Treatment Of Deflection Of Guide Column Of Large Butterfly Valve

- Nov 14, 2019-

In order to solve the gap existing in the closing of the main and auxiliary butterfly plates of the water intake valve, it is necessary to eliminate the deflection of four guide columns. The water intake valve is installed inside the dam body, there is no working platform in the valve chamber, and the site does not have the conditions for replacing and hot riveting the guide column. Because the deflection angle of the guide column is very small and there is no crack in the column body, the method of grinding the deviation part of the guide column from the normal contour instead of the deviation part is adopted to deal with the deflection deformation defect of the guide column.

Deflection measurement of guide column

In the operation site, direct measurement method is used to detect the deflection degree of guide column. Slightly flatten the end faces of the guide column holes of the original and auxiliary butterfly plates, and make sure that the four end faces are in the same plane. Place a 5mm thick cold-rolled plate which has been reamed corresponding to the guide column on the end faces of the holes as the measuring platform. Check, adjust and fix the auxiliary butterfly plate to make it horizontal, and then adjust the steel plate to make it close to the auxiliary butterfly plate and level. Place the right angle ruler on the steel plate so that it is always perpendicular to the steel plate, and move it near the guide column, with the bottom right angle edge pointing to the center of the guide column (Fig. 1). Use vernier caliper to measure the distance L between the ruler angle and the guide column along the circumference of the column body. The maximum value point of L is the direction of the deflection of the guide column, and the locus of the vertex (L value) of the right angle ruler is arc-shaped. The deviation part of the end face of the guide pillar from the normal contour is the part that should be polished off. Then measure the height h between the end face of the guide column and the steel plate respectively, and it can be concluded that the radial offset of the end face center of the guide column is (1 + 5 / h) l (Table 1).

Butterfly valve

Guide post repair

According to the measured deviation and deflection direction of the end face center of the guide column (Fig. 2), the section to be grinded shall take the deflection direction as the center line, the section to be grinded on the end face shall be crescent shaped, the section to be grinded on the column body shall be a right triangle in front along the axial direction, and the parabola distribution shall be seen on the side, that is, the maximum grinding thickness on the end face is the end face center deviation, and the grinding thickness at the root shall be 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. During the grinding, the auxiliary butterfly plate is fixed vertically. First, the angle phase grinder is used for rough grinding, and then the file is used for fine grinding to make smooth transition. After meeting the closure requirements, the cylinder body shall be polished with 400 mesh abrasive cloth to improve the surface finish as much as possible. Test the axial grinding straightness of the grinding part of the cylinder body with the light transmission method. In order to facilitate the grinding of the column body, the deflection direction of the guide column should be vertical and upward. After the local preliminary grinding treatment, the main and auxiliary butterfly plates shall be subject to no external force closing test, and then the grinding treatment shall be conducted according to the contact range between the guide column and the positioning hole until the main and auxiliary butterfly plates are closed tightly and evenly and are assembled without jamming. Finally, the cylinder body is polished to improve the surface finish.

According to the analysis of the grinding amount, the maximum grinding section accounts for about 13% of the section area, and the grinding section transits from the approximate ellipse to the circle gradually. Although the rigidity of the guide column is reduced, it can meet the rigidity requirements of the valve switch.

epilogue

Butterfly valve (hereinafter referred to as water intake valve) is a common water intake equipment for small-scale water turbine generator set. Compared with gate type water intake equipment, butterfly valve has the advantages of simple structure, low project cost, reliable work, easy installation, easy operation and maintenance, and is widely used in small-scale hydropower projects. Fengman Power Plant uses 1 × 2 and 2 × water turbine generators with one pipe and two units, which share one butterfly valve water intake equipment and are set in the dam body. The valve is a disc vertical shaft butterfly valve with a nominal diameter of DN1600mm. During the overhaul, the auxiliary butterfly plate of the valve cannot be completely closed with the main butterfly plate due to the deflection of the guide column. The normal operation of the valve is restored by analyzing the cause of the failure and proper treatment.

The water intake valve is composed of driving mechanism, butterfly plate and valve seat body. The driving mechanism is gear transmission and manual operation, which is composed of gear pair driving the main butterfly plate to rotate, gear pair driving the horizontal displacement of auxiliary butterfly plate and slider reversing device. The butterfly plate is composed of separable main butterfly plate and auxiliary butterfly plate. The auxiliary butterfly plate is guided and positioned by the guide column (brass material) inside and the positioning hole (copper sleeve) inside the main butterfly plate, and the horizontal displacement of the auxiliary butterfly plate is realized by the reversing transmission device inside the butterfly plate. The valve seat body is composed of the valve seat and the upper cover, which supports the driving mechanism and the butterfly plate and seals the valve chamber, and both sides are connected with the steel pipe. During valve maintenance and disassembly, it was found that there was a gap between the sealing surfaces of the main and auxiliary butterfly plates due to inclusion of foreign matters. Although the auxiliary butterfly plates were forced to close by external force, the gap still existed. If the butterfly plate is used in the pipeline for a long time, the butterfly plate will be in vibration state, affecting the safe operation of the valve.

According to the analysis of valve structure, the main and auxiliary butterfly plates are steel castings with thickness greater than 50mm, which are not easy to deform. The positioning hole is embedded in the main butterfly plate by thick wall copper tube, which is not easy to deform. The guide column of the auxiliary butterfly plate is a cantilever structure, which is hot riveted on the auxiliary butterfly plate. Its rigidity is relatively low, and it is easy to produce deflection deformation in the cantilever part. Judging from the circumferential distribution and shape of the clearance on the sealing pair, the formation of the clearance is the forced closing (valve opening) operation under the condition that the main and auxiliary butterfly plates are clamped with foreign matters, so that the four guide columns of the auxiliary butterfly plates deflect to the opposite side of the clearance, resulting in the deviation between the guide column and the auxiliary butterfly plates.

Treatment plan

stainless steel Check valve

After the treatment of the valve guide column, 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 flows, meeting the operation requirements of the water intake valve. During the use of the valve after maintenance, the valve was opened and closed for 4 times in total, no abnormal phenomenon was found, and there was no obvious liquid leakage at the packing box of the upper cover of the valve seat, which indicated that the vibration of the butterfly plate in the flow passage was significantly lower than that before maintenance, and also indicated that the grinding process of the guide column was feasible.