Leakage reasons and treatment of electric release valve

The reason for the leakage of the imported 102 -TAL MATIC electric release valve was analyzed. Through the corresponding improvement, effectively solve the valve leakage problem, to ensure the performance of the valve. 1. Introduction Huaneng Nantong Power Plant's No. 1 and No. 2 boilers are sub-critical, intermediate reheat and natural circulation coal-fired boilers manufactured by the United States B & W Company. The rated boiler evaporation capacity is 1085.1 t / h. In the boiler drum, superheater outlet and reheater import and export with spring-loaded safety valve. In order to ensure the performance of the superheater safety valve installed in the main steam outlet pipe installed in foreign-made 102-TAL MATIC electric release valve. The valve rated operating pressure of 18.476MPa, back seat pressure of 17.897MPa, emissions of 119t / h. The valve lift pressure and seat back pressure can be automatic and manual operation, and emissions smaller. Therefore, it has an important role in protecting the safe and economical operation of boilers. However, when the unit was put into operation, the leakage of the electric release valve occurred more frequently, which affected the working performance of the valve and threatened the safe operation of the boiler. 2, working principle Electric release valve by the main valve, control valve and control device 3 parts (Figure 1). Steam from the main valve inlet into the gap between the main valve body and the valve chamber bushing through the upper part of the valve chamber bushing into the valve cavity, one part of the valve flap, the other part of the valve into the control valve. When the control valve is closed, the force F1 applied to the underside of the valve flap by the steam is greater than the force F2 acting on the perimeter above the valve flap, keeping the main valve sealed (Figure 2). When the main steam pressure reaches the value of electric release valve action, the electric contact pressure gauge connected to the control part of the solenoid coil power supply. Strong magnetic field generated by the electromagnetic coil will push the core down, acting on the lever, the control valve opens. At the same time the role of the main valve flap below the steam through the steam pipe and control valve into the atmosphere, the main valve to lose the role of pushing up force, then the role of the main valve flap above the main valve flap steam valve pushed down to open the main valve, Vapor discharge to the air. When the pressure drops to 17.897MPa, that is, the pressure of the electric release valve returns to the seat, the control valve coil will lose power and the iron core will move upward. The control valve rod will move up by the force of the spring, and the control valve will return to seat and the main valve will close. 3, Analysis of Leakage 3.1 Control Valve Lever adjustment screw and stem for point contact, the center of the adjustment screw from the main valve center is less than the center of the control valve stem and the center distance of the main valve about 0.5mm (Figure 3). This shows that the two parts center is not in the same central axis. The main steam pipe due to changes in steam flow will occur in varying degrees of vibration, causing the lever up and down movement, driven by adjusting screw hit the valve stem, and valve stem deformation (control valve spring and steam will control the valve stem upward push force only Can overcome the impact of adjusting screw force, can not overcome the stem deformation force), the sealing surface displacement, causing leakage. 3.2 The main valve gasket main valve nozzle contact with the main valve seat is greater than the contact surface of the main valve seat and gasket, the friction between the nozzle and the valve seat is greater than the friction between the main valve seat and gasket. So tightening the compression nut, due to friction differences so that the main seat along with the transfer, so that the drain pipe hit the body hydrophobic pipe wall, resulting in lack of seat on the seat gasket caused by the main valve gasket leakage. 3.3 The main valve sealing surface Because the size of the air valve in the system is smaller than the diameter of the drain valve, when the boiler is under pressure and discharging water, the system will generate a short negative pressure and the main valve siphon (buffer spring can not be overcome) Oxide within the drain valve above the valve falls, embedded between the valve disc and seat sealing surface, resulting in leakage. 4, improvement 4.1 adjustment screw will lever adjustment screw spherical to plane, about 2 spherical point and point of contact instead of plane contact with the point (Figure 4), the plane roughness Ra <0.08μm, the choice of screw material 2Cr13, by Oil quenching. This not only enhances the hardness and oxidation resistance of the adjusting screw plane, but also ensures the action performance due to the smoothness of the surface to reduce the friction force between the plane and the valve rod spherical surface when moving relative to each other. 4.2 Assembly Process When reassembling the valve, do not install the drain pipe. A little viscosity between the nozzle, the valve seat and the compression nut oil, through the main valve body drain hole into the main valve seat hydrophobic hole in a Φ6mm iron bar and stuck counterclockwise to be pressed After the tight nut is tightened, remove the iron rod. This ensures that the main valve of the hydrophobic flow. Electric release valve parts grinding abrasive grinding, the surface Ra <0.08μm. Control valve stem and seat sealing surface contact surface should be more than 80% of its width. Parts should be carefully cleaned, the valve can not be foreign objects, the valve shall not be opened before operation. 4.3 Operation method Whenever the boiler is shut off with pressure and water is discharged, the pressure of the system is reduced to 0.588 ~ 0.785MPa, and the brake release valve and its bypass valve of the electric release valve are closed. 5. Conclusion After the improvement, the leakage of the electric release valve is reduced. In addition to the normal maintenance work, the maintenance work on the valve needs only 1 or 2 times a year. To improve the 1/6 of the previous workload, Safe and economical operation