Common fault analysis and solutions for pilot solenoid valves

In the case of the electromagnetic head of the electromagnetic pilot valve (no output force of the electromagnetic head), the force of the spring acts on the stem, and the stem presses the valve core on the seat and keeps the seal. When the electromagnetic head is energized, the lifting force is generated, the force of the spring is overcome, the stem is lifted, the spool is separated from the valve seat, and the system medium is discharged.
1. Valve position indicator
2. Electromagnetic head
3, yoke
4. Spring
5. Formation of stem valve core
6. Valve body
7, seat
Common malfunction of pilot solenoid valve
1, the upper pin hole of the valve core is worn, and the inner side of the pin hole has a more obvious groove formed by the grinding pressure. The micro morphology shows the features of the abrasive debris and short scratches, and the edge of the grinding mark is the shape of the metal debris which is squeezed and rolled. There are obvious wear marks at the bottom of the inner cavity of the valve core and the adjusting screw, and a circular pit is formed by the middle position. The micromorphology shows the microscopic characteristics such as exfoliation and corrosion of micropores.
2, there is partial wear on the outer surface of the stem only, and there is partial exfoliation, and the local area leaves the groove characteristics which are basically parallel to the axial direction. It can be considered that there is a circumferential relative motion between the valve core and the stem.
3. There are obvious wear and grooves on the ends of the pins, and visible micro spalling and scratching on the surface.
Cause analysis of pilot solenoid valve
After testing, the chemical composition of the valve core, stem, adjusting screw and pin material is consistent with the technical requirements of the design. The hardness test results show that the hardness of the adjusting screw is about 280HV, the hardness of the spool is about 440HV, the stem hardness is about 500HV, and the pin hardness is about 550HV. The analysis determines that when the valve is opened, the components, such as the valve core, produce small vibration and relatively small rotation along the circumference, resulting in the local wear of the pin, pin hole and the outer surface of the valve stem. For adjusting screw thread parts, macro analysis and microscopic analysis show that the location is mainly caused by contact fatigue failure. Due to a certain gap in the thread connection, the direct contact and relative motion of the metal surface under the contact stress and the vibration load caused by the leakage cause the surface of the screw thread with relatively low hardness to be exfoliated (the results of energy spectrum analysis show that the wear surface has migrated the metal). The flaking debris and the shedding particles of the matrix also cause abrasive wear on the surface and corrosion wear at the same time, resulting in failure of the threaded part. Metallographic analysis shows that there are obvious deformation rheology marks on the outer surface of the threaded part, which indicates that the thread part has greater stress. To adjust the corrosion spot and corrosion spot at the screw thread, and after the pilot valve is opened for a long time, the electromagnetic head is maintained to produce magnetism, which causes the difference in the electrode potential between the adjusting screw and the stem material, so that the electrochemical corrosion between the screw thread and the stem increases the failure of the thread. For adjusting the top of the lower end of the screw, the difference between the electrode potential of the valve core and the adjusting screw leads to the surface roughness and the decrease of the contact strength caused by the electrochemical corrosion in the valve core, resulting in the adhesive wear between the top of the screw and the contact surface of the valve core. (the metal produced on the surface of the wear surface can also be seen in the spectrum analysis. Migration), with the axial vibration load caused by the leakage and the continuous action of the circumferential rotation load, the top of the soft screw will be steadily leveled along with the adhesion wear, which eventually leads to the failure of the screw contact end. Failure analysis of components shows that failure is not caused by one-way high load, but a cyclic load (such as vibration) phenomenon.
Improvement measures of pilot solenoid valve
In order to eliminate the vibration problem of the spool assembly, the effective method is to eliminate the free movement of the spool when the pilot valve is in an open state. Therefore, the valve core component has been improved.
1. Cancel the upper seal of the stem, increase the cylinder length of the spool, and control the stroke of the valve with the spool and the stem sleeve.