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Pneumatic control valves without positioners can cause slow movements

Update:24-12-2018
Summary:

The action of the regulating valve is unstable. The sym […]

The action of the regulating valve is unstable. The symptoms and causes are as follows:

1. The air source pressure is unstable.

A. The compressor capacity is too small;

B. The pressure reducing valve is faulty.

2. The signal pressure is unstable.

A. The time constant of the control system (T=RC) is not appropriate;

B. The regulator output is unstable.

3. The gas source pressure is stable and the signal pressure is also stable, but the action of the regulating valve is still unstable.

A. The ball valve of the amplifier in the positioner is not tightly damaged by dirt, and the output oscillation occurs when the gas consumption is particularly increased;

B. The nozzle flapper of the amplifier in the positioner is not parallel, and the baffle cover cannot cover the nozzle;

C.The output pipe and the line leak;

D. The rigidity of the actuator is too small;

E. The frictional resistance in the valve stem movement is large, and there is a blockage at the contact portion.

The pneumatic diaphragm regulator valve vibrates. The symptoms and causes are as follows:

1. The regulating valve vibrates at any opening.

A. The support is unstable;

B. There is a vibration source nearby;

C. The valve core and the bushing are seriously worn.

2. The regulating valve vibrates when it is close to the fully closed position.

A. The regulating valve is selected to be large, and is often used at a small opening;

B. The flow direction of the single seat valve is opposite to the closing direction.

The adjustment valve is slow. The symptoms and causes of dullness are as follows:

1. The valve stem is only slow in one direction.

A. Diaphragm breakage leakage in pneumatic diaphragm actuators;

B. "O" seal leakage in actuators.

2. The valve stem is dull when reciprocating.

A. There is stickiness in the valve body;

B. Polytetrafluoroethylene filler metamorphic hardening or graphite-asbestos filler lubricating oil drying;

C. Filling too tight, friction resistance increases;

D. Frictional resistance due to valve stem not straight Large;

E. Pneumatic control valves without positioners can also cause slow movements.

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