A pneumatically actuated control valve which opens on air failure has a:ans.Direct acting actuator and direct acting valve.Is typically used for a burner firing rate control valveDirect acting actuator and reverse acting valve.Reverse acting actuator and direct acting valve. Previous Marked for Review Next

The correct answer is: "Reverse acting actuator and direct acting valve."

Here's why:

1. A pneumatically actuated control valve that opens on air failure is known as a "fail-open" valve. This means that if the air supply fails, the valve will open.

2. A reverse acting actuator is used in a fail-open valve. In a reverse acting actuator, the valve stem moves up when the actuator is de-energized (or when air supply fails). This is the opposite of a direct acting actuator, where the valve stem moves down when the actuator is de-energized.

3. A direct acting valve is one where the flow direction changes in the same direction as the valve stem. So, when the valve stem moves up (as it does in a reverse acting actuator when air supply fails), the valve opens.

Therefore, a pneumatically actuated control valve that opens on air failure has a reverse acting actuator and a direct acting valve.