Pneumatic Single Seat Control Valves Common Failures and Releases

When the pneumatic single-seat control valve adopts graphite-asbestos as the filling material, a lubricant should be added on the filler for about three months to ensure that the regulating valve is flexible and easy to use. If the filler pressure cap is found to be very low, fillers should be added. If it is found that the polytetrafluoroethylene dry filler is hardened, it should be replaced in time. Attention should be paid to the operation of the regulating valve in the inspection, check the valve position indicator and regulator. The output is consistent; for a pneumatic single-seat regulating valve with locator, the gas source should be checked frequently, and the problem should be solved in time; the hygiene of the pneumatic single-seat regulating valve and the complete and easy use of the components should always be maintained.

Common failures of pneumatic single seat regulators and their causes:

(a) The pneumatic single seat regulator valve does not operate. The symptoms and causes are as follows:

1. No signal, no air source.

1 The air source is not open;

2 Because the air source contains water in the winter ice, leading to blockage of the air duct or malfunction of the filter and pressure reducing valve;

3 compressor failure;

4 Air source leakage.

2. There is gas source, no signal.

1 regulator failure;

2 signal pipe leakage;

3 positioner bellows leak;

4 Adjust the web membrane damage.

3. The positioner has no air source.

1 filter plugging;

2 pressure reducing valve failure;

3 The pipe leaks or jams.

4. Positioner has gas source, no output. The retainer throttle block.

5. There is signal, no action.

1 spool off;

2 spool and society or stuck with the valve seat;

3 valve stem bent or broken;

4 valve seat core freezing or coke block dirt;

5 The actuator spring rusted because it was not used for a long time.

(b) The operation of the pneumatic single seat regulator valve is not stable. The symptoms and causes are as follows:

1. The source pressure is not stable.

1 compressor capacity is too small;

2 pressure relief valve failure.

2. The signal pressure is not stable.

1 The time constant of the control system (T=RC) is inappropriate;

2 Regulator output is not stable.

3. The air supply pressure is stable and the signal pressure is also stable, but the operation of the regulating valve is still unstable.

1 The ball valve of the amplifier in the positioner is loosely shut off due to the wear of the contaminants. If the air consumption increases, the output oscillation will occur.

2 The nozzle baffle of the amplifier in the positioner is not parallel and the baffle cannot cover the nozzle;

3 output pipe, line leakage;

4 The actuator rigidity is too small;

5 The frictional resistance in the movement of the valve stem is large, and there is a blockage in the contact part.

(c) Pneumatic single seat regulator valve vibration. The symptoms and causes are as follows:

1. The regulator valve vibrates at any opening.

1 support instability;

2 nearby vibration source;

3 The valve plug and bushing wear badly.

2. The regulator valve vibrates near the fully closed position.

1 Larger control valve, often used in small opening;

2 single seat valve medium flow direction and closing the opposite.

(d) The pneumatic single-seat control valve is dull. The phenomenon of dullness and causes are as follows:

1. The valve stem is only dull when operated in one direction.

1 Diaphragm breakage and leakage in pneumatic diaphragm actuators;

2 "O" seal leakage in the actuator.

2. The valve stem is dull when reciprocating.

1 There is sticky blockage in the valve body;

2 Polytetrafluoroethylene filler metamorphosing hardening or graphite-asbestos filler lubricant drying;

3 too tight packing, friction resistance increases;

4 due to the valve stem is not straight, resulting in large frictional resistance;

5 Pneumatic control valves without a positioner can also cause dull movements.

(e) Increased leakage of pneumatic single-seat control valves. The reason for the leak is as follows:

1. When the valve is fully closed, the leakage amount is large.

1 valve core is worn, the inner leakage is serious,

2 The valve is not adjusted properly.

2. The valve does not reach the fully closed position.

1 medium pressure difference is too large, the actuator rigidity is small, the valve is not strict;

2 foreign objects in the valve;

3 bushings are sintered.

(6) The flow adjustable range becomes smaller. The main reason is that the spool is corroded and the adjustable minimum flow rate is increased. Understand the symptoms and causes of the malfunction of the pneumatic control valve and take measures to resolve it.