Servo valve failures, causes and troubleshooting

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Servo valve failures, causes and troubleshooting Servo valve failures are often discovered when the electro-hydraulic servo system is debugged or is not working properly. So sometimes it's a system problem, including faults in the amplifier, feedback mechanism, actuator, etc. Sometimes it's really a servo valve problem. So first we need to figure out whether it is a system problem or a servo valve problem. A common way to solve this problem is to: 1. If possible, remove the valve and retest it on the test bench. 2. In most cases, this condition does not exist. In this case, a simple method is to open the system, use a standby independent DC power supply, and then supply positive and negative currents of different magnitudes to the servo valve through a multimeter, and judge from the valve output whether there is a problem with the valve and what the problem is. If the cutting problem is not big, then look for system problems, for example: If the internal leakage of the actuator is too large, the system will slow down, cause hysteresis, or even fail to work. ； The feedback signal is disconnected or abnormal, etc. The amplifier problem is that the output signal is distorted or does not work. System problems are not discussed here. Let’s mainly talk about the valve failure. (1) The reasons why the valve does not work are:: The motor coil is disconnected and desoldered. ； There are also oil inlet or oil inlet and outlet ports connected reversely. Another possibility is that the prestage is blocked, causing the valve core to get stuck in the middle dead zone. Of course, this chance of the valve core getting stuck in the middle position is less. If the motor coil is connected in series or in parallel and the two coils are connected in reverse, the magnetic force formed by the two coils will cancel out. (2) The valve has a fixed output but is out of control.: The pre-stage nozzle is blocked, the valve core is stuck by stolen goods, the valve core is deformed, etc., or the internal protection filter is blocked by stolen goods. To replace the filter element, return it to the factory for cleaning and repair. (3) Reasons such as slow valve response and slow response: The oil supply pressure of the system is reduced, the protection filter is partially blocked, the zero-setting mechanism of some valves is loose, other parts of the motor are loose, or the moving coil of the moving coil valve and the control valve core are loose. Excessive internal leakage of the actuating power components in the system is another reason. In addition, the oil is too dirty, the valve resolution becomes poor, and the hysteresis loop widens is also one of the reasons. (4) Reasons for higher frequency vibration and noise in the system: The amount of air mixed in the oil is too large and the oil is too dirty. ； The system gain is adjusted too high, the power supply noise comes from the amplifier, the servo valve coil is not well insulated from the valve shell and the ground wire, there is no communication, the flutter signal is too large or the resonance phenomenon is caused by the relationship with the system frequency, and a servo valve with a high frequency is selected for a relatively low system. (5) The valve output fluctuates between positive and negative, and cannot be continuously controlled. It becomes a "switch" control. reason: The feedback mechanism in the servo valve fails, or the system feedback is disconnected, otherwise some kind of positive feedback phenomenon occurs. (6) Cause of oil leakage: The surface processing quality of the mounting base is poor and cannot be sealed. There is a quality problem with the valve port sealing ring, and the sealing ring on the valve plug, etc. is damaged. If there is oil leakage between the motor cover and the valve body, it may be caused by a rupture of the spring tube or a rupture of the internal oil pipe. When troubleshooting servo valves, some of them can be rectified by yourself, but for many faults, the valve must be sent to the manufacturer and put on the experimental bench for repair and debugging. I emphasize it again.: Do not disassemble the valve yourself, as it is easy to damage the servo valve components. Units that use many servo valves can install a simple experimental bench to determine whether it is a system problem or a valve problem. What is wrong with the valve and whether it can be reused.