US20080014082A1

US20080014082A1 - Multi Stage Diffuser Pump

Info

Publication number: US20080014082A1
Application number: US11/774,729
Authority: US
Inventors: Katsutoshi Kobayashi; Hayato Shimizu; Tetsuya Yoshida; Yoshimasa Chiba
Original assignee: Hitachi Plant Technologies Ltd
Current assignee: Hitachi Plant Technologies Ltd
Priority date: 2006-07-12
Filing date: 2007-07-09
Publication date: 2008-01-17
Also published as: CN101105190A; CN101105190B; JP2008019752A

Abstract

The object of the present invention is to provide a pump structure that can reduce a hydraulic force applied to a casing of a multi stage diffuser pump, which includes multiple stages of impellers fixed to a rotary shaft rotatably supported in the casing and multiple stages of guide vane diffusers and return blade passages fixed on the casing in correspondence with the multiple stages of impellers, thereby reducing the vibrations and noises of the pump. In a multi stage diffuser pump of the type which includes multiple stages of impellers fixed to the rotary shaft and multiple stages of guide vane diffusers and return blade passages fixed on circular disks in the casing in correspondence with the multiple stages of impellers, in the impellers of the two stages of front and rear stages, which are equivalent in the form and number of blades, the phases of positions in the peripheral direction of the blades of the impellers of at least one pair of front and rear stages are deviated from each other by 0.47 pitch or more and 0.53 pitch or less. With this, a hydraulic force in the axial direction applied to the casing can be reduced and hence the vibrations and noises of the pump can be reduced.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a multi stage diffuser pump.
2. Description of the Related Art
To reduce the vibrations and noises of a multi stage diffuser pump, there have been known a method of increasing the gap between the inlet of a guide vane diffuser and the outlet of an impeller to reduce vibrations and noises, and a method of twisting the outlet of the impeller on the skew three-dimensionally to lessen the interference between both of the impeller and the guide vane diffuser to thereby reduce the vibrations and noises.
In Patent Application Laid-Open Publication No. H5-14120, the following equation is proposed as a method for fixing impellers and guide vanes so as to reduce vibrations and noises.
Σ[sin{k _min N _iω(t−β _ij/ω)−β_dj(k _min±1)}]=0 [Equation 1]
However, the first and second means of the related art have a drawback of impairing the efficiency and other characteristics of a multi stage diffuser pump. Hence, when considering these characteristics, the means cannot be expected to produce a large effect and hence presents a problem that the means lack in feasibility.
Moreover, third means is a method for reducing a hydraulic force in a radial direction applied to the diffuser and does not refer to a reduction in the hydraulic force in an axial direction that has the largest effect on the noises of the pump.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a multi stage diffuser pump in which vibrations and noises can be reduced.
The foregoing object is achieved by the following construction: in a multi stage diffuser pump of the type which includes a rotary shaft rotatably supported in a casing, multiple stages of impellers fixed to the rotary shaft, and multiple stages of guide vanes and return blades fixed to circular disks in the casing in correspondence with the multiple stages of impellers, the impellers are combinations of two stages of front and rear stages, which are equivalent in the form and number of blades, and the phases of positions in a peripheral direction of the blades of the impellers of at least one pair of front and rear stages are deviated from each other by 0.5 pitch.
Further, the foregoing object is achieved by a construction in which the phases of positions in the peripheral direction of blades of the impellers of at least the one pair of front and rear stages are deviated from each other by 0.47 pitch or more and 0.53 pitch or less.
Still further, the foregoing object is achieved by a construction in which the number of blades of the impeller is an even number.
Still further, the foregoing object is achieved by a construction in which the number of blades of the impeller is an odd number.
Still further, the foregoing object is achieved by a construction in which phases of positions in the peripheral direction of the guide vanes and the return blades fixed to the circular disks are made to be equivalent to each other for all of the stages.
According to the present invention, it is possible to provide a multi stage diffuser pump in which vibrations and noises can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, objects and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a cross-sectional view of an impeller having a first embodiment;

FIG. 2 is a cross-sectional view along a line A-A′ in FIG. 1;

FIG. 3 is a cross-sectional view to show the structure of a multi stage diffuser pump;

FIG. 4 is a conceptual view to illustrate the structure of the multi stage diffuser pump;

FIG. 5 is a graph to show a temporal change in a hydraulic force applied to a guide vane and a return blade;

FIG. 6 is a graph to show the acoustic pressure level of noises of the multi stage diffuser pump;

FIG. 7 is a graph to show a second embodiment of a multi stage diffuser pump according to the present invention; and

FIG. 8 is a diagram corresponding to FIG. 2 having another embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

By the way, as described by taking the means in the patent document 1 as examples, countermeasures have been taken against a hydraulic force in a radial direction in a multi stage diffuser pump, but at that time they did not give thought to a hydraulic force in an axial direction.
The inventors of the present invention have further studied the cause of the noises of the multi stage diffuser pump and this time have found that the hydraulic force in the axial direction has an effect on the vibrations and noises.
The mechanism of developing the hydraulic force in the axial direction will be described briefly with reference to FIG. 3.
FIG. 3 is a cross-sectional view of a multi stage diffuser pump.
In FIG. 3, a reference numeral 1 denotes a multi stage diffuser pump. In this multi stage diffuser pump 1, an impeller 6 is fixed to a rotary shaft 4. A reference numeral 7 denotes a guide vane and 8 a denotes a return blade fixed to a circular disk 8. Plural sets of the impeller 6, the guide vane 7, and the return blade 8 a are fixed as plural stages in the axial direction. These parts are covered with a casing 9.
Fluid discharged in a centrifugal direction from the trailing edge of the impeller 6 causes turbulence near the trailing edge. This turbulence causes the fluid to flow in such a way as to cover the circular disk 8 to produce a pressure difference in the axial direction between in the front and rear portions of the circular disk 8. It was found that this pressure difference vibrated the circular disk 8 in the axial direction and that this vibration was transmitted to the casing 9 to cause noises.
Describing further, it is recognized from theoretical computation and experiment that as for the hydraulic force in the axial direction to be applied to the casing 9, only a component of an integer times the product m×N×Z (m=1, 2, 3, 4, . . . ) of the number of blades N of the impeller 6 and the rotational frequency N of the impeller 6 is selectively increased. The hydraulic force to be applied to the casing 9 vibrates the casing 9 in the axial direction to cause the noises of the multi stage diffuser pump.
To reduce the vibrations and noises of the multi stage diffuser pump 1, there have been known a method for enlarging the gap between the inlet of the guide vane 7 and the outlet of the impeller 6 to reduce the vibrations and noises and a method for twisting the outlet of the impeller 6 on the skew three-dimensionally to lessen the interference between the guide vane 7 and the impeller 6 to thereby reduce the vibrations and noises.
However, this kind of technique could not produce sufficient effect. Hence, the inventors of the present invention have studied various techniques for reducing the vibrations and noises and have obtained the following embodiments.

Embodiment 1

There will be described an embodiment of a multi stage diffuser pump that includes multiple stages of impellers fixed to a rotary shaft rotatably supported in a casing and multiple stages of guide vanes and return blades fixed on the casing in correspondence with the multiple stages of impellers.
FIG. 1 is a cross-sectional view of an impeller having a first embodiment of the present invention.
FIG. 2 is a cross-sectional view along a line A-A′ in FIG. 1.
FIG. 3 is a cross-sectional view of an assembled multi stage diffuser pump.
In FIG. 1 and FIG. 2, this embodiment shows a case in which the number of blades of an impeller 6 is seven and the impeller 6 shows a state in a certain stage. Solid lines show the positions in a peripheral direction of blades of the impeller 6 and broken lines show the positions in the peripheral direction of blades of an impeller 6 a of the next stage of the impeller 6. A reference numeral 2 denotes s shroud, 3 denotes a hub, and 4 denotes a rotary shaft.
In FIG. 3, plural stages each including the impeller 6, a guide vane 7, and a return blade 8 a are fixed in the axial direction and these stages are housed in a casing 9.
FIG. 4 is a conceptual view in which a pump part of the multi stage diffuser pump is illustrated in a plane.
In FIG. 4, a reference numeral 9 denotes a casing forming the outer case of the multi stage diffuser pump 1. The multi stage diffuser pump 1 illustrated in FIG. 4 is constructed of six stages of pumps each of which is constructed of the impeller 6, the guide vane 7, and the return blade 8 a. The casing 9 has the guide vanes 7 and the return blades 8 a fixed thereto at specified intervals.
The blades of the impeller 6, the guide vanes 7, and the return blades 8 a of each stage are identical in form and number. Further, the positions in the peripheral direction where the guide vanes 7 and the return blades 8 a are fixed are identical to each other for all stages.
In the multi stage diffuser pump, as shown in FIG. 2, with respect to the phases of positions (shown by solid lines) in the peripheral direction of blades of the impeller 6 of a certain stage, the phases of positions (shown by broken lines) in the peripheral direction of blades of the impeller 6 a of a stage fixed immediately after the certain stage are deviated by 0.5 pitch.
For example, as shown in FIG. 4, with respect to the phases of positions in the peripheral direction of blades of the impeller of a first stage (J=1), the phases of positions in the peripheral direction of blades of the impeller of a second stage (J=2) are deviated by 0.5 pitch. With this, the phase of a hydraulic force in the axial direction applied to the side plates of the guide vanes 7 and the return blades 8 a of the first stage (J=1) is deviated by 180 degrees from the phase of a hydraulic force in the axial direction applied to the side plates of the guide vanes 7 and the return blades 8 a of the second stage (J=2), so the hydraulic forces in the axial direction of the first and second stages are cancelled.
FIG. 5 shows a result obtained by finding a temporal change in the 2NZ component of the hydraulic force in the axial direction applied to the side plates of the guide vanes 7 and the return blades 8 a of the first stage (J=1) and a temporal change in the 2NZ component of the hydraulic force in the axial direction applied to the side plates of the guide vanes 7 and the return blades 8 a of the second stage (J=2) from the hydraulic analysis result of the multi stage diffuser pump shown in FIG. 3.
According to FIG. 5, the phase of the hydraulic force shown by a solid line is deviated by 180 degrees from the phase of the hydraulic force shown by a broken line, so it can be found that the hydraulic forces in the axial direction are cancelled. With this, the hydraulic force in the axial direction to be applied to the casing 9 is reduced and hence vibrations in the axial direction of the casing 9 can be reduced. Hence, a reduction in the vibrations and noises of the multi stage diffuser pump can be achieved.
Here, when the phases of positions in the peripheral direction of the blades of the impellers 6 of at least one pair of front and rear stages fixed adjacently in the axial direction are deviated from each other by 0.5 pitch, the effect of reducing the vibrations and noises can be produced. That is, when the phases of positions in the peripheral direction of the blades of the impellers of at least one pair of front and rear stages of the respective pairs of front and rear stages of J=1 and 2, J=3 and 4, and J=5 and 6, which are fixed adjacently in the axial direction as shown in FIG. 4, are deviated from each other by 0.5 pitch, the effect of reducing the vibrations and noises can be produced. As a matter of course, even when the phases of positions in the peripheral direction of the blades of the impellers of each pair of front and rear stages are deviated from each other by 0.5 pitch for all pairs of front and rear stages, the effect of reducing the vibrations and noises can be produced.
Here, even when the phases of positions in the peripheral direction of the blades of the impellers are arbitrary for the respective pairs of front and rear stages, the effect of reducing the vibrations and noises can be produced. For example, when the phases of positions in the peripheral direction of the blades of the impellers of even stages (J=2, 4, 6) shown in FIG. 4 are deviated by 0.5 pitch from the phases of positions in the peripheral direction of the blades of the impellers of odd stages (J=1, 3, 5), which are fixed immediately before the even stages and pair with the even stages, the phases of positions in the peripheral direction of the blades of the impellers of the odd stages (J=1, 3, 5) of the respective pairs of odd and even stages may be arbitrary.
FIG. 6 shows acoustic pressure levels around the casing 9 obtained by performing structure simulation in the multi stage diffuser pump constructed of five stages of impellers each having seven impeller blades to which the foregoing method for fixing the impeller blades is applied.
As shown in FIG. 6, the acoustic pressure level of a component the frequency of which is larger than 5NZ is a negligible value, so the acoustic pressure level of the component is not shown. Hollow bar charts show the acoustic pressure levels when the impellers of even stages (J=2, 4) are fixed in such a way that the phases of positions in the peripheral direction of the blades of the impellers of the even stages are deviated by 90 degrees from the phases of positions in the peripheral direction of the blades of the impellers of the odd stages (J=1, 3) which are fixed immediately before the even stages and pair with the even stages. As is clear from shaded bar charts shown in FIG. 6, when compared with acoustic pressure levels when the phases are deviated from each other by 90 degrees, the present method can reduce the acoustic pressure level by 61% for a frequency of NZ, by 31% for a frequency of 2NZ, by 17% for a frequency of 3NZ, by 16% for a frequency of 4NZ, and by 53% for a frequency of 5NZ.

Embodiment 2

There will be described an embodiment of a multi stage diffuser pump that includes multiple stages of impellers fixed to a rotary shaft rotatably supported in a casing and multiple stages of guide vanes and return blades fixed to the casing in correspondence with the multiple stages of impellers.
FIG. 7 shows the relationship between a deviation in the phases of positions in the peripheral direction of the blades of a pair of impellers of two stages of front and rear stages, which are fixed adjacently in the axial direction, and the amplitude value of the resultant hydraulic force in the axial direction at the frequencies of NZ, 2NZ, 3NZ, 4NZ, and 5NZ, the hydraulic forces being applied to the side plates of the guide vanes and the return blades of the front and rear stages. This is a result obtained from the hydraulic analysis result shown in FIG. 5. As is clear from FIG. 7, when a deviation in the phase is 0 pitch or 1 pitch, that is, when the phases are not at all deviated from each other, the amplitude value of the hydraulic force is not reduced, whereas when the deviation in the phase is 0.5 pitch, the amplitude value of the hydraulic force is reduced to the minimum.
Usually, when the impellers are fixed without considering the relationship of the phases of positions of the blades of the impellers of the front and rear stages, the hydraulic force in the axial direction is reduced nearly to an average value shown in FIG. 7. To obtain the sufficient effect of reducing the vibrations and noises of the pump, it is thought to be reasonable that the average value of the hydraulic forces in the axial direction is reduced to one-half or less. Hence, it can be found from FIG. 7 that the deviation in the phases of the impellers of the front and rear stages to produce the sufficient effect of reducing the vibrations and noises of the pump is 0.47 pitch or more and 0.53 pitch or less.
FIG. 8 shows one embodiment of impellers 15, 16 having the one embodiment of the present invention. In the impellers of combinations of two stages of front and rear stages, the phases of positions in the peripheral direction of blades of the impellers of at least one pair of front and rear stages are deviated from each other by 0.47 pitch or more and 0.53 pitch or less.
By employing the method for fixing the impellers, just as with the embodiment 1, the hydraulic force in the axial direction of the casing can be reduced, vibrations in the axial direction of the casing can be reduced and hence the noises of the pump can be reduced.
Here, just as with the embodiment 1, when the phases of positions in the peripheral direction of the blades of impellers of at least one pair of front and rear stages are deviated from each other by 0.47 pitch or more and 0.53 pitch or less, the effect of reducing the vibrations and noises can be produced. As a matter of course, even when the phases of positions in the peripheral direction of the blades of impellers of each pair of front and rear stages are deviated from each other by 0.47 pitch or more and 0.53 pitch or less for all pairs of front and rear stages, the effect of reducing the vibrations and noises can be produced.
Here, just as with the embodiment 1, even when the phases of positions in the peripheral direction of the blades of the impellers are arbitrary for the respective pairs of front and rear stages, the effect of reducing the vibrations and noises can be produced.
As described above, according to the present invention, in the impellers of combinations of two stages of front and rear stages, which are equivalent in the form and number of blades, the phases of positions in the peripheral direction of the blades of the impellers of at least one pair of front and rear stages are deviated from each other by 0.47 pitch or more and 0.53 pitch or less, whereby a multi stage diffuser pump capable of reducing noises can be realized.
Moreover, the present invention can realize a multi stage diffuser pump that can not only reduce the hydraulic force in the axial direction, which is applied to the casing at the frequencies of mNZ (m=1, 2, 3, 4, . . . ), but also reduce vibrations in the axial direction of the casing, which are developed by the hydraulic force, to thereby reduce noises.
As described above, the present invention is:
1) in a multi stage diffuser pump of the type which includes a rotary shaft rotatably supported in a casing, multiple stages of impellers fixed to the rotary shaft, and multiple stages of guide vanes and return blades fixed to circular disks in the casing in correspondence with the multiple stages of impellers, the improvement wherein the impellers are combinations of two stages of front and rear stages, which are equivalent in the form and number of blades, and wherein the phases of positions in the peripheral direction of the blades of the impellers of at least one pair of front and rear stages are deviated from each other by 0.5 pitch;
2) the multi stage diffuser pump wherein the phases of positions in the peripheral direction of blades of the impellers of at least the one pair of front and rear stages are deviated from each other by 0.47 pitch or more and 0.53 pitch or less;
3) the multi stage diffuser pump wherein the number of blades of the impeller is an even number;
4) the multi stage diffuser pump wherein the number of blades of the impeller is an odd number; and
5) the multi stage diffuser pump wherein phases of positions in the peripheral direction of the guide vanes and the return blades fixed to the circular disks are made to be equivalent to each other for all of the stages.

Claims

1. In a multi stage diffuser pump of the type which includes a rotary shaft rotatably supported in a casing, multiple stages of impellers fixed to the rotary shaft, and multiple stages of guide vanes and return blades fixed to circular disks in the casing in correspondence with the multiple stages of impellers,

wherein: the impellers are combinations of two stages of front and rear stages, which are equivalent in form and number of blades; and

phases of positions in a peripheral direction of the blades of the impellers of at least one pair of front and rear stages are deviated from each other by 0.5 pitch.

2. The multi stage diffuser pump according to claim 1,

wherein the phases of positions in the peripheral direction of blades of the impellers of at least the one pair of front and rear stages are deviated from each other by 0.47 pitch or more and 0.53 pitch or less.

3. The multi stage diffuser pump according to claim 1,

wherein the number of blades of the impeller is an even number.

4. The multi stage diffuser pump according to claim 1,

wherein the number of blades of the impeller is an odd number.

5. The multi stage diffuser pump according to claim 1,

wherein phases of positions in the peripheral direction of the guide vanes and the return blades fixed to the circular disks are made to be equivalent to each other for all of the stages.