Nitrogen, argon and helium: one brief per medium

ANYI's factory record groups nitrogen, argon and helium into a single medium category holding eight models. Their recorded working pressures range from 15MPa through 20MPa, 23MPa, 25MPa and 30MPa, with 2175Psi appearing as well, and the recorded bore across the group is Φ4mm.

A grouping like that is easy to misread. It is a filing decision in the product record, made because these gases are handled by a similar family of valves. It is not a statement that a valve suitable for one is suitable for the others, and it is not permission to write one enquiry for all three.

One category, three requirements

The practical consequence is that if you buy nitrogen, argon and helium, you have three requirements, not one. They may well end up pointing at related models, and they may well be quoted together. But the brief that produces them should be written once per medium, because the details that differ are exactly the details that decide the answer.

Helium is the clearest case. Its behaviour at a joint is not nitrogen's, and an assembly that is satisfactory on nitrogen is not automatically satisfactory on helium. Stating the medium explicitly, rather than writing "inert gas", is what lets a supplier tell you whether the record supports what you are assuming.

What each brief should state

• Name the gas, not the groupWrite "helium" rather than "inert gas". The group name is our filing; the gas is your requirement.
• Give the service pressure per gasThe same installation often runs different gases at different pressures. One figure for all three hides that.
• Give the cylinder thread per gasCylinders sourced from different suppliers for different gases frequently differ at the neck. Check rather than assume they match.
• Give the outlet per gasOutlet designations are often deliberately different between gases on the same site. That is a safety feature, not an inconsistency to be tidied away.
• Say if purity mattersIf your process has a purity requirement, state it. It changes which questions we have to put to the factory.

A higher number is not a better fit

One more thing worth saying plainly, because the pressure figures above invite it: a higher recorded working pressure does not make a model better. Within this group the range runs from 15MPa to 30MPa, and every one of those is a limit recorded for a specific model. Choosing the highest number available is not a conservative choice; it is a choice made without reference to your conditions, and it can put you on a connection or a bore you did not want.