Poppet vibration and cavitation, two representative phenomena in relief valves, are considered as the roots of the violent noise, erosion, and structure damage. In this paper, the interactions between the poppet vibration characteristics and cavitation property in relief valves with the unconfined poppet are investigated experimentally. Tests have been performed in stable and unstable valves under cavitation and noncavitation conditions. The valve housing is fabricated by Perspex for flow visualization. As for the influence of cavitation on vibration characteristics, it is found that the generated cavitation bubbles in the downstream circuit decrease the flow coefficient and fluid viscosity, and decrease the hydrodynamic spring in turn. The location of cavitating flow, characterized by the low local pressure, changes the thrust on poppet and poppet lift, affecting the radial stiffnesses of mechanical spring and hydrodynamic spring, respectively. On the other hand, as for the influence of vibration on cavitation property, it is found that the poppet vibration leads to a dramatic increase of the noise comparing to the fixed poppet conditions. Spectrum analysis shows that augmented noise in unstable valves mainly comes from the intensification of cavitation noise. A reason for this is that the vibration of poppet leads to a quick and violent collapse of large amount of cavities developed from the throttling region, which should be performed as attached cavities and avoided from collapse in the stable poppet conditions.

The poppet valve is a fundamental component in fluid power systems. Under particular conditions, annoying "squeal" noises may be generated in hydraulic poppet valves. In the present study, the frequency spectrum of the squeal noise is obtained by analyzing the sampling data from the accelerometer mounted on the valve body. It is found that the flow velocity, pressure, and structural parameters have crucial effects on the properties of squeal noise, especially frequency. Larger valve chamber volume or lower backpressure leads to lower fundamental frequency of the squeal noise. An explanation for the squeal noise, as a result of Helmholtz resonance, is suggested and proved by experimental results.