Some questions about FC/FO/FL of valves!
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I have a question: We know that FC/FO refers to the state of the actuator when it loses air pressure, that is, fail close/fail open. Does this mean that the valve opens or closes when there is no air pressure? It seems that the solenoid valves also experience situations where they are powered on and powered off? I don’t know much about instruments, so I’d like to ask what they each do! ? What is the function of each part on the control valve? What are the signals for each part respectively? What is the purpose of the instrument air connected to the locator? ? What impact does its pressure have on regulation? Is there anyone who can find a control loop and provide a detailed explanation of it? Or could you tell me in which book I can find the answer? ?
1. If the valve is marked as FC, it indicates that it is a gas-open valve; if it is marked as FO, it indicates that it is a gas-close valve. Based on industrial control considerations, a decision is made as to whether to use a gas-open valve or a gas-close valve. 2. Solenoid valves are used to control the on and off state of the air supply; generally, they allow air flow when powered and stop it when power is cut off. 3. The regulating control valves include: operating mechanism, actuator, positioner, and pressure-reducing filter. 4. Actuators come in direct-acting and reverse-acting types: when the air duct is at the upper position, it is a direct-acting type ； The air duct exerts a reaction force in the downward direction – this applies only to cylinders with a single drive. 5. The forward and reverse reactions of the positioner merely indicate the relationship between its input signal and output signal; they do not indicate whether the valve is open or closed. When air is supplied, the valve opens; in Figure 1, the actuator consists of air intake below the diaphragm ； For Figure 2, the actuator features air intake above the diaphragm. The final deflation state is always the deflation shutdown. These are suitable for applications where pressure relief or discharge is required in the event of a failure. The gas shut-off function means that the valve closes when air is supplied to it; in Figure 1, the actuator consists of air intake above the diaphragm ； For Figure 2, the actuator features air intake below the diaphragm. The final deflation state is always the deflation shutdown. These are suitable for applications that require pressure retention and leak prevention in the event of a failure. Impact on the field: When the air supply valve is opened, air is released; when it is closed, leakage is controlled by the spring force of the spring diaphragm ； A pneumatic shut-off valve is a valve that opens when air pressure is lost; its leakage level when closed is related to the pressure of the air supply.
When air is supplied, the valve opens; in Figure 1, the actuator consists of air intake below the diaphragm； For Figure 2, the actuator features air intake above the diaphragm. The final deflation state is always an open deflation (there was a typo above)