Pneumatic Double Seat Control Valve Performance Characteristics and Fault Maintenance

Pneumatic double seat control valve adopts double number guiding structure, equipped with multi-spring recruiting and executing mechanism. Pneumatic diaphragm double seat control valve has the advantages of compact structure, light weight, sensitive action, large capacity, precise flow characteristics, easy to disassemble and so on. Pneumatic diaphragm double seat control valve is widely used in precise control of gas, liquid, steam and other media process parameters such as pressure, flow, temperature, liquid level at a given value. Pneumatic diaphragm double-seated control valves are especially suitable for large differential pressure, allow leakage is also larger and not very clean media occasions. Pneumatic double seat control valve is widely used in petroleum, chemical, pharmaceutical, metallurgy, power station and other industrial control departments, mainly control gas, liquid, steam and other media.

(A)Pneumatic double seat control valve fault repair

(i) The control valve does not operate. Fault phenomena and causes are as follows:

1. No signal, no gas source.

① gas source is not open

② due to the gas source containing water in the winter icing, resulting in blocked ducts or filters, pressure reducing valve blockage failure.

③ Compressor failure;

③ Compressor failure.

④ Leakage of air source main pipe.

2. There is a gas source, no signal.

① regulator failure;

② signal pipe leakage;

Leakage of signal pipe;

③ Leakage of positioner bellows;

④ Damage to the regulator net diaphragm.

3. No air supply to the positioner.

① Filter clogging;

② pressure reducing valve failure I Pipe leakage or blockage.

4. Positioner has air source, no output. The throttle hole of the positioner is blocked.

5．Signal, no action.

① Valve spool falls off.

② Valve spool and society or with the valve seat jammed;

③ Valve stem bent or broken;

④ Valve seat spool frozen or coke block dirt;

⑤ Actuator spring rusted due to long-term unused.

Grinding is not only the mechanical process of abrasives on metal, but also has a chemical effect. The grease in the abrasive can make the processed surface form an oxidized film, thus accelerating the grinding process.

(ii) The action of the control valve is not stable.

Fault phenomena and causes are as follows:

(1) The pressure of the gas source is unstable.

① Compressor capacity is too small;

② pressure reducing valve failure.

2. Signal pressure instability.

① control system time constant (T = RC) is not appropriate;

② regulator output is not stable.

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

The ball valve of the amplifier in the positioner is not closed tightly due to wear and tear of dirt, and output oscillation occurs when the gas consumption increases particularly;

② positioner amplifier nozzle baffle is not parallel, the baffle can not cover the nozzle;

③ Output pipe and line leakage;

④ The rigidity of the actuator is too small;

⑤ The friction resistance in the movement of the valve stem is large, and there is blockage in the contact area with the phase.

(C) control valve vibration

Fault phenomena and causes are as follows:

1. The control valve vibrates in any opening degree.

① support instability;

② vibration source nearby;

③ Valve spool and liner wear.

2. Control valve vibration near the fully closed position.

① control valve selected large, often used in small openings;

② single-seat valve medium flow direction opposite to the closing direction.

(D) the action of the control valve is slow

Sluggish phenomenon and the reasons are as follows:

1. Valve stem only in a single direction when the action is sluggish.

① pneumatic thin-film actuator diaphragm damage leakage;

② actuator in the “O” seal leakage.

2. Valve stem in the reciprocating action are sluggish phenomenon.

(1) the valve body is blocked with sticky material;

② PTFE packing deterioration and hardening or graphite and asbestos packing lubricant drying;

③ The packing is too tight, the friction resistance increases;

④ High friction resistance due to the valve stem is not straight;

⑤ Pneumatic control valve without positioner can also lead to sluggish action.

(E) Increased leakage of control valve

The causes of leakage are as follows:

1. Large leakage when the valve is fully closed.

① valve spool is worn, serious internal leakage.

② valve is not adjusted to close not tight.

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

① medium pressure difference is too large, the rigidity of the actuator is small, the valve is not closed tightly;

② foreign matter in the valve;

③ bushing sintering.

(F) adjustable range of flow becomes smaller

The main reason is that the spool is corroded small, so that the adjustable flow becomes larger.

Understand the failure of the pneumatic control valve phenomenon and the reasons, you can take measures to solve the problem.