Why don't we throttle with gate valves?

• A. They are designed to be fully opened or closed. Throttling could erode the gate over time.
• B. They are the most economical option.
• C. They require frequent lubrication.
• D. They are visually hard to inspect.

Answer: (A)

Gate valves are built for on/off service. The gate sits in the flow path and seals against the seats when closed, and when fully open, the flow path is mostly unobstructed. If you try to throttle them, the gate sits only partway across the bore, creating a narrow clear area around the gate edge. The fluid speeds up and jets through that small gap, causing erosive wear on the gate and seats over time. The partially open position also leads to rubbing between the gate and seats and inconsistent seating, which can cause leaks and poor shut-off later. Because of these wear and control issues, gate valves aren’t suitable for precise flow regulation; other valve types designed for throttling, like globe valves, provide better control and less wear in partial openings.