Blown O rings?

[derwoodwithasherwood]

Makes sense, though... except that it seems like the yoke should be rotated over in the same direction as you're tightening the knob. Looking from the back, as you're tightening the knob clockwise, at the end you should make sure the yoke is also clockwise as far as it will go. That way, if it were to rotate counter-clockwise, that would tend to tighten the threading. Or do I have that wrong?--Marek

Ummm, no, you have that right. I didn't phrase it quite right, did I? I guess I was trying to say you rotate the yoke counterclockwise against the valve as you tighten the clamp behind it. Anyway, you got the idea. As for yokes I think the idea is that if they start to stretch, the o-ring will blow out and releive the pressure before they will break. After all, if there's enough pressure there to stretch steel, that poor little rubber o-ring doesn't stand a chance.

 

[Marek K]

I understood the principle advantage of DIN over yoke is that a yoke is far more susceptible to loosening up under pressure and that's what blows o-rings during a dive. There's two factors involved: first, a yoke can stretch slightly -- more so as cylinder pressure increases.

I just found some Sherwood technical manuals and service bulletins online. Interesting... Service Bulletin No. 102 from November 1988 discussed the "new" DIN valves and fittings. Sherwood apparently believed strongly in them even back then, predicting that "DIN is the connection of the future." It also discusses the potential yoke-bending factor. "With a good added factor of safety the yoke system is quite safe at 3000 psi. However, above that, because of the requirement that the yoke span around the outside of the valve, higher pressures tend to straighten the yoke sides. This results in a release of the o-ring causing a loss of air at the inlet." Sherwood goes on to explain how the DIN fitting is more secure for higher pressures.

Note that there's no mention of a yoke o-ring being less secure at pressures up to 3,000 psi -- even though it was pretty obvious that Sherwood was committed to the new DIN fittings and was trying to "sell" their merits.

Also interesting that in Service Bulletin No. 104 from September 1989, Sherwood noted that even DIN fittings weren't perfect either. "Any rotational movement of the regulator in relation to the valve face when the gas pressure is turned off may loosen the connection, which increases the chance of o-ring extrusion and gas leakage. For this reason SHERWOOD recommends the diver check that the DIN handwheel is tightened firmly just before the air is turned on." Pretty common-sense, but they apparently felt the need to stress that.

--Marek

 

[ScubaSarus]

I cant ageee more with thos predive checks of minor snugging up of connections.

 

[carlislere]

I have seen one blow underwater and I had an oring blow on my O2 cylinder a couple of days ago. THAT was exciting for a short period! That's all in 27 years of diving. Every time I VIP my tanks I replace the orings (tank valve and yoke).