Experiment study of noise in a flapper-nozzle valve under pulsing inlet pressure of the nozzle

The flapper-nozzle valve as the pilot stage of an electrohydraulic servo-valve used in the hydraulic control system is often troubled by the self-excited noise. The pressure pulsation can induce the oscillation of the flow field in the flapper-nozzle valve. This paper presents an experiment study of noise characteristics in a flapper-nozzle valve at sixteen different flow conditions with various inlet pressure pulsation conditions at different mean inlet pressures, 6 MPa, 8 MPa, 10 MPa and 12 MPa of the nozzle. In the experiments, for each mean inlet pressure of the nozzle, four groups inlet pressure pulsation conditions of the nozzle are considered. The pressure pulsation characteristics at the nozzle inlet and in the chamber of the flapper-nozzle valve and noise characteristics are measured and analyzed by using FFT method. Then, the comparisons of pressure pulsation characteristics and noise characteristics for these sixteen different inlet pressures (including all the mean inlet pressures and inlet pressure pulsation conditions) are carried out. The results confirm that the noise and pressure pulsation in the chamber of the flapper-nozzle valve are increased with the increment of the mean inlet pressures and inlet pressure pulsation conditions of the nozzle. This study reveals that the flow-acoustic resonance and resulting self-excited noise felt as squeal noise may occur when the pressure pulsation in the chamber of the flapper-nozzle valve is sufficient larger at the particular frequency.