What are the three types of casing seals?

• A. Mechanical seal, liquid film seals, and dry gas seals
• B. Labyrinth seal, mechanical seal, and dry gas seal
• C. O-ring, gasket, and packing seal
• D. Ring seal, lip seal, and PTFE seal

Answer: (A)

Three main kinds of casing seals are used on rotating equipment: mechanical seals, liquid film seals, and dry gas seals. Mechanical seals rely on two mating faces pressed together, with a barrier or process fluid forming a thin lubricating film between them so the shaft can rotate while the faces stay sealed. A spring or bellows keeps the faces pressed together and accommodates shaft movement, delivering reliable sealing in a wide range of liquids and speeds. Liquid film seals depend on a continuous layer of lubricant circulating between the seal faces to provide lubrication and carry away heat, creating a barrier without relying on hard contact. This approach works well where a suitable liquid barrier is available and helps minimize wear. Dry gas seals use a non-contact gas film to separate the seal faces; pressurized gas supports the faces, so there is essentially no rubbing even at high speeds, which is ideal for high-speed gas service and minimizes leakage.

Other seal types exist, but they operate differently and aren’t the primary casing seal categories in this context.