The power supply and control signals for the actuator of the EBV are electric, pneumatic (gas or air), or hydraulic fluid. In each of these cases, the power and control system driving the actuator must be available during an emergency condition. To avoid spurious trips during normal operation, power sources should be very dependable, especially for fail-safe EBVs.
An electrically controlled actuator must be connected to an emergency power source so that it will function during any emergency, including a power outage. This power source should be backed up by a UPS. If the actuator cannot be connected to an emergency power source, then electricity should not be the power supply.
Power to the electrical motor’s starter should be backed up by an emergency power generator or the motor control center should be double-ended and fed from two independent power sources.
A pneumatically powered or controlled actuator (or both) must be connected to a highly reliable source of clean and dry air or gas, which will not be lost during an emergency. To ensure that the EBVs have power and control signals if the plant loses air, install reserve tanks or an air system backed up by a plant-wide nitrogen system for emergency use. Dedicated high-pressure air or nitrogen cylinders also provide a reliable power source.
Make sure the air or gas is clean and dry; or the actuator may fill up with water, corrode, and malfunction during an emergency.