A control valve with a plug that moves upward to close the port is classified as:

A control valve that features a plug that moves upward to close the port is known as a reverse acting valve. This classification means that the valve operates in opposition to the direction of the valve actuator. In this case, when the actuator receives a signal to close, it moves the plug upward against the seat, thereby stopping the flow.

In general, reverse acting valves are often used in applications where a fail-safe mode is required—if the actuator loses power or control signal, the valve will automatically fail to the open position, allowing for continued flow and preventing damage due to pressure buildup. This is particularly useful in systems where maintaining a certain flow is critical for safe operation.

Understanding this mechanism is essential for anyone working with control valves, as it directly affects how the valve responds to control signals and how it will behave in emergency situations.