Common Fault Cause Analysis and Relief Method of Rexroth Relief Valve In the use of the overflow valve, common faults include noise, vibration, radial locking of the valve core and failure of voltage regulation.
(1) Noise and Vibration Components in the hydraulic device that are prone to noise are generally considered to be pumps and valves, and the valves are mainly composed of relief valves and electromagnetic reversing valves. There are many factors that generate noise. The noise of the relief valve is two types of flow sound and mechanical sound. Noise in the flow sound is mainly caused by oil vibration, holes and hydraulic shock. The noise generated by mechanical shock 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 Rexroth pilot type relief valve is an easy-vibration part as shown in Fig. 3. When overflowing under high pressure conditions, the axial opening of the pilot valve is small, only 0.003 to 0.006 cm. The flow area is small, the flow rate is very high, up to 200 m / s, which is easy to cause uneven pressure distribution, causing the radial force of the cone valve to be unbalanced and generate vibration. In addition, the ovality generated during the processing of the cone valve and the cone valve seat, the dirt of the pilot valve port and the deformation of the pressure regulating spring may also cause the vibration of the poppet valve. Therefore, the pilot valve is generally considered to be the source of the vibration source. Due to the presence of elastic elements (springs) and moving mass (cone valve), a condition for generating oscillation is formed, and the front chamber of the pilot valve acts as a resonant cavity, so that the vibration of the poppet valve easily causes the entire valve. Resonance generates noise, and when noise occurs, it is often accompanied by severe pressure jump.
(2) Noise generated by holes When air is drawn 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 to form bubbles, which are in the low pressure zone. When the oil flows to the high pressure zone, it is compressed, and the volume suddenly becomes smaller or the bubble disappears. Conversely, if it is in the high pressure zone, the volume is originally small, and when it flows to the low pressure zone, the volume suddenly increases. The phenomenon of rapid changes in bubble volume in oil. A sudden change in bubble volume produces noise, and as this process occurs in an instant, it will cause local hydraulic shock and vibration. The pilot valve and the main valve port of the pilot type relief valve vary greatly in oil flow rate and pressure, and cavitation is prone to occur, thereby generating noise and vibration. Analysis and troubleshooting of common fault causes of Rexroth relief valve
(3) Noise generated by hydraulic shock When the Rexroth pilot type relief valve is unloaded, pressure shock noise will occur due to a sudden drop in the pressure of the hydraulic circuit. The higher the pressure and the larger the working condition, the larger the impact noise is. This is because the relief time of the relief valve is short and the hydraulic shock is caused. When the unloading occurs, the sudden change of 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 generated by itself is very small, but as the oil is transferred to the system, if it resonates with any mechanical part, it may increase vibration and enhance noise. Therefore, when hydraulic shock noise occurs, it is generally accompanied by system vibration.
(4) Mechanical noise The mechanical noise emitted by the Rexroth pilot type relief valve is generally caused by the impact of the parts and the friction of the parts due to machining errors. Among the noise emitted by the pilot type relief valve, there is sometimes a mechanical high-frequency vibration sound, which is generally called self-excited vibration sound. This is the sound of the main valve and pilot valve due to high frequency vibration. Its incidence is related to the configuration of the return line, flow, pressure, oil temperature (viscosity) and other factors. Under normal circumstances, the pipe diameter is small, the flow rate is low, the pressure is high, the viscosity of the oil is low, and the incidence of self-excited vibration is high. Measures to reduce or eliminate the noise and vibration of the pilot type relief valve are generally to add a vibration damping element to the pilot valve portion. The vibration absorbing sleeve is generally fixed in the front chamber of the pilot valve, that is, in the resonant cavity, and cannot move freely. Various damping holes are provided on the vibration damping sleeve to increase damping to eliminate vibration. In addition, since the components are added to the resonant cavity, the volume of the resonant cavity is reduced, and the rigidity of the oil at the time of the negative pressure is increased. According to the principle that the component having a large rigidity is less likely to resonate, the possibility of resonance can be reduced. The vibration absorbing pad generally cooperates with the resonant cavity and can move freely. The anti-vibration pad has a throttle groove on the front and back sides, and the oil can generate a damping effect when flowing to change the original flow condition. Due to the addition of the vibration absorbing pad, a vibration element is added, disturbing the original resonance frequency. The resonant cavity adds a vibration absorbing pad, which also reduces the volume and increases the stiffness of the oil under pressure to reduce the possibility of resonance. The gas-suppressing plug has a gas storage hole and a throttle edge, and air is trapped in the gas-storing hole, and the air is compressed when pressed, and the compressed air has a vibration-absorbing effect, which is equivalent to a micro-vibrator. When the air in the small hole is compressed, the oil is filled, and when it expands, the oil is hydraulically discharged, thus adding an additional flow to change the original flow. It can also reduce or eliminate noise and vibration. In addition, if the relief valve itself is improperly assembled or used, it will also cause vibration and noise. Such as three concentric relief valves, three sections of concentric mismatch during assembly, excessive or too small flow during use, abnormal wear of the cone valve. In this case, you should carefully check the adjustments or replace the parts.
(2) The radial clamping of the valve core is caused by the machining accuracy, which causes the main valve core to be radially clamped, so that the main valve is not opened or the main valve is closed without releasing pressure, and the radial clamping is caused by pollution.
(III) Pressure regulation failure Rexroth relief valve sometimes has a pressure regulation failure during use. There are two cases of pilot-type relief valve pressure regulation failure: one is to adjust the pressure regulating handwheel to establish pressure, or the pressure does not reach the rated value; the other adjustment hand wheel pressure does not drop, and even continuously boosts. There is a failure of the pressure regulation. In addition to the radial clamping of the valve core due to various reasons, there are the following reasons:
The first is that the main valve body (2) damper is blocked, the oil pressure is not transmitted to the upper chamber of the main valve and the front chamber of the pilot valve, and the pilot valve loses the regulating effect on the pressure of the main valve. Since the upper valve has no oil pressure and the spring force is small, the main valve becomes a direct-acting relief valve with a small spring force. When the pressure in the inlet chamber is very low, the main valve opens. Flow, the system can not build pressure. The reason why the pressure does not reach the rated value is that the pressure regulating spring is deformed or incorrectly selected, the compression spring has insufficient compression stroke, the internal leakage of the valve is too large, or the partial valve of the pilot valve is excessively worn.
The second is that the damper (3) is blocked, the oil pressure is not transmitted to the cone valve, and the pilot valve loses the regulation of the pressure of the main valve. After the damper (small hole) is blocked, the cone valve will not open the overflow oil under any pressure, there is no oil flowing in the valve, the pressure of the upper and lower chambers of the main valve is always equal, because the annular pressure area of ​​the upper end of the main valve core is larger than The lower end of the annular bearing area, so the main valve is always closed, does not overflow, the main valve pressure increases with the increase of load. When the actuator stops working, the system pressure will increase indefinitely. In addition to these reasons, it is necessary to check whether the external control port is blocked, and whether the cone valve is installed well.
(4) Other faults In the assembly or use, the Rexroth overflow valve may cause undue external leakage due to the damage of the O-ring seal, the combined seal ring, or the looseness of the mounting screws and pipe joints. If the cone valve or the main spool is worn too much, or the sealing surface is not well contacted, it will cause excessive internal leakage and even affect normal operation. Common faults of the electromagnetic spill valve include the failure of the first conductive magnetic valve, the failure of the main valve, and the impact noise during unloading. The latter can be reduced or eliminated by adjusting the added buffer. If there is no buffer, a back pressure valve can be added to the main valve overflow. (The pressure is generally adjusted to about 5kgf/cm2, which is 0.5MPa)
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