Cause analysis and troubleshooting methods of 4 types of failures such as overflow valve noise and pressure regulation failure（1）

Cause analysis and troubleshooting methods of 4 types of failures such as overflow valve noise and pressure regulation failure（1）

When the overflow valve is in use, common faults include noise, vibration, radial clamping of the valve core, and pressure regulation failure. This article shares common failure causes and troubleshooting methods of overflow valves.

1 Noise and vibration

The noise-prone components in hydraulic devices are generally considered to be pumps and valves, and the valves are mainly overflow valves and electromagnetic reversing valves. There are many factors that cause noise. The noise of the overflow valve has two types: velocity sound and mechanical sound. The sound of flow velocity is mainly caused by oil vibration, cavitation and hydraulic shock. The mechanical sound is mainly caused by the impact and friction of parts in the valve.

(1) Noise caused by uneven pressure

The pilot valve part of the pilot-operated relief valve is a vibration-prone part. When overflowing under high pressure, the axial opening of the pilot valve is very small, only 0.003 to 0.006 cm. The flow area is very small and the flow velocity is very high, up to 200 m/s. It is easy to cause uneven pressure distribution and make the cone valve radial force imbalance and vibration.

In addition, the ovality generated during the processing of the cone valve and the cone valve seat, the sticking of the dirt on the pilot valve port and the deformation of the pressure regulating spring, etc., will also cause the cone valve to vibrate.

Therefore, it is generally considered that the pilot valve is the vibration source of noise. Due to the existence of elastic elements (spring) and moving mass (cone valve), it constitutes a condition for generating oscillation, and the front cavity of the pilot valve acts as a resonance cavity. Therefore, the vibration of the cone valve can easily cause the entire valve to fail. Resonance generates noise, and when noise occurs, it is usually accompanied by severe pressure jumps.

(2) Noise generated by holes

When air is sucked into the oil due to various reasons, or when the oil pressure is lower than the atmospheric pressure, part of the air dissolved in the oil will separate out to form bubbles. These bubbles are relatively large in the low pressure area. When the liquid flows to the high-pressure zone, it is compressed and the volume suddenly becomes smaller 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, and the volume of bubbles in the oil is so rapid. The phenomenon of change.

The sudden change of bubble volume will produce noise, and because this process occurs in an instant, it will cause local hydraulic shock and vibration. In the pilot valve port and main valve port of the pilot-operated relief valve, the oil flow rate and pressure vary greatly, and cavitation is prone to occur, resulting in noise and vibration.

(3) Noise generated by hydraulic shock

When the pilot-operated relief valve is unloading, the pressure of the hydraulic circuit will drop sharply, resulting in pressure shock noise. The more high-pressure and large-capacity working conditions, the greater the impact noise. This is due to the short unloading time of the relief valve and the hydraulic shock. During unloading, the sudden change in the oil flow rate causes a sudden change in pressure. The impact of pressure waves.

The pressure wave is a small shock wave, and the noise produced by itself is very small, but when the oil is transmitted to the system, if the resonance occurs with any mechanical part, it may increase the vibration and increase the noise. Therefore, when hydraulic shock noise occurs, it is usually accompanied by system vibration.

(4) Mechanical noise

The mechanical noise emitted by the pilot-type relief valve generally comes from the impact of the parts and the friction of the parts due to machining errors. In the noise emitted by the pilot-type relief valve, there are sometimes mechanical high-frequency vibrations, which are generally called self-excited vibrations. This is the sound of the main valve and pilot valve due to high-frequency vibration.

Its incidence is related to factors such as the configuration, flow, pressure, and oil temperature (viscosity) of the oil return pipeline. In general, if the pipe diameter is small, the flow rate is small, the pressure is high, and the oil viscosity is low, the occurrence rate of self-excited vibration is high. The measure to reduce or eliminate the noise and vibration of the pilot type relief valve is generally to add a vibration absorbing element to the pilot valve part.

The anti-vibration sleeve is generally fixed in the front cavity of the pilot valve, that is, in the resonance cavity, and cannot move freely. There are various damping holes on the vibration absorbing sleeve to increase damping to eliminate vibration. In addition, due to the addition of parts in the resonant cavity, the volume of the resonant cavity is reduced, and the stiffness of the oil increases when the oil is under negative pressure. According to the principle that components with high stiffness are not prone to resonate, the possibility of resonance can be reduced.

The anti-vibration pad generally cooperates with the resonant cavity and can move freely. There is a throttling groove on the front and back of the anti-vibration pad, which can produce a damping effect when the oil is flowing, so as to change the original flow condition. Due to the addition of the anti-vibration pad, a vibration element is added, which disturbs the original resonance frequency. The resonant cavity adds a vibration absorbing pad, which also reduces the volume and increases the rigidity of the oil under pressure to reduce the possibility of resonance.

The vibration absorbing screw plug is equipped with air storage holes and throttle edges. Because the air is left in the air storage holes, the air is compressed when it is pressurized. The compressed air has the effect of absorbing vibration, which is equivalent to a miniature vibration absorber. When the air in the small hole is compressed, the oil is filled in, and when it is expanded, the oil is hydraulically discharged, thus adding an additional flow to change the original flow. Therefore, noise and vibration can be reduced or eliminated.

In addition, if the overflow valve itself is improperly assembled or used, it will also cause vibration and noise. Such as the three-section concentric relief valve, the three sections are not properly matched during assembly, the flow is too large or too small when used, and the cone valve is abnormally worn. In this case, check and adjust carefully, or replace parts.