Can a pneumatic control valve be used as an emergency shut-off valve?
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Can pneumatic control valves be used as emergency shut-off valves? According to SH/T 3005-2016, Standards for the Selection and Design of Automation Instruments in Petrochemical Industries, 10.1.1.4 states that, unless there are special requirements from the process, the allowable leakage level for control valves should be set at level IV as specified by GB/T4213 or ANSI/FCI 70-2 standards； When the process requires a tight shut-off (TSO) function from the control valve or involves emergency shutdown interlocks, the allowable leakage class for such valves should be Grade V or higher as specified in the GB/T4213 or ANSI/FCI 70-2 standards. This specification states that control valves can have requirements for tight shut-off and can be part of emergency shutdown interlocks. However, it’s not entirely clear whether such a control valve can function as an emergency shutdown valve itself, or whether it is not actually an emergency shutdown valve but rather serves only as an auxiliary to one
This control valve can itself function as an emergency shut-off valve, only with higher requirements regarding the leakage level
When used as an emergency shut-off valve, pneumatic control valves must meet the specified requirements; however, the emergency shut-off function is not inherent in the pneumatic control valve itself, but is generated by a control device that sends out the emergency shut-off signal.
Based on the SIL level, 0 and 1 can be used
So does that mean the control valve receives two signals: one is the control signal for normal operation, and the other is the emergency shut-off signal? And must the actuator also have the capability to shut off quickly?
Yes. The emergency shut-off actuator is usually a three-way solenoid valve, used to switch the air path of the pneumatic control valve.