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How to repair the inclination of the butterfly valve guidepost

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Table of Contents

 

Summary    There is a large gap between the main butterfly plate and the auxiliary butterfly plate of the butterfly valve of the water turbine generator water intake pipe due to improper operation. Under the premise of not affecting the valve switching performance, it is proposed to perform local grinding treatment on the guidepost to eliminate defects and ensure Normal operation of the valve.

 

Overview

 

Butterfly valve (hereinafter referred to as the water intake valve) is a commonly used water intake equipment for small hydroelectric generator sets. Compared with gate-type water intake equipment, the butterfly valve has the advantages of simple structure, low engineering cost, reliable work, easy installation, and simple operation and maintenance. Widely used in engineering. Example: The No. 1 and No. 2 hydroelectric generators used in a power plant are arranged with one tube and two generators, and the two generators share a butterfly valve water intake device, which is set in the dam body. This valve is a disc-type vertical shaft butterfly valve with a nominal diameter of DN1600mm. During the overhaul, the auxiliary disc of the valve could not be completely closed with the main disc due to the deflection of the guide column. Through analysis of the cause of the failure and proper treatment, the normal operation of the valve was restored.

 

Description of the problem

 

Water intake butterfly valve is composed of three parts: the drive mechanism, the butterfly plate, and the valve seat body. The drive mechanism is gear transmission and manual operation. It is driven by the gear pair that drives the main butterfly plate to rotate and the gear pair and the slider for the horizontal displacement of the auxiliary butterfly plate are reversed. Equipment and other components. The butterfly plate is composed of a detachable main butterfly plate and an auxiliary butterfly plate. The auxiliary butterfly plate is guided and positioned through the inner guide column (brass material) and the positioning hole (copper sleeve) inside the main butterfly plate. The reversing transmission device realizes the horizontal displacement of the auxiliary butterfly plate. The valve seat body is composed of a valve seat and an upper cover, supports the drive mechanism and the butterfly plate, and seals the valve cavity, and both sides are connected with steel pipes. During valve maintenance and decomposition, it was found that there was a gap between the sealing surfaces of the main and auxiliary discs due to foreign matter. Although the auxiliary disc was forcibly closed by an external force, the gap still exists. If the disc is used in the pipeline for a long time, the disc will be It is in a state of vibration, which affects the safe operation of the valve.

 

Reason analysis

 

From the analysis of the valve structure, the main and auxiliary discs are steel castings with a thickness greater than 50mm, which are not easy to deform. The positioning holes are embedded in the main disc by thick-walled copper pipes, and they are not easy to deform. The guide column of the auxiliary disc is a cantilever structure, which is hot riveted on the auxiliary disc, and its rigidity is relatively low, and the cantilever part is prone to skew deformation. Judging from the circumferential distribution and shape of the gap on the sealing pair, the formation of the gap is the forced closing (opening of the valve) operation in the case of the main and auxiliary discs clamping foreign matter so that the 4 guideposts of the auxiliary disc are facing the gaps. The side is skewed, causing the guidepost and the auxiliary disc to be not perpendicular.

 

Repair

 

4.1 Repair plan

In order to solve the gap between the main and auxiliary butterfly plates of the water intake valve, it is necessary to eliminate the deflection state of the 4 guideposts. The water intake valve is installed inside the dam, and there is no working platform in the valve room. The site does not have the conditions for replacement and hot riveting of the guideposts. Since the deflection angle of the guide column is very small and there is no crack in the column body, the method of grinding the part of the guide column that deviates from the normal contour instead of dealing with the part of the normal contour is used to deal with the deflection and deformation of the guide column.

 

4.2 Determination of guide column deflection

At the job site, the direct measurement method is used to detect the deflection of the guide column. The end surface of the guide post hole of the original auxiliary butterfly plate is slightly smoothed, and its 4 end surfaces are determined to be in the same plane, and a cold-rolled plate with a thickness of 5mm that has been processed by the corresponding guide post reaming is placed on the end of the hole for measurement. platform. Check and adjust the fixed auxiliary butterfly plate to make it level, and then adjust the steel plate to make it close to the auxiliary butterfly plate and level, place the right-angle seat ruler on the steel plate so that it is always perpendicular to the steel plate, and move it to the vicinity of the guide column, the bottom right-angled side Point to the center of the guide column (Figure 1), use a vernier caliper along the circumference of the column to measure the distance between the corner of the ruler and the guide column. The maximum point of L in the direction of the deflection of the guide column and the vertex of the right-angle ruler (L value) The trajectory is distributed in an arc shape. The part of the end face of the guide column that deviates from the normal contour is the part that should be trimmed, and then measure the height h of the end face of the guide column from the steel plate. From this, the radial offset of the center of the end face of the guide column can be obtained as (1+5/h ) L. (Table 1)

 

 Table 1      Radial offset of the center of the end face of the guidepost              unit: mm
ItemColumn 1   Column 2Column 3Column 4
Height of column end from steel plate h198199197199
Maximum distance between seat ruler angle and guidepost L3.423.443.423.42
The radial offset of the center of the end face of the guide column (measured value) △L3.513.533.513.51

 

4.3 Guidepost repair

According to the measured offset and deflection direction of the center of the end face of the guide column (Figure 2), the part that needs to be ground is centered in the deflection direction, the cross-section of the part that needs to be ground is crescent-shaped, and the part of the column that needs to be ground. Along with the axial view, it is a right-angled triangle with a parabolic distribution in the side view, that is, the maximum grinding thickness on the end face is the offset of the end face center, and the grinding thickness at the root is reduced to 0.

 

 

 

According to the measurement results (Table 1), the maximum grinding amount is determined as 3.52mm according to the average value, and the initial value is 3.00mm. When grinding, the auxiliary disc is fixed vertically, first rough grinding with an angle grinder, and then fine grinding with a file. , Make the transition smoothly everywhere. After meeting the closing requirements, use a 400-day emery cloth to fine grind the cylinder to improve the surface finish as much as possible. Use the light transmission method to test the axial straightness of the grinding part of the cylinder. In order to facilitate the grinding of the column body, the deflection direction of the guide column should be vertically upward. After the partial initial grinding treatment, the main and auxiliary discs shall be closed without external force. The grinding treatment shall be carried out according to the contact range of the guide column and the positioning hole. , Until the main and auxiliary butterfly plates are closed tightly and evenly, and there is no jam in the assembly. Finally, the cylinder is refined to improve the surface finish. From the analysis of the amount of grinding, the maximum grinding section accounts for about 13% of the cross-sectional area. The grinding section gradually transitions from an approximate ellipse to a circular shape. Although the stiffness of the guide column is reduced, it can meet the rigidity requirements of the valve switch.

 

Conclusion

 

After the valve guide column is processed, the opening and closing of the auxiliary butterfly plate and the main butterfly plate are normal without jamming, and no abnormal vibration is found when the pipeline is over-current, which meets the operational requirements of the water intake valve. In the use of the valve after maintenance, a total of 4 switching operations were found, and no abnormal phenomenon was found. There was no obvious leakage at the stuffing box on the valve seat, indicating that the vibration of the butterfly plate in the overcurrent was significantly lower than before the maintenance, and it also showed that the guide column The grinding process is feasible.

 

 

Author: Wang Xinglong, Xing Chunyu

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