Multistage centrifugal pump for conveying a fluid

Abstract

A multistage centrifugal pump for conveying a fluid includes a pump housing, two first stage impellers, a last stage impeller and a shaft. The two first stage impellers and the last stage impeller convey the fluid from a housing inlet to a housing outlet. The shaft rotates each impeller about an axial direction, each impeller comprising a suction side to receive the fluid and a discharge side to discharge the fluid. The last stage impeller is a double suction impeller, having a first suction side and a second suction side, and the last stage impeller is arranged between the two first stage impellers with respect to the axial direction. Each impeller of the two first stage impellers is arranged with the suction side of a respective first stage impeller facing one of the first and second suction sides of the last stage impeller.

Claims

1. A multistage centrifugal pump for conveying a fluid, comprising: a pump housing with an inlet and an outlet for the fluid; two first stage impellers and a last stage impeller configured to convey the fluid from the inlet to the outlet, the first stage impellers each configured as single suction impellers; and a shaft configured to rotate each impeller about an axial direction, each impeller comprising a suction side to receive the fluid and a discharge side to discharge the fluid, the last stage impeller configured as a double suction impeller, having a first suction side and a second suction side, and the last stage impeller arranged between the two first stage impellers with respect to the axial direction, each impeller of the two first stage impellers arranged with the suction side of a respective first stage impeller facing one of the first and the second suction sides of the last stage impeller.

2. The multistage centrifugal pump in accordance with claim 1, wherein the suction side of each impeller of the first stage impellers is in fluid communication with the inlet by a suction line, with each suction line arranged within the pump housing.

3. The multistage centrifugal pump in accordance with claim 1, wherein the two first stage impellers and the last stage impeller are the only three impellers.

4. The multistage centrifugal pump in accordance with claim 1, further comprising two crossover lines, each of the two crossover lines connecting the discharge side of one of the first stage impellers with one of the first and the second suction sides of the last stage impeller.

5. The multistage centrifugal pump in accordance with claim 1, further comprising a first set of impellers and a second set of impellers, wherein each set of the first and second sets of impellers comprises one of the first stage impellers, and the first set of impellers or the second set of impellers comprises at least one intermediate stage impeller.

6. The multistage centrifugal pump in accordance with claim 5, wherein each of the first set of impellers and the second set of impellers comprises an intermediate stage impeller.

7. The multistage pump in accordance with claim 6, further comprising two crossover lines, each of the two cross over lines connecting the discharge side of one of the intermediate stage impellers with one of the first and the second suction sides of the last stage impeller.

8. The multistage centrifugal pump in accordance with claim 7, wherein at least one crossover line of the two crossover lines is configured as an external line arranged outside the pump housing.

9. The multistage centrifugal pump in accordance with claim 7, wherein each crossover line of the two crossover lines is configured as an external line arranged outside the pump housing.

10. The multistage centrifugal pump in accordance with claim 5, wherein the first set of impellers and the second set of impellers are configured in a back-to-back arrangement.

11. The multistage centrifugal pump in accordance with claim 5, wherein the first set of impellers and the second set of impellers comprise the same number of impellers.

12. The multistage centrifugal pump in accordance with claim 1, wherein the multistage centrifugal pump is a between-bearing pump.

Description

BREIF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in more detail hereinafter with reference to the drawings.

(2) FIG. 1 is a multistage centrifugal pump according to the prior art.

(3) FIG. 2 is a first embodiment of a multistage centrifugal pump according to the invention, and

(4) FIG. 3 is a second embodiment of a multistage centrifugal pump according to the invention.

DETAILED DESCRIPTION

(5) FIG. 1 shows a schematic representation of a multistage centrifugal pump 1′ according to the prior art and configured as a two stage centrifugal pump 1′. Since FIG. 1 has already been explained hereinbefore in the description of the prior art no further explanations are necessary. In order to differentiate the prior art arrangement over the embodiments according to the invention, the components of the pump 1′ representing prior art are designated in FIG. 1 with reference numerals having a prime (inverted comma) behind the respective reference numeral.

(6) FIG. 2 shows a schematic representation of a first embodiment of a multistage centrifugal pump according to the invention, which is designated in its entity with reference numeral 1. The pump 1 is designed as a centrifugal pump for conveying a fluid, for example a liquid such as water.

(7) The multistage centrifugal pump 1 comprises a pump housing 2 having an inlet 3 and an outlet 4 for the fluid to be conveyed. The centrifugal pump 1 further comprises two first stage impellers 5 and a last stage impeller 6 interposed between the two first stage impellers 5, as well as a shaft 7 for rotating each impeller 5, 6 about an axial direction A. The axial direction A is defined by the axis of the shaft 7. Each impeller 5, 6 is mounted to the shaft 7 in a torque proof manner. The shaft 7 has a drive end 71, which can be connected to a drive unit (not shown) for driving the rotation of the shaft 7 about the axial direction A. The drive unit can comprise, for example, an electric motor. The other end of the shaft 7 is referred to as non-drive end 72.

(8) Each of the first stage impellers 5 is in fluid communication with the inlet 3. A first suction line 81 constitutes the fluid communication between the inlet 3 and the first stage impeller 5 on the left side in FIG. 2, and a second suction line 82 constitutes the fluid communication between the inlet 3 and the first stage impeller on the right sight of FIG. 2. Each suction line 81, 82 can be configured as a channel which is delimited by the pump housing 2 or an inlet housing (not shown) that is part of the pump housing 2. The inflow I of the fluid to be conveyed enters the pump housing 2 through the inlet 3 and is then divided in a first stream passing through the first suction line 81 and a second stream passing through the second suction line 82.

(9) The first stage impellers 5 are each configured as single suction impellers 5, i.e. as impellers 5 having only one suction side S. The suction side S of the impeller 5 is the side where the eye of the impeller 5 is arranged, i.e. the side, from which the fluid approaches the impeller 5. Each impeller has a discharge side D, i.e. the side where the fluid is discharged from the impeller 5. Regarding the first stage impellers 5 a volute or a diffusor may be arranged at the discharge side D.

(10) The last stage impeller 6 is configured as a double suction impeller 6, i.e. the fluid approaches the impeller 6 from both sides regarding the axial direction A. Thus the last stage impeller 6 has a first suction side S1 on the left side in FIG. 2 and a second suction side S2 at the right side in FIG. 2. The last stage impeller 6 has a discharge side D which is in fluid communication with the outlet 4 of the pump. The outflow of the fluid discharged through the outlet 4 is indicated by the arrow O in FIG. 2.

(11) The first embodiment of the multistage centrifugal pump 1 is configured as a two stage centrifugal pump 1 with the two first stage impellers 5 and the last stage impeller 6 constituting the second stage impeller 6.

(12) The two first stage impellers 5 are arranged with the suction side S of the respective first stage impeller 5 facing one of the first S1 and second suction side S2 of the last stage impeller 6. The first stage impeller 5 on the left side of FIG. 2 is arranged such that its suction side S faces the first suction side S1 of the last stage impeller 6. The first stage impeller 5 on the right side of FIG. 2 is arranged such that its suction side S faces the second suction side S2 of the last stage impeller 6. Thus, the two suction sides S of the first stage impellers 5 are facing each other. Therefore, the axial thrust generated by one of the first stage impellers 5 compensates the axial thrust generated by the other one of the first stage impellers 5. The residual thrust generated by the two first stage impellers 5 is at least approximately zero.

(13) Since the last stage impeller 6 is configured as a double suction impeller 6 with the first suction side S1 and the second suction side S2, the residual axial thrust generated by the last stage impeller 6 is at least approximately zero.

(14) For guiding the first stream from the discharge side D of the first stage impeller 5 to the first suction side S1 a first crossover line 91 is disposed between the discharge side D of the first stage impeller 5 and the first suction side S1 of the last stage impeller 6. For guiding the second stream from the discharge side D of the first stage impeller 5 to the second suction side S2 a second crossover line 92 is disposed between the discharge side D of the first stage impeller 5 and the second suction side S1 of the last stage impeller 6. Each crossover line 91, 92 may include a diffuser.

(15) It has to be noted that each of the crossover lines 91, 92 can be configured as an internal line completely arranged inside the pump housing 2 or as an external line arranged at least partially outside the pump housing 2 as it is indicated by the dash dotted lines 90 in FIG. 2.

(16) The centrifugal pump 1 comprises bearings (not shown) on both ends of the shaft 7, namely at or near the non-drive end 72 of the shaft, and near the drive end 71 of the shaft 7, i.e. the centrifugal pump 1 is designed as a between-bearing pump.

(17) During operation of the multistage pump 1 the inflow I of the fluid enters the pump housing 2 through the inlet 3 and is then divided into the first stream passing through the first suction line 81 to the suction side S of the left first stage impeller 5 (according to the representation in FIG. 2) and the second stream passing through the second suction line 82 to the suction side S of the right first stage impeller 5 (according to the representation in FIG. 2).

(18) The first stream is discharged at the discharge side of the first stage impeller 5 in the first crossover line 91 and guided to the first suction side S1 of the last stage impeller 6. The second stream is discharged at the discharge side D of the first stage impeller 5 in the second crossover line 92 and guided to the second suction side S2 of the last stage impeller 6. At the last stage impeller 6 the first stream and the second stream are reunited with each other and leave the pump 1 through the outlet 4 as outflow O.

(19) FIG. 3 shows a schematic representation of a second embodiment of a multistage centrifugal pump 1 according to an embodiment of the invention. In the following description of the second embodiment of the multistage centrifugal pump 1 only the differences from the first embodiment are explained in more detail. The explanations with respect to the first embodiment are also valid in the same way or in analogously the same way for the second embodiment. Same reference numerals designate the same features that have been explained with reference to the first embodiment or functionally equivalent features.

(20) The second embodiment is configured as a multistage pump 1 having more than two stages. Here the multistage pump 1 is configured as a three stage centrifugal pump. It has to be noted that the number of three stages is only exemplary. In other embodiments, the multistage pump 1 may comprise more than three stages.

(21) Furthermore, it has to be noted that the module comprising the inlet 3, the two first stage impellers 5 and the last stage impeller 6 is essentially the same as in the first embodiment. It is an important advantage that said module may be configured essentially in the same manner independent from the total number of stages of the centrifugal pump 1.

(22) According to the second embodiment the multistage centrifugal pump 1 comprises a first set of impellers 51 and a second set of impellers 52, wherein each set of impellers 51, 52 comprises one of the first stage impellers 5. In addition, each set of impellers 51, 52 comprises at least one intermediate stage impeller 55.

(23) In other embodiments only the first set of impellers 51 or only the second set of impellers 52 comprises at least one intermediate stage impeller 55.

(24) In the second embodiment each of the first set and the second set of impellers 51, 52 comprises exactly one intermediate stage impeller 55.

(25) In other embodiments each of the first set and the second set of impellers 51, 52 comprises more than one intermediate impeller 55.

(26) Preferably and as it is shown in FIG. 3 the first set of impellers 51 and the second set of impellers 52 are configured in a back-to-back arrangement.

(27) In the second embodiment the first set of impellers 51 and the second set of impellers 52 comprise the same number of impellers 5, 55.

(28) In other embodiments, the first set of impellers 51 and the second set of impellers 52 comprise different numbers of impellers 5, 55.

(29) Each intermediate stage impeller 55 is arranged downstream of one of the first stage impellers 5 and upstream of the last stage impeller 6.

(30) In the second embodiment the first crossover line 91 connects the discharge side D of the left first stage impeller 5 (according to the representation in FIG. 3) with the intermediate stage impeller 55 of the first set 51 of impellers. The second crossover line 92 connects the discharge side D of the right first stage impeller 5 (according to the representation in FIG. 3) with the intermediate stage impeller 55 of the second set of impellers 52.

(31) A third crossover line 93 is configured to connect the discharge side D of the intermediate stage impeller 55 of the first set of impellers 51 with the first suction side S1 of the last stage impeller 6. In addition, a fourth crossover line 94 is configured to connect the discharge side D of the intermediate stage impeller 55 of the second set of impellers 52 with the second suction side S2 of the last stage impeller 6.

(32) During operation of the multistage pump 1 the inflow I of the fluid enters the pump housing 2 through the inlet 3 and is then divided into the first stream passing through the first suction line 81 to the suction side S of the left first stage impeller 5 (according to the representation in FIG. 3) and the second stream passing through the second suction line 82 to the suction side S of the right first stage impeller 5 (according to the representation in FIG. 3). The first stream is discharged at the discharge side D of the first stage impeller 5 in the first crossover line 91 and guided to the suction side S of the intermediate stage impeller 55 of the first set of impellers 51. After having passed this intermediate stage impeller 55, the first stream is guided by the third crossover line 93 to the first suction side S1 of the last stage impeller 6. The second stream is discharged at the discharge side D of the first stage impeller 5 in the second crossover line 92 and guided to the suction side S of the intermediate stage impeller 55 of the second set of impellers 52. After having passed this intermediate stage impeller 55, the second stream is guided by the fourth crossover line 94 to the second suction side S2 of the last stage impeller 6. At the last stage impeller 6 the first stream and the second stream are reunited with each other and leave the pump 1 through the outlet 4 as outflow O.

(33) The skilled person will easily understand how this configuration can be expanded to more than three stages.