Selection of FO and FC for control valves?
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How are the FO and FC of the control valve selected? Are the FO and FC of the control valve related to the interlock requirements? Do they need to be consistent? For example, I require the valve to be fully open in interlock mode, but my valve is an FC valve – is there a problem with such a setting?
The selection of FO and FC for control valves is determined based on process requirements, with emphasis placed on ensuring the safety of process equipment in the event of failures. For example, in the case of a gas control valve for a heating furnace, it is necessary to cut off the gas in case of a system failure, so as to prevent the furnace from being damaged; therefore, an FC control valve should be chosen.
The FO (air-shut, i.e., the valve opens in case of a fault) and FC (air-open, i.e., the valve closes in case of a fault) settings of the control valve are selected in accordance with the safety requirements of the process, taking into account the fail-safe valve position in the event of an air-loss (no power supply) situation. If the interlock requires the valve to be fully open, but the valve is a fail-closed pneumatic valve, it is still possible to use an interlock solenoid valve (connected to a air supply with a pressure range suitable for full opening of the valve). When the air supply is functioning properly, after the interlock activates, a signal is sent to this solenoid valve to switch circuits, thereby applying a certain pressure directly to the pneumatic actuator and opening the valve fully.
It is necessary to analyze the consequences of closing during gas shutdown or opening all of them during gas supply, before determining FC or FO
May I ask how this is classified? Is there any instruction on the control valve purchased? Or is it determined after installation, based on on-site requirements or the purpose of installation?
The selection of FO and FC for control valves is first determined from a safety perspective, and secondly from the standpoint of process quality; that is, the state of the valve in the event of an accident must ensure both system safety and process quality. For example, in the case of boiler water level control valves, these should be in an fully open position during accidents, in order to prevent safety incidents caused by a lack of water in the boiler; therefore, FO air-operated shut-off valves should be chosen.
Are the FO and FC of the control valve related to the interlock requirements? Do they need to be consistent?
FO means fault on, FC means fault off
Both the de-pressurization position and the interlock position are determined by the process; the instrument only needs to determine whether it is an \"electrification interlock\" or a \"de-energization interlock\" for the solenoid valve. Example: The compressor return valve is of the FC type, and the interlock requires it to be fully open. @jiaguoyun
It should be the state that exists when the valve position gets out of control in case of an emergency at the control end; it depends on the actual conditions on site
The nameplate of a regular control valve usually indicates the fault conditions, but that only reflects the state of the valve when there is no air or power supply; it may not be applicable to your actual production processes. The selection of fault locations should be based on safety considerations in the production process; this requirement should be specified at the time of procurement