the shroud 12), and, as the directions of the leading edges of the longer and shorter working vanes are clearly different (the difference in the directions being approximately 20 to 45 degrees), the two different wave fronts will be mixed together and thereby dampen one another.
(11) FIG. 4 illustrates schematically a partial cross-section of the impeller in accordance with a first preferred embodiment of the present invention, the cross-section being taken along line C - C of FIG. 3. In other words, the tops of the longer working vanes 16 have been cut away so that the leading edges 30 of the shorter intermediate working vanes 18 may be seen. Especially FIG. 4, which shows the important dimensions of the working vanes 16 and 18. In other words, the foot length Lfs of the shorter intermediate working vane 18, the edge length Les thereof, and the foot length Lfl of the longer working vane 16. The foot length Lfs of the shorter intermediate working vane 18 is measured along the curved line formed in the intersection of the centreline plane of the intermediate working vane 18 and the front face 20 of the shroud 12. The edge length Les is measured along the curved line formed in the intersection of the centreline plane of the shorter intermediate working vane 18 and the front edge 32 of the working vane 18. The foot length Lfl of the longer working vane 16 is measured along the curved line formed in the intersection of the centreline plane of the longer working vane 16 and the front face 20 of the shroud 12. In accordance with a preferred embodiment of the present invention the foot length of the shorter intermediate working vane 18 Lfs=1.2*Les3.0*Les, and the edge length Les=0.3*Lfl0.5*Lfl.
(12) Referring to the functional features of the working vanes, and especially to the wave fronts formed at the leading edge of the working vanes, it may be seen in FIG. 4 that the leading and trailing edges of the longer working vanes 16 are substantially, but not necessarily, parallel, taking into account the curved nature of the working vanes 16, whereas the corresponding directions of the shorter intermediate working vanes 18 differ significantly, just for accomplishing a clear difference between the wave front directions of the shorter and longer working vanes. The same may be stated also by saying that the directions of the leading edges (30 and 40) of the longer working vanes and those of the shorter intermediate working vanes are not the same, i.e. the angles of inclination thereof are not the same. The angle of inclination is, generally speaking, measured, as explained already earlier, i.e. the inclination angle is an angle between the leading edge (30 or 40) of a working vane (16 or 18) and an imaginary line drawn on the front face 20 of the shroud 12 and being a tangent to the centreline plane of the working vane (16 or 18) at the point of intersection between the leading edge (30 or 40) and the front face 20 of the shroud. The difference in the orientation or the direction or the angles of inclination of the leading edges is of the order of 20-45 degrees.
(13) Another feature of the impeller worth mentioning is the different main function of the longer and shorter working vanes. The longer working vanes by extending to the inlet opening of the pump and being designed as shown in the drawings ensure a low required NPSH and high efficiency ratio, whereas the shorter intermediate working vanes increase the pulse frequency by moving pulses having possibly a higher amplitude outside the critical frequency range, and by fighting the secondary pulses created by the longer working vanes 16 by means of a wave front advancing in a direction different from that of the longer working vanes 16. The result is that there is no need for inclining the working vanes 16 and 18 as taught, for instance, by EP-B1-0515466.
(14) FIG. 5 illustrates a partial cross-section of an impeller 10 in accordance with a second preferred embodiment of the present invention, the cross-section being taken along line C-C of FIG. 3. The second preferred embodiment comprises, in addition to the intermediate shorter working vanes 18 of the first embodiment, balance openings 42 extending through the shroud 12 and positioned in the shroud 12 inside the inner circumference Cll of the foot parts (at the intersection between the leading edge 40 of the longer working vanes 16 and the front face 20 of the shroud 12) of the leading edges 40 of the longer working vanes 16. The balancing openings or holes are needed, as, like it is well known in the art, when pumping liquid or a suspension by a centrifugal pump and thus increasing the pressure of the liquid in front of the impeller shroud, liquid is entrained into a space behind the impeller shroud of the centrifugal pump. The shaft sealing of the pump is then subjected to considerable pressure, whereby there is a clear risk of damaging the sealing. Therefore, by using balancing holes the pressure is allowed to escape from behind the impeller shroud to the front side of the shroud.
(15) The pressure affecting the sealing may be reduced, even without using the balancing holes, by arranging rear vanes on the rear face of the shroud, the vanes creating a pressure preventing the liquid to be pumped from entering to the rear side of the shroud. The rear vanes are normally dimensioned so that they operate optimally only in a certain capacity range of the pump, whereby deviation in either direction from said capacity range results in that the pressure prevailing within the area of the rear vanes and also in the seal space changes. If the output of the pump is increased, the rear vanes generate, in the worst case scenario, a negative pressure, which can, at its worst, make the liquid in the seal space boil, especially when pumping liquids at a higher temperature. Correspondingly, when decreasing the capacity of the pump, for example, by constricting such by a valve, the pressure behind the impeller increases and the stresses increase. At the same time, naturally also the stress on the bearings increases.
(16) In other words, also in cases where rear vanes are used, balancing holes are needed to balance the pressure conditions on the opposite sides of the impeller shroud.
(17) FIG. 6 illustrates a partial cross-section of an impeller 10 in accordance with a third preferred embodiment of the present invention, the cross-section being taken along line C - C of FIG. 3. The third preferred embodiment comprises, in addition to the intermediate shorter working vanes 18 of the first embodiment, gas discharge openings 44 positioned in the shroud 12 between the longer working vanes 16 well outside the circumference Cll formed by the foot parts of the leading edges 40 of the longer working vanes 16. Simultaneously, the gas discharge openings 44 are within the circumference Cls formed by the foot parts of the leading edges 30 of the shorter intermediate working vanes 18, whereby the shorter intermediate working vanes 18 do not interfere the gas discharge. Additionally, the gas discharge openings 44 are positioned at the reduced pressure area behind the longer working vanes 16, i.e. close to the concave rear face of the longer working vane 16 to a position the separated gas collects first.
(18) And finally, as a fourth preferred embodiment of the present invention may be mentioned an impeller construction, which has the shorter intermediate working vanes 18 of the first embodiment, the balancing openings 42 of the second embodiment and the gas discharge openings 44 of the third embodiment.
(19) Earlier in the specification it was mentioned that the impeller may be provided with non-spinning means for preventing collection of fibres at the leading and trailing edges of the working vanes and at the balance and/or gas separation openings.
(20) Such means at the leading and/or the trailing edges of the working vanes (both longer and shorter working vanes) may be a rounding R1 (FIG. 7) at the edges, the rounding having a radius preferably, but not necessarily, between *S-*S. By the thickness S of a working vane is, in this specification, generally understood the average Z-direction dimension of a working vane outside the rounded edge area. The non-spinning impeller vanes have been discussed in more detail in WO-A1-2015000677.
(21) The openings, both balancing ones 42 (see FIG. 5) and gas separation ones 44, may preferably, but not necessarily, be provided with a corresponding rounding R2 (FIG. 7) at both their inlet and outlet. The rounding may, again be dimensioned to have a radius preferably, but not necessarily, between *T-*T, where T is the thickness of the shroud at the opening.
(22) As can be seen from the above description a novel centrifugal pump impeller construction has been developed. While the invention has been herein described by way of examples in connection with what are at present considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations and/or modifications of its features and other applications within the scope of the invention as defined in the appended claims.
