GB2053368A - An open impeller for a centrifugal pump - Google Patents

Abstract

There is disclosed an open impeller 2 for a centrifugal pump 1, for example an effluent pump, in which the blades comprise two groups, with the blades 3 of one group being of a width, measured parallel with the rotational axis of the impeller, which is at least 15% greater than that of the blades 4 of the other group. The blades 3 are interspersed with the blades 4 about the rotational axis of the impeller and the blades of each group are arranged symmetrically about the rotational axis of the impeller so that radial flow symmetry is preserved. The provision of the blades of different height in the impeller has the effect of avoiding clogging of the impeller in operation by solids, and in particular textile pieces, to which prior impellers used in similar conditions were subject. <IMAGE>

Description

SPECIFICATION An open impeller for a centrifugal pump This invention relates to an open impeller for a centrifugal pump, more particularly for a free-flow pump.

Impellers of this kind are used primarily for conveying liquids which contain solid constituents, for example effluent. Textiles must be particularly mentioned in this context, since they cause particular difficulties when in the form of pieces of large area. Experiments and the inspection of pumps of this kind which have failed show that such pieces of cloth frequently stick over the impeller by their entire surface, are retained by the impeller suction, and thus greatly obstruct the inflow to the impeller and further conveyance. Apart from disturbing pump operation, there is another more serious risk: the power consumption of the electric motor driving the pump is so increased that motor overloading must be expected after just a short period.

Centrifugal pumps with open impellers are already known which have auxiliary means for keeping solid constituents out of the range of the impellers. For example, the centrifugal pump according to German Patent Specification 22 00 847 has a projection, e.g. a pin, disposed on the bladed side of the impeller near the shaft, to break up the flow symmetry in front of the impeller.

However, a projection or pin can be applied only to an impeller of the kind in which the blades do not extend as far as the hub zone. If the blades extend as far as the hub zone, the inlet conditions are changed so that a projection in the impeller no longer guarantees that textiles will also be conveyed.

This difficulty has been obviated by a centrifugal pump according to German Offenlegungsschrift 27 14 376, in which one or more strip-like sections are provided with a tearing or cutting edge adjacent the impeller. The strip-like portions also break up the flow symmetry at the impeller. Solid constituents already in the impeller zone and projecting beyond the impeller diameter are engaged by such strips and torn away from the rotating impeller.

Both the above steps provide adequate coconveying only at relatively high speeds and up to an average impeller size. If the speed is too low, the centrifugal force of the solids which are also to be conveyed drops sharply. Excessive impeller diameter prevents operation of the tearing means on the impeller periphery. In addition, it is precisely the larger pumps that usually have to carry greater quantities of solids. The proportion of fabrics made from plastic fibres which are very difficult to rot down increases continuously, particularly in effluents for treatment.

An object of this invention is to improve the ability of pumps to convey solids as well in the case of larger-diameter impellers and low-speed operation.

This object is achieved according to the invention by an open impeller for a centrifugal pump, more particularly for a free-flow pump, the impeller having blades of different heights, the difference in blade heights being at least 15%.

In an advantageous embodiment of the invention, blades of like height are arranged symmetrically to one another on the impeller in each case.

Preferably the delivery sides of the tall and/or of the short blades have an inclination of at least 6".

The said blade height differences result in a change of the axial flow. The axial flow pattern develops in proportion to the blade heights and their differences. As a result of these different axial flows inside an impeller, intaken large-area pieces of fibre cannot be drawn between and slip over the blades, but are only partly or relatively loosely engaged by the impeller. Even textiles occupying a large area - such as cleaning rags, are so kept away from the impeller by this axial flow that they slide along and down the blades of the impeller in a movement which takes place in a different form from the rotation of the impeller.

The symmetrical arrangement of blades maintains the radial flow symmetry.

The effect of bevelling delivery sides is that the solid entraining process is additionally accelerated, because the ability of the individual blades to retain fibre constituents is greatly reduced.

The impeller construction according to the invention is free from clogging, and this is so irrespective of the degree of wear, and this is maintained over the entire pump operating time.

The fact that the solids are also conveyed with practically no contact results in constant delivery characteristics. No allowance therefore has to be made for the design of the hydraulics and the motor as was hitherto necessary for conveying the fibres as well.

An embodiment of the invention is explained in detail below, by way of example, with reference to the accompanying drawings, wherein: Figure 1 is a view in axial section of an impeller embodying the invention, showing the different blade heights, Figure 2 is an end view of this impeller and Figures 3 and 4 are partial side elevation views respectively of a tall blade and a short blade.

The impeller 2 disposed in a pump housing 1 comprises four blades 3 which are of greater height, in the sense of extending further in the direction parallel with the rotational axis of the impeller, than the remaining blades, which are constituted by four blades 4. The blades 3 are herein referred to as the tall blades and the blades 4 as the short blades. Blades of like height are, in each case, arranged symmetrically about the rotational axis of the impeller. The tall blades 3 are at least 15% greater in height than the short blades 4.

As will be seen from Figures 3 and 4, the blades 3 and 4 are bevelied on their delivery side, that is to say, the surface of each blade which faces in the direction of rotation of the impeller, indicated by an arrow in Figure 2, is inclined, preferably at an angle of at least 60, to the direction parallel to the rotational axis of the impeller, so that the root portion of each blade which is nearer the impeller web leads slightly, in the direction of rotation, the free edge portion remote from the impeller web.

This further reduces the possibility of fibrous constituents sticking.

The use of the invention is, of course, not restricted to impellers having blades which are curved as viewed in the axial direction (c.f. Figure 2), as in the example shown. It can also be applied to blades which are not curved radially.

Claims (5)

1. An open impeller for a centrifugal pump, more particularly for a free-flow pump, the impeller having blades of different heights, the difference in blade heights being at least 15%.

2. An open impeller according to claim 1, in which blades of like height are arranged symmetrically to one another about the rotational axis of the impeller.

3. An open impeller according to claim 1, in which the delivery sides of the tall and/or of the short blades have an inclination of at least 60.

4. An open impeller substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

5. Any novel feature or combination of features described herein.