What best describes a dry gas seal?

• A. It operates like a mechanical seal but uses gas instead of seal flush oil.
• B. It uses liquid lubricants to reduce wear.
• C. It seals without any moving parts.
• D. It is used only in water-based systems.

Answer: (A)

A dry gas seal works by creating a thin, pressurized gas film between the rotating and stationary seal faces to prevent leakage, instead of using liquid lubrication. It is built like a traditional mechanical seal—two seal faces that mate and rotate with a small gap—but the sealing medium at the interface is gas, not oil. The barrier or purge gas supplied to the seal chamber both lubricates the seal faces through gas-film dynamics and carries away heat and any leaked fluid, keeping the faces separated and reducing wear. This setup eliminates the risk of oil contamination in the process fluid and is well-suited for handling volatile or hazardous services.

That description aligns with why this is the best choice: it highlights the key feature—the use of gas instead of seal flush oil to lubricate and seal—while staying true to the mechanical-face nature of the device. The other options imply no liquid lubrication (which isn’t accurate for dry gas seals, since gas provides the lubrication within a gas film), suggest there are no moving parts (there are still rotating faces), or limit usage to water-based systems (dry gas seals are used with a wide range of media).