PCB Fabrication

Find faults and fault solutions for servo valves

by:A-TECH      2021-03-22
Servo valve failures are often discovered when the electro-hydraulic servo system is debugged. We have to figure out whether it is a system problem or a servo valve problem. Common ways to solve this problem are:    conditionally remove the valve and retest it on the test bench That's it. In most cases, there is no such condition. At this time, a simple method is to open the loop of the system, reserve an independent DC power supply, and supply currents of different positive and negative values u200bu200bto the servo valve through a multimeter, and judge whether the valve is faulty from the output of the valve. What's wrong. The valve problem is not big, then look for the system problem.  (1) The valve does not work.    The reasons are: motor coil disconnection, desoldering; and the oil inlet or outlet port is connected reversely. It is also possible that the pre-stage is blocked, so that the spool is stuck in the middle dead zone position. Of course, there is less chance that the spool is stuck in the middle position. If the motor coils are connected in series or in parallel, the magnetic force formed by the two coils just cancels out.   (2) The valve has a fixed output, but it is out of control.    Reasons: the pre-stage nozzle is blocked, the valve core is stuck by stolen goods and the valve body is deformed to cause the valve core to block, etc., or the internal protection filter is blocked by stolen goods. To replace the filter element, return to the factory for cleaning and repair. (3) The valve response is slow, the response becomes slow, etc.: The system oil supply pressure is reduced, the protection filter is partially blocked, some valve zero adjustment mechanism is loose, and other parts of the motor are loose, or the moving coil of the moving coil valve and the control spool are loose. Between loose. Excessive internal leakage of executive power components in the system is another reason. In addition, the oil is too dirty, the valve resolution becomes poor, and the hysteresis is widened. (4) Reasons for the higher frequency of vibration and noise in the system: too much air mixed in the oil, the oil is too dirty; the system gain is adjusted too high, the power noise from the amplifier, the servo valve coil and valve housing and ground The line insulation is not good, it is the resonance phenomenon caused by the connection and failure, the flutter signal is too large or the relationship with the system frequency, and then the relatively low system and the too high frequency servo valve are selected.   (5) The valve output fluctuates positively and negatively, and cannot be controlled continuously, and becomes a 'switch' control.   Reason: The feedback mechanism in the servo valve fails, or the system feedback is disconnected, otherwise there is a positive feedback phenomenon.  (6) Oil leakage    Reason: The surface processing quality of the mounting seat is not good, and the seal cannot be sealed. The quality of the valve port sealing ring, and the sealing ring on the valve plug and other places are damaged. If oil leaks between the motor cover and the valve body, the spring tube may be broken or the internal oil tube may be broken.   Servo valve troubleshooting, some can be eliminated by yourself, but many failures require the valve to be sent to the manufacturer, put on the test bench for repair and debugging, and again: do not disassemble the valve by yourself, it is easy to damage the servo valve parts.   Units with more servo valves can install a simple test bench by themselves to determine whether it is a system problem or a valve problem, and whether there is any problem with the valve and whether it can be used again.
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