GB2150221A - Multistage centrifugal pumps - Google Patents

Abstract

The improvement of the efficiency of a pump through the reduction of the liquid leakage between the cover (9) and the impeller (10) of each pump stage is achieved by providing a gasket (17) between the cover and the impeller, the gasket (17) being assembled in a seat (24) of the cover (9) and engaging a raised seal (23) on the impeller. The gasket allows a clearance between the cover and the impeller, needed for construction reasons. A diffuser (11) comprises crescent shaped blades (26) which define channels (27) shaped so as to reduce turbulence. The pump may be submerged in a well containing water. <IMAGE>

Description

SPECIFICATION Improved multistage centrifugal pump of the enclosed impeller type The present invention relates to an improved multistage centrifugal pump of the type having an enclosed impeller, by which improved efficiency is achieved.

Multistage centrifugal pumps with enclosed impellers are devices of limited size and consequently of reduced encumbrance, normally used for the conveying of pressure liquids. More particularly these pumps are of limited diameter, the stages of which are arranged along the pump axis so that the pump takes an essentially elongated shape.

The individual stages of a pump of this type consists of a cover having a central hole, coaxial with respect to the impeller, which from one side rotatably receives the pump shaft and on the other side houses a corresponding seat of the impeller.

The impeller is in turn contained in a hollow space defined between the cover and the diffuser.

Of course both the impeller and the subsequent diffuser are provided with coaxial holes for receiving the pump shaft, the first of these holes defining also the inlet of the liquid to the impeller.

For reasons of construction, pumps of this type have a clearance between the impeller and the said cover, in both the axial and lateral directions with respect to the main axis of the pump.

More particularly the lateral clearances serve to compensate possible variations of misalignment between the impeller and the cover and thus prevent interference of the circular edges of the impeller with the cover.

In turn the clearances in the axial direction have the function of compensating variations of the relative axial spacing between the elements of individual stages as their number increases.

As the number of stages increases, if the axial clearances are omitted, the impeller might be pressed against the cover or against the diffuser, thereby generating a frictional force, which, besides being per se harmful, might also cause the impeller to be blocked and consequently the pump to break down.

The presence of these clearances, however permits significant amounts of liquid to blow by or leak out through the hollow spaces created by the same clearances, thereby reducing the efficiency of the pump.

More precisely the lateral and axial clearances as above described give rise to hollow spaces formed respectively between the hole of the cover and the corresponding seat of the impeller, and between the impeller and the surface of the cover wall facing towards the impeller itself.

It is furthermore to be observed that the amount of clearance in the axial direction is particularly important in conventional pumps as above described, since these clearances must ensure that the frictional forces between the impeller and the cover are such that not only is the rotation not hindered, but also that motion is allowed without excessive effort.

The friction surface between the impeller and the cover in a conventional pump is at least that resulting from the surface of the impeller facing towards the cover upstream with respect to the direction of flow of the liquid.

For reasons of construction, the greater the number of stages, the greater must be the size of the clearances of the impeller with respect to the cover, -whereby an increase in the number of stages involves a corresponding increase in leakage, resulting in a reduction of the overall efficiency of the pump.

Conventionally, diffusers are provided on their upstream sides with more or less protruding blades, serving to guide the liquid flow towards the impeller of the next stage.

The blades in conventional pumps of this type however are only roughly shaped and are so slightly protruding and insufficiently delimited as to permit turbulence to occur, so that their contribution to the correct orientation and guidance of the fluid threads is very small.

Consequently, there is a need for a pump which without altering other parameters (RPM, number of stages, size, etc.) permits a greater efficiency to be obtained compared to standard pumps through the reduction of the above described losses and through improved guidance of the fluid threads.

Thus, it is an object of the present invention to obviate or mitigate the problems associated with efficiency losses due to the presence of clearances in the impeller and with inadequate guidance of the liquid flow in the diffuser. Accordingly, the present invention provides a multistage centrifugal pump, of the type having an enclosed impeller, wherein each stage comprises: a cover provided with a central hole; a bladed impeller having a raised central seat provided with a central hole aligned with that of the said cover; and a diffuser having a plurality of fixed blades, the blades being disposed on the delivery side of the diffuser and including liquid tight seal means mounted so as to be interposed between said cover and said impeller, said sealing means being of suitable size and shape to leave clearances between said cover and said impeller.

According to another aspect of the pump of the invention, said diffuser comprises blades consisting of shims having a respectively internal and external profile, said blades being crescent shaped and said internal and external profiles having different curvatures so as to define a number of divergent channels, the pattern of which is in accordance with the theoretical profile of the liquid threads coming from the blades of the diffuser and directed towards the impeller of the next stage.

The improvement in the efficiency of the pump is achieved, according to the invention, by reducing by a significant amount the losses of liquid between the impeller and the cover and by making the profile of the fluid threads in the delivery section of the diffuser conform more closely to the theoretical profile corresponding to a pressure drop.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a perspective view of a pump embodying the invention submerged in the water of a well; Fig. 2 is a partial longitudinal cross-section of the upper or operative portion of the pump of Fig. 1; Fig. 3 is an exploded cross-section of one stage of the pump of Fig. 1; Fig. 4 is a pian view in detail of the cover and gasket ring; and Fig. 5 is a plan view of the delivery side of the diffuser of the stage of Fig. 3.

Referring now to Fig. 1, a pump embodying the invention is indicated generally by the reference numeral 1 and comprises an elongated body consisting of an upper portion 2 for housing the operating stages, and a lower portion 3 containing driving means.

The pump 1 further comprises an inlet grid 4 through which water is sucked, a cable 5 for the electrical power supply to the driving means and an outlet pipe 6.

In Fig. 1, the pump of the invention is illustrated submerged under the level L of the water in a well 7.

In Fig. 2 the upper portion 2 of the pump of Fig. 1 is illustrated together with part of the lower portion 3 housing a motor 8. Within the portion 2 the individual stages of the pump are housed, the first of which is indicated in bold line. The first stage comprises a cover 9, an impeller 10 and a diffuser 11; the next stage begins with a cover 12 positioned against the delivery side of the diffuser 11.

Also shown in Fig. 2 are the power shaft 13, a spacer 14 and a wearing bush 15 at the outlet end of the pump.

The individual components of each stage are shown in the exploded view of Fig. 3.

Besides the previously mentioned members 9, 10, and 11, Fig. 3 also shows a gasket ring 17 and a wearing washer 18.

As can be seen from the drawings, each member of the individual stages of the pump is provided with a central hole through which the power shaft 13 passes.

In Fig. 3 the path of the water through the stage is indicated by dashed lines.

In pumps of this type, for reasons of construction and owing to the high number of stages, it is necessary to provide relative clearances, in both the lateral and axial directions, between the impeller 10 and the cover 9.

More particularly, the function of the lateral clearances is that of preventing (especially in the later stages) the outer annular edge 19 of the impeller 10 from coming into contact with the corresponding inner edge 20 of the cover, thereby compromising the correct flow of the fluid in stage, and affecting the free motion of the impeller.

The clearances in axial direction are necessary to prevent (again, mainly in the later stages) the impeller from sliding at the delivery side 21 with an excess force against the corresponding inner wall 22 of the cover 9, so as to determine, also owing to the high extension of the surfaces being into contact, the blocking of the rotating parts.

Lateral clearances are provided, in standard pumps and in that of the invention, by forming in the cover 9 a hole of internal diameter D9 greater than the external diameter D23 of the corresponding seatofthe impeller 19.

The impeller includes, on its downstream side, a raised seat 23 adapted to be housed in the central hole of the cover 9.

The axial clearances provided by forming a relatively wide chamber between the cover 9 and the diffuser 11 for receiving the impeller, which can thus be positioned at the desired level, for construction reasons, on the shaft 13. There are disadvantages associated with these axial clearances, however, since hollow spaces are defined through which the liquid tends to leak out, thereby reducing the efficiency of the pump.

These leakages occur particularly in the hollow spaces between the internal wall of the hole of the cover 9 and the external wall of the seat 23 of the impeller 10, and therefrom between the wall 22 of the cover 9 and the corresponding wall 21 of the impeller 10.

The construction of the stage in accordance with the invention prevents the formation of such leakages, whilst the clearances between the impeller and the cover are maintained, the latter being as previously stated, necessary for the said construction reasons.

In orderto prevent the aforementioned leakages an annular sealing member 17, as previously mentioned is provided.

The sealing member 17, upon assembly, is housed in a corresponding seat 24 provided at the bottom of the cover 9 thereby forming a water-tight seal with the impeller 10, which is engaged with the cover 9 through the ring 17 and hole of the cover 9, by means of its raised seat 23.

To ensure an efficient seal, the diameter D23 of the seat 23 is equal to the internal diameter D17 of the ring 17.

The ring 17 is in turn maintained in position in the seat 24 of the cover 9 with a lateral clearance d (Fig.

4).

According to the preferred embodiment, the outer edge of the ring 9 is of polygonal shape, the faces of which are engaged with raised portions 25 of the seat 24, their spacing defining the aforesaid spacing dwith the ring 17 centered on the hole of the cover 9.

In this mannerthe ring 17, when in position on the seat 23 of the impeller 10, permits lateral displacement of said impeller with respect to the cover 9 (due to the fact the diameter D23 is less than the diameter D9) and simultaneously provides a liquid sealing action between the parts.

The problems associated with the liquid leakage are thus obviated or mitigated. It is furthermore to be observed that, in contrast to standard construction, the wall 21 of the impeller at the downstream side is no longer fully in sliding contact with the wall 22 of the cover, but only with the portion thereof abutting against the surface 30 of the ring 17 (stationary with respect to the cover).

The ring 17, which is of anti-friction material, thus significantly reduces the losses due to friction between the aforesaid surfaces and consequently in comparison with known pumps and for the aforesaid reasons, permits the lateral clearances and friction losses generally to be reduced.

On the upper surface or delivery side of the diffuser 11 blades 26 are provided, each having an internal profile R1 and an external profile R2, having a different curving, variable according to the pattern of the liquid threads on the delivery side of the diffuser (Fig. 5).

At the outlet of the diffuser a number of diverging channels 27 is thus defined, which practically follow the theoretically desired profile for the fluid threads on the delivery side of the diffuser.

In this way the turbulences of the liquid on the diffuser are reduced with attendant reduction of the pressure losses and increase of the pump efficiency.

Claims (6)

1. A multistage centrifugal pump, of the enclosed impeller type, wherein each stage comprises: a cover provided with a central hole; a bladed impeller having a relieved central seat provided with a central hole aligned with that of said cover; and a diffuser having a plurality of fixed blades, the blades being disposed on the delivery side of the diffuser and a central hole aligned with the above mentioned holes of said cover and said impeller and including liquid-tight sealing means mounted so as to be interposed between said cover and said impeller, said sealing means being of suitable size and shape to leave axial and lateral clearances between said cover and said impeller.

2. A pump according to claim 1, wherein said liquid sealing means comprises a body of essentially annular shape housed in a corresponding seat provided within said cover, and engaging said raised seat of the impeller, said annular body providing clearances with respect to at least one of said cover and said impeller.

3. A pump according to claims 1 and 2 wherein said seat of the cover is provided with raised portions, adapted to cooperate with said annular body to prevent it from rotating with respect to said cover, said raised portions being spaced from said annular body when it is centered with respect to the cover, so as to define lateral clearances between said cover and said annular body.

4. A pump according to claim 1, wherein said annular body is of anti-friction material and liquidproof.

5. A multistage centrifugal pump, of the enclosed impeller type, wherein each stage comprises: a cover having a central hole; a bladed impeller having a raised central seat provided with a central hole aligned with that of the said cover; and a diffuser having a plurality of fixed blades, the blades being disposed on the delivery side of the diffuser and a central hole aligned with the above mentioned holes of said cover and said impeller wherein said blades of the diffuser consist of shims having a respectively internal and external profile, said blades being crescent-shaped and said internal and external profiles having different curvatures so as to define a number of diverging channels the pattern of which is in accordance with the theoretical profile of the liquid threads coming from the diffuser blades and directed towards the impeller of the next stage.

6. A multistage centrifugal pump substantially as hereinbefore described with reference to the accompanying drawings.