NGO threads, thread data?

[Prometheus21]

Hello everyone,

I am currently designing some new filling equipment for the compressed gas industry in my country. Relevant gases include oxygen, nitrogen, acetylene, hydrogen, helium, phosgene, phosphine ect.

Looking into the different cylinder valve outlet connections, I am familiar with the ISO 5145, DIN 477 & DS 2404 as these are quite common in Europe. A typical thread: W21,8 x 1/14 is described in detail in DIN 477; thread size, thread dimensions, thread tolerances and recommended tap diameters. The standard also describes the required sizes for outlets, gaskets, connectors, union nuts and screw caps. The Maryland Metrics thread chart also describes the thread form in detail, and is of great use.

I am however stumped when it comes to the CGA fittings and the NGO threads as I am unfamiliar with them. Does any of you know which standard(s) describe the following fittings and accompanying threads?

CGA540 - 0,903"-14 NGO ext.

CGA580 - 0,965"-14 NGO int.

CGA680 - 1,045"-14 NGO int.

Thank you for any input you may have!

 

[3DDave]

CGA - Compressed Gas Association

https://www.cganet.com/

NGO - National Gas Outlet

CGA 540 describes the entire interface - the internal mating parts as well as the connection threads - solely for Oxygen service.

I don't know exactly why, but in searching I saw no dimensions other than the reference OD/ID of the threads. Even the CGA site doesn't make the information obvious.

I can guess that the industry doesn't want people to create their own, potentially dangerous, adapters from unsuitable materials or with unsuitable control of variation. They depend on safe use of compressed gases and if someone is killed using a compressed gas system they know the news won't report the use of a home-made adapter.

 

[Prometheus21]

3DDave: Thank you for the input.

Yes, so CGA 540 would be the european DIN equivalent of DIN 477 No. 9. This describes the entire interface as well; washer, screw cap, outlet, gasket, connector and union nut. Then again, Europe is special; every country has its own personal adaption of a standard. An example: northern Europe uses DIN 477 No. 6 for oxygen, not No.9. Its a complete mess.

The only documentation I am able to find is a 1977 description of the connection from a CGA pamphlet (limited snippet attached). An updated version would be preferable, but it seems impossible to find. Emuge Franken (company) are also able to provide GO NO/GO thread gauges and rings for the actual manufacturing inspection. I have therefore requested the following data on threads and sizes, typically seen in DIN 477:

Thread
Minor dia
Pitch dia
major dia
countersink
hexagon size
Hole
Chamfer
Full thread (depth minimum)
Bore depth
Length (minimum)

My problem is this: my company has a request for 12 different gas fittings, valves and the likes. The fittings are from different standards, ranging from German standard, Italian, CGA, Danish and ISO. We are able to manufacture every one, but we struggle with the CGA fitting as this is relatively new ground (My company last produced a CGA fitting in the 1980s). It's a shame because we can fulfill every other customer requirement like material specs, precision cleaning requirements, inspection, ignition testing, hydrostatic testing ect.

I understand where you are coming from regarding compressed gas safety and home-made adapters. But with the limited information available even long standing, professional, manufacturing suppliers are stumped. Which makes it quite hard for a European supplier to provide gas fittings for CGA cylinder valves.

 

[Prometheus21]

If anyone should stumble upon this thread in the future:

NGO threads and CGA fittings are described in detail in the CGA V-1.

If you want the really old documentation you can also search up "The National Bureau of Standards Handbook H8 Screw Thread Standards Part 2". It's old, but it contains more in depth information and history around the different threads, for those who find that interesting.