Centrifugal electric pump with axial suction

Abstract

 A centrifugal electric pump with axial suction comprises at least two impellers (6) hydraulically mounted in series in the main casing and in which, D being the distance between the central axis (17) of the delivery opening (5) and the first connecting plane (13) defined by the suction opening (4), A being the distance between the axis of rotation (X) of the impellers (6) and the electric pump (1) supporting plane (10), and B being the distance between the axis of rotation (X) and the second connecting plane (20) defined by the delivery opening (5); the following relations apply:



and

Description

[0001] The present invention relates to centrifugal electric pumps with axial suction, and in particular centrifugal electric pumps with nominal deliveries of less than 350 m³/h and nominal heads of less than 100 m.

[0002] At present many types of centrifugal electric pumps with axial suction of the above-mentioned type are known and marketed.

[0003] Although they are very widespread electric pumps with relatively good performance, they are still far from perfect pumps.

[0004] In this situation, the technical purpose which forms the basis of the present invention is to provide centrifugal electric pumps with axial suction which are an improvement on prior art centrifugal electric pumps.

[0005] In particular, the technical purpose of the present invention is to provide centrifugal electric pumps with axial suction which, the nominal performance being equal, allow the achievement of greater efficiency and quietness than the corresponding conventional electric pumps.

[0006] The present invention also has for a technical purpose to provide centrifugal electric pumps with axial suction which, the external dimensions being equal to those of prior art electric pumps, allow higher nominal performance and wider performance curves, thus allowing manufacturers to cover a predetermined range of pumps with a lower number of models than is currently the case.

[0007] The technical purpose specified and the aims indicated are substantially achieved by a centrifugal electric pump with axial suction made as described in the claims herein.

[0008] Further features and advantages of the present invention are more apparent in the detailed description below, with reference to several preferred, non-limiting embodiments of a centrifugal electric pump with axial suction, illustrated in the accompanying drawings, in which:

• Figure 1 is a side view, partly in cross-section, of a centrifugal electric pump with axial suction made in accordance with the present invention;
• Figure 2 is a front view of the electric pump of Figure 1;
• Figure 3 shows the electric pump of Figure 2 without the flanges for connection to the delivery and suction pipes; and
• Figure 4 is an enlarged view of the hydraulic part of the electric pump of Figure 1 without the flanges for connection to the delivery and suction pipes.

[0009] With reference to the accompanying drawings, the numeral 1 denotes as a whole a centrifugal electric pump with axial suction made in accordance with the present invention.

[0010] In general, a centrifugal electric pump with axial suction comprises a pump casing 2 having a base 3, a suction opening 4 and a delivery opening 5, in which an impeller 6 is inserted, having an axis of rotation X. Both the suction opening 4 and the delivery opening 5 preferably have a circular cross-section.

[0011] An electric motor 7 is fixed to the pump casing 2 on the opposite side to the suction opening 4. The motor shaft (not illustrated) is operatively connected to a main shaft 8 on which the impeller 6 is mounted. The axis of the main shaft 8 therefore corresponds with the impeller 6 axis of rotation X. As the accompanying drawings show, the base 3 of the pump casing 2 has two supporting feet 9 whose lower supporting surfaces, together with a third foot 9 integral with the electric motor 7, form a supporting plane 10 substantially parallel with the axis of rotation X. In practice, the supporting plane 10 is usually horizontal.

[0012] The suction opening 4 is coaxial with the impeller 6 and is fitted with a first annular connecting flange 11 which has a first flat annular connecting surface 12. The first flat surface 12, which lies in a first connecting plane 13 substantially perpendicular to the axis of rotation X, can be connected, in practice, to a suction pipe (not illustrated). For this purpose, the first annular flange 11 has several first through-holes 14 through which it is possible to insert the fixing bolts 15 of a first threaded fixing plate 16 which can be joined to the suction pipe (Figure 1).

[0013] The delivery opening 5 is centred on its own central axis 17 parallel with the first connecting plane 13. It is also fitted with a second annular connecting flange 18 which has a second flat annular connecting surface 19. The second flat annular surface 19 lies in a second connecting plane 20 substantially parallel with the supporting plane 10, and can be connected, in practice, to a delivery pipe. For this purpose, the second annular flange 18 has several second through-holes (not illustrated in the accompanying drawings) through which it is possible to insert the fixing bolts 15 of a second threaded fixing plate 22 which can be joined to the delivery pipe.

[0014] The present invention is the result of in-depth studies carried out by the Applicant, which allowed the identification of a combination of features that allow the above-mentioned aims to be achieved, in particular with regard to centrifugal electric pumps of the type described above, with nominal deliveries of less than 350 m³/h and nominal heads of less than 100 m.

[0015] Therefore, in accordance with the present invention, inside the main casing there are at least two impellers 6 hydraulically positioned in series one after the other (in the sense that the delivery flow for the first impeller 23 is the suction flow of the second impeller 24). The two impellers 6 are coaxial and both keyed on the main shaft 8.

[0016] Moreover, also in accordance with the present invention, several size ratios between the various parts of the pump casing 2 must be complied with.

[0017] Where:

D is the distance between the central axis 17 of the delivery opening 5 and the first connecting plane 13;

A is the distance between the axis of rotation X and the supporting plane 10; and

B is the distance between the axis of rotation X and the second connecting plane 20;

the following relations must apply:



and

The Applicant was able to ascertain that the combined use of two coaxial impellers 6 in series, together with sizing of the pump casing 2 in accordance with the above-mentioned relations, allows the present invention to achieve the preset aims.

[0018] Relative to what is indicated above, the present invention is particularly advantageously applied when the distance D between the central axis 17 of the delivery opening 5 and the first connecting plane 13 is within the range

and/or the distance A between the axis of rotation X and the supporting plane 10 is within the range

and/or the distance B between the axis of rotation X and the second connecting plane 20 is within the range

In addition, when the distance D between the central axis 17 of the delivery opening 5 and the first connecting plane 13 is within the range 80 mm ≤ A ≤ 100 mm, the following relations preferably apply



and

In contrast, when the distance D between the central axis 17 of the delivery opening 5 and the first connecting plane 13 is within the range 125 mm ≤ A ≤ 160 mm, the following relations preferably apply



and

The pump casing 2 of an electric pump 1 made in accordance with the present invention is shown in cross-section in Figure 4.

[0019] As can be seen, the pump casing 2 consists of an external containment cover 25 forming the suction opening 4 and the delivery opening 5, and also consists of an element 26 for connection to the motor through which the main shaft 8 extends. The containment cover 25 and the connecting element 26 are fixed to one another with a hydraulic seal, whilst the hydraulic seal between the main shaft 8 and the connecting element 26 is guaranteed by a suitable seal element 27. Correct positioning of the seal element 27 is guaranteed by an elastic element 28 coaxial with the central shaft which acts by pushing on the seal element 27.

[0020] The inside of the pump casing 2 is also divided by a specific diffuser element 29 into a first and a second pumping chamber 30, 31, each housing one of the two impellers 6.

[0021] The diffuser element 29 is shaped in such a way that it axially conveys by suction to the second impeller 24 the radial-tangential flow from the first impeller 23.

[0022] Around the second chamber 31 there is a pipe 32 extending in a circular arc with an increasing cross-section (Figure 3) radially connected to the second chamber and, at its end with the bigger cross-section, connected to the delivery opening 5. However, in other embodiments, there may be different solutions.

[0023] Finally, between the diffuser element 29 and the first impeller 23 and between the connecting element 26 and the second impeller 24 there are two third chambers 33 in fluid connection, by means of suitable passages 34, with the zones downstream respectively of the first and second impellers 23, 24.

[0024] The present invention brings important advantages.

[0025] Firstly, thanks to the present invention it was possible to make centrifugal electric pumps with axial suction which, the nominal performance being equal, allow the achievement of greater efficiency and quietness than the corresponding conventional electric pumps.

[0026] Also, tests carried out allowed it to be established that in pumps made in accordance with the present invention, mechanical stresses are less than for corresponding pumps made in accordance with the prior art.

[0027] Secondly, the external dimensions being equal to those of prior art electric pumps, the centrifugal electric pumps disclosed allow higher nominal performance and wider performance curves, thus allowing manufacturers to cover a predetermined range of pumps with a lower number of models than is currently the case.

[0028] It should also be noticed that the present invention is relatively easy to produce and even the cost linked to implementation of the invention is not very high.

[0029] The invention described above may be modified and adapted in several ways without thereby departing from the scope of the inventive concept.

[0030] All details of the invention may be substituted by other technically equivalent elements and, in practice, all of the materials used, as well as the shapes and dimensions of the various components, may be any according to requirements.

Claims

1. A centrifugal electric pump with axial suction comprising:

a pump casing (2) having a base (3), a suction opening (4) and a delivery opening (5); and

an impeller (6) inserted in the pump casing (2) and having an axis of rotation (X);

the base (3) identifying a supporting plane (10) substantially parallel with the axis of rotation (X);

the suction opening (4) being coaxial with the impeller (6) and having a first flat annular connecting surface (12) which can be connected, in practice, to a suction pipe, the first flat surface (12) lying in a first connecting plane (13) substantially perpendicular to the axis of rotation (X); and

the delivery opening (5) being centred on its own central axis (17) parallel with the first connecting plane (13), and having a second flat annular connecting surface (19) which can be connected, in practice, to a delivery pipe, the second flat surface (19) lying in a second connecting plane (20) substantially parallel with the supporting plane (10);

the electric pump being characterised in that it comprises at least two impellers (6) hydraulically mounted in series in the main casing;

and in that, D being the distance between the central axis (17) of the delivery opening (5) and

the first connecting plane (13), A the distance between the axis of rotation (X) and the supporting plane (10), and B being the distance between the axis of rotation (X) and the second connecting plane (20); the following relations apply:



and

2. The electric pump according to claim 1, characterised in that the distance D between the central axis (17) of the delivery opening (5) and the first connecting plane (13) is within the range

3. The electric pump according to claim 1 or 2,
characterised in that the distance A between the axis of rotation (X) and the supporting plane (10) is within the range

4. The electric pump according to claim 1, 2 or 3, characterised in that the distance B between the axis of rotation (X) and the second connecting plane (20) is within the range

5. The electric pump according to any of the foregoing claims, characterised in that for 80 mm ≤ D ≤ 100 mm, the following relations apply



and

6. The electric pump according to any of the claims from 1 to 4, characterised in that for 125 mm ≤ D ≤ 160 mm, the following relations apply



and

Drawing