GB2066899A - Centrifugal pumps and turbo- generators - Google Patents

Abstract

A pump for use with corrosive liquids comprises an impeller 24 driven by an electric motor, the rotor assembly 11 of which is positioned in a chamber 39 formed by a stainless steel liner 26. The rotor assembly is mounted on a stainless steel tube 41 in a stainless steel can 30. The impeller chamber 37 communicates with the chamber 39 via ports 4 and the chamber 39 is sealed by 'O' rings 6, 33. The impeller hub is screwed to the tube 41 which rotates on a P.T.F.E. lining 10 of a fixed rod 25. The pump may alternatively operate as a turbo generator. <IMAGE>

Description

SPECIFICATION Turbo-electrical machine This invention relates to a turbo-electrical machine, that is to say either an electrically-driven fluid pump or a turbo-generator.

Electrically-driven pumps are well known in which an impeller is coupled to a rotor assembly disposed within a stator assembly so that on driving the impeller a pumping action is exerted on fluid admitted to a pressure chamber in which the impeller is disposed. Conventionally, the impeller and rotor assembly are secured to a common, rotatable shaft. Typically, the design of such a machine as used for pumping liquids is such that liquid usually seeps from the pressure chamber in which the impeller is disposed into the region between the rotor and stator assemblies so that in use the rotor is running immersed in liquid. This presents sealing problems so that conventionally rotary seals, known as sealing glands, are employed to prevent seepage of liquid out of the main casing by way of the shaft end bearing.However, periodically the sealing glands have to be renewed, normally owing to wear, and it would therefore be clearly advantageous to devise a construction which avoids the need to use such glands. In addition, when using such pumps for pumping food liquids or corrosive fluids, it is usually imperative that no chemical reaction with or contamination of such liquids can take place. Particularly in the case of the sealing glands few if any materials might in some instances be suitable to ensure adequate sealing while being inert to the pumped liquid. Furthermore, it is known to try to make the rotor and stator assemblies inert by impregnating the rotor and stator windings in a suitable material but it is usually found that even the materials which, overall, are best suited for this purpose can, over a period of time, become corroded or pitted.In addition, the totai bearing support area for the rotor shaft, typically supported at each end, is relatively small and this increases the loading on the shaft per unit area and hence the rate of wear of the bearings.

According to one aspect of present invention, there is provided a turbo-electrical machine for pumping a fluid, comprising a main housing structure having therewith in a fluid-flow pressure chamber provided with fluid inlet and outlet means, a stator assembly outside said pressure chamber, a further chamber communicating with said pressure chamber, and a rotor assembly comprised of a rotor winding structure in said further chamber and a fluid-co-operating structure in said pressure chamber for driving said fluid, the whole of that surface area of said rotor assembly which is exposed to said fluid and the whole of that surface area of said stator assembly which is exposed to said fluid being formed of material which is non-corrodible by substantially all fluids consumable by human beings.

In this way, the machine can be used for pumping relatively corrosive liquids consumable by human beings, for example vinegar or lemon juice, without any difficulties being encountered in meeting the very stringent standards laid down for human alimentation production.

According to another aspect of the present invention, there is provided a turbo-electrical machine, comprising a main housing structure having therewithin a fluid-flow pressure chamber provided with fluid inlet and outlet means, a stator assembly outside said pressure chamber, a further chamber communicating with said pressure chamber, a rotor assembly comprised of a rotor winding structure in said further chamber and a fluid-co-operating structure in said pressure chamber, and a shaft readily releasably fastened to said main housing structure and mounting said rotor assembly for rotation of said rotor assembly thereon, said shaft and said rotor assembly being readily removable from said main housing structure.

It is thereby possible not only to dispense completely with rotary seals, but also to remove the shaft and rotor assembly rapidly from the housing structure for internal cleaning of the machine and/or replacement of internal elements of the machine.

According to a further aspect of the present invention, there is provided a turbo-electrical machine, comprising a main housing structure having therewithin a fluid-flow pressure chamber provided with fluid inlet and outlet means, a stator assembly outside said pressure chamber, a further chamber communicating with said pressure chamber, and a rotor assembly comprised of a rotor winding structure in said further chamber and a fluid-co-operating structure in said pressure chamber, said further chamber communicating with said pressure chamber by way of ports which link to said pressure chamber portions of said further chamber which would otherwise be relatively dead space during operation of said machine.

Such avoidance of relatively dead space is particularly useful during human alimentation production, since the risk of the product becoming stale there is removed.

According to a yet further aspect of the present invention, there is provided a turbo-electrical machine comprising a main housing structure having therewithin a fluid-flow pressure chamber provided with fluid inlet and outlet means, a stator assembly which is positioned within the main housing structure outside the pressure chamber and laterally bounds a further chamber which extends in the longitudinal direction of the machine, a rotor shaft secured within the main housing structure, and a rotor assembly which is rotatably mounted on said shaft and comprises a rotor winding structure of the induction type disposed within the secondmentioned chamber and a rotor blade structure disposed within the first-mentioned chamber, the rotor assembly being additionally supported between the rotor winding structure and rotor blade structure by means of a bearing which is mounted in the main housing structure and is of such construction as to allow passage of fluid through the bearing from the first-mentioned chamber to the secondmentioned chamber, the whole of that surface area of the rotor assembly which is exposed to the fluid in the second-mentioned chamber, as well as the whole of that surface area of the remainder of the turbo-electrical machine which is likewise exposed, each being fluid-tight.

By virtue of the mounting of the rotor assembly on the shaft secured within the main housing structure there is no need for any sealing glands. Furthermore, a substantial part of the outer surface of the rotor shaft can be made available for supporting the rotor assembly, thereby significantly reducing wear on the bearing surfaces.

The material from which the various components of the turbo-eiectrical machine which provide the said exposed surface areas are made will of course depend upon the fluid which is to be pumped, but a particularly suitable material for general all-round performance is stainless steel, connections between adjacent stainless steel parts being by way of sealing parts.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a vertical axial section through an electrically-driven pump taken along the line B-B of Figure 2; and Figure 2 is a half-sectional view taken along the line A-A of Figure 1 and a half-end view which is partly cut away to show a support arrangement for a main housing structure of the pump.

Referring to the drawings, the motor-driven pump comprises essentially a main housing structure 42 which comprises a cylindrical motor casing 12 provided at an outer end with an end cover 3 and slotted at its inner end into a motor flange 40 onto which is bolted a pump casing 18 having an axial inlet port 22 and a tangential outlet port 17 (Figure 2).

The casing 12 is formed in one part with a stator assembly 43 which consists of a stator laminations ring 13 supporting stator windings 38. A number of tie rods 27 are screwed at inner ends into screwthreaded blind bores in the flange 40 and project at their outer ends through the end cover 3 where nuts 28 and washers 29 on the free ends of the tie rods serve to clamp the end cover 3 and motor flange 40 tightly against the opposite ends of the casing 12.

A non-magnetic cylindrical stator tube or liner 26, which is a sliding fit within the stator laminations ring 13, is disposed within the housing structure 42, this liner being sealed at an inner end to the motor flange 40 by an O-ring seal 33 and at the outer end, by means of an O-ring seal 6, to a radial flange 46 of a rotor shaft 25 fixed to the cover 3. Projecting through a centering and supporting bush 5 and the end cover 3 and extending in the main housing structure 42 along the longitudinal axis of the pump is the rotor shaft 25 which is releasably secured to the main housing structure by a clamping nut 1 on the shaft end which is tightened against an end cover washer 2 on the cover 3.

The stationary rotor shaft 25 carries a rotor assembly 44 which comprises a rotor bearing sleeve 41, a rotor winding structure in the form of a rotor laminations assembly 11 supporting a squirrel cage winding 14, and an impeller 24 in the pump casing 18 whose hub, in the form of a tubular boss, is secured to the inner end of the sleeve 41 by means of a screwthreaded connection 47. The outer peripheral surface of the impeller hub is supported within a central bearing aperture 45 within the flange 40. This bearing aperture, and also the outer, peripheral surface of the shaft 25, are provided with linings 19, 10 of low-friction wear-resistant material such as PTFE. The rotor assembly 44 is secured axially in one direction by means of the flange 46 on the motor shaft, against which a rotor sleeve plate 9 welded to the sleeve 41 abuts by way of a thrust washer 7.The rotor assembly is secured in the other axial direction by means of a thrust bearing 20 which is held in position relative to the shaft by means of a retaining circlip 23.

The stator liner 26, a flange 40 and shaft flange 46 together bound a chamber 39 which, in use, becomes filled with the fluid being pumped owing to communication with the pressure chamber 37 in the pump casing 18. In particular in the case when pumping a liquid, this leakage of liquid into the chamber 39 is deliberate to assist in reducing the friction on the bearing surfaces at the items 7 and 10 of the rotor assembly, but, to confine the liquid to the chamber 39, the latter is hermetically sealed by means of the aforementioned seals 6 and 33. Thus, the whole of that surface area of the stator which is exposed to the liquid in the chamber 39 is fluid-tight and so it is impossible for any contact to arise between the fluid being pumped and the working parts, in particular the windings, of the stator assembly.The liner 26 and the flanges 40 and 46 will generally be made of a suitable corrosion-resistant material. Stainless steel is particularly suitable when using the pump for pumping liquid foods.

The rotor winding structure is likewise protected from the liquid in the chamber 39, the fluid-tight protection being provided by means of a nonmagnetic stainless steel rotor can 30 covering the peripheral surface and the inner end surface of the rotor winding structure, the aforementioned sleeve plate 9 positioned at the outer end of the rotor winding structure, and the aforementioned sleeve 41 which provides the internal bearing surface of the rotor assembly. An O-ring seal 8 provides a fluidtight connection between the can 30 and the rotor sleeve plate 9 and further O-ring seals 15 and 16, provide fluid-tight connections between the impeller hub and the can 30 and between the impeller hub and the sleeve 41, respectively. Thus, the liquid in the chamber 39 is unable to penetrate into the rotor winding structure, to come into contact with the rotor iron or the squirrel cage conductors. Suitably, the can 30, the sleeve plate 9 and the sleeve 41 are all made of stainless steel, as in the case of the exposed stator parts.

To avoid the presence of significant relatively dead spaces, i.e. areas in the fluid of low or zero velocity, there can be provided circulating parts 4 through the wall 40 and inter-communicating the chambers 37 and 39 and parts 4' through the impeller 24 and inter-communicating the same chambers. The parts 4 and 4' are oblique to the axis of the machine. These parts produce a continuous interchange of the pumped fluid in the rotor winding structure zone during start and stop. At the same time the cavity at the outer axial end of the rotor winding structure is made very small so there is a greater tendency for the fluid to centrifuge and add to the movement through the air gap between the can 30 and the liner 26. During the time of starting, therefore, any fluid left during the stop period will be immediately interchanged.This does not in any way impairthe performance for continuous operation.

In operation, with the pump primed and the stator windings 38 energised, currents will be induced in the squirrel cage winding to cause the rotor assem bly 44 to rotate thereby drawing in fresh liquid through the inlet port 22 and expelling it under increased pressure through the outlet port 17. Of course, the pump is suitable for pumping gases as well as liquids.

The pump described offers a number of advan tages. Firstly, it will be appreciated that because of the provision of the stationary shaft 25 on which the rotor assembly 44 runs in the chamber 39, rotary seals are not required. In addition, the relatively large bearing area of the shaft 25 employed results in reduced wear and thereby less maintenance is required. Also, the hermetic sealing protecting the statorwindings, and the hermetic sealing around the stator windings, protect the two sets ofwindings from the action of the fluid being pumped. Furth ermore, the additional bearing surface on the impel ler boss enhances the stability of the overhung shaft 25 and allows passage of liquid from the pressure chamber 37 through the bearing for reducing fric tional forces acting on the rotor assembly.All components in contact with the medium being pumped are either stainelss steel or suitable corro sion-resistant materials for the bearings and the various seals. A particular advantage is the ease with which the stainless steel components can be re moved for cleaning prior to a radical change in the pumped liquid or for inspection. In addition, the design affords easy replacement of the stator assem bly and motor casing unit merely by removing the nuts 28 and the shaft nut 1 and then withdrawing the end cover 3 and the stator/casing unit. After dis mounting of the casing 18, which is readily achieved by unscrewing bolts 34, the impeller 24 can easily be removed. Most of the components slide together sealed with O-rings and no great force is required to separate them. A main bearing change can be effected at the same time, if necessary. The bearings can be readily replaced to suit their material to the liquid to be pumped.

It will be noted that the motor flange 40 simul taneously serves as a motor end flange and a pump end flange, thereby avoiding the need for separate flanges.

Finally, it is to be noted that the machine can be adapted to function as a turbo-generator, in which case by supplying a fluid under pressure to the port 17, electrical powerwill be generated in the stator windings.

Claims (18)

1. A turbo-electrical machine for pumping a fluid, comprising a main housing structure having therewithin a fluid-flow pressure chamber provided with fluid inlet and outlet means, a stator assembly outside said pressure chamber, a further chamber communicating with said pressure chamber, and a rotor assembly comprised of a rotor winding structure in said further chamber and a fluid-co-operating structure in said pressure chamber for driving said fluid, the whole of that surface area of said rotor assembly which is exposed to said fluid and the whole of that surface area of said stator assembly which is exposed to said fluid being formed of material which is non-corrodible by substantially all fluids consumable by human beings.

2. A machine as claimed in claim 1, wherein said material comprises non-magnetic stainless steel.

3. Aturbo-electrical machine, comprising a main housing structure having therewithin a fluid-flow pressure chamber provided with fluid inlet and outlet means, a stator assembly outside said pressure chamber, a further chamber communicating with said pressure chamber, a rotor assembly comprised of a rotorwinding structure in said further chamber and a fluid-co-operating structure in said pressure chamber, and a shaft readily releasably fastened to said main housing structure and mounting said rotor assembly for rotation of said rotor assembly thereon, said shaft and said rotor assembly being readily removable from said main housing structure.

4. A machine as claimed in claim 3, wherein said main housing structure includes a substantially radial wall intermediate said pressure chamber and said further chamber.

5. A machine as claimed in claim 4, wherein said main housing structure includes pressure chamber covering means bounding said pressure chamber at its side opposite said wall and readily releasably fastened to said wall, whereby said fluid-cooperating structure can be removed from said main housing structure.

6. A machine as claimed in claim 4 or 5, wherein said main housing structure includes stator assembly covering means readily releasably fastened to said radial wall, whereby said shaft and said rotor winding structure can be removed from said main housing structure.

7. A machine as claimed in claim 4,5 or 6, wherein said rotor assembly is borne on said shaft and in said wall by respective sleeve-form bearings which are readily replaceable.

8. A machine as claimed in any one of claims 3 to 7, wherein said stator assembly is readily removable from said main housing structure.

9. A machine as claimed in any one of claims 3 to 8, wherein said shaft is formed adjacent an outer axial end of said rotor winding structure with an annular flange which is at only a very small spacing from said rotor winding structure.

10. A turbo-electrical machine, comprising a main housing structure having therewithin a fluidflow pressure chamber provided with fluid inlet and outlet means, a stator assembly outside said pressure chamber, a further chamber communicating with said pressure chamber, and a rotor assembly comprised of a rotor winding structure in said further chamber and a fluid-co-operating structure in said pressure chamber, said further chamber communicating with said pressure chamber by way of ports which link to said pressure chamber portions of said further chamber which would otherwise be relatively dead space during operation of said machine.

11. A machine as claimed in claim 10, wherein said parts are oblique to the axis of rotation of said rotor assembly.

12. A machine as claimed in claim 1,2,3, 10 or 11, and further comprising a shaft fixed relative to said main housing structure and mounting said rotor assembly for rotation of said rotor assembly thereon.

13. A machine as claimed in claim 12, and not comprising any rotary seal.

14. A machine as claimed in claim 1,2,3,4,5,6, 10 or 11, and further comprising a bearing whereby said rotor assembly is mounted on said shaft, said bearing extending over a major amount of the axial dimension of said rotor assembly.

15. A machine as claimed in claim 4,5, or 6, and further comprising a bearing whereby said fluid-cooperating structure is rotatably mounted in said wall.

16. A machine as claimed in claim 4,5,6 or 15, wherein said fluid-co-operating structure includes a tubular boss which is received over and releasably connected to a sleeve of said rotor winding structure and which is rotatably received in said wall.

17. Aturbo-electrical machine comprising a main housing structure having therewithin a fluidflow pressure chamber provided with fluid inlet and outlet means, a stator assembly which is positioned within the main housing structure outside the pressure chamber and laterally bounds a further chamber which extends in the longitudinal direction of the machine, a rotor shaft secured within the main housing structure, and a rotor assembly which is rotatably mounted on said shaft and comprises a rotor winding structure of the induction type disposed within the second-mentioned chamber and a rotor blade structure disposed within the firstmentioned chamber, the rotor assembly being additionally supported between the rotor winding structure and rotor blade structure by means of a bearing which is mounted in the main housing structure and is of such construction as to allow passage of fluid through the bearing from the first-mentioned cham berto the second-mentioned chamber, the whole of that surface area of the rotor assembly which is exposed to the fluid in the second-mentioned chamber, as well as the whole of that surface area of the remainder of the turbo-electrical machine which is likewise exposed, each being fluid-tight.

18. Aturbo-electrical machine, substantially as hereinbefore described, with reference to, and as shown in, the accompanying drawings.