A pneumatically actuated globe type control valve that opens upon air failure is characterized by what type of actuator?

In the context of a pneumatically actuated globe type control valve, the classification of the actuator is crucial for understanding how it responds to air failure. A direct acting actuator is designed to open the valve when there is a loss of air pressure. This means that the actuator relies on the pressure of the pneumatic supply to hold the valve closed during normal operation. When air pressure decreases—such as during an air failure—the actuator loses its ability to maintain the closed position, allowing the valve to open.

This type of actuator is particularly useful in safety applications, where opening upon failure can help prevent damage or hazards in a system. It is important that operators recognize this behavior, as it impacts how systems are designed for safety and operational efficiency. Direct acting actuators are contrasted with reverse acting actuators, which would require air pressure to close the valve and thus would behave differently in the event of an air failure.