The present invention relates to a base connection for a runner. More specifically, the invention relates to a base connection for a runner for a hydraulic fluid flow machine, the runner including a runner hub and a plurality of vanes distributed around the centre axis of the runner and reieasably attached to the runner hub by means of bases that complementarily fit grooves in the runner hub.

Runners for fluid machines such as pumps and turbines may be subject to considerable wear. Particularly liable are runners passing particle-containing fluids. For example, arenaceous river water has turned out to be able to wear out runners in hydraulic fluid flow machines after a short time in use.

From the patent document NO 327520 Bl, a runner for a fluid machine with vanes reieasably connected to the runner is known. The vanes are connected to a runner hub by means of bases, which complementarily fit grooves in the runner hub, and screw connections. The vanes are thus held in place by means of a simple friction coupling between the base and the runner hub. The patent document also discloses how the vanes and other runner components can be hard-coated with, for example, a carbide to increase the wear resistance and thereby the lifetime of a fluid machine which is subject to extensive wear and erosion.

The patent document US 20080286130 Al discloses a runner with releasable and flexibly positionable vanes.

It has turned out that known solutions are not sufficiently robust to resist particularly hard strains during extreme operation, for example during racing or great changes in load on the runner. This may result in the base slipping in the groove of the runner hub, both radially and tangentially, whereby the screw connections may be subjected to great shear stresses and, at worst, break. By the base slipping in the groove, a possible hard coating on the side faces of the base could also crack (craze) at the side edges in the groove of the runner hub, and thus reduce the life of the vanes. The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art or at least to provide a useful alternative to the prior art.

The object is achieved through features which are specified in the description below and in the claims that follow.

In a first aspect, the invention relates to a runner device for a hydraulic fluid flow machine, the runner including a runner hub and a plurality of vanes distributed around the centre axis of the runner and releasably attached to the runner hub by means of bases that complementarily fit grooves in the runner hub, characterized by one of the bases or the grooves being formed with recesses on a side facing the other one of the bases or grooves, and the other one of the bases or the grooves being formed with keys complementarily fitting the recesses.

In one embodiment, the recesses on one of the bases and the grooves may be formed with a trapezoidal section. A key formed with a complementarily fitting trapezoidal section may be keyed into the recess, whereby a tight friction coupling is created between the base and the runner hub at the inclined planes between the key and the recess. The coupling of the base to the runner hub will thus be arranged to absorb lateral forces without the external faces of the base, which may be hard-coated, being strained.

The actual key connection between the base and the runner hub does not need to be hard-coated even if the vanes are coated with the hard coating, as the key coupling will be shielded from the fluid in the runner. An advantage of this is that the position accuracy of the base in the groove may be improved compared with a prior-art coupling. This is because a relatively large uncertainty arises in the thickness of the hard coating in consequence of standard methods of application known per se. The eccentricity of the runner can thereby be reduced, whereby, in terms of reliability, the operation of the hydraulic fluid flow machine will be improved .

In one embodiment, it may be the bases that are formed with recesses, while the grooves in the runner hub are formed with keys complementarily fitting the recesses of the bases.

In an alternative embodiment, it may be the grooves that are formed with recesses, while the bases are formed with keys complementarily fitting the recesses of the grooves. In one embodiment, the recesses of one of the bases or the grooves, and thus also the keys of the other one of the bases or the grooves, may extend over substantially the entire length of the bases or the grooves. In alternative embodiments, the key connection between the recess and the key may extend over a smaller portion of the length of the bases and the grooves.

In one embodiment, the bases may further be attached to the runner hub by means of screw connections. The screw connections may be of types known per se.

In a second aspect, the invention relates to a method of providing a runner for a hydraulic fluid flow machine, the runner including a runner hub and a plurality of vanes distributed around the centre axis of the runner and releasably attached to the runner by means of bases that complementarily fit grooves in the runner hub, characterized by the method including:

- forming one of the bases or the grooves with recesses on a side facing the other one of the bases or the grooves; and

- forming the other one of the bases or the grooves with keys complementarily fitting the recesses.

A hydraulic fluid flow machine including a runner in accordance with the above description is described as well.

Further, a turbine including a runner in accordance with the above description is described.

In what follows, an example of a preferred embodiment is described, which is visualized in the accompanying drawings, in which:

Figure 1 shows, in perspective, a prior-art runner hub;

Figure 2 shows, in a side view, a section of a coupling between a base and a runner hub in accordance with the prior art;

Figure 3 shows, in a side view, a section of a coupling between a base and a runner hub in accordance with the present invention; and

Figure 4 shows, in a side view, a section of an alternative coupling between a base and a runner hub in accordance with the present invention.

In what follows, the reference numeral 1 indicates a runner in accordance with the present invention. The runner 1 includes a runner hub 2 to which a plurality of vanes 4 are arranged to be attached in a releasable manner.

In figure 1, the runner 1 is shown with a runner hub 2 to which nine vanes 4 are arranged to be attached to the runner hub 2 arou nd a centre axis S of the runner 1, but in which only eight vanes 4 are shown for the sake of exposition. The vanes 4 are formed with hollow keys 43 that form transitions between the vanes 4 and bases 41 that are used in the attachment of the vanes 4 into grooves 21 in the runner hub 2, as shown in the figures that follow. The vanes 4 have a curvature which is substantially adapted to the curvature of the grooves 21. In a situation of application, the runner 1 could also include a ring, not shown, to which the upper portion of the vanes 4 may be attached in a manner corresponding to that in which the lower portions of the vanes 4 are attached to the runner hub 2.

Figure 2 shows a section through a portion of a vane 4 which is attached to a runner hub 2 with a prior-art coupling. A screw connection in the form of a bolt 3 has been screwed into the base 41 of the vane 4 from the bottom side of the runner hub 2, whereby the vane 4 is attached to the runner hub 2 by means of a simple friction coupling. As described in the above, it has turned out that a friction coupling of this type is not strong enough to prevent the base 41 from slipping in the groove 21 by particularly great stresses. Large centrifugal forces from racing could cause radial slipping of the base 41 in the groove 21, whereas other strains on the vanes 4, for example large changes in load, could give a tangential slippage. This could give large shear forces on the bolt 3 which, at worst, could break. Typically, there could be a clearance of up to a few tenths of a millimetre between the base 41 and the side edges of the groove 21 to allow the base 41 to be fitted into the groove 21. The clearance is not easily visible in the figures on the scale shown. Pressure between the base 41 and the side edges of the groove 21 because of slippage could ruin a possible hard coating on the vanes 4 and, thus, reduce the life of the runner 1.

Figure 3 shows a section through a portion of a vane 4 which is attached to a runner hub 2 by means of a key coupling in accordance with the present invention. The base 41 is formed with a recess 413 with a trapezoidal section, whereas the groove 21 in the runner hub 2 is formed with a key 211 complementarily fitting the recess 413. The key 211 thus forms a key coupling with the recess 413. The base 41 is pulled further down into the groove 21 by means of the bolt 3, in a manner corresponding to that mentioned above, whereby a friction coupling between bevels 21 If on the key 211 and bevels 413f in the recess 413 is maintained. The key coupling will absorb lateral forces against the base 41, so that there will be no stress on the bolt 3 from shear forces.

Figure 4 shows an alternative embodiment of a key coupling in accordance with the present invention. In this embodiment, the base 41 of the vane 4 is formed with a projecting key 411 complementanly fitting a recess 213 in the groove 21 of the runner hub 2. Bevels 411f on the key rest against bevels 213f in the recess in a manner corresponding to that described above.