Experimental study on the correlation between erosion microstructure and performance degradation of hydraulic servo spool valve

Surface topography plays an important role in determining the performance of hydraulic components, which often leads to component failure. The dual nozzle electro-hydraulic servo valve is composed of torque motor, pilot nozzle flapper valve and servo spool valve, whereas the failure is at the level of servo spool valve. In more details, the degradation of the static characteristic parameters of the hydraulic servo valve, which is experimentally studied by artificially controlling the fillet radius of the spool working edges, is one of these failures. In addition, the microstructure characteristics of the MOOGJ761 valve working edges and the circumferential distribution law of the fillet radius are obtained. The research shows that valve orifice erosion caused fillet on the working edges and increases the dispersion of the circumferential distribution. The erosion micromorphology of the working edge is mainly characterized by surface peeling, notches, grooves, and chamfers. The average and variance of the fillet of the spool working edge at the high-pressure oil exceed those of the working edge of the return oil. When the average fillet radius of the working edge increases by 2.71 times and the average fillet variance increases by 2.55 times, the maximum leakage increases by 5.08 times, the flow gain decreases, and the positive and negative flow gains are asymmetric, decreasing by 7.78% and 1.75%, respectively. The pressure gain decreases significantly by 40.30%. The relation between the microstructure of the orifice working edge and the performance degradation provides a new idea for the performance evaluation and manufacture of hydraulic spool servo valve.