Question

Which of the following is a rotating shaft control valve?

• A. Butterfly valve
• B. Single seat plug valve
• C. Double seat plug valve
• D. Lifting gate valve

Hint:

To remember the difference, think of the motion: If it "twists" to open, it's rotary (Butterfly, Ball, Plug). If it "slides" or "lifts" to open, it's linear (Globe, Gate, Diaphragm).

Answer 1

The Correct Option is A

Control valves are broadly classified based on the mechanical motion of their closure members, typically divided into linear motion and rotary (rotating shaft) motion categories. 1. Rotary Motion Valves: In rotating shaft valves, the closure member (like a disc, ball, or plug) rotates on a shaft to open or obstruct the flow path. These valves are often more compact and require less force to operate than linear valves.

• Butterfly Valve: This consists of a circular disc mounted on a rotating shaft. When the shaft turns, the disc rotates to be either parallel or perpendicular to the flow. It is the classic example of a rotating shaft control valve.

2. Linear Motion Valves: In contrast, linear valves move the closure member in a straight line to regulate flow.

• Single and Double Seat Plug Valves: These are globe-style valves where a plug moves up and down (linearly) into a seat.

• Gate Valve: The "gate" or wedge is lifted or lowered linearly to open or close the passage.

3. Why Butterfly Valves are Preferred: Rotating shaft valves like the butterfly type are highly efficient for large-scale flow applications because they provide high capacity with relatively low pressure drop and take up very little space in the piping system.