JPH10169598A - Centrifugal fluid machinery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve unstable characteristics caused by reduction of all pump head in a low flow rate region by forming a blade outlet diameter of a spurn water blade smaller than a stage push outer diameter arranged on a sliding part between a stage and a main shaft. SOLUTION: In centrifugal fluid machinery, the entrifugal force by turning at an inlet part of an impeller 3 generates flow from a core plate side in a radial direction, and reverse flow is generated in the vicinity of an inlet side plate of the impeller 3. When the reverse flow is invaded into a return flow passage 7, pre-turning component is enlarged in an equation of a theoretical pump head, and thereby, a unstable characteristic of a pump head characteristic is generated as well as reducing the all pump head. The outlet diameter ϕD of a spurn water blade 6 is formed smaller than an outer diameter ϕD' of a stage bush 8. When it is suppressed that flow in a return flow passage 7 is influenced by reverse flow of a low flow rate region, reduction of the all pump head is eliminated, and the stable characteristic is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multistage centrifugal fluid machine having a water return blade on a stage, and more particularly to a centrifugal fluid machine suitable for a boiler feed pump installed in a thermal power plant.

[0002]

2. Description of the Related Art A stage having a water return blade is constituted by a suction side plate, a discharge side plate, and a water return blade. In a centrifugal fluid machine having water return blades, a stage bush is attached to a sliding portion between a stage and a shaft.

[0003] Generally, as shown in FIG.
In a centrifugal fluid machine including the diffuser 4, the curved flow path 5, the water return blades 6, the return flow path 7, and the stage bush 8, the relationship between the pressures acting on the stage bush 8 (P>
To prevent the stage bush 8 from coming off due to the fluid force acting on the stage bush 8 from P ′), the stage bush 8 discharges a stage composed of the diffuser 4, the curved channel 5, the water return blade 6, and the return channel 7. Assembled from the side. For this reason, the water return blade outlet diameter is configured to be larger than the outer diameter of the bush.

In the case of a centrifugal type fluid machine, in a low flow rate region, at a diffuser inlet downstream of a centrifugal impeller (hereinafter simply referred to as an impeller), a flow separates from a diffuser impeller negative pressure surface and a total head is reduced. It causes unstable characteristics (indentation of the head curve). For this reason, Japanese Unexamined Patent Publication No.
As disclosed in Japanese Unexamined Patent Publication, there is a structure in which a rectifying blade is provided at a diffuser inlet portion along the diffuser blade.

Further, in the low flow rate region, the backflow generated on the shroud side of the impeller inlet portion causes an extra swirl in the flow in the return passage, so that the total head is reduced and the instability characteristic of the pump (head curve) Dents). In order to optimize the flow in the return flow path, it is necessary to remove the extra pre-turn caused by the backflow. For this reason, there is a structure in which a straight blade is installed in the return flow path to improve the unstable characteristics and prevent the pump efficiency from decreasing.

[0006] The straight blade removes an extra swirl in the return flow path generated by the backflow at the impeller inlet, and prevents unstable characteristics occurring in a low flow rate region.

[0007]

In a structure in which a straight blade is installed in the return flow passage, it is convenient to remove an extra swirl in a low flow rate region, but attention is paid to the flow at the design flow point. Absent. The water return blades and the volute casing are designed so that a flow suitable for the inlet of the next stage impeller flows in at a design flow point. Therefore, if a straight blade is attached downstream of this flow, the flow suitable for the inlet of the next stage impeller will be extra swirled at the design flow point, and the performance of the centrifugal fluid machine will be reduced.

SUMMARY OF THE INVENTION The present invention provides a centrifugal fluid machine which does not adversely affect the performance at the design flow point and improves instability characteristics due to a decrease in the total head in a low flow rate region.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a centrifugal impeller which is mounted on a main shaft and rotates together with the main shaft, and which guides outwardly the flow of fluid exiting from the centrifugal impeller and located on the outer periphery of the centrifugal impeller. A pressure-recovering diffuser, a curved flow channel that directs outward flow exiting the diffuser to axial flow,
A side plate that guides the flow flowing out of the curved flow path inward and collects the water return blades integrally formed with the blades, and a stage formed by a return flow path that leads to the inlet of the next-stage centrifugal impeller. In the centrifugal fluid machine provided in the above, the blade outlet diameter of the water return blade is made smaller than the outer diameter of a stage bush attached to a sliding portion between the stage and the main shaft. Is done.

The object is also to provide a centrifugal impeller which is mounted on a main shaft and rotates together with the main shaft, and a diffuser located on the outer periphery of the centrifugal impeller for guiding fluid flowing out of the centrifugal impeller outward to recover static pressure. A curved flow channel for guiding an outward flow from the diffuser to an axial flow, a water return blade integrally formed with a side plate and a blade for guiding the flow from the curved flow channel inward and a centrifugal impeller of the next stage In a centrifugal fluid machine in which a stage formed by a return flow path leading to an inlet is arranged in multiple stages in the axial direction, a blade for removing a swirling flow is provided downstream of the water return blade. You.

Still another object of the present invention is to provide a centrifugal impeller which is attached to a main shaft and rotates together with the main shaft, and a diffuser which is located on the outer periphery of the centrifugal impeller and guides a flow of fluid flowing out of the centrifugal impeller outward to recover a static pressure. A curved flow passage for guiding an outward flow from the diffuser to an axial flow, a water return blade integrally formed with a side plate and a blade for guiding the flow emerging from the curved flow passage inward, and a next-stage centrifugal blade In a centrifugal fluid machine in which a stage formed by a return flow path leading to a vehicle entrance is arranged in multiple stages in an axial direction, a stage bush attached to a sliding portion between the stage and a main shaft is provided by the stage. The structure is such that the diameter of the water return blade is smaller than the outer diameter of the stage bush.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of a multi-stage boiler feed pump according to the present embodiment, and FIG. 2 is a longitudinal sectional view of a main part of a first stage of FIG. In FIG. 1, 1 is a suction port for sucking fluid, 2 is a main shaft, 3 is an impeller mounted on the main shaft 2, and 4 is a diffuser blade provided on a diffuser D located on the outer periphery of the impeller 3. . 5 is a curved flow channel that guides the outward flow of the fluid to an inward flow, 6 is a water return blade that collects the flow of the fluid passing through the curved flow channel 5 inward,
Reference numeral 7 denotes a return flow path that guides the inward flow passing through the water return impeller 6 to the inlet of the next stage impeller 3 '. Reference numeral 9 denotes a discharge port for discharging the pressurized fluid to the outside of the pump.

The multi-stage boiler feed pump shown in FIG.
The impeller 3, the diffuser blade 4, the curved flow path 5, the water return blade 6, and the return flow path 7 in FIG. 2 are arranged in multiple stages in the direction of the main shaft 2, and the stages from the pump suction port 1 to the discharge port 9 are arranged in multiple stages. It is composed.

The boiler feed pump of the above-described embodiment is characterized by a water return blade 5, the details of which are shown in FIG. The outlet diameter φD of the water return blade 6 is set to the outer diameter φ of the stage bush 8.
D 'is smaller than D'.

The reason for setting as described above will be described. In the case of a centrifugal type fluid machine, in a low flow rate region, a radial flow occurs from the core plate side due to centrifugal force due to swirling at the inlet of the impeller 3, and a backflow occurs near the side plate side of the inlet of the impeller 3. .
Further, when this backflow enters the return flow path, the pre-swirl component becomes large in the equation of the theoretical head, so that the total head is reduced, resulting in unstable characteristics of the head curve.

For this reason, if the outlet diameter of the water return blade 6 is made smaller than the outer diameter of the stage bush 8 to make the flow in the return flow passage 7 less susceptible to the backflow in the low flow rate region, There is no decrease and stable characteristics can be obtained. FIG. 3 shows another embodiment for assembling the stage bush 8 from the suction side to prevent the stage bush 8 from coming off, FIG. 4 shows another embodiment, and FIG. 5 shows another embodiment.

FIG. 3 is an explanatory view of a structure for preventing the detachment when the stage bush 8 is assembled from the suction side. A in the figure,
A ′ represents a step area facing the flowing water portion on the suction side and the discharge side of the stage bush 8. In order for the stage bush 8 not to come off, the following equation may be established from the relationship between the pressures P and P 'acting on the suction side and the discharge side.

P × A <P ′ × A ′ (1) Therefore, the cross-sectional areas A and A ′ satisfying the expression (1)
If the stage bush 8 is formed in such a shape, it can be prevented from coming off. Further, as shown in FIG. 4, the structure in which the stage bush 8 is fixed with the screw portion 8B can also prevent the stage bush 8 from coming off.

Further, as shown in FIG. 5, even when the key 8C for locking the movement of the bush 8 in the axial direction is attached to the outer periphery of the bush 8, the detachment can be prevented.

According to this embodiment as described above,
Excessive swirling in the return flow path due to the flow backward from the impeller inlet in the low flow rate region is reduced, and unstable characteristics are eliminated.

FIG. 6 shows still another embodiment of the present invention.
FIG. 6 is a sectional view of the stage section of FIG. As shown in the figure, a blade 10 different from the water return blade 6 is attached downstream of the water return blade 6 to remove the swirling flow.

According to this structure, an unnecessary swirl component in the return flow path in the low flow rate region can be removed, and according to the present embodiment, assembly becomes easier.

[0023]

According to the present invention, when the centrifugal type fluid machine has multiple stages, by making the exit diameter of the water return impeller smaller than the outer diameter of the stage bush, the backflow at the impeller inlet portion in the low flow rate region is achieved. Excessive swirling in the return channel caused by the influence of the above can be eliminated, and unstable characteristics of the pump (indentation of the head curve) can also be avoided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a multi-stage boiler feed pump according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of a main part of a first stage of FIG. 1;

FIG. 3 is an explanatory view when the stage bush according to the present invention is assembled from the suction side.

FIG. 4 is an explanatory view of another embodiment when assembling the stage bush according to the present invention from the suction side.

FIG. 5 is an explanatory view of still another embodiment when assembling the stage bush according to the present invention from the suction side.

FIG. 6 is a sectional view of a stage section according to still another embodiment of the present invention.

FIG. 7 is a structural view of a conventional stage bush.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Pump suction port, 2 ... Spindle, 3 ... Impeller, 4 ... Diffuser, 5 ... Curved flow path, 6 ... Water return blade, 7 ... Return flow path, 8 ... Stage bush, 9 Pump outlet, 10 Blade for removing swirling flow.

Claims (3)

[Claims] 1. A centrifugal impeller mounted on a main shaft and rotating together with the main shaft, a diffuser located on an outer periphery of the centrifugal impeller to guide a flow of fluid flowing out of the centrifugal impeller outward to recover static pressure, and from the diffuser A curved flow path that guides an outgoing outward flow to an axial flow, a side plate and a vane that integrally guides and collects a flow exiting from the curved flow path, and guides to a next-stage centrifugal impeller inlet. In a centrifugal fluid machine in which a stage formed by a return flow path is arranged in multiple stages in the axial direction, a blade outlet diameter of the water return blade is attached to a sliding portion between the stage and the main shaft. A centrifugal fluid machine having a structure smaller than an outer diameter of a stage bush. 2. A centrifugal impeller which is mounted on a main shaft and rotates together with the main shaft, a diffuser located on the outer periphery of the centrifugal impeller to guide a flow of a fluid flowing out of the centrifugal impeller outward to recover a static pressure, and from the diffuser. A curved flow path that guides an outgoing outward flow to an axial flow, a side plate and a vane that integrally guides and collects a flow exiting from the curved flow path, and guides to a next-stage centrifugal impeller inlet. A centrifugal fluid machine in which a stage formed by a return flow path is arranged in multiple stages in the axial direction, wherein a blade for removing a swirling flow is attached downstream of the water return blade. machine. 3. A centrifugal impeller mounted on a main shaft and rotating together with the main shaft, a diffuser located on the outer periphery of the centrifugal impeller to guide a flow of fluid flowing out of the centrifugal impeller outward to recover static pressure, and from the diffuser. A curved flow path that guides an outgoing outward flow to an axial flow, a side plate and a vane that integrally guides and collects a flow exiting from the curved flow path, and guides to a next-stage centrifugal impeller inlet. In a centrifugal fluid machine in which a stage formed by a return flow path is arranged in multiple stages in the axial direction, a stage bush attached to a sliding portion between the stage and the main shaft is moved from a discharge side of the stage. A centrifugal fluid machine, wherein the diameter of the outlet of the water return blade is smaller than the outer diameter of the stage bush.