Problem of pressure release of instrument air at the site due to wind-on valves and wind-off valves
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The unit was shut down, and a closed flow control valve (FC) at the site was causing instrument air to be released. It was initially thought that it was an instrument air leak; upon asking the instrumentation staff, it was stated that either the flow control valve was in its fully closed position or the flow stop valve was in its fully open position, which meant that instrument air needed to be released from the site in order to relieve pressure； I doubt his claims; please, experts, help me understand this.
The valve of the FC must be closed, and the diaphragm head/cylinder must be vented – that’s correct. Other components should not exhaust air; at most, there may be slight leakage of air from pneumatic components (which is normal). @jiaguoyun