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A redundant control system for emergency shutdown valves

| By Mary Page Bailey and Gerald Ondrey

The ASCO 141 Series advanced redundant control system (ARCS; photo) provides a redundant solution for a variety of emergency-shutdown valve applications. The system includes various redundant solenoid configurations to enhance the reliability of the process and meet specific safety or reliability requirements in automation processes. The single-inlet/single-outlet design provides a streamlined installation process compared to traditional bypass systems, while almost eliminating potential failure points, according to the manufacturer. The ASCO 141 Series ARCS is designed for use as a component in safety instrumented systems, and it functions as a redundant pneumatics-tripping device to control the pilot-air signal to a process-valve actuator. The ARCS features either two or four electrically actuated solenoid valves, visual indicators and a manually controlled bypass or isolation valve. The unique control functionality allows for maintenance of the solenoid valves without having to shut down the process valve. Furthermore, the use of the maintenance bypass or isolation valve is not required for functional testing of the ARCS unit — a downtime-reducing feature not possible with common bypass functions. — Emerson Industrial Automation, St. Louis, Mo.