EP0038389A1

EP0038389A1 - Pump for solids handling

Info

Publication number: EP0038389A1
Application number: EP80301254A
Authority: EP
Inventors: Michael Leslie Ryall; John Mcfarlane Taylor
Original assignee: Weir Pumps Ltd
Current assignee: Weir Pumps Ltd
Priority date: 1980-04-18
Filing date: 1980-04-18
Publication date: 1981-10-28

Abstract

A cone or barrel pump comprises a hollow rotary impeller (2) having at least a portion of its internal surface (6) of non-circular cross section providing the impeller with rotary internal pumping lobes (4). Consequently the pump does not require an internal drive shaft carrying vanes. The impeller (2) is preferably made of glass-reinforced plastics, and the arrangement provides an economic cone or barrel pump which is particularly immune from clogging.

Description

This invention relates to pumps for low head duties of the general type described in UK Patent No.1464762, in which a spiralling liquid vortex with an air core is created inside a vertical rotating impeller wall; the lower end of this impeller being below the liquid surface of the reservoir or sump from which it draws suction- the impeller serving to lift the liquid by "centrifugal"action from this sump to a higher level through the formation of the aforementioned spiralling vortex.
As described previously, the input torque required to create the spiralling vortex of liquid has been applied from the impeller to the liquid by one or more vanes, generally of spiral form, attached to the inside surface of the rotor outer wall, and extending from or near the bottom of the rotor to a level at or near, but not generally above, the top of the rotor. These vanes have generally, but not necessarily, been attached to a central driving shaft, through which torque has been applied to the impeller.
While this construction of rotor has proved technically very effective as a self-regulating pumping device for low head duties, and has shown itself to be capable of pumping many types of solids in suspension, nevertheless where the incoming liquid stream contains stringy, fibrous, or woven material, there is a tendency for such material to wrap itself over the leading edges of the vanes, or become trapped between the leading edges and the internal surface of the outer shroud of the impeller. Separation of solids in suspension upstream of the pump can be conducted to avoid this problem, but such separation is often inconvenient , as for instance in raw sewage pumping installation, where the level of the incoming effluent is often comparatively inaccessible being several metres below ground level.
For such installations, or for pumping applications where it is a requirement to pump solids in suspension as part of a process( e.g. pumping of fish or vegetables) the potential obstruction to solids flow imposed by the impeller vanes can limit the applicability of this type of pump.
The object of the present invention is to overcome these solids handling limitations.
According to the present invention a cone or barrel pump comprises .a hollow impeller rotatable about an axis and having an internal annular working surface, said internal annular working surface having cross-sections of non-circular form whereby said working surface creates a pumping effect on rotation of the impeller. By this arrangement, the impeller need not carry vanes.
It is a general feature of this invention that the previous barrel . pump comprising an outer containment shroud of a substantially circular cross-section symmetrically disposed about the drive shaft, and spirally mounted driving vanes connecting this shroud with the drive shaft is replaced by a pump having an impellor with an internal cross-sectional form defining internal lobe means with preferably two or more lobes disposed about the impeller vertical axis. This 'lobed' rotor is not fitted with internal vanes to impart the torque directly to the spiralling vortex, but imparts the torque to this vortex by virtue of variations in pressure which will occur on the inner working surface of the lobe walls.
In a preferred embodiment, the wall of the impeller carries two longitudinal upstanding formations. A greater number of upstanding formations may be used provided that the symmetry of cross section throughout the length of the impeller about the vertical axis is maintained. The changing radial length of the working surface of the impeller at transverse sections due to the provision of the upstanding formations, has the effect of providing the impeller with internal "lobes".
The upstanding formations may be of straight longitudinal form or alternatively may be helically arranged.
The cross-section of the non-circular working surface may be of approximate rectangular form, but with two facing concavely curved ends. Alternatively, the upstanding formations can be such as to provide the cross section with two facing pairs of curved portions, one concave the other convex whereby the lobed arrangement is emphasised.
In a further preferred embodiment, the impeller has an intermediate working portion of non-circular (lobed) form blending into circular cross-sectioned mouth and discharge portions at either end of the intermediate portion.
It is furthermore a preferred feature of this invention that transition from a symmetrically disposed circular cross section impeller inlet at its lower extremity to a lobed cross section is progressive and not sudden, so that all surfaces, with which the spiralling vortex makes contact during its progression up the impeller, present smoothly varying profiles to the flow with no sudden discontinuities. It is also a preferred feature of this invention that there is a smooth transition from a 'lobed' section of the impeller, over its 'pumping' length to a symmetrically disposed circular section at its outlet, to effect even discharge of liquid from the rotor around its periphery at outlet.
The discharge portion may discharge into a reservoir via a bell-mouth or a diffuser could be provided intermediate the impeller and the reservoir, and the impeller mouth or inlet may also be of bell-mouth form and so arranged that liquid can enter the pump without substantial obstructions. Preferably the impeller is axially supported by means of a shaft having an end connected to the upstanding formations, and an external rotary bearing may be provided engaging the external wall of the impeller for radial support thereof. The impeller may be driven by a drive to the impeller's external wall. In an alternative arrangement, bearing means are provided engaging the outer wall of the impeller for both axial and radial support of the impeller. The impeller may be made of glass fibre reinforced plastics material, with the longitudinal formations bonded to the impeller wall.
Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings wherein:

Fig. 1 shows a cross-sectional elevation of a lobed cone pump according to the present invention;
Figs. 2 to 8 show various cross sections of the pump impeller of Fig.1;
Fig. 9 shows variation in the axial profile of the impeller working surface.
Figs. 10 to 12 show alternative forms of cross-section of the impeller working surface;
Fig. 13 shows the pump of Fig. 1 but with alternative support means.
Fig. 14 shows a pictorial view of an impeller according to a further embodiment of the invention and with the impeller outer wall transparent for illustrative convenience; and Fig. 15 is a side-elevation of the pump of Fig. 14 showing the two helical formations of the impeller working surface. Referring to Fig. 1 a pump 1 for land drainage work has a 2 -lobed impeller or rotor 2 with rotational axis A-A. A series of horizontal sections through the rotor 2 are defined, numbered 0 to X1V, and some of these are shown in Figs. 2 to 8. The inlet 3 to the rotor 2 is of bellmouth shape, and receives an unobstructed flow of liquid from a lower reservoir R1 the outlet of the bellmouth (Section 0) being circular (Fig. 2) in cross section. Between Sections . 0 and II, an internal cross section of the rotor with lobes 4 defining the impellers working surface, is progressively formed ( see Section 0, I and II, Fig. 2-4. Specifically, the cross section is of approximate rectangular form but with a pair of concave ends 5. This lobed cross section is achieved by fitting wall formations 6 to the impellers inner surface. The lobed internal section is then continued, with an increasing outer diameter of the lobes until Section VII (Fig. 5).

Between Sections VII and X, (Fig. 7) in the example shown, driving vanes or spokes 7 are introduced internally to permit the impeller rotor 2 to be mounted on a central drive shaft 8. These vanes 7 are disposed so that they provide no real obstruction to the flow of the rotor 2, such flow being in the form of a vortex flow 9 and confined to the channels up the rotor 2, defined by the lobes 4 by the time the flow has reached Section VII, i.e. the free surface 10 of the vortex is radially outwith the vanes 7.
Between Sections VII and X the lobes progressively change to a circular cross section at Section X (Fig. 7) which in this example is the upper limit of the pumping (or torque input) portion of the rotor 2.
The portion of the rotor 2 between Sections X and XIV (Fig. 8) is a simple coned section of upwardly diverging form.
The lobe sections between Section 0 and Section X may either be disposed axially in line with each other as shown in Fig. 1 or (preferably) may be angularly displaced or 'screwed round' relative to each other as in Figs.14 and 15 in any prescribed form to induce efficient flow of liquid axially and radially outward into the lobes 4, and up the lobe channels.
The external surface of the impeller rotor 2 is circular at all sections 0 to XIV, the diameter at each section being that required to circumscribe the lobed or circular internal cross section ( as shown in Figs. 2 to 8).
To operate as a pump impeller the rotor 2 as described is mounted vertically with its bellmouth 3 below the surface of the suction sump Rl from which it draws. When the impeller 2 is rotated at a suitable operating speed, liquid is drawn through the bellmouth 3 into the impeller and flows upwards and radially outwards into the lobes 4, where whirl is progressively imparted to the liquid. This whirl causes the liquid to flow up the internal channels in the rotor shroud formed by the lobes 4, and a free surface 10 is formed on the inner diameter of the liquid vortex 9. The design of the impeller rotor lobes, the rotational speed, and the immersion depth of the bottom of the rotor in the suction sumps are all arranged so that by the time the liquid has risen up the rotor to Section VII, as a result of the whirl applied to it, it is fully confined to the lobe channels, with an internal free surface; and the support and drive vanes or ribs mounted between Sections VII and X to connect the rotor to the vertical drive shaft above it do not therefore interfere with the lobe channel flow in any way. Whirl imparted to the liquid vortex is progressively increased up to section X. From this section the liquid then flows into the conical diffusing part of the rotor between Sections X and XIV, in which some of its velocity energy is converted to potential energy. From Section XIV, the liquid is then discharged into a rotating (not shown) or stationary diffusing section 15 ( as shown) in which further recovery of potential energy from velocity energy is effected.
Because of the progressively increasing radial depth and horizontal cross section area of the lobe channels from section 0 upwards, as the liquid level in the suction sump rises, more radial depth of liquid is entrained
within the impeller rotor and the liquid flow in the impeller increases, while the whirl imparted to this liquid is little altered. Thus this impeller is self regulating, pumping more liquid as suction level rises Ll and less as suction level Ll reduces, which results in an almost proportional relationship between input power and flowrate.
As solid material is drawn into the impeller 2, it meets only gradual changes in surface, with large radii of curvature, which ensures that such material is swept through the pump by the liquid flow with the minimum of resistance, thus, effectively inhibiting solid blockages. Any fibrous material approaching the bellmouth inlet 3 at its periphery will be thrown away from the rotor by "centrifugal" effects. The large inlet bore of the rotor with no reduction in area due to vanes, ensures easy passage of very large suspended items, since practical full scale pumping installations of this type for raw sewage and land drainage will in general have inlet diameter of upwards of o.5 metres.
As described above and illustrated in Fig.l. the impeller rotor is mounted on, and driven by, a vertical drive shaft 8 by vanes 7,radial location being also provided at a lower position, preferably above the liquid surface, by three or more rollers 11 engaging a ring 12 which forms part of the rotor shroud and is able to rotate
In an alternative mounting and drive arrangement shown in Fig.13, the impeller rotor 2 is radially and axially restrained entirely by rollers 11 in contact with two or more rings 12 attached to the outer shroud, and the drive shaft and vanes can be eliminated. In this arrangement, input torque to the rotor is preferably provided by a toothed belt 13 or chain drive from a prime mover or motor 14 mounted alongside the impeller 2, the belt 13 drivingly engaging a ring ( e.g. ring 12 bn the impeller 2.
In the example illustrated, two lobes are used in the impeller cross section. These lobes may be of any cross section_' form consistent with ease of manufacture, smooth internal surfaces, and good liquid entrainment capacity. Any number of lobes may be chosen but in .general two or three lobes have been found to be the most suitable. Instead of a general rectangular cross section (as shown in Figs. 2 to 8), a cross section comprising facing pairs of concave and convex curves could well be used, to give more pronounced lobe portions 4. Figs 10 to 12 illustrate such alternative cross sections and these can be achieved by suitability shaping the formations 6 on the impeller internal wall. In the cross sections shown, all of which have the same outside impeller wall diameter if the cross section in Fig. 10 is taken as having a vortex wedge area of 100 units then the cross section in Fig. 11 has a vortex wedge area of 170 units and the cross section in Fig. 12 a vortex wedge area of 200 units.
The impeller 2 with internal wall formations 6 could be of glass reinforced plastics material with the formations 6 formed integral with or bonded to the impeller outer circular wall, or the impeller could be formed by castings.

Claims

1. A cone or barrel pump comprising an impeller (2) rotatable about a vertical axis (A-A ) and having an annular working surface (6) characterised in that the annular working surface is an internal working surface (6) having cross-sections of non-circular form (Figs. 3-6) whereby said working surface (6) creates a pumping effect on rotation of the impeller (2).

2. A pump as claimed in claim 1 characterised in that the impeller (2) has an internal lobe (4) of circular or non-circular cross section located eccentric to the impeller vertical axis (A -A).

3. A pump as claimed in claim 1 or 2, characterised in that two or more lobes (4) are provided disposed about the impeller vertical axis (A -A ).

4. A pump as claimed in any one of the preceding claims, wherein the wall of the impeller (2) carries at least one longitudinally - extending upstanding formation (6) to provide the non-circular cross sectional form.

5. A pump as claimed in claim 4, characterised in that two opposed formations (6) are provided.

6. A pump as claimed in claim 2, wherein the impeller (2) has an intermediate working portion(sections I-X) of non-circular lobed form blending into circular cross-sectioned mouth (sections O-I) and discharge portions (sections X-X1V) at either end of the intermediate portion.

7. A pump as claimed in claim 4, characterised in that the impeller (2) is axially supported by means of a shaft (8) having an end connected to the upstanding formations (6).

8. A pump as claimed in claim 7, characterised in that an external rotary bearing (12) is provided engaging the external wall of the impeller (2) for radial support thereof,

9. A pump as claimed in any one of the preceding claims, characterised in that the impeller (2) is made of plastics material.

10. A pump as claimed in claim 9, characterised in that plastics longitudinal formations (6) are bonded to a circular plastics impeller wall (2)