Common faults of overflow valves in use include noise, vibration, radial clamping of valve core, and pressure regulation failure.

（1） Noise and vibration

The components that are prone to noise in hydraulic devices are generally considered to be pumps and valves, with relief valves and electromagnetic directional valves being the main ones in valves. There are many factors that can generate noise.

The noise of the overflow valve can be divided into two types: flow velocity sound and mechanical sound. The flow velocity noise is mainly caused by oil vibration, cavitation, and hydraulic impact. Mainly in mechanical sound

Noise generated by the impact and friction of components in the valve.

(1) Noise caused by uneven pressure

The pilot valve part of the pilot relief valve is a vibration prone area as shown in Figure 3. When overflow occurs under high pressure, the axial opening of the pilot valve is very small, only 0.003~

0.006 centimeters. The overcurrent area is very small and the flow velocity is very high, up to 200 meters per second, which can easily cause uneven pressure distribution, resulting in unbalanced radial force of the cone valve and vibration. another

The ellipticity, dirt sticking to the guide valve port, and deformation of the pressure regulating spring generated during the processing of the outer cone valve and cone valve seat can also cause vibration of the cone valve. So it is generally believed that the pilot valve

It is the vibration source where noise occurs.

Due to the presence of elastic elements (springs) and moving mass (cone valves), a condition for oscillation is formed, and the front chamber of the pilot valve also serves as a resonant chamber

As a result, the vibration of the cone valve can easily cause resonance and noise throughout the valve, which is usually accompanied by severe pressure fluctuations.

(2) Noise generated by voids

When air is sucked into the oil due to various reasons, or when the oil pressure is lower than atmospheric pressure, some of the air dissolved in the oil will precipitate and form bubbles

These bubbles have a larger volume in the low-pressure zone, but when they flow with the oil to the high-pressure zone, they are compressed and their volume suddenly decreases or the bubbles disappear; On the contrary, if in the high-pressure zone

The volume is originally small, but when it flows into the low-pressure zone, the volume suddenly increases, causing a rapid change in the volume of bubbles in the oil. Sudden changes in bubble volume can generate noise

Sound, as this process occurs instantaneously, will cause local hydraulic shock and vibration. The pilot valve port and main valve port, oil flow rate and pressure of the pilot relief valve

The changes are significant, and it is easy to experience cavitation, resulting in noise and vibration.

(3) Noise generated by hydraulic impact

The pilot operated relief valve will produce pressure shock noise during unloading due to a sudden drop in pressure in the hydraulic circuit. The higher the working conditions with high voltage and large capacity, the more this impact

The greater the impact noise, the more hydraulic shock is generated due to the short unloading time of the relief valve. During unloading, the rapid change in oil flow rate causes a sudden change in pressure, resulting in

The impact of pressure waves. A pressure wave is a small shock wave that produces very little noise, but when transmitted to the system with the oil, if it is the same as any mechanical component

Resonance may increase vibration and enhance noise. So when hydraulic shock noise occurs, it is usually accompanied by system vibration. (4) Mechanical noise

The mechanical noise emitted by pilot operated relief valves generally comes from the impact of parts and friction caused by machining errors.

In the noise emitted by the pilot operated relief valve, there may sometimes be mechanical high-frequency vibration sound, which is generally referred to as self-excited vibration sound. This is due to high-frequency vibration of the main valve and pilot valve

The sound that occurs while moving. Its incidence is related to factors such as the configuration, flow rate, pressure, and oil temperature (viscosity) of the return oil pipeline. In general, when the diameter of a pipeline is small

Low flow rate, high pressure, and low oil viscosity result in a high incidence of self-excited vibration.

The measures to reduce or eliminate the noise and vibration of the pilot relief valve are generally to add vibration damping elements in the pilot valve section.

The vibration damping sleeve is generally fixed in the front chamber of the pilot valve, which is the resonance chamber, and cannot move freely.

There are various damping holes on the vibration damping sleeve to increase damping and eliminate vibration. In addition, due to the addition of components in the resonance chamber, the volume of the resonance chamber is reduced, and the oil

When the stiffness increases under negative pressure, according to the principle that components with high stiffness are less likely to resonate, the possibility of resonance can be reduced.

The vibration damping pad is generally coordinated with the resonant cavity and can move freely. There is a throttling groove on both sides of the vibration damping pad, which can produce damping effect when the oil flows, in order to improve the damping effect

Change the original flow situation. Due to the addition of vibration damping pads, a vibration element was added, which disrupted the original resonance frequency. The resonant cavity has added vibration damping pads, which also reduce

Reduced volume increases the stiffness of the oil under pressure to reduce the possibility of resonance.

There are gas storage small holes and throttling edges on the vibration damping screw plug. Due to the presence of air in the gas storage small holes, the air is compressed under pressure, and the compressed air has a vibration absorbing effect, which is quite significant

In a miniature vibration absorber. When the air is compressed in the small hole, the oil is filled in, and when it expands, the oil is squeezed out, which adds an additional flow to change the original flow

Dynamic situation. Therefore, it can also reduce or eliminate noise and vibration.

In addition, improper assembly or use of the overflow valve itself can also cause vibration and noise. Like a three section concentric relief valve, when assembled, the three sections are the same

Improper coordination of the heart, excessive or insufficient flow during use, abnormal wear and tear of the cone valve, etc. In this case, careful inspection and adjustment, or replacement of parts, should be carried out.

（2） Radial clamping of valve core

Due to the influence of machining accuracy, the main valve core is radially clamped, causing the main valve to fail to open and release pressure or close without releasing pressure. In addition, radial clamping is caused by pollution.

（3） Pressure regulation failure

The overflow valve may sometimes experience pressure regulation failure during use. There are two situations where the pilot relief valve fails to regulate pressure: one is that the pressure regulating handwheel cannot be established

Pressure, or pressure not reaching the rated value; Another way is to adjust the pressure of the handwheel without decreasing, and even continuously increase it. Pressure regulation failure occurs, except for valve core caused by various reasons

There are also some reasons for tightening, such as:

The first is that the damper of the main valve body (2) is blocked, and the oil pressure cannot be transmitted to the upper chamber of the main valve and the front chamber of the pilot valve, causing the pilot valve to lose its regulating effect on the pressure of the main valve. Due to the main valve

There is no oil pressure in the upper chamber, and the spring force is very small, so the main valve has become a direct acting relief valve with very small spring force. When the pressure in the inlet chamber is very low, the main valve

Open the overflow, the system cannot establish pressure.

The reason why the pressure cannot reach the rated value is that the pressure regulating spring is deformed or selected incorrectly, the compression stroke of the pressure regulating spring is insufficient, the internal leakage of the valve is too large, or the cone of the pilot valve part

Excessive wear and tear of valves, etc.

The second reason is that the damper (3) is blocked, and the oil pressure cannot be transmitted to the cone valve, causing the pilot valve to lose its ability to regulate the pressure of the main valve. After the damper (small hole) is blocked,

Under any pressure, the cone valve will not open to overflow oil, and there is always no oil flow inside the valve. The pressure in the upper and lower chambers of the main valve is always equal, due to the annular pressure surface at the upper end of the main valve core

The accumulation is greater than the lower annular pressure bearing area, so the main valve is always closed and will not overflow. The pressure of the main valve increases with the increase of load. When the executing mechanism stops working

The overall pressure will increase infinitely. In addition to these reasons, it is necessary to check whether the external control port is blocked and whether the cone valve is installed properly.

（4） Other faults

During the assembly or use of the overflow valve, damage to the O-ring or combination seal, or loosening of the installation screws or pipe joints may cause the valve to malfunction

The leakage of information.

If the wear of the cone valve or main valve core is too large, or if the sealing surface has poor contact, it will also cause excessive internal leakage and even affect normal operation.

Common faults of electromagnetic overflow valves include pilot solenoid valve failure, main valve pressure regulation failure, and impact noise during unloading. The latter can be adjusted by adding buffering

Use tools to reduce or eliminate. If there is no buffer, a back pressure valve can be added to the overflow port of the main valve. (The pressure is generally adjusted to around 5kgf/cm2, which is 0.5MPa).