DIN over 3000 PSI?

[Leadking]

I've just been lurking since being soundly thrashed last week for saying 3442 psi is the same as 230 bar, but since this thread comes up again and again, can somebody clue me in- where does 3442 come from??

The European standard is 230 bar @ 15c this is temperature corrected to 3442 psi @ 70f, which is the CGA standards temperature. You are allowed to use any "recognized standard" under CGA rules and the European standard meets that criteria.

Lee
www.seapearls.com

 

[Leadking]

All modern regulator yokes can easily withstand 4000 psi. Same with the yoke valve and O rings. However, the valve itself must have been manufactured after 1977 (Sherwood) and be in good shape. For use above 3000 psi, you really should use the high pressure urethane O ring. This is milky white in appearance and is fairly hard (90 durometer). Years ago, I machined some yoke valves to fit the PST HP tank which has a 7/8 UNF thread. Never had a problem. The standards committees are not necessarily experts. They just have to check around to get some opinions and vote. It means little. The manufacturers, once they see the new standard, adjust the performance claims to meet the standard. It should be the other way around but the standards committees set conservative limits to account for old, obsolete equipment which may be still in service.

We have been testing new yokes and finding that under pressure are stretching as much as .010 inch. This stretch allows the outlet o-ring to extrude and when the pressure is reduced, to pinch the o-ring. Please be sure to inspect your o-rings frequently when using a yoke fitting on a higher pressure cylinder (3300+).

Lee
www.seapearls.com

 

[pescador775]

My white O rings last 10 years. I have not seen a pinched O ring since 1976. This occurred in two instances that year. One instance involved a Nemrod valve which required a European O ring. The other involved a new Sherwood valve, the first of type with the new, skinny O ring. Replacement with a white O ring solved the problem, permanently. Later model Sherwood valves with the same thin O ring groove did not have this problem and even soft, black O rings would work OK. I don't recommend them for high pressure because I believe in using the best O ring available.

I just came back from my dive locker. I placed a caliper on the yoke of a MK 25 first stage which was attached to an HP tank. The stretch measured 0.002 when the yoke was pressurized to 3500 psi. That's about the same stretch as a DIN threaded connection.The caliper is accurate to 0.001 inch.

Keep checking, LOL

Pesky

 

[oxyhacker]

Interesting. Have you found any relationship between the pressure ratings of the yokes, and the amount they stretch? Oh and any advice as to which brands seem to be best and worst in regard to stretch?

We have been testing new yokes and finding that under pressure are stretching as much as .010 inch. This stretch allows the outlet o-ring to extrude and when the pressure is reduced, to pinch the o-ring. Please be sure to inspect your o-rings frequently when using a yoke fitting on a higher pressure cylinder (3300+).

Lee
www.seapearls.com

 

[captndale]

I used to use adapters to fill high pressure tanks with DIN valves. The adapters are solid brass devices which screw into the DIN valves and are made to take Yoke fill fittings. They have standard O-rings. Very often the o-rings would extrude during filling - usually at about 3500 psi.

 

[bradshsi]

For use above 3000 psi, you really should use the high pressure urethane O ring. This is milky white in appearance and is fairly hard (90 durometer).

I'm curious as to why you would recommend this material ? Many urethane grades are affected by humidity or water and have a quite limited temperature range as well.

EPDM is a superior material for general sealing duties involving water, air and oxygen.

If you want extrusion resistance at high pressures you need to control the o ring hardness (rather than changing the material) and the sealing groove geometry/tolerances. Ceteris paribus, yoke stretch is also important as others have posted

 

[SCUBA-J]

DIN IS BETTER . I just can't see the arguemunt ...................................

 

[oxyhacker]

There are a lot of O-ring parameters which are not easily reduced to numbers, like mechanical strength. Urethane is probably the "toughest" O-ring material made, which makes it ideal when extrusion is a problem. However it is expensive and not terribly good in dry running dynamic applications, so most reg and valve manufacturers only use it when nothing else will do.

Just going to a higher duro nitrile or EPDM isn't a perfect solution because. While the higher duro improves resistance to extrusion, it is often at the expense of sealing qualities. And it doesn't necessarily make the O-ring any stronger - just harder - so while it will resist extrusion better in the short run, it will often break down sooner than a urethane O-ring would in the same application.

That said, urethane O-rings are often hard to find when you need them, so I always keep 90 duro EPDMs around, for valve necks and yoke face seals, for when I don't have a urethane ring handy.

I'm curious as to why you would recommend this material ? Many urethane grades are affected by humidity or water and have a quite limited temperature range as well.

 

[Leadking]

I'm curious as to why you would recommend this material ? Many urethane grades are affected by humidity or water and have a quite limited temperature range as well.

EPDM is a superior material for general sealing duties involving water, air and oxygen.

If you want extrusion resistance at high pressures you need to control the o ring hardness (rather than changing the material) and the sealing groove geometry/tolerances. Ceteris paribus, yoke stretch is also important as others have posted

We are now suppling our Pro valves with a uretahne o-ring. Finding an urethane o-ring that is compatable with o2 and marine enviroment was difficult and the cost is 20x buna and EPDM even in bulk purchases.

Lee
www.seapearls.com

 

[Leadking]

All the testing was done at Themo's lab in Japan and I'm not privy to that info nor do I think they will give it to me as I belive they do not want to cause a conflint among the mfr.s.