Selecting the proper seal is one of the most important decisions when building high and ultra‑high vacuum systems. Two dominant options are the copper gasket and the Viton O‑ring, and each fits distinct vacuum levels, temperature ranges and process conditions. Mixing them up can lead to leaks, excessive outgassing or premature seal failure.
A copper gasket is an all‑metal seal designed mainly for CF knife‑edge flanges. Usually manufactured from oxygen‑free high‑conductivity copper, it creates a hermetic seal through plastic deformation under bolt compression. It can withstand baking temperatures up to 450 °C and achieves ultra‑low helium leak rates required for UHV environments. Since copper deforms permanently after compression, a new copper gasket is generally recommended every time the flange is opened. It is ideal for particle accelerators, surface analysis tools and semiconductor UHV chambers, and it pairs perfectly with our CF vacuum bellows and flanges.
On the other hand, a Viton O‑ring is an elastomer seal commonly used with KF and ISO vacuum fittings. It is reusable, easy to install and more affordable for routine high‑vacuum setups. Viton offers excellent resistance to many oils, chemicals and moderate heat, with a typical continuous working limit around 200 °C. However, it cannot survive high bake‑out temperatures and has a noticeably higher outgassing rate than a copper gasket. If exposed to excessive heat or aggressive process gases, Viton will degrade, swell or crack, introducing virtual leaks and contaminating the vacuum cavity.
For quick assembly, frequent disassembly and medium‑high vacuum without baking, the Viton O‑ring is a practical choice. If you need UHV performance, high bake capability and minimal gas release, the copper gasket is the only reliable solution. Many vacuum labs and coating facilities keep both types on hand for different sections of one system.
We stock precision copper gaskets for all standard CF sizes and durable Viton O‑rings for KF and ISO connections, alongside vacuum bellows, flanges and other vacuum components. Contact our engineering team if you need help selecting seals or full vacuum assembly parts for your project.