From the ISA Meeting: Solenoid shutoff uses online diagnostics to ensure safety

By Alan S. Brown
Managing Editor, Chemical Online

Two-out-of-two (2oo2) voting solenoid shutoffs are the safety standard in the process industry. Both solenoids must trip in order to actuate the showdown.

This keeps spurious trips to a minimum, so large processing plants do not shut down accidentally when a solenoid trip coil burns out. While solenoids last about 15 years, a plant with 100 solenoids might have one or two burnouts annually.

Gauging the status of solenoids has always been a problem for process engineers. The solution, from Sis-Tech Solutions LCC (Houston, TX), is a smart 2oo2 solenoid system that tests itself and sends status information back to a process loop controller (PLC).

The system consists of two pneumatic solenoid-operated valves, a key actuated pneumatic bypass valve, three pressure switches, and a terminal strip for electrical connections.

"Engineers can set up the system to perform an automatic sequential query," says Sis-Tech senior consultant Bryan A. Zachary. "The unit drops the first solenoid valve. It checks the pressure and makes sure it returns to the safe state. If it passes, it then checks the second valve.

"You can set it up to run a check every week, every day, or every hour. The entire operation is invisible to your process. It only informs the operator if there is a failure," says Zachary.

Bypassing is not required for testing. The key-actuated bypass switch permits maintenance without process interruption. The unit is designed for use in pneumatic systems with pressures between 3-150 psi.

Sis-Tech has licensed the design to Asco Valve Inc. (Florham Park, NJ), which plans to commercialize it this fall.

For more information: Asco Valve Inc., Hanover Rd., Florham Park, NJ 07932. Tel: 973-966-2000. Fax: 973-966-2628.