product knowledge

Common faults of relief valves in use include noise, vibration, radial stuck valve core, pressure regulation failure, etc.

(1) noise and vibration

The noise-prone components in hydraulic devices are generally regarded as pumps and valves. The valves are mainly relief valves and electromagnetic directional valves. There are many factors that generate noise. Noise from the relief valve includes flow rate sound and mechanical sound. Flow velocity noise is mainly caused by oil vibration, cavitation and hydraulic impact. Mechanical noise is mainly caused by the impact and friction of parts inside the valve.

(2) Noise caused by uneven pressure

The pilot valve part of the pilot relief valve is a part that is prone to vibration. During high-pressure relief, the axial opening of the pilot valve is very small, only 0.003~ 0.006 cm. The overflow area is small and the flow rate is high, as high as 200m/s, which may easily cause unbalanced radial force on the cone valve, resulting in uneven pressure distribution and vibration. In addition, the ovality generated during the processing of conical valves and conical seats, the adhesion of dirt on the pilot valve port, and the deformation of the pressure regulating spring can also cause vibration of the conical valve. Therefore, pilot valves are generally considered to be a vibration source of noise.

Due to the presence of the elastic element (spring) and the moving mass (conical valve), it constitutes a condition for vibration, and the front cavity of the pilot valve acts as a resonant cavity. Therefore, the vibration of the conical valve can easily cause resonance and noise of the entire valve. Noise is usually accompanied by severe pressure jumps.

(3) Noise generated by holes

When air is sucked into the oil for various reasons, or when the oil pressure is lower than atmospheric pressure, part of the air dissolved in the oil will precipitate and form bubbles. These bubbles are very large in the low pressure region. When they flow with the oil to the high-pressure zone, they are compressed and the volume suddenly decreases or the bubbles disappear; on the contrary, if the volume is originally small in the high-pressure zone, but when it flows to the low-pressure zone, the volume suddenly increases, the volume of the bubbles in the oil changes rapidly. Sudden changes in bubble volume produce noise, and since this process occurs instantaneously, local hydraulic shocks and vibrations can be caused. At the pilot port and main port of the pilot relief valve, the oil flow and pressure vary greatly, which is prone to cavitation, noise and vibration.

(4) Noise caused by hydraulic impact

When the pilot relief valve is unloaded, pressure impact noise will occur due to the sudden drop in the pressure in the hydraulic circuit. The higher the high-pressure and large-capacity working condition, the greater the impact noise caused by the hydraulic impact caused by the short unloading time of the relief valve. During unloading, sharp changes in oil flow rate will cause sudden changes in pressure and impact of pressure waves. The pressure wave is a small shock wave that produces very little noise by itself, but it is transmitted into the system with the oil. If resonance occurs with any mechanical part, it may increase vibration and noise. Therefore, when hydraulic impact noise occurs, it is usually accompanied by system vibration.