Which shaft sealing material is commonly used in small steam turbines?

• A. Carbon rings
• B. Labyrinth glands
• C. Rope packing and lantern rings
• D. Mechanical seals

Answer: (A)

In small steam turbines, the sealing material needs to provide a reliable seal with minimal friction, tolerate steam temperatures, and be simple and maintenance-friendly. Carbon rings (graphite-based seals) fit this need well because they are self-lubricating and wear-resistant, which allows them to ride smoothly on the shaft while still sealing effectively. They handle the steam environment and can accommodate minor shaft runout without requiring complex adjustments, making them a practical, economical choice for small turbines.

Rope packing and lantern rings require more frequent adjustment and produce more friction and heat, leading to higher leakage and maintenance. Labyrinth glands rely on a tortuous path to reduce leakage but demand precise machining and tight tolerances, which aren’t as convenient for small units. Mechanical seals are excellent in many applications but add complexity and cost that aren’t typically justified in smaller turbines, where carbon rings provide the simplest, reliable sealing solution.