Which of the following is not a part of a flow control valve?

• A. Needle
• B. Check valve
• C. Flow restrictor
• D. Vane

Answer: (D)

Flow control valves regulate how quickly air flows by throttling the passage. The thinning or narrowing is typically done with a needle that slides into an orifice, giving fine, adjustable control over the flow rate. A check valve is included in many assemblies to prevent backflow, so air can go in one direction only. A flow restrictor provides a fixed resistance to flow, setting a constant rate or limiting speed when combined with the throttle. A vane, on the other hand, is not a typical component used to control or guide flow in a flow control valve; vanes are found in other devices like vane-type pumps or dampers, not in the throttling mechanism of a flow control valve. Therefore, the vane is not part of a flow control valve.