Pneumatic air valve uses compressed air as the power source, cylinder as the actuator, and drives the valve with the help of valve positioners, converters and other accessories to realize switching or proportional adjustment, and accepts the control signal of the industrial automation control system to complete the adjustment of the pipeline medium. flow, pressure, temperature, and other process parameters.
At present, pneumatic air valves are widely used in coking, electric power, metallurgy and other process industries, and are an indispensable and important link in the control system. Therefore, it is very important to ensure the stable and reliable operation of the pneumatic air valve. When the pneumatic regulating valve fails, it can be checked according to the common faults of the regulating valve, and the cause of the fault can be found out in time.
1 Air source failure
The on-site air source is not turned on;
The air source contains water, and the weather is cold and icy;
The supply of purified air is stopped;
The air pressure is too low due to the leakage of the air source main pipe or the blockage of the air line, and the regulating valve cannot be fully opened or fully closed, or even does not operate;
The air filter pressure reducer is used for a long time, and there is too much dirt. The black knob under the pressure reducing valve opens and leaks air, so that the output air pressure is lower than the specified pressure, so that the regulating valve cannot be fully opened and fully closed, or even does not operate;
The on-site air line leaks and the joint is loose, resulting in insufficient air pressure, and the regulating valve cannot be fully opened or closed, or even does not operate;
The failure of the filter pressure reducing valve causes the wind pressure to be unstable and causes the adjustment valve to oscillate.
2 line failure
The terminals of the power cord are loose, fall off, short-circuited, or open-circuited. Too much dust on the circuit board leads to poor contact, signal fluctuation, and vibration of the control valve;
After heavy rain or typhoon, the equipment will be wetted by water and the wiring will be short-circuited, resulting in the regulating valve not being able to be fully opened or fully closed;
If the polarity is reversed, the regulating valve will not operate;
The middle section of the power line is faulty, due to the failure of the insulating tape, the insulation of the wire falls off, causing a short circuit between the wires, and the wire is broken due to on-site vibration, resulting in discontinuous oscillation of the regulating valve action, which cannot be fully opened or fully closed or even not. action;
Due to the wrong wiring of the regulating valve after maintenance, the regulating valve is faulty;
The output signal of the control valve is unstable, causing the operation of the control valve to fluctuate.
3 Locator failure
The fixed nut of the feedback rod is loose and falls off, and the spring on the feedback rod falls off, causing the feedback rod to loosen, fall off, and jam, causing the regulating valve to oscillate;
The position sensor in the locator is faulty. When the vibration reaches a dead point, it will cause the central control room to display overtravel, and it will return to normal after a while, which can be solved by replacing it;
The PID parameter setting of the positioner is not suitable;
4 Control valve body failure
The valve core or valve seat of the regulating valve is worn (scouring of the medium, scratches and wear of dirt such as rust, welding slag, etc.), jamming (blocking of various impurities in the medium), and poor sealing (wearing of the sealing ring), resulting in the valve When it is fully closed, the medium is still too much and cannot be controlled;
The control valve disc is pressed too tightly or too loosely. If it is too tight, the valve stem of the control valve will move slowly or jump. If it is too loose, the medium will leak. If the heavy oil is likely to burn, it will cause a big accident;
When the regulating valve is installed, the pipeline and the valve body are not concentric, so that the regulating valve is subjected to excessive additional stress, resulting in vibration, which cannot be fully opened or fully closed;
The valve stem of the regulating valve and the fixing nut of the connecting piece are loose, and the valve stem and the valve core are not concentric, so that the valve does not close, and the stress increases, causing the valve stem to vibrate at high frequency, or even break;
Due to the failure of the diaphragm head of the regulating valve, due to the long-term use of the diaphragm, the aging and deterioration, the reduction of elasticity, the poor sealing performance, the air leakage of the diaphragm, the aging of the compression spring, the reduction of elasticity, and the fracture, resulting in the regulating valve not being able to be fully opened or closed or even The valve core of the out-of-control regulating valve falls off, the valve core and the valve seat are stuck, and the valve stem is bent or broken, which will cause the regulating valve to operate normally, but it will not play a role in regulating.