Fisher 4220 Electronic Position Transmitter

About Pneumatic control valve 4220

Pneumatic control valve 4220 is to compressed air as the power source, to the cylinder as the actuator, and with the help of electrical valve positioner, converter, solenoid valve,

The holding valve and other accessories drive the valve, realize the switching quantity or proportional adjustment, and receive the control signal of the industrial automation control system to complete the adjustment

Pipeline medium flow, pressure, temperature and other process parameters. Pneumatic control valve is characterized by simple control, rapid response, and intrinsically safe

All, do not need to take additional explosion-proof measures.

Pneumatic control valve actuator working principle:

Pneumatic control valve action is divided into two types of gas open and gas close. Air to Open (Air to Open) is when the air pressure above the film increases, the valve increases

When the upper limit of input pressure is reached, the valve is in full open state. Conversely, when the air pressure decreases, the valve closes

In the closed direction, the valve is completely closed when there is no input air. Therefore, sometimes the gas open valve is also called the failure to Close FC.

The direction of action of the Air to Close type is exactly the opposite of the air to open type. When the air pressure increases, the valve moves in the direction of closing; Air pressure

When reduced or absent, the valve is open in the open direction or fully open. Therefore, it is sometimes called Fail to Open FO. Pneumatic control valve

The gas on or off is usually achieved through the positive and negative action of the actuator and the different assembly methods of the valve structure.

The choice of gas opening and closing is considered according to the safety Angle of process production. When the air source is cut off, the regulating valve is in the closed position

Is the open position safe?

For example, in the combustion control of a heating furnace, the regulating valve is installed in the fuel pipe, according to the temperature of the furnace or the heated material in the heating

The temperature of the furnace outlet controls the fuel supply. At this time, it is safer to use the gas open valve, because once the gas supply stops, the valve is closed

A closed valve is better than a fully open valve.

If the air supply is interrupted and the fuel valve is fully open, excessive heating will be dangerous. Another example is a heat exchange device cooled by cooling water, and the hot material is in

The heat exchanger is cooled by heat exchange with the cooling water, and the regulating valve is installed on the cooling water pipe to control the cooling water with the temperature of the material after heat exchange

When the air supply is interrupted, the regulating valve should be safer in the open position, and the gas-closed (i.e. FO) regulating valve should be selected.

Common faults and causes

(1) The regulating valve does not operate. The fault symptoms and causes are as follows:

1. No signal, no air source. ① The air source is not opened, ② because the water of the air source freezes in winter, resulting in the blockage of the air pipe or the blockage of the filter and the pressure reducing valve

Ling, ③ compressor failure; ④ Air source pipe leakage.

2. There is air source, no signal. ① regulator failure; ③ Positioner bellows leak; ④ The omental plate is damaged.

3. The locator has no air source. ① The filter is blocked; ② The reducing valve is faulty |③ the pipeline is leaking or blocked.

4. The locator has air source and no output. The throttle hole of the locator is blocked.

5. Signal, no action. ① The spool falls off, ② the spool is stuck with the society or the seat; ③ The valve stem is bent or broken; ④ The valve core of the seat is frozen or

Coke dirt; ⑤ The actuator spring rusts to death due to long-term use.