In the electromagnetic pilot valve (below) electromagnetic head is not energized (electromagnetic head no output force), the role of the spring force acting on the stem, the stem will be the valve stem on the valve seat and keep the seal. When the solenoid energized produce lifting force to overcome the spring force, the valve stem lift valve stem off the valve seat, the system media emissions. 1, the valve position indicator 2, the electromagnetic head 3, the yoke 4, the spring 5, the valve stem valve assembly 6, the valve body 7, seat pilot solenoid valve common fault 1, the upper pin hole wear, pin hole inside There are obvious grooves formed by pressure reduction. The micro-morphology shows the characteristics of wear debris and short scratches. The edge of the wear scar is the shape of squeezed and rolled metal debris. The contact between the bottom of the valve core cavity and the adjustment screw shows obvious signs of abrasion. A circular depression is formed by the middle position. The microscopic appearance shows the microscopic characteristics such as peeling and corrosion of micropores. 2, the valve stem only partial wear on the outer surface, there is some spalling, the local area left with a substantially parallel axial groove features can be thought of the spool and the valve stem relative movement between the existence of the circumferential. 3, both ends of the pin have obvious wear and groove, the surface has visible flaking and short scratches and other microscopic features. Pilot solenoid valve Analysis After testing, the chemical composition of the valve plug, stem, adjusting screw and pin material are consistent with the design requirements. Hardness test results show that the adjustment screw hardness of about 280HV, spool hardness of about 440HV, stem hardness of about 500HV, pin hardness of about 550HV. The analysis confirmed that when the valve is opened, the valve core and other components produce slight vibration in the axial direction and relatively small circumferential rotation, resulting in partial wear of the pin, the valve pin hole and the outer surface of the valve rod. For the screw thread adjustment site, macroscopical analysis and microscopic analysis showed that the site is mainly due to fatigue caused by contact fatigue. Due to the existence of a certain gap in the threaded connection, the direct contact and the relative movement of the metal surface caused by the contact stress and the vibration load caused by the leakage can cause the screw thread surface with relatively low hardness to peel (energy spectrum analysis results show that the worn surface Metal migration occurred). Peeling debris and matrix off the particles in turn make the surface of the abrasive wear, both corrosion and wear, resulting in the failure of the thread. Metallographic analysis shows that the outer surface of the thread portion has obvious deformation and deformation traces, indicating that there is a greater stress on the thread portion. Adjusting the screw thread corroded pitting and corrosion spots, coupled with long-term pilot valve open, the magnetic head to maintain its magnetic charge, causing the adjustment screw and stem material between the electrode potential differences, so that the adjustment screw thread at the stem Electrochemical corrosion accelerates the failure at the threads. For the top of the lower end of the adjusting screw, due to the difference in electrode potential between the valve core and the adjusting screw, electrochemical corrosion of the valve core causes surface roughness and contact strength to drop, resulting in adhesive wear between the top of the adjusting screw and the valve core Spectrum analysis can also be seen on the wear surface of metal migration), with the leakage caused by the axial vibration load and the continuous role of the circumferential rotation load, the softer screw top will continue with the adhesive wear leveling flat, and ultimately Leading to failure of the screw contact end face. Failure analysis of the components shows that the failure is not due to one-way high load, but rather a cyclic load such as vibration. Pilot Solenoid Valve Improvements In order to eliminate the vibrations of the spool assembly, an effective method is to eliminate the spool's freedom of movement when the pilot valve is open. Therefore, the spool assembly has been improved. ①cancel the valve stem on the seal, the spool of the cylinder length increases to spool and stem sleeve control valve stroke. ② remove the adjustment screw, no longer adjust the screw to adjust the valve stroke, to avoid the material caused by different electrode potential difference caused by electrochemical corrosion. Stem lengthened, the top of the round head, the material is still used Inconel, close to the spool material. ③ pin diameter Φ3mm increased to Φ5mm, increased strength, in order to open the valve in the valve stem under the force transmitted to the spool, the spool seal on the valve stem sleeve to prevent the valve open The valve core vibrates in the case of steam flow. The valve stroke is adjusted by the length of the cylinder body. In the early stage of the pilot valve assembly, the stroke is controlled by the inverted seal end of the valve body and the pilot valve stroke is controlled to be negative. The valve seat and seat sealing surface are ground After its stroke to take positive deviation, so that even if the valve core and seat sealing surface after grinding can also ensure that the pilot valve stroke within the allowable error range. After the improvement of the valve core assembly, a pilot switch valve with a new structure was tested for switching emissions through the thermal test bench 500 times. After the test was completed, the spool assembly was disassembled, no signs of abrasion caused by vibration. After three months of actual operation on site, disassembly and inspection were carried out. The pilot valve was in good condition and no abrasion marks were found on the spool parts. This proves that the defect that the solenoid pilot valve can not be opened for a long time has been eliminated. 1, Valve position indicator 2, Electromagnetic head 3, Yoke 4, Spring 5, Valve stem assembly 6, Valve body 7, Valve seat