JP2013011241A - Sectional type multistage pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multistage pump with improved tansporting performance.SOLUTION: The multistage pump includes a rotating shaft 1, a plurality of impellers 2 fixed at the rotating shaft 1, and a pump casing 3 that accommodates the plurality of impellers 2. The pump casing 3 has a suction casing 10, a discharging casing 30 and an intermediate casing 50. A suction volute 20 connected to a suction flow path 11a is formed at the suction casing 10. The suction volute 20 extends from the suction flow path 11a to a liquid inlet of a first stage of the impellers 2.

Description

  The present invention relates to a ring-cut multistage diffuser pump (hereinafter simply referred to as a multistage pump), and more particularly to a casing structure of a multistage pump.

  The multistage pump has a plurality of impellers fixed to a rotating shaft (see, for example, Patent Document 1). The liquid is introduced into the pump casing from the suction port, is sequentially pressurized by the impeller, and is discharged from the discharge port. Multistage pumps are used for transferring various liquids such as fresh water and seawater, and are used in various places.

JP 2000-130400 A

  The liquid transfer capability of the multi-stage pump greatly depends on the suction performance (also referred to as cavitation performance) and the normal performance (also referred to as general performance). Conventionally, various ideas have been made to improve suction performance and normal performance. Therefore, an object of the present invention is to provide a multistage pump with improved liquid transfer performance.

  In order to achieve the above-described object, one aspect of the present invention includes a rotation shaft, a plurality of impellers fixed to the rotation shaft, and a pump casing that accommodates the plurality of impellers. Has a suction casing having a suction flow path, a discharge casing having a discharge flow path, and an intermediate casing disposed between the suction casing and the discharge casing, wherein the suction casing is The multi-stage pump has a suction volute connected to a suction flow path, and the suction volute extends from the suction flow path to a liquid inlet of a first stage impeller of the plurality of impellers.

In a preferred aspect of the present invention, the multistage pump includes a balance mechanism for supporting a thrust force acting on the rotating shaft, a balance chamber in which the balance mechanism is accommodated, and liquid in the balance chamber in the suction casing. The suction casing has a side chamber isolated from the suction volute, and one end of the balance pipe is connected to the balance chamber and the other end is connected to the side chamber. It is characterized by that.
In a preferred aspect of the present invention, the suction volute is provided with a guide plate for guiding the flow of the liquid.

In a preferred aspect of the present invention, the discharge casing includes a discharge port in which the discharge flow path is formed, and a peripheral wall that forms an annular flow path in which the liquid discharged from the impeller turns. The discharge port and the peripheral wall are connected via a connecting portion having a curved cross-sectional shape, and the connecting portion includes an upstream-side bending portion and a downstream-side bending portion, The upstream curved portion is located upstream of the downstream curved portion with respect to the rotational direction of the impeller, and the curvature radius of the upstream curved portion is larger than the curvature radius of the downstream curved portion. And
In a preferred aspect of the present invention, the discharge flow path has a shape in which the cross-sectional area gradually decreases along the liquid flow direction.

  The suction casing having the above-described configuration can improve the suction performance of the multistage pump. Therefore, pump performance can be improved. Furthermore, the discharge casing having the above-described configuration can improve the normal performance of the multistage pump. Therefore, the pump performance can be further improved.

FIG. 1A is a side view of a multistage pump according to an embodiment of the present invention, and FIG. 1B is a view as seen from the direction indicated by arrow A in FIG. (C) is the figure seen from the direction shown by the arrow B of Fig.1 (a). It is sectional drawing of a ring-cut type multistage diffuser pump. It is a figure which shows a suction casing. It is sectional drawing of a suction casing. It is a figure which shows the result of having analyzed the flow of the liquid in a suction casing. It is a figure which shows the result of having analyzed the flow of the liquid in the conventional suction casing. It is a graph which shows NPSHR (necessary effective suction head) which is a parameter | index which shows the suction performance of a pump. It is a figure which shows a discharge casing. It is sectional drawing of a discharge casing. It is a figure which shows the result of having analyzed the flow of the liquid in a discharge casing. It is a graph which shows the change of the cross-sectional area of a discharge flow path.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1A is a side view of a multistage pump according to an embodiment of the present invention, and FIG. 1B is a view as seen from the direction indicated by arrow A in FIG. (C) is the figure seen from the direction shown by the arrow B of Fig.1 (a). FIG. 2 is a cross-sectional view of the multistage pump. The multistage pump includes a rotating shaft 1 that extends horizontally, a plurality of impellers 2 fixed to the rotating shaft 1, and a pump casing 3 that houses these impellers 2. The rotating shaft 1 is rotatably supported by bearings 9 and 9. One end of the rotating shaft 1 is connected to a driving source such as a motor, and the rotating shaft 1 and the impeller 2 are rotated by this driving source.

  The pump casing 3 includes a suction casing 10 having a suction port 11, a discharge casing 30 having a discharge port 31, and an intermediate casing 50 disposed between the suction casing 10 and the discharge casing 30. Yes. The intermediate casing 50 has a structure in which a plurality of annular casing pieces 50a are stacked in the axial direction. A diffuser 4 is disposed on the radially outer side of each impeller 2. A set of impellers 2 and a diffuser 4 are arranged in each casing piece 50a. The suction casing 10, the intermediate casing 50, and the discharge casing 30 are fixed to each other by a through bolt 6 and a nut 7.

  The suction casing 10 and the discharge casing 30 are detachably attached to the intermediate casing 50. That is, the suction casing 10 and the discharge casing 30 can be separated from the intermediate casing 50 by removing the through bolts 6 and the nuts 7.

  This multistage pump is configured to be able to change the number of stages of the impeller 2. When the number of stages of the impeller 2 is increased, a desired number of impellers and diffusers and casing pieces corresponding to the impellers are added to the multistage pump. On the other hand, when reducing the number of stages of the impeller 2, a desired number of impellers and the diffusers and casing pieces corresponding to the impellers are removed from the multistage pump. Thus, this multistage pump can be made into the desired number of stages according to the use.

  The rotary shaft 1 extends through the suction casing 10 and the discharge casing 30. On the outside of the suction casing 10 and the discharge casing 30, shaft sealing mechanisms 55 and 55 are provided, respectively. As the shaft sealing mechanisms 55, 55, a mechanical seal, a gland packing, or the like is used. The bearings 9 and 9 are accommodated in bearing casings 65 and 65, respectively. Bearing covers 67 and 67 are fixed to the bearing casings 65 and 65 by bolts, respectively. Each bearing casing 65 is filled with lubricating oil, and this lubricating oil is cooled by a cooling pipe 66.

  A balance mechanism 70 is provided in the discharge casing 30. The balance mechanism 70 includes a balance disk 71 that rotates integrally with the rotary shaft 1, and a balance disk sheet 72 that is disposed to face the balance disk 71. The balance mechanism 70 has a function of balancing the thrust force acting on the rotating shaft 1 by supporting the thrust force generated due to the pressure difference between the suction side and the discharge side of the impeller 2. The balance mechanism 70 is disposed in the balance chamber 73. The liquid pressurized by the impeller 2 passes through a minute gap between the balance disk 71 and the balance disk sheet 72 and flows into the balance chamber 73.

  Inside the suction casing 10, a side chamber 25 adjacent to the first stage impeller of the multistage impeller 2 is formed. A part of the liquid pressurized by the first stage impeller flows into the side chamber 25. The balance chamber 73 and the side chamber 25 are connected by a balance pipe 75. Therefore, the pressure in the balance chamber 73 and the pressure in the side chamber 25 are substantially the same.

  FIG. 3 is a view showing the suction casing 10. The suction casing 10 has a suction port 11 in which a suction passage is formed, and four bolt bases 12, 13, 14, 15 in which insertion holes 12A, 13A, 14A, and 15A of through bolts 6 are formed. doing. These four bolt bases 12, 13, 14, 15 are provided at equal intervals in the circumferential direction of the rotating shaft 1.

  Legs 80 are fixed to the suction casing 10 by fastening bolts 85. The leg portion 80 is formed with a through hole 80a into which a fastening bolt is inserted, and the suction casing 10 can be fixed to the common base by the fastening bolt.

  FIG. 4 is a cross-sectional view of the suction casing 10. The suction casing 10 is formed with a suction volute 20 connected to the suction flow path 11a and a side chamber 25. The suction volute 20 and the side chamber 25 are separated by a partition wall 26. The side chamber 25 is adjacent to the first stage impeller (see FIG. 2), and a part of the liquid pressurized by the first stage impeller flows into the side chamber 25. The pressure in the side chamber 25 is close to the discharge pressure of the first stage impeller.

  The suction volute 20 is a spiral flow path. The suction volute 20 extends from the suction passage 11 a to the liquid inlet of the first stage impeller, and the liquid is guided to the first stage impeller through the suction volute 20. The suction volute 20 is provided with a guide plate 21 that guides the flow of liquid. The guide plate 21 has a role of rotating the liquid from the suction passage 11 a along the suction volute 20. At the downstream end of the suction volute 20, a tongue 22 is formed that protrudes toward the center of the first stage impeller.

  FIG. 5 is a diagram illustrating a result of analyzing the flow of the liquid in the suction casing 10. As can be seen from FIG. 5, the liquid flows smoothly in the suction volute 20, and a uniform flow is formed from the suction flow path 11 a to the liquid inlet of the impeller 2 (first stage impeller). The liquid is sucked into the first stage impeller while turning in the rotation direction of the first stage impeller, and there is no great disturbance in the flow of the liquid. As a result, the liquid inflow angle coincides with the inlet angle of the first stage impeller, and the suction performance of the multistage pump is improved (that is, cavitation is less likely to occur), and at the same time, the pump performance is improved. Furthermore, noise and vibration are also reduced.

  FIG. 6 is a diagram showing the result of analyzing the flow of liquid in a conventional suction casing. In the conventional suction casing 105, the suction volute 20 is not formed, and only the guide plates 110 and 111 are provided along the center line. The liquid flows on both sides of the guide plates 110 and 111 and is sucked into the liquid inlet of the impeller 112. As can be seen from FIG. 6, the liquid collides with the inner surface of the suction casing 105 or the guide plate 111, and the flow is disturbed. As a result, the inflow angle of the liquid does not coincide with the inlet angle of the impeller 112, the suction performance of the multistage pump is reduced (that is, cavitation is likely to occur), and the pump performance is reduced. In some cases, loud noise or severe vibration may occur. As can be seen from comparison with FIGS. 5 and 6, the suction casing 10 having the suction volute 20 can form a uniform liquid flow, and can improve suction performance and pump performance.

  The suction casing 10 has the 1st connection port 27 connected to the balance piping 75 (refer FIG. 2). The first connection port 27 communicates with the side chamber 25, and the high-pressure liquid in the balance chamber 73 is returned to the side chamber 25 through the balance pipe 75. As described above, since the side chamber 25 is separated from the suction volute 20 by the partition wall 26, the liquid flowing into the side chamber 25 does not collide with the liquid flowing through the suction volute 20. Therefore, the liquid flowing through the suction volute 20 is not disturbed. Furthermore, since the inside of the side chamber 25 is filled with a high-pressure liquid, cavitation hardly occurs. As a result, the suction performance can be improved.

  The suction casing 10 further has a second connection port 28 that communicates with the suction volute 20. From the viewpoint of not disturbing the liquid flowing through the suction volute 20, the liquid in the balance chamber 73 is preferably returned to the side chamber 25 through the first connection port 27. However, the balance pipe 75 may be connected to the second connection port 28 depending on the application or installation location of the multistage pump. The second connection port 28 can be omitted.

  FIG. 7 is a graph showing NPSHR (necessary effective suction head) which is an index indicating the suction performance of the pump. As can be seen from FIG. 7, NPSHR (shown by a solid line) when the balance pipe 75 is connected to the side chamber 25 connects the balance pipe 75 to the suction volute 20 in the entire flow area from the partial flow area to the excessive flow area. It is lower than NPSHR (indicated by a dotted line). This indicates that cavitation is less likely to occur in the suction casing 10 when the balance pipe 75 is connected to the side chamber 25.

  FIG. 8 is a view showing the discharge casing 30. The discharge casing 30 has four bolt bases 32, 33, 34, 35 in which a discharge port 31 having a discharge passage formed therein and insertion holes 32 </ b> A, 33 </ b> A, 34 </ b> A, 35 </ b> A of through bolts 6 are formed. And have. These four bolt bases 32, 33, 34 and 35 are provided at equal intervals in the circumferential direction of the rotating shaft 1.

  Legs 81 are fixed to the discharge casing 30 by fastening bolts 85. The leg portion 81 is formed with a through hole 81a into which a fastening bolt is inserted, and the casing 30 can be fixed to the common base by discharging with the fastening bolt.

  FIG. 9 is a cross-sectional view showing the discharge casing 30. As shown in FIG. 9, the discharge casing 30 includes a peripheral wall 37 that forms an annular flow path 36 in which the liquid discharged from the impeller 2 turns. The connecting portion between the peripheral wall 37 and the discharge port 31 has a curved cross-sectional shape, and constitutes an upstream curved portion 41 and a downstream curved portion 42. The upstream curved portion 41 is located upstream of the downstream curved portion 42 with respect to the rotational direction of the impeller 2 indicated by the arrow H. The upstream curved portion 41 is curved larger than the downstream curved portion 42. That is, the curvature radius of the upstream curved portion 41 is larger than the curvature radius of the downstream curved portion 42.

  FIG. 10 is a diagram illustrating a result of analyzing the flow of liquid in the discharge casing 30. As can be seen from FIG. 10, the liquid flows along the upstream curved portion 41. On the other hand, the liquid is stagnant around the downstream curved portion 42.

  The reason why the curvature radius of the upstream curved portion 41 is increased is to reduce the flow velocity at the connection portion between the peripheral wall 37 and the discharge port 31. It is known that when high-temperature water flows through a flow path at high speed, corrosion of the flow path material is promoted. Such a phenomenon is called FAC (Flow Accelerated Corrosion). Since the liquid is pressurized by the rotating impeller 2, the liquid passing through the discharge casing 30 becomes high temperature. As a result, corrosion of the inner wall of the discharge casing 30 may be promoted. In the present embodiment, the flow velocity at the connection portion between the peripheral wall 37 and the discharge port 31 can be lowered by increasing the radius of curvature of the upstream curved portion 41. Therefore, local corrosion of the discharge casing 30 can be prevented.

  Further, by increasing the radius of curvature of the upstream curved portion 41, the area where liquid is discharged and peeled from the inner surface of the port 31 can be reduced. As a result, the liquid is discharged smoothly and the pump performance is improved. On the other hand, the reason why the radius of curvature of the downstream curved portion 42 is reduced is to reduce the area where the liquid is stagnated so as not to disturb the flow of the liquid flowing through the discharge flow path 31a. Thus, the shape of the discharge casing 30 of the present embodiment can prevent the promotion of corrosion and improve the pump performance.

  FIG. 11 is a graph showing changes in the cross-sectional area of the discharge flow path 31a. As shown in FIGS. 11 and 9, the discharge passage 31a of the discharge casing 30 has a shape in which the cross-sectional area gradually decreases along the liquid flow direction. This is because the separation region in the discharge flow path 31a is reduced by increasing the speed of the liquid flowing through the discharge flow path 31a to some extent. Therefore, the pump performance can be further improved.

  In the multistage pump described above, four through bolts 6 are used, but when the diameter of the impeller is large to some extent, eight through bolts are used. The present invention is also applicable to a multistage pump having eight through bolts.

  The embodiment described above is described for the purpose of enabling the person having ordinary knowledge in the technical field to which the present invention belongs to implement the present invention. Various modifications of the above embodiment can be naturally made by those skilled in the art, and the technical idea of the present invention can be applied to other embodiments. Accordingly, the present invention is not limited to the described embodiments, but is to be construed in the widest scope according to the technical idea defined by the claims.

DESCRIPTION OF SYMBOLS 1 Rotating shaft 2 Impeller 3 Pump casing 4 Diffuser 6 Through bolt 7 Nut 9 Bearing 10 Suction casing 11 Suction port 20 Suction volute 21 Guide plate 22 Tongue part 25 Side chamber 26 Partition wall 27, 28 Connection port 30 Discharge casing 31 Discharge Port 41 Upstream curved portion 42 Downstream curved portion 50 Intermediate casing 55 Shaft seal mechanism 65 Bearing casing 66 Cooling pipe 70 Balance mechanism 75 Balance piping 80, 81 Legs

Claims (5)

A rotation axis;
A plurality of impellers fixed to the rotating shaft;
A pump casing containing the plurality of impellers,
The pump casing includes a suction casing having a suction flow path, a discharge casing having a discharge flow path, and an intermediate casing disposed between the suction casing and the discharge casing.
The suction casing has a suction volute connected to the suction passage, and the suction volute extends from the suction passage to a liquid inlet of a first stage impeller of the plurality of impellers. . The multi-stage pump is
A balance mechanism for supporting a thrust force acting on the rotating shaft;
A balance chamber in which the balance mechanism is accommodated;
A balance pipe for guiding the liquid in the balance chamber to the suction casing;
The suction casing has a side chamber isolated from the suction volute;
The multistage pump according to claim 1, wherein one end of the balance pipe is connected to the balance chamber, and the other end is connected to the side chamber.   The multistage pump according to claim 1 or 2, wherein a guide plate for guiding the flow of the liquid is disposed in the suction volute. The discharge casing has a discharge port in which the discharge flow path is formed, and a peripheral wall that forms an annular flow path in which the liquid discharged from the impeller swirls,
The discharge port and the peripheral wall are connected via a connection portion having a curved cross-sectional shape,
The connecting portion is composed of an upstream curved portion and a downstream curved portion, and the upstream curved portion is located on the upstream side of the downstream curved portion with respect to the rotation direction of the impeller,
The multistage pump according to any one of claims 1 to 3, wherein a curvature radius of the upstream curved portion is larger than a curvature radius of the downstream curved portion.   The multistage pump according to any one of claims 1 to 4, wherein the discharge flow path has a shape in which a cross-sectional area gradually decreases along a liquid flow direction.

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