Pneumatic and electric motors are not inherently fail-safe. They must be energized to operate and move the valve to the safe position. Motors usually operate EBVs with gate and globe valves because they require a high thrust to work.
To make the systems reliable, consider these factors: testing, fireproofing, and accessibility:
• Establish a frequent testing of the motors, preferably once a month.
• Fireproof motors, any controls, and electrical conduit inside the fire hazard area.
• Back up the electrical power to the starter motor with an emergency power generator or make sure the motor control center is double-ended and fed from two independent power sources.
• For pneumatic motors, install reserve tanks with a low-pressure alarm and double-check valves on the supply line or back up the supply pressure with a secure form of gas pressure, such as a plant-wide nitrogen system.
• Review the time needed to operate these emergency valves fully because the horsepower required is in proportion to the speed of operation.
• Make sure spare motors are available when problems are highlighted during testing.
• Train maintenance people on these specialized drivers.
• Provide safe access during an emergency to the manual override gearbox.