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Faults, causes, and troubleshooting of servo valves. Faults in servo valves are often detected during the calibration of electro-hydraulic servo systems or when these systems are not operating properly. So sometimes it is a system issue involving faults in the amplifier, feedback mechanism, actuator, etc., and sometimes it is indeed a problem with the servo valve. So first, it’s necessary to determine whether it’s a system issue or a problem with the servo valve. The common way to resolve this issue is: first, remove the valve if possible and retest it on a laboratory bench. II. In most cases, this condition is not met; in such situations, a simple approach is to operate the system in open-loop mode, use a separate DC power supply, and supply the servo valve with currents of different magnitudes in both positive and negative directions using a multimeter. By observing the output from the valve, it is possible to determine whether there is a fault in the valve and what the nature of that fault is. The valve isn’t the main issue; look for problems within the system. For example, excessive internal leakage in the actuator can cause the system to operate more slowly, result in severe hysteresis, or even prevent it from functioning ； Issues such as an open or abnormal feedback signal, amplifier problems like distorted output signals or failure to operate – system-related problems will not be discussed here; instead, we will focus on valve failures. (1) The valve does not function. Reasons include: broken motor coil, desoldering ； There may also be an inversion of the oil inlet or outlet ports. Another possibility is blockage in the upstream stage, which causes the valve spool to get stuck in the middle dead zone; of course, this scenario is less likely. The two coils of the motor are connected in series or parallel with their polarities reversed, causing the magnetic forces generated by those two coils to cancel each other out. (2) The valve has a fixed output but is out of control. Reasons: clogging of the pre-stage nozzle, the valve spool getting stuck due to debris, deformation of the valve body that causes the spool to get stuck, or the internal protection filter being blocked by debris. To replace the filter element, it must be sent back to the factory for cleaning and repair. (3) Slow valve response and delayed reactions: Causes include a decrease in the system’s oil supply pressure, partial blockage of the protection filter, loose zero-setting mechanisms in certain valves, loose components in the motor, or looseness between the moving coil of the dynamic coil valve and the control spool. Excessive internal leakage in the power components operating within the system is another reason. Furthermore, if the oil is too dirty, the valve resolution deteriorates, and an enlarged hysteresis loop is also one of the causes. (4) Frequent vibrations and noise in the system: Cause: Excessive amount of air mixed in the oil, and the oil is too dirty ； The system gain is set too high; there is power supply noise coming from the amplifier. The insulation between the servo valve coil, the valve housing, and the ground is inadequate. There may also be issues related to whether current is flowing or not, excessive flutter signals, or resonance phenomena caused by the relationship with the system frequency. Additionally, a servo valve with an excessively high frequency was selected for a system with a relatively low frequency. (5) The valve output alternates between positive and negative values, preventing continuous control and resulting in a \"on/off\" type of control. Reason: The internal feedback mechanism in the servo valve has failed, or the system feedback is disconnected; otherwise, some form of positive feedback would occur. (6) Oil leakage: Cause: Poor surface finish of the mounting base, resulting in inadequate sealing. Quality issues with the valve port seals, as well as damaged seals in areas such as the valve plugs. If oil leaks between the motor cover and the valve body, it may be due to a cracked spring tube or cracked internal oil pipes. Troubleshooting of servo valves – some issues can be resolved on one’s own, but many problems require sending the valve to the manufacturer, where it can be repaired and adjusted on a testing bench. Once again, do not try to disassemble the valve by yourself, as this can easily damage its components. Units that use a large number of servo valves can install a simple testing bench on their own to determine whether the problem lies with the system or the valves, what issues exist with the valves, and whether they can still be used. Phone number: 021-56656744 Fax: 021-64677999 Address: No. 90 Yonghe Road, Zhabei District, Shanghai Servo Valve Department Contact person: Li Bo Phone number: 13818018452