The shafts of high output, high temperature steam turbines are usually sealed using:

• A. Garter springs
• B. Carbon rings
• C. Packing rings
• D. Labyrinth glands

Answer: (D)

Labyrinth glands are used because they provide a non-contact seal that can endure the extreme conditions of a high-output, high-temperature turbine shaft. The seal consists of a complex path of grooves and surfaces that create multiple tiny resistance barriers. As steam tries to leak past, it must navigate this long, tortuous path, which greatly reduces leakage without relying on sliding contact. Since there is no continuous metal-to-metal or elastomeric contact, the seal can withstand high speeds, high temperatures, and shaft expansion with minimal wear and maintenance.

Other seal types would involve sliding contact or materials that degrade under heat. Packing rings rely on packing material that rubs against the shaft and wears quickly at turbine speeds and temperatures. Carbon rings and similar sliding seals can tolerate high temperature to some extent but still suffer wear and require lubrication or special conditions. Garter springs are components used to preload some seals but do not constitute the seal method itself, and would not by themselves provide the robust high-temperature, high-speed sealing needed.