Withee Works, LLC
Small Molecule Gases
I.
CONCERN
Hydrogen and helium have very small molecules. They are notoriously difficult to contain, to avoid
leakage. Hydrogen is especially a concern as it is a “burning” gas, even “explosive.” Helium is a
noble gas, not interacting with Oxygen, so it does not burn. As a result, Helium is the smallest gas
molecule which can safely be used for pressure and leak testing.
But the question is, how can you best contain gases such as these in laboratory settings?
II.
VALVE
Start with the valve. Valves should be constructed to ensure maximum protection against leakage,
and should be tested for same. The higher the purity of gas for which the valve is designed, the
better the resistance to leakage.
For instance, the two purity ends of BROEN gas valves have the following excellent leak rates:
2.0
6.0
III.
maximum 10-3 mbarl/sec measured with Helium
maximum 10-7 mbarl/sec measured with Helium
PIPE/TUBE/HOSE
Different materials have different uses.
 Commonly black iron is used with burning gases.
 Copper is used with other gases, but not burning gases due to likely chemical reactions.
 Stainless steel can be used virtually anywhere, and should be used with high purity gases.
 Plastic hose is increasingly used with all except burning gases (which includes hydrogen).
When it comes to gases like hydrogen in particular, to avoid potential leakage, BROEN
recommends stainless steel lined hose for best containment.
IV.
PIPE-TO-VALVE CONNECTOR
The last potential leak source is at the connector used to attach the pipe/tube/hose to the valve.
While most typical connectors work adequately in general, the extensive manual handling of the
varied pieces involved increases the likelihood of leakage.
BROEN’s UniFlexTM system includes double-seal connectors (twice the protection) already factory
applied to hose to ensure maximum protection from leakage.
V.
SYNOPSIS
To best protect against leakage of small molecule gases, select the correct materials: fixtures for
higher purity, stainless steel lined hose and proper connectors between the two.
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Withee Works, LLC * Suite 104, 1540 Capitol Drive, Green Bay, WI 54303 USA * 920.737.8477 * [email protected]