For a pneumatically operated ball valve with single-electronic-control spring return, what signals are transmitted to the control system during interlock control?
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As an emergency vent valve, what signals are transmitted by a single-electric-control spring-return pneumatic ball valve? Should this valve be set to open automatically and close manually, or to switch automatically?
The emergency vent valve must send feedback on its open and closed positions to the DCS; it has to operate automatically, manual operation is not allowed.
DO: Valve open. DI: Valve in open position, valve in closed position, local/remote, fault. Are the signal points correct and complete? Is the valve reset manual or automatic?
This can be set up to open automatically via interlock; the conditions for such interlocking are determined by the process control requirements. For example, in the event of overpressure, it is necessary to close the valve again. The interlock should only be disabled once the danger has passed, and the valve should be closed manually indoors. Only after all interlock parameters are normal can the interlock function be reactivated (i.e., the automatic mode).
For emergency vent valves, a gas-actuated type should be chosen. As the name suggests, its function is to allow venting. From a safety perspective, an normally open type would be more appropriate; valve position feedback and a DO output should be provided. On the DCS, interlock switching buttons can be installed. At the beginning of furnace operation, when no gas supply is available, the vent valve needs to remain open, so the interlock is disabled temporarily and the valve is opened manually. Once normal gas supply is established, the vent valve is closed and the interlock is reactivated.