EP0079433B1

EP0079433B1 - Centrifugal pump

Info

Publication number: EP0079433B1
Application number: EP82107809A
Authority: EP
Inventors: Seiji Yanagisawa; Masao Yoshida; Hideki Shinotsuka; Tatsuya Ishigaki; Kinya Morioka
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1981-11-16
Filing date: 1982-08-25
Publication date: 1988-01-07
Also published as: JPS5885398A; DE3277927D1; EP0079433A1; KR880001488B1; KR840001306A

Description

This invention relates to a centrifugal pump of the kind described in the pre-characterizing part of patent claim 1. Such a centrifugal pump is for example known from CH-A 428444.
In a centrifugal pump equipped with a volute chamber covering an outlet port of a pump runner, it has hitherto been necessary to improve the shape and configuration of the pump runner and a casing to obtain improved pump peformance.
When the width of the volute chamber near its inlet is greater than the width of the outlet of the pump runner, it has generally been believed that a portion of the water discharged through the outlet port of the pump runner tends to return to the inlet port side of the pump runner by flowing along an innerwall surface of the volute chamberto thereby reduce pump performance. To prevent this return flow of water, proposals have been made to reduce the width of the volute chamber in the vicinity of its inlet to be approximate to the width of the outlet port of the pump runner to thereby increase the resistance offered to the flow of fluid by this part of the pump. However, no marked improvement in pump performance has ever been achieved by reducing the width of the volute chamber near its inlet, probably because a reduction in width causes a large amount of high velocity component flowing in counter current to a fluid flux discharged through the pump runner to be produced in a fluid flux returning to the outlet port of the pump runner along the inner wall surface of the volute chamber, to thereby interfere with smooth outflow of the fluid flux discharged through the pump runner.
To obviate the aforesaid problem, proposals have been made to reduce the gap between a front shroud or rear shroud of the pump runner and an inner wall surface of a casing or a casing cover in spaced juxtaposed relation thereto, to thereby reduce a return flow of fluid from the outlet port of the pump runner toward the inlet portthereof. This solution, although it is possible to reduce the return flow, increases the friction of a disc of the pump runner, making it relatively impossible to provide improvements in pump performance. Also, since the pump runner moves in sliding movement in an axial direction as the pump operates, difficulties are encountered in regulating the clearance between the front shroud or rear shroud of the pump runner and the inner wall surface of the casing or casing cover in spaced juxtaposed relation thereto, resulting in collision between the pump runner and the inner wall surface of the casing or casing cover.
Various proposals have thus been made in the past to provide an improved pump construction, but none of them has proved to have effect in obtaining improved pump performance by avoiding a return flow of fluid from the outlet port of the pump runnertoward the inlet port thereof, without causing some other trouble or rendering machining of parts or assembling thereof difficult to perform.
CH-A 428444 discloses a centrifugal pump having a pump casing enclosing the outlet port of a pump runner and forming a volute chamber around said pump runner. Said volute chamber has an inlet opening limited by wall portions of the volute chamber having inner wall surfaces which are inclined with respect to the pump runner opening. Afluid flux returning along the inner wall surface of said volute chamber toward said outlet port of the pump runner produces a counter current with a component in the opposite direction of the fluid flow discharged through the outlet port of the pump runner, reducing thereby the pump performance.
This invention has been developed for the purpose of obviating the aforesaid problem of the prior art. Accordingly, the invention has as its object the provision of a centrifugal pump of improved construction capable- of obtaining increased pump performance.
According to the invention this object is solved by a centrifugal pump of the kind referred to in the pre-characterizing part of patent claim 1 comprising the features disclosed in the characterizing part of patent claim 1.
The subclaims are directed on preferred embodiments of the centrifugal pump according to the invention.
Preferred embodiments of the centrifugal pump according to the invention will now be described with reference to the drawings.

Brief Description of the Drawings

Fig. 1 is a sectional view of the centrifugal pump comprising one embodiment of the invention;
Fig. 2 is a sectional view, on an enlarged scale, of the essential portions of the centrifugal pump shown in Fig. 1;
Fig. 3 is a sectional view of the centrifugal pump comprising another embodiment;
Figs. 4 and 5 are sectional views of the centrifugal pump comprising still another embodiment;
Fig. 6 is a view in explanation of the details of the deflecting wall;
Fig. 7 is a view in explanation of the distribution of speeds of a flow flux discharged from the pump runner;
Fig. 8 is a view in explanation of one example of fluid flow in the volute chamber;
Fig. 9 is a sectional view of the centrifugal pump comprising still another embodiment;
Figs. 10-13 are sectional views of centrifugal pumps each comprising still another embodiment.

Description of the Preferred Embodiments

A preferred embodiment of the centrifugal pump in conformity with the invention will be described by referring to Fig. 1. Fig. 2 shows, on an enlarged scale, the essential portions of the pump shown in Fig. 1. A pump runner 1 is mounted on a rotary shaft 2, and a pump casing 3 of cast iron encloses a front shroud 4 and an outlet port 5 of the pump runner 1, to provide a volute chamber 6 around the pump runner 1. To assemble the pump runner 1, the pump casing 3 has an opening 8 on the side of a rear shroud 7 of the pump runner 1 which is closed by a casing cover 9 of cast iron.
Deflecting walls 11 extend from an inner wall surface of the casing in the vicinity of the inlet of the volute chamber 6 toward the outlet port 5. The deflecting walls extend annularly to the vicinity of end faces 12 of the front shroud 4 and rear shroud 7 of the pump runner 1. More specifically, a surface 11a of the deflecting walls 11 on the pump runner 1 extends toward the outlet port 5 of the pump runner 1 with a small clearance between it and the end faces 12 of the front shroud 4 and rear shroud 5, and a surface 11 b of the deflecting walls 11 on the side of the volute chamber 6 extends toward the outlet port 5 of the pump runner 1 in a manner to be substantially perpendicular to the direction of flow of a fluid flux L discharged through the outlet port 5 of the pump runner 1. Thus the direction of flow of the fluid flux L discharged through the outlet port 5 of the pump runner 1 is substantially perpendicular to the rotary shaft 2 of the pump runner 1, so that the surface 11 b of the deflecting walls 11 on the side of the volute chamber 6 will constitute a cylindrical surface centered at the rotary shaft 2 and substantially parallel thereto.
As the pump of this construction starts operating, fluid drawn by suction through an inlet port 10 of the pump runner 1 is discharged into the volute chamber 6 through the outlet port 5 of the r_"'mp runner 1. The fluid discharged into the I _Jlute chamber 6 has the direction of its flow changed therein, so that a portion of the fluid becomes a fluid flux I flowing along the inner wall surface of the volute chamber 6 toward the vicinity of the inlet of the volute chamber 6. The fluid flux I flowing along the inner wall surface of the volute chamber 6 has its direction of flow altered along the surface 11 of the deflecting walls 11 contiguous with the inner wall surface of the volute chamber 6, so that it becomes a fluid flux m directed toward the outlet port 5 of the pump runner 1. After intersecting the fluid flux L from the outlet port 5 of the pump runner 1 along the surface 11b of the deflecting walls 11 substantially perpendicularly thereto, the fluid flux m is fed into the volute chamber 6 along with the fluid flux L because the fluid flow L is absolutely greater in volume than the fluid flux m. At this time, the fluid flux m has no velocity component (oriented in the direction n in Fig. 2) in counter current to the direction of the fluid flux L, so that the flow of the fluid flux L is not interfered with. In this way, direct confrontation of the fluid flux m flowing in return flow along the inner wall surface of the volute chamber 6 with the fluid flux L discharged through the outlet port 5 of the pump runner 1 is avoided to eliminate the risk of development of an eddy current.
In the centrifugal pump of the aforesaid construction, the fluid flux I flowing in return flow along the inner wall surface of the volute chamber 6 is prevented from interfering with the outflow of the fluid flux L discharged through the outlet port 5 of the pump runner 1. By reducing the clearance between the surface 11 a of the deflecting walls 11 and the end faces 12 of the pump runner at its discharge side to increase the resistance offered to the flow of fluid by this portion ofthe pump and restrict the flow of a circulating current o returning toward the inlet port 10 of the pump runner 1, it is possible to minimise a loss of friction of the disc of the pump runner 1. The deflecting walls 11 extend substantially parallel to the rotary shaft 2 on the outside of the end faces 12 of the pump runner 1 on its discharge side. By virtue of this arrangement, the pump performs in the same manner as if there were no axial movement of the pump runner 1, even if the pump runner 1 moves axially during operation. More specifically, a reduction in eddy loss and disc friction loss causes a rise in the discharge pressure of the centrifugal pump and an increase in the flow rate of fluid delivered by the pump while reducing an axial drive force, to thereby increase the efficiency of the pump.
Another embodiment shown in Fig. 3 will now be described in detail. In this embodiment, a deflecting wall extends from the casing cover toward the outlet port of the pump runner to cause a fluid flux returning toward the outlet port of the pump runner along the inner wall surface of the volute chamber to be deflected, so as to avoid the production therein of a velocity component counter current to the fluid flux discharged from the pump runner.
More specifically, 13 is a deflecting wall extending from the casing cover 9 toward the outlet port 5 of the pump runner 1 and arranged, like the deflecting walls 11 described by referring to Figs. 1 and 2, annularly with a small clearance between it and the end face of the rear shroud 7 of the pump runner 1 on the outlet side. The surface of the deflecting wall 11 on the side of the volute chamber 6 is contiguous with the inner surface of the casing 3 and constructed such that its extended surface is substantially perpendicular to . the direction of flow of the fluid flux L discharged from the pump runner 1, to prevent a velocity component counter current to the fluid flux L from being produced in the fluid flux m returning along the inner wall surface of the volute chamber 6 toward the outlet port 5 of the pump runner 1. The provision of the one deflecting wall 13 on the side of the casing cover 9 as aforesaid enables the width W of the casing 3 in the vicinity of the inlet of the volute chamber 6 to be increased as the casing 3 is viewed singly. Since the casing 3 is formed of casting, this construction is conducive to increased operability because the width W thereof in the vicinity of the inlet of the volume chamber 6 is preferably increased in view of facilitating removal of casting sand after casting is performed. By facilitating casting sand removal following casting of the casing 3, folding of casting surface in the volute chamber 6 can be prevented, thereby contributing to improvement of pump performance. In this type of centrifugal pump, the positional relation between the outlet port 5 of the pump runner 1 and the deflecting walls 11 and 13 raises an important problem. This problem can be obviated by working on and assembling the parts as presently to be described. After an end face 11 c of the deflecting wall 11 of the casing 3 formed of casting, a spigot joint surface 3a of the casing 3 is worked. Then a spigot joint surface 9a of the casing cover 9 and an end face 13c of the deflecting wall 13 are worked. By performing working in this way, the parts concerned can be finished in a predetermined dimensional relation. When the parts are assembled, the pump runner 1 is assembled with the casing cover 9, and the casing 3 is assembled with the casing cover 9 after making sure that the pump runner 1 and the deflecting wall 11 are in correct positional relation. This enables quality control of a centrifugal pump to be carried out by a simple process. Moreover, the use of this construction enables assembling of the pump runner 1 having an outlet port 5 of a different width to be effected with the casing cover 9 by merely altering the dimensions of the casing cover 9 to be machined, allowing realization of benefits from common use of parts to be achieved.
Another embodiment shown in Figs. 4 and 5 will be described. In this embodiment, the deflecting walls for deflecting a fluid flux returning along the inner wall surface of the volute chamber toward the outlet port of the pump runner to avoid production therein of a velocity component flowing in counter current to a fluid flux discharged through the outlet port of the pump runner are in the form of tubes and mounted in the vicinity of the inlet of the volute chamber. In Fig. 4, the pump runner 1 is enclosed by a casing 3 defining a volute chamber 4, a casing cover.16 located on the side of a front shroud 4 and a casing cover 9 located on the side of a rear shroud 7. 14 and 15 are deflecting walls in the form of tubes including large thickness portions 14a and 15a. The deflecting wall 14 is held in position while its large thickness portion 14a is held between the casing 3 and casing cover 16, and the deflecting wall 15 is likewise held in position while its large thickness portion 15a is held between the casing 3 and casing cover 9. A suitable dimension may be selected for small thickness portions 14b and 15b of the deflecting walls 14 and 15 in such a manner that they will be arranged on the side of the end face of the pump runner 1 on its discharge side when the centrifugal pump is assembled. The small thickness portions 14b and 15b are contiguous at their surfaces facing the volute chamber 6 with the inner wall surface of the casing 3 and located substantially perpendicular to a fluid flux discharged from the pump runner 1. In ordinary centrifugal pumps, the direction in which fluid is discharged therefrom is substantially perpendicular to the rotary shaft 2, so that the surfaces of the small thickness portions 14b and 15b of the deflecting walls 14 and .15 on the side of the volute chamber 6 should be substantially parallel to the rotary shaft 2. When the deflecting walls are formed of other material than the materials forming the casing 3 and casing cover 9, replacements of the old deflecting walls 14 and 15 by new ones can be readily effected when wear is caused thereon.
The centrifugal pump shown in Fig. 5 is distinct from that shown in Fig. 4 in that the casing 3 and the casing cover 16 are not separate entities but are formed as a unit in the latter. The deflecting walls 14 and 15 shown in Figs. 4 and 5 may be produced by cutting tubular material crosswise and machining same. In this case, an annular member may be cut out in part and arranged in compressed condition in a groove 3d formed in the casing 3 (Fig. 5) or in grooves 9d and 16d formed between the casing 3 and casing covers 9 and 16 respectively (Fig. 4), so that spring-back of the compressed annular member may be utilized to place the deflecting walls 14 and 15 securedly in the groove 3d or grooves 9d and 16d.
Fig. 7 shows the velocity distribution of the fluid flux L discharged from the pump runner 1. In the figure, it will be seen that the velocity tends to be higher on the side of the rear shroud 7. When a centrifugal pump provided with this type of pump runner 1 is driven, a strong flow L₁ discharged and located on the side of the rear shroud 7 might, when it changes its direction within the volute chamber 6 as shown in Fig. 8, produce a secondary flow which might interfere with a weak flow L₂ discharged and located on the side of the front shroud 4, thereby bringing about a loss of mixing.
In the embodiment shown in Fig. 9, means is provided for minimizing -the production of a secondary flow in the volute chamber 6 to reduce a loss of mixing. More specifically, the volute chamber 6 in the casing 3 is extended toward the side of the front shroud 4 in which the flow of fluid discharged from the pump runner 1 has a lower velocity. This embodiment has, of course, the deflecting walls 11 located in the vicinity of the inlet of the volute chamber 6 to deflect the fluid flux m returning along the inner wall surface of the volute chamber 6 toward the outlet port 5 of the pump runner 1 so as to avoid production therein of a velocity component flowing in counter current to the fluid flux L discharged from the pump runner, as is the case with the embodiments shown and described hereinabove. When the centrifugal pump of this construction is driven for operation, the flow L₁ of high velocity discharged from the runner 1 and located on the side of the rear shroud 7 is led toward the interior of the volute chamber 6 extended to the side of the front shroud 4. The flow L₁ regains pressure and has its velocity reduced within the volute chamber 6, so that it does not interfere with the flow L₂ of lower velocity discharged and located on the side of the front shroud 4. Thus this construction can eliminate head-on collision between the flow L₁ of higher velocity and the flow L₂ of lower velocity, thereby reducing a loss of mixing in the volute chamber 6 and improving pump performance. The deflecting walls 11 achieve the same effects as described by referring to the embodiments shown in Figs. 1-5, so that the description thereof shall be omitted.
In the embodiments shown and described hereinabove, two deflecting walls are provided in the vicinity of the inlet of the volute chamber in positions corresponding to the end faces of the front shroud and the rear shroud. The invention is not limited to this specific number of deflecting walls and one of the deflecting walls may be provided on one side of the vicinity of the inlet of the volute chamber in a position facing the end face of the front shroud or the rear shroud. In the embodiments shown and described hereinabove, the forward end of each deflecting wall (the end face on the side of the outlet port of the pump runner) is extended to a point immediately before it faces the outlet port. However, the deflecting walls may be shaped such that the spacing between the end faces of the deflecting walls is greater than the diameter of the outlet port of the pump runner. Also, in the embodiments shown and described hereinabove, the surfaces of the deflecting walls facing the volute chamber are cylindrical in shape and substantially parallel to the rotary shaft. However, the deflecting walls may be constructed such that their forward ends are slightly inclined toward the center of the volute chamber.
Figs. 10-13 show other embodiments. In the embodiment shown in Figs. 10 and 11, the spacing W between the deflecting walls is greater than the inner diameter of the outlet port 5 of the pump runner 1 and smaller than the outer diameter thereof. In the embodiment shown in Fig. 12, the deflecting wall 11 formed on the side of the casing 3 is located substantially flush with the end face 12 of the outlet port 5 on the side of the front shroud 4. In the embodiment shown in Fig. 13, the deflecting walls 11 extend along the vicinity of extensions of the end faces 12 of the outlet port 5 near the front and rear shrouds 4 and 7 and are juxtaposed against the front and rear shrouds 4 and 7 respectively.

Claims

1. A centrifugal pump comprising:

a pump runner (1) fixedly mounted on a rotary shaft (2) and provided with a front (4) and rear (7) shroud, said pump runner (1) being adapted to suction a fluid in an axial direction of the rotary shaft (2) and discharge the same in a radial direction thereof;

a pump casing (3) enclosing a front surface and an outlet port (5) of said pump runner and forming a volute chamber (6) around said pump runner (1), said volute chamber directly communicating with the outlet port, and said pump casing (3) is kept apart from said front surface of the pump runner (1);

characterized by
deflecting wall means (11, 13, 14, 15) being fixed parts or parts of the pump casing for deflecting a fluid flux returning along an inner wall surface of said volute chamber (6) toward said outlet port (5) of said pump runner (1) to be deflected so as to avoid a counter current between the fluid flow discharged through said outlet port (5) of said pump runner (1) and the fluid flow returning along the inner wall surface of the volute chamber (6), each of said deflecting wall means (11, 13, 14, 15) comprising deflecting wall surfaces being located near an inlet port of said volute chamber (6) and extending substantially perpendicularly to a discharge flow from said pump runner (1).

2. A centrifugal pump claimed in claim 1, characterized in that each of said deflecting wall means is formed integrally with said pump casing at the inlet port of said volute chamber, and is of a cylindrical shape extending coaxially with the rotary shaft.

3. A centrifugal pump claimed in claim 1, characterized in that each of said deflecting wall means is a tube of a cylindrical shape extending coaxially with the rotary shaft.

4. A centrifugal pump as claimed in claim 3, characterized in that said deflecting wall means of tubular form are located near end faces of outlet ports of the front shroud and the rear shroud of said pump runner.

5. A centrifugal pump claimed in claim 4, characterized in that each of said deflecting means of tubular form has a longitudinal slit.

6. A centrifugal pump claimed in claim 4 or 5, characterized in that each of said deflecting means of tubular form is fitted at its one end to a respective annular groove formed in the inner surface of the volute chamber near the inlet port of said volute chamber.

7. A centrifugal pump claimed in claim 1, characterized in that one of said deflecting wall means is formed integrally with said pump cover and located radially opposite to the outlet port end surface of the rear shroud of the pump runner.

8. A centrifugal pump claimed in claim 7, characterized in that said one of deflecting means is of cylindrical shape extending coaxially with the rotary shaft.

9. A centrifugal pump claimed in claim 2, or 7, characterized in that a pair of said deflecting wall means are arranged radially opposite to the outlet port end surfaces of the front and rear shrouds of the pump runner, respectively.

10. A centrifugal pump claimed in claim 9, characterized in that said pair of the deflecting wall means are arranged opposite to each other with an interposed distance less than a thickness of said pump runner measured at a periphery thereof but greater than a width of the outlet port of the pump runner.