What happens to the valve positions of control valves and isolation valves when the hydrogen instrument air is interrupted?

1. Please have the instrumentation team verify whether the signal wires are connected correctly. The valves and air connections on site should be fine; check the signal wires. 2. The wind pressure should be above 4.5 bar to be normal; the impact is minimal. As long as it’s not too low so that the valve cannot be adjusted.

Cut off the air distribution valve and the air shut-off valve; considering design and safety aspects, problems start to arise when the pressure at the instruments falls below 3 kilograms, and it’s basically unusable when the pressure is below 2 kilograms. It’s best to integrate the nitrogen into the instrument air as soon as possible; even if it needs to be disconnected after an accident, prevent the instrument air from mixing with the nitrogen

1. After the instrument air is cut off, the control valve that operates in emergency shutdown mode shows a valve position different from that indicated by the DCS; the DCS indicates 100%, while the valve is actually closed outdoors. Why can’t the actual signal from the valve be transmitted to the DCS? If the valve position signal is sent to the DCS using a valve position transmitter or switch, it is necessary to have the instrumentation technician check and adjust it. I wonder if it’s different only when the instrument air is cut off, or is it different even under normal conditions? It is estimated that it is usually in the reverse position, or it did not move in sync with the valve this time. 2. To what extent is the valve position of the cut-off valve affected by wind pressure? Instrument air pressure affects valve operation, but it has no direct relationship with valve position feedback. Valve position feedback is only related to the valve position.

If you set the opening to 100, but it’s a pneumatic control valve, then the instrument air supply stops, and indoor control becomes ineffective. Ordinary control valves do not provide feedback on their valve position, which results in inconsistent displays.

The DCS provides a 4-20MA electrical signal, which is converted by a transmitter into a 20-100KPA pneumatic signal; only then can the control valve carry out the corresponding action. When there is no air supply, the actuator cannot function, resulting in a mismatch between the display and the actual operation.

1: The DCS valve position is 100%; you need to determine whether it is the regulator’s output value or the valve’s feedback value. The air-on/air-off setting of the on-site control valve is determined at the time of installation. As you said, it’s just that the instrument settings are reversed. 2: The cut-off valve is a two-position valve that can only be in either an “open” or “closed” state. It opens or closes when the instrument air pressure drops to a certain level; whether it opens or closes depending on whether it is an air-open valve or an air-close valve.

After the instrument air is cut off, the control valve for emergency shutdown operates; the valve position shown by the DCS differs from the actual value, with the DCS indicating 100% while the valve is closed outdoors. Why can’t the actual signal from the valve be transmitted to the DCS? If the valve position signal is sent to the DCS using a valve position transmitter or switch, it is necessary to have the instrumentation technician check and adjust it. I wonder if it’s different only when the instrument air is cut off, or is it different even under normal conditions? It is estimated that it is usually in the reverse position, or it did not move in sync with the valve this time.

1. After the instrument air is cut off, the control valve that operates in emergency shutdown mode shows a valve position different from that indicated by the DCS; the DCS indicates 100%, while the valve is actually closed outdoors. Why can’t the actual signal from the valve be transmitted to the DCS? Control valves come in two types: air-open and air-close. The valve position indicated on the DCS refers generally to the output signal; 100% for an air-open valve means the valve is fully open in reality, while 100% for an air-close valve means the valve is fully closed in reality. For our systems, it is generally required that the instruments be configured in the DCS backend to invert the signal of the air shut-off valve, thereby ensuring that the display in the DCS matches the actual valve position on site. However, this operation is only suitable for different control valves; control valves with interlock functions have solenoids, and in order to enable the DCS to determine the actual valve position on site, a feedback signal from that position needs to be sent to the DCS. 2. To what extent is the valve position of the cut-off valve affected by wind pressure? Isolation valves are generally “two-position,” meaning fully open or fully closed. Generally, as long as the air pressure at the shut-off valve remains above 0.3 MPa, the valve will not close. In addition, all shut-off valves are equipped with self-protection mechanisms; the valve will not operate unless clean air leaks out slowly and continuously until the air pressure drops to a safe level. The air supply for the cut-off valve generally enters the valve body in two streams, one from above and one from below; even if this supply is interrupted, the air pressure inside the valve body remains unchanged and the valve does not move. It will only operate if the solenoid valve responsible for control fails and releases all the air pressure.