Shaft sealing of small steam turbines is typically accomplished with which option?

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

Answer: (C)

Shaft seals on small steam turbines must keep steam out of the bearing area while withstanding high speed, heat, and moisture, with minimal maintenance. Carbon rings, made from graphite-based material, are self-lubricating and wear-resistant, so they can maintain a tight seal on a rotating shaft without requiring constant adjustment or lubrication. This combination gives reliable sealing under steam conditions and long service life in a compact, simple seal arrangement—ideal for small turbines. Rope packing and lantern rings require periodic tightening and often leak, generating heat and more maintenance. Labyrinth seals reduce leakage but don’t provide a true, consistent seal, and mechanical seals, while very tight, are more complex and expensive for small machines. So carbon rings offer the best balance of sealing effectiveness, reliability, and maintenance for these applications.