Low specific speed fire pump impeller

Abstract

This invention relates to a low specific speed fire pump impeller, comprising a front cover plate, a rear cover plate, and a plurality of front and rear blades distributed between the front and rear cover plates. The front and rear blades are staggered in the circumferential direction, with the front blades closer to the impeller inlet and the rear blades closer to the impeller outlet. The low specific speed fire pump impeller provided by this invention effectively reduces blade inlet squeezing and improves cavitation resistance through the leading edge position distribution of the two types of blades, solving the problem that low specific speed fire pump impellers are prone to failing to meet performance requirements at high flow rates due to blade inlet squeezing. Simultaneously, the trailing edge position distribution of the two types of blades improves flow separation during high flow rate operation, resulting in a more uniform impeller outlet velocity distribution, reduced pressure pulsation frequency, lower noise and vibration, and improved reliability and stability of fire pump operation.

Description

Technical Field

[0001] This invention relates to a fire pump impeller, specifically to a low specific speed fire pump impeller that improves the reliability and stability of fire pump operation. Background Technology

[0002] Fire pumps, as core equipment in fire hydrants, sprinklers, and other fire protection systems, are widely used in residential, industrial, and public places where people are densely populated, property is valuable, and there is a risk of fire.

[0003] According to section 6.4.2 of my country's national standard for fire pumps GB6245-2006, fire pumps should meet the following performance requirements: Operating Condition 1: When the suction depth is 1m, the rated flow rate (Qn) and rated pressure (Pn) requirements should be met. At the same time, the working pressure should not exceed 1.05 times the rated pressure.

[0004] Operating Condition 2: When the suction depth is 1m, the flow rate is 1.5Qn, and the working pressure should not be less than 0.65Pn.

[0005] Condition 1 requirements are similar to those of conventional pumps and are relatively easy to meet. Condition 2 requires fire pumps to have a wider operating range, which requires fire pumps to not only have good cavitation performance, but also good operational reliability and stability when deviating significantly from the design conditions.

[0006] The impeller is the core component that determines the performance of a fire pump. Existing low-specific-speed fire pump impellers have a centrally symmetrical blade arrangement. Combined with the relatively narrow flow channel of the low-specific-speed fire pump impeller, the following problems are highly likely to occur: (1) At the impeller blade inlet, the centrally symmetrically distributed blade thickness leads to severe cavitation, resulting in poor cavitation performance, which cannot reach the 1.5Qn flow rate, or the head cannot meet the standard requirements at the 1.5Qn flow rate.

[0007] (2) At the impeller outlet, the width of the impeller outlet of a low specific speed fire pump is generally narrow. The thickness of the conventional impeller blades, the blockage caused by the boundary layer, and the flow separation at the high flow point increase the unevenness of the velocity distribution downstream of the impeller outlet. In addition, the pressure pulsation caused by the centrally symmetrical blade distribution increases the vibration and noise, reducing the stability and reliability of the low specific speed fire pump operation.

[0008] (3) The flow rate and head curve is relatively flat, and it is easy to have a hump or an unstable performance curve shape. Summary of the Invention

[0009] To address the aforementioned problems, the main objective of this invention is to provide a low specific speed fire pump impeller that improves the reliability and stability of fire pump operation.

[0010] The present invention solves the above-mentioned technical problems through the following technical solution: a low specific speed fire pump impeller, including a front cover plate, a rear cover plate, and a plurality of front blades and rear blades distributed between the front cover plate and the rear cover plate. Each front blade and rear blade includes a leading edge near the impeller inlet and a trailing edge near the impeller outlet. The front blades and rear blades are staggered in the circumferential direction, with the front blades closer to the impeller inlet and the rear blades closer to the impeller outlet. When the number of impeller blades is even, the front blades and rear blades are evenly distributed. When the number of blades is odd, there are exactly two front blades or two rear blades arranged adjacent to each other.

[0011] In a specific embodiment of the present invention, the leading edge of the front blade is close to the impeller inlet, and the axial distance from the intersection of the blade with the streamline of the front cover plate on the axial projection diagram to the edge of the impeller inlet is 5%-15% of the maximum distance from the impeller inlet to the streamline of the front cover plate of the impeller.

[0012] In a specific embodiment of the present invention, compared with the leading edge of the front blade, the leading edge of the rear blade is located downstream of the leading edge of the front blade, and the minimum distance between the rear blade and the leading edge of the front blade on the axial projection diagram is 5%-30% of the difference between the impeller inlet diameter and the hub diameter.

[0013] In a specific embodiment of the present invention, the trailing edge of the rear blade is flush with the outer diameter of the front and rear cover plates of the impeller.

[0014] In a specific embodiment of the present invention, the trailing edge of the front blade is located upstream of the trailing edge of the rear blade, and the minimum distance between the front blade and the trailing edge of the rear blade on the axial projection diagram is 5%-30% of the outer diameter of the impeller.

[0015] In a specific embodiment of the present invention, both the leading edge of the front blade and the rear blade adopt an elliptical profile.

[0016] In a specific embodiment of the present invention, the trailing edge of the front blade is not parallel to the axis in the axial projection view, and the angle between it and the line parallel to the axis is 20°-30°. The distance from the trailing edge intersecting with the front cover plate to the axis is even greater.

[0017] In a specific embodiment of the present invention, the trailing edge of the front blade is asymmetrically thinned and rounded.

[0018] The positive and progressive effects of this invention are as follows: The low specific speed fire pump impeller provided by this invention has the following advantages: The low specific speed fire pump impeller provided by this invention can effectively reduce blade inlet squeezing and improve anti-cavitation performance by distributing the leading edge positions of the two types of blades. This solves the problem that the low specific speed fire pump impeller is prone to failing to meet performance requirements at high flow points due to blade inlet squeezing. At the same time, the distribution of the trailing edge positions of the two types of blades can improve the flow separation of the low specific speed fire pump impeller when operating at high flow rates, making the impeller outlet velocity distribution more uniform. It also reduces the pressure pulsation frequency, reduces noise and vibration, and improves the reliability and stability of fire pump operation. Attached Figure Description

[0019] Figure 1 Planar projection view of the impeller of this invention.

[0020] Figure 2 Projection view of the impeller shaft surface of this invention.

[0021] Figure 3 Partial view of the leading edge profile of the front and rear blades.

[0022] Figure 4 Partial view of the trailing edge profile of the leading blade.

[0023] The following are the names corresponding to the reference numerals in this invention: Figures 1-4 In the middle: front cover plate 1, rear cover plate 2, front blade 3, rear blade 4, leading edge of front blade 5, trailing edge of front blade 6, leading edge of rear blade 7, trailing edge of rear blade 8, impeller inlet edge 9. Detailed Implementation

[0024] The preferred embodiments of the present invention are given below with reference to the accompanying drawings to illustrate the technical solution of the present invention in detail.

[0025] Figure 1 Impeller planar projection diagram of the present invention. Figure 2 The impeller axial projection diagram of this invention is as follows: Figures 1-2 As shown: This invention proposes a low specific speed fire pump impeller, including a front cover plate 1, a rear cover plate 2, and a plurality of front blades 3 and rear blades 4 distributed between the front and rear cover plates. Each front blade 3 includes a leading edge 5 and a trailing edge 6, and each rear blade 4 includes a leading edge 7 and a trailing edge 8. When the total number of blades is even, the front blades and rear blades are arranged in a uniform alternating pattern. When the number of blades is odd, the front blades and rear blades are arranged in a pattern where there are exactly two front blades or two rear blades arranged adjacent to each other.

[0026] exist Figure 2On the axial view, abef represents the flow surface of the leading blade in the axial projection, where points a and b are the intersections of the leading edge of the leading blade with the front and rear shrouds, and points e and f are the intersections of the trailing edge of the leading blade with the front and rear shrouds. cdgh represents the flow surface of the trailing blade in the axial projection, where points c and d are the intersections of the leading edge of the trailing blade with the front and rear shrouds, and points g and h are the intersections of the trailing edge of the trailing blade with the front and rear shrouds. The distance from point a to the impeller inlet edge is X, the distance from the impeller inlet edge 9 to point g is Y, the impeller inlet diameter is D1, the impeller hub diameter is Dh, the impeller outer diameter is D2, and the angle between the trailing edge 6 of the blade and the line parallel to the axis in the axial projection is β.

[0027] To improve the cavitation resistance of low specific speed fire pumps, the front blade 3 is extended forward and close to the impeller inlet edge 9, with the X value being 5%-15% of the Y value. This allows the blade to transfer energy to the medium earlier, improving the impeller's cavitation resistance. Simultaneously, the leading edge 7 of the rear blade is positioned downstream of the leading edge 5 of the front blade. The minimum distance between the leading edge 7 and the leading edge 5 on the axial projection is 5%-30% of the impeller inlet diameter D1 and the hub diameter Dh. This staggered arrangement of the leading and rear blades effectively reduces blade inlet displacement and increases the effective inlet area, further improving the impeller's cavitation resistance and ensuring the fire pump's performance meets standard requirements at 1.5Qn.

[0028] To improve the reliability and stability of low specific speed fire pump operation, the trailing edge 6 of the front blade and the trailing edge 8 of the rear blade are designed and arranged differently. The trailing edge 8 of the rear blade is flush with the outer diameter D2 of the front and rear cover plates of the impeller. The trailing edge 6 of the front blade is distributed upstream of the trailing edge 8 of the rear blade. The minimum distance between the front blade trailing edge 6 and the trailing edge 8 of the rear blade on the axial projection diagram is 5%-30% of the outer diameter D2 of the impeller. The staggered arrangement of the trailing edges 6 and 8 of the front blade can reduce the blade extrusion at the impeller outlet, improve the flow separation of the low specific speed fire pump impeller when running at high flow rate, and at the same time reduce the pressure pulsation frequency, noise and vibration.

[0029] In a specific implementation example, the trailing edge 6 of the front blade in this invention is designed to be inclined on the axial projection and the angle β between it and the line parallel to the axis is 20°-30°, so that the streamline of the front cover plate ae and the streamline of the rear cover plate bf are approximately equal, thereby reducing or eliminating the humps or unstable performance curves that are prone to occur in low specific speed fire pumps.

[0030] like Figure 3 The blade profiles at the leading edge 5 of the front blade and the leading edge 7 of the rear blade are both elliptical to further improve the cavitation resistance of the low specific speed fire pump.

[0031] like Figure 4The trailing edge of the front blade is asymmetrically thinned and rounded at 6 points to make the flow at that point and downstream more uniform, reduce the influence of jet and wake, and prevent the generation of vortex streets.

[0032] This invention provides a low specific speed fire pump impeller that effectively reduces blade inlet squeezing and improves cavitation resistance through the distribution of two types of blade leading edge positions. This solves the problem that low specific speed fire pump impellers are prone to failing to meet performance requirements at high flow rates due to blade inlet squeezing. At the same time, the distribution of the two types of blade trailing edge positions improves flow separation in low specific speed fire pump impellers during high flow rate operation, making the impeller outlet velocity distribution more uniform. It also reduces pressure pulsation frequency, lowers noise and vibration, and improves the reliability and stability of fire pump operation.

[0033] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as defined by the appended claims and their equivalents.

Claims

1. A low specific speed fire pump impeller, comprising a front cover plate, a rear cover plate, and a plurality of front blades and rear blades distributed between the front cover plate and the rear cover plate, each front blade and rear blade comprising a leading edge near the impeller inlet and a trailing edge near the impeller outlet, characterized in that: The front and rear blades are staggered in the circumferential direction, with the front blades closer to the impeller inlet and the rear blades closer to the impeller outlet. When the number of impeller blades is even, the front and rear blades are evenly distributed. When the number of blades is odd, there are exactly two front or rear blades arranged adjacent to each other.

2. The low specific speed fire pump impeller according to claim 1, characterized in that: The leading edge of the front blade is close to the impeller inlet, and the axial distance from the intersection of the blade and the streamline of the front cover plate on the axial projection diagram to the edge of the impeller inlet is 5%-15% of the maximum distance from the impeller inlet to the streamline of the front cover plate.

3. The low specific speed fire pump impeller according to claim 2, characterized in that: Compared to the leading edge of the front blade, the leading edge of the rear blade is located downstream of the leading edge of the front blade. The minimum distance between the rear blade and the leading edge of the front blade on the axial projection diagram is 5%-30% of the difference between the impeller inlet diameter and the hub diameter.

4. The low specific speed fire pump impeller according to claim 1, characterized in that: The trailing edge of the rear blade is flush with the outer diameter of the front and rear cover plates of the impeller.

5. The low specific speed fire pump impeller according to claim 1, characterized in that: The trailing edge of the leading blade is located upstream of the trailing edge of the trailing blade, and the minimum distance between them on the axial projection diagram is 5%-30% of the impeller outer diameter.

6. The low specific speed fire pump impeller according to claim 1, characterized in that: Both the leading and trailing blades adopt an elliptical profile at their leading edges.

7. The low specific speed fire pump impeller according to claim 1, characterized in that: The trailing edge of the front blade is not parallel to the axis in the axial projection diagram, and the angle between it and the line parallel to the axis is 20°-30°. The distance from the trailing edge that intersects with the front cover plate to the axis is even greater.

8. The low specific speed fire pump impeller according to claim 1, characterized in that: The trailing edge of the leading blade is asymmetrically thinned and rounded.

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