Materials, Seals & Flanges — Quick Reference

Module 04 — Materials, Seals & Flange Systems  |  VacTech Fundamentals

Vacuum Range Typical Materials Seal Type Flange Standard Max Bakeout Temp Key Considerations
Rough
>1 mbar		 Mild steel, aluminium NBR (Buna-N) O-ring KF (quick-clamp) 150 °C Lowest cost; adequate for roughing lines. NBR has highest outgassing of common elastomers. Acceptable where ultimate pressure is not critical.
Fine
1 → 10−3 mbar		 SS 304 / 316 Viton (FKM) O-ring ISO-K (claw clamp) 200 °C Viton outgasses ~50× less than NBR. Stainless steel resists corrosion and has low permeation. ISO-K allows rapid assembly.
High
10−3 → 10−7 mbar		 SS 316L (electropolished) Viton O-ring or
OFHC Cu gasket		 ISO-K or CF
(knife-edge)		 200 °C (Viton)
450 °C (Cu/CF)		 Electropolishing reduces surface area & outgassing ~10×. CF flanges required for bakeout above 200 °C. Transition zone where elastomer seals reach their limit.
UHV
<10−7 mbar		 SS 316LN (electropolished) OFHC copper gasket CF (knife-edge) 450 °C All-metal seals mandatory. OFHC Cu deforms into knife-edge for leak-tight metal-to-metal seal. Full bakeout required to reach UHV. Low-nitrogen steel (316LN) minimises hydrogen outgassing.

Practical Notes

  • CF flanges are single-use gaskets — the copper gasket deforms permanently during tightening. Always use a new gasket when re-making a CF joint.
  • KF fittings use centering rings with integrated O-rings — fast to assemble but limited to rough/fine vacuum.
  • Bakeout compatibility — never bake a Viton-sealed joint above 200 °C; the elastomer will decompose and contaminate the system.
  • Outgassing hierarchy (lowest to highest): OFHC Cu < SS (EP) < Al < SS (as-received) < PTFE ≈ Viton < NBR.
  • Selkirk atmospheric pressure: ~950 mbar (altitude-corrected for elevation).
VIS-M04-005  |  VacTech Fundamentals — Selkirk College  |  Print-friendly reference card