According to the needs of operation and overhaul of hydropower stations, in the water diversion system of hydraulic turbines, corresponding gates or valves are usually installed on the water diversion pipes of the hydraulic turbine or in front of the volute, and the valves in front of the volute of the turbine are called inlet valves. The butterfly valve is a commonly used inlet valve. The butterfly valve is mainly composed of a hydraulic annular servo, a bypass valve, a cylindrical valve body, a valve pivoting around its axis, and other components. Under the action of the hydraulic annular servo, when the butterfly valve is closed, the circumference of the valve contacts with the valve body to close the water flow path; when it is opened, the flow direction of the valve is parallel, and the flow of water flows around the valve. Compared with other types of inlet valves, butterfly valves have the advantages of simple structure, small size, light weight, low cost, and easy operation. The disadvantage is that the valve affects the flow state of the water and the hydraulic loss is large. Among the components of the butterfly valve, the hydraulic annular servo is the main component of the operating valve, and its working performance will directly affect the safe and stable operation of the hydraulic turbine generator set.
2. Electric butterfly valve switching operation principle
The opening and closing of the butterfly valve is completely accomplished by the rotation of the hydraulic annular servo. The power of butterfly valve hydraulic annular servo mainly comes from the hydraulic system. The hydraulic pressure operating system consists of two pressure oil pumps, oil valves, hydraulic valves, four-way slide valves, and oil pipelines. The hydraulic annular servo consists of a butterfly valve spindle, an annular cylinder, a piston, an action arm, a half-key, a partitioned baffle, and an oil discharge hole. The butterfly valve and the main shaft are integrated, and the main shaft is connected to the acting arm by means of a half key. Under the effect of pressure oil, the hydraulic annular servomotor uses the main shaft of the butterfly valve as the rotation center to move along the annular cylinder, and then pushes the main shaft of the butterfly valve through the action arm connected with the piston, and the spindle drives the valve to rotate so as to achieve the opening and closing of the butterfly valve. the goal of.
The reason why the butterfly valve's opening and closing process selects the hydraulic annular servo to operate is because of the outstanding advantages of the hydraulic annular servo: In the fixed axis rotary drive, the initial and limit zones of the straight cylinder servo drive can be overcome. The shortcomings of the force arm and the dispersion of the force. However, the relative position of the annular servo cylinder body and the butterfly valve spindle, that is, the concentricity of the center of the annular cylinder body and the butterfly valve spindle, the verticality of the cylinder center annular plane and the axis of the butterfly valve spindle, is difficult to manufacture and process. Guaranteed.
3. Problems in the process of switch of electric butterfly valve and its treatment measures
Butterfly valve diameter of 1.75m, relying on two hydraulic annular servo operation. Due to the rigid connection between the piston and the working arm of the hydraulic annular servomotor, there is a seal between the piston and the cylinder. The main function of the seal is to prevent the leakage of pressure oil in the oil chamber. When operating, the hydraulic annular servo piston rotates in the cylinder body under the action of pressure oil, thereby driving the spindle to rotate to achieve the purpose of opening and closing the valve. In the process of use, the hydraulic annular servo often has some problems in the operation of the butterfly valve valve, so that the opening and closing of the valve can not be normally performed, and the opening or closing of the valve is once, ranging from several minutes to as many as ten minutes, and sometimes it is not at all. Can not open or close, this seriously threatens the safe and stable operation of the unit. The inspection found that the main reason is due to the eccentric wear of the piston and the annular cylinder, and the larger the diameter of the eccentric grinding point. This not only causes great resistance to the movement of the piston, but also leaks a large amount of oil pressure in the gap. The lack of force on the main shaft and the valve causes the butterfly valve to open and close. The reason for the analysis is mainly because the relative position error of the annular cylinder body and the butterfly valve spindle is too large to cause serious damage to the piston.
In the process of transforming the butterfly valve hydraulic annular servo, the connection form of the action arm and the piston is mainly changed from a rigid connection to an elastic connection, so that the piston can automatically generate a radial displacement in the movement along the annular cylinder. The arm that can be used to take action is not limited by its rigidity, but can also automatically adjust the misalignment in manufacturing and installation, thereby improving the working performance of the hydraulic annular servo and achieving satisfactory results.
Due to the limitation of machining, the thrust disc on the piston was mainly processed. Fit the thrust disk with the shaft and hole of the action arm, and change from the original transition joint to the dynamic match to ensure that the radial displacement of the thrust disk is greater than or equal to 2mm, and still use the 6 M16 screw holes of the action arm shaft end , increase the connection between the thrust plate and the action arm; the matching clearance between the quasi-20 points of the bolt 2 and the hole Φ30 should be less than 2.5mm, and the axial clearance is 0.05-0.1mm, so as to ensure that the piston is not blocked when moving radially, but also The axial displacement is controlled, and the sealing cover 1 and the sealing gasket 3 are pressed by a screw and a thrust disk to form a sealing device.
4. Conclusion
Butterfly valve hydraulic annular servo piston after processing, the manual operation test, in the no-load state, butterfly valve opening and closing time only 15s; in the static state, the butterfly valve to open and close once takes 18 ~ 25s, greatly reducing the open Turn off the time, and the butterfly valve opens and closes smoothly, and there is no oil leakage in the hydraulic annular connector. After the automatic system is formed, the butterfly valve can be quickly and reliably closed under the condition that the water guide mechanism is out of control, which creates favorable conditions for the safe and stable operation of the unit.
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