VCR Face Seal vs Compression Fitting
End connections decide how clean and how serviceable a gas line will be. VCR face seals and compression fittings both appear on specialty gas panels, but they belong in different parts of the system.
How a VCR face seal works
A metal gasket is compressed between two polished faces by a gland and nut. The seal is metal-to-metal, has very little internal volume and can be re-made repeatedly with a new gasket, which is why it dominates tool hook-up and panel connections.
Where compression fittings fit
Compression fittings grip the tube with a ferrule. They are convenient for field-installed instrument and utility lines, but they create a small cavity and depend on correct ferrule installation, so they are kept off the most sensitive process paths.
Butt weld as a third option
Orbital butt welding removes the joint entirely. It is the preferred choice for permanent high purity headers, at the cost of being non-serviceable and requiring qualified welding and inspection.
Practical allocation
Use butt welds for permanent headers, VCR face seals for anything that must be disconnected, and compression fittings for instrument and utility lines downstream of the UHP boundary.
Installation discipline
Use a fresh gasket, correct torque and clean gloves. A scratched face or a reused gasket is a common source of a leak that appears only after a panel is fully assembled.
Related reading
UHP Diaphragm Valves
Ultra high purity diaphragm valves for specialty gas delivery. 316L VIM/VAR bodies
Valve Installation & Purging Practice
Field practice for installing UHP valves: handling, face seal assembly, leak check
How to Select a Specialty Gas Valve
A practical selection guide for specialty gas valves: gas compatibility, pressure, Cv
Specialty Gas Safety & Material Compatibility
Safety principles for specialty gas valves: gas compatibility, fail-safe state
How to Select a Specialty Gas Valve
A practical selection guide for specialty gas valves: gas compatibility, pressure, Cv
Diaphragm Valve vs Bellows Valve
Compare UHP diaphragm valves and bellows sealed valves for specialty gas: dead volume, temperature
UHP Valve Helium Leak Rate Standard
How helium mass spectrometer leak testing is specified for UHP valves: inboard versus across-seat
Frequently Asked Questions
Can a VCR gasket be reused?
No. Use a new gasket every time the joint is re-made.
Are compression fittings acceptable on UHP process lines?
They are better kept on instrument and utility legs; use VCR or welded ends on the process path.