Mechanical fail-safe solutions exist for electric driven valves, however mainly for on-off applications. For control valves often the only solution is ‘stay-put’ upon electric power failure.
The axial flow valves from Mockveld require very low forces, since they are fully pressure balanced. This design feature makes electric fail-safe control valves possible, even for large or high-pressure valves. Two options exist for a fail-safe action in case the power supply is lost: spring action, or a power pack (such as a capacitor).
In the case of a spring, extra electric power is required and the pressure balanced axial flow concept makes this possible. Mokveld supplied two 10-inch ASME 1500 lbs subsea anti-surge control valves equipped with spring opening fail-safe electric actuators. These anti-surge valves protect the subsea compressor by opening in <2 seconds.
The second solution is a fail action by power pack. In this case by capacitors, these valves are installed on an M&R station (Metering and pressure Reducing station). Two 12-inch ASME 600 lbs control valves in an active/monitor configuration regulate downstream pressure. The latest generation capacitors are reliable and can be constantly monitored to further improve reliability and availability. This solution can also be used to improve plant availability and production, and control can continue in case the power in the plant is lost.
