JPH0227196A - Centrifugal pump with small specific speed - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an impeller and a casing of a pump having the lowest specific speed among centrifugal pumps that handle liquid or gas.

[Conventional technology]

When a high pressure is required for the flow rate based on the impeller's rotational speed, the impeller shape of a turbo fluid machine will inevitably change to an axial flow type, mixed flow type, or centrifugal type. Are known. The specific speed, which represents the shape of the impeller, decreases from the axial type to the centrifugal type. Among the centrifugal types, those with higher pressure, that is, those with lower specific speeds, have a considerably flat impeller, which tends to lower the maximum efficiency, and eventually it becomes impossible to realize a centrifugal pump, so a positive displacement type is adopted. Or use a multi-stage centrifugal type.

FIG. 2 is a partial sectional view near the tip of the impeller, showing a conventional example of a centrifugal pump with such an extreme range of minimum specific speed.

An impeller 1 supported by a boss (not shown) is a car plate 2) a side plate 3
and a plurality of blades 4 between them, and is surrounded by a casing 7 having a guide path 5 and a volute 6. Flow rate -
For reasons such as setting the pressure characteristics to accurate values, the outer diameter of the impeller 1 is machined or press-worked to have a small error, thereby forming a cylindrical surface. Casing 7 facing this
The inner surface of the cylinder is also machined to create a cylindrical surface with a small gap in the radial direction to reduce leakage.

[Problem to be solved by the invention]

In the prior art, the maximum efficiency of the centrifugal pumps with flat impellers and minimum specific speeds is generally lower than those with higher specific speeds. The solution is to use a positive displacement type, a centrifugal type with multiple stages, or increase the number of stages if there are already multiple stages, thereby lowering the pressure borne by each stage, increasing the specific speed, and improving the maximum efficiency. However, the structure is complex and the number of parts is large.

The object of the invention is to improve the maximum efficiency of single or multi-stage centrifugal pumps in the extreme range of minimum specific speed.

[Means to solve the problem]

This invention is described below.

(2) A centrifugal pump with a small specific speed in which a casing guide path is provided in the radial direction of an impeller consisting of a car plate, a side plate, and a blade, and a conical surface is provided on the outer periphery of the car plate and the side plate.

2) A centrifugal pump with a low specific speed according to 1) above, in which a conical surface is provided on the inner surface of the casing opposite to the conical surface on the outer periphery of the vehicle plate and side plate.

3) A centrifugal pump with a low specific speed, in which the conical surface on the outer periphery of the car plate or side plate extends to the blades of the impeller.

[Effect]

1) The fluid that has received energy due to the rotation of the impeller 11 flows out from the blades 4 at high speed and flows into the guide path 5 again through the radial gap with the casing 17. At this time, in the radial gap, a so-called rapid expansion and rapid contraction of the cross-sectional area within the pipe occur close to each other, which not only creates fluid resistance but also causes turbulence in the flow. Further, on the outermost wall of the side plate 13 of the car plate 12 which is in contact with the outlet of the blade 4, there is a microscopic wake that attempts to join the main stream flowing out of the blade 4. By the way, in a pump with a minimum specific speed in the extreme range, the width (axial length) of the blade 4 is extremely narrow, so compared to a wider blade, the wake penetrates deeper into the mainstream of this part and mixes at a deeper depth. A large proportion of Therefore, the conical surface 22.23
As the angle θ is decreased from 90°, the depth at which the wake penetrates and mixes with the mainstream decreases, and the directions become consistent, improving pump efficiency.

2) When a conical surface is provided on the inner surface of the casing, the above-mentioned rapid decrease in cross-sectional area is largely eliminated, and its influence becomes greater as the blade width with lower specific speed becomes narrower, improving pump efficiency.

3) In the case where the conical surface extends to the blade 4, there is no slight cylindrical surface on the impeller side, and the adverse effect of the wake is further reduced, and the slight protrusion 26 on the casing side also disappears. Main flow turbulence is reduced and pump efficiency is improved.

〔Example〕

FIG. 1 is a sectional view of the embodiment, showing the final stage of the multistage centrifugal pump.

The impeller 11 supported by the boss 9 on the shaft 8 is mounted on a wheel plate 12)
A pair of casings 17 (1
7a, 17b). The illustrated casing 17 is the final stage and has a discharge port 20 and a return passage 21 in the previous stage.

The wheel plate 12 and side plate 13 of the impeller 11 each have a conical surface 2 having an angle θ on the outer periphery, leaving a minute cylindrical portion on the opposite sides.
2.23 is formed. Further, the casings 17a, 17b also form a conical surface 24.25, which is approximately the same as θ, on the inner surface facing the conical surface 22.23.

The width of the guide path 5 is the same or narrower than the width (length in the axial direction) of the blade 4, so that there is no deviation in the axial direction (the cylindrical portion left in the impeller 11 is relatively large, and the conical surface 22 facing the impeller 11 is relatively large). and 24 (or 23 and 25) and when the casing 17 (7a, 17b) is opposed to the outer diameter of the impeller 11 with a smaller gap in the radial direction, A minute protrusion 26 is formed inside the guide path 5 as shown in the figure.This protrusion 26 may be omitted and the conical surface 24 or 25 may be directly connected to the surface of the guide path 5.

Other conditions, such as the wide guideway 5 or the conical surface 22
When the distance between and 24 (or 23 and 25) is narrow and θ is large, the protrusion 26 is not formed geometrically.

In any case, as far as the protrusion 26 is concerned, it is better that the protrusion 26 be absent or small. Therefore, the car plate 12 or side plate 1
3 does not have a cylindrical part, and the conical surface 22 or 23 covers the entire thickness of the wheel plate 12 or side plate 13, and the impeller 1
It is preferable that it extends to the outer periphery of the first blade 4. Further, the conical surface may be only the conical surface 22, 23 of the impeller 11, and the casing may not be provided with the conical surface 24, 25, so that the pump may have a combination having a considerable cylindrical surface in the axial direction as in the conventional example. The guide path 5 may be provided with guide vanes.

The conical surfaces 22, 23, 24, 25 also include conically curved surfaces.

The best value for θ is about 30°, and it can be set at 15-50°.

According to experiments, the axial movement cuff of a pump that handles water is 50W.

A comparison of two types of pumps with 3 stages and a cut-off lift of 50 m, which were made by simply machining the same parts to have conical surfaces or not, revealed that the maximum efficiency of the pump was 29% for the conventional model;
It was 36.5% of that of the example. 34% had a conical impeller and a conventional casing. In addition, shaft power 1. The experimental results for IKW were approximately similar.

〔Effect of the invention〕

This invention improves the flow from the impeller to the guide path of the casing by providing a conical surface on the impeller of the centrifugal pump, and in some cases on the casing. This has the effect of improving the efficiency of narrow pumps.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the embodiment, and FIG. 2 is a sectional view of the conventional example. 1.11... impeller, 2,12... car plate, 3,13
...Side plate, 4...Blade, 5...Guideway,? ,
17.17a. 17b...Casing, 22.23, 24.25...
・Conical surface.

Claims (1)

[Claims] 1) A centrifugal pump in which a casing guide path is provided in the radial direction of an impeller consisting of a car plate, a side plate, and a blade, characterized in that a conical surface is provided on the outer periphery of the car plate and the side plate. Centrifugal pump with low specific speed. 2) The centrifugal pump with a low specific speed as set forth in claim 1, characterized in that a conical surface is provided on the inner surface of the casing opposite to the conical surface on the outer periphery of the car plate and the side plate. pump. 3) A centrifugal pump with a low specific speed according to claim 1, characterized in that a conical surface on the outer periphery of the wheel plate or the side plate extends to the blade of the impeller.