Which fitting type incorporates an O-ring at the face of the fitting and is commonly manufactured using Buna-N or Viton seals?

• A. O-ring Boss fittings
• B. Orifice
• C. ORFS
• D. Union

Answer: (C)

O-Ring Face Seal fittings are designed so the seal sits on the face of the fitting rather than along the threaded interface. An O-ring is placed in a groove on the face, and when two fittings mate, the O-ring is compressed against a precisely machined, flat sealing surface on the counterpart. This face-seal arrangement provides a reliable, leak-tight seal even if threads aren’t perfectly perfect or when there’s some surface imperfection at the threaded connection. Materials like Buna-N (nitrile) or Viton (fluorocarbon) are commonly used because they offer good compatibility with hydraulic fluids and can handle the temperatures encountered in hydraulic systems.

This is why the choice is the ORFS option: it specifically describes the O-ring on the face that seals against the mating surface. Other options refer to different sealing concepts or connection types and do not describe this face-seal arrangement. For example, O-ring Boss fittings seal in a way tied more to the port interface rather than a dedicated face seal; Orifice is about flow restriction, not a sealing method; Union refers to a basic joining style that may use gaskets but does not define the face-seal O-ring arrangement.