Faults of the MOOG servo valve are often found when the electro-hydraulic servo system is commissioned or not working properly. So sometimes there are system problems including faults such as amplifiers, feedback mechanisms, and actuators. Sometimes it is a servo valve problem. So first of all, it must be clear whether it is a system problem or a servo valve problem.
The common way to solve this problem is:
First, the valve can be unloaded conditionally, on the test bench can be retested.
Second, most conditions without this condition, then a simple way is to open the system, standby independent DC power supply, after the multimeter to the servo valve for different positive and negative value current, from the valve output to determine whether the valve What are the problems? The problem is not serious, so look for system problems. For example, if the internal leakage of the actuator is too large, it will cause the system to slow down, the hysteresis will be serious, and even it will not work; the feedback signal will be disconnected or out of order, and the amplifier will have a distortion of the output signal. Not working, system problems are not talked about here.
The following mainly talk about the failure of the valve.
(1) The valve does not work because: The motor coil is broken, and the welding is disconnected; there is also oil inlet or outlet port reversed. Another possibility is that the pre-stage blockage causes the spool to be stuck in the middle dead zone. This is of course less likely that the spool is stuck in the middle. The two coils of the motor coil are connected in series or in parallel, and the magnetic force formed by the two coils just cancels out.
(2) The valve has a fixed output, but the reason has been out of control: the prepositioned nozzle is blocked, the valve plug is stuck on the stolen object and the valve body is deformed to cause the spool to jam, or the internal protection filter is blocked by the stolen material. To replace the filter, return to factory cleaning and repair.
(3) Responsiveness of valve response, slow response, etc.: There is a decrease in system oil supply pressure, partial blockage of the protective filter, loosening of some valve zero adjustment mechanisms, looseness of other parts of the motor, or dynamic coil of the dynamic ring valve and the control valve core Loosening. Excessive leakage of power elements in the system is another reason. In addition, the oil is too dirty, the valve resolution becomes worse, and hysteresis widening is also one of the reasons.
(4) The system has a high frequency of vibration and noise reasons: the amount of air mixed in the oil is too large, the oil is too dirty; the system gain is adjusted too high, the power supply noise from the amplifier, the servo valve coil and the valve housing and ground The line insulation is not good, is a non-pass, flutter signal is too large or resonant phenomenon caused by the system frequency relationship, and then a relatively low system and chose a servo valve of high frequency.
(5) The output of the valve is suddenly positive and negative, and it cannot be controlled continuously. It becomes a "switch" control. Cause: The feedback mechanism in the servo valve fails, or the system feedback is disconnected, otherwise some positive feedback phenomenon occurs.
(6) Oil leakage: The surface of the mounting seat is not of good quality and cannot be sealed. Valve sealing ring quality problems, seals on valve plugs, etc. are damaged. If the oil leaks between the motor cover and the valve body, the spring tube may be broken and the internal oil pipe may be broken. Servo valve troubleshooting, and some can be ruled out, but many faults to the valve to the production plant, put on the test bench to repair and re-emphasize, and then stressed again: Do not own valve, it is very easy to damage the servo valve parts. A unit with more servo valves can be equipped with a simple test bench to determine whether it is a system problem or a valve problem. If there is any problem with the valve, it can be used again.
MOOG servo valve working principle:
MOOG servo valve is composed of permanent magnet torque motor, nozzle, baffle, valve core, valve sleeve and control chamber. When the input coil is connected to the current servo valve, the baffle moves to the right, so that the throttling effect of the right nozzle is strengthened, the flow decreases, and the right back pressure rises; at the same time, the throttling effect of the left nozzle is reduced and the flow rate is increased. Pressure drops. The force at both ends of the spool loses its balance and the spool moves to the left. High pressure oil flows from S to C2 to the load. The load return oil flows through the oil return port through C1 and enters the fuel tank. The displacement of the spool is proportional to the input current of the torque motor. The hydraulic pressure acting on the spool balances the spring force. Therefore, in the balanced state, the differential current of the torque motor is proportional to the displacement of the spool. If the input current is reversed, the flow is also reversed. The table is a classification of the servo valve.
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