What causes an HP oring to extrude?

[wKkaY]

I had my gear setup and pressurized. About 5-10 minutes later, I heard air freeflowing out of the first stage. Fortunately we were still on the boat and haven't gone into the water yet.

It turned out that the HP o-ring for my SPG hose extruded out. We removed the hose, inspected the o-ring for damage, and put it back. It pressurized without leaking and I completed the dive without problems, although I did feel a bit nervous about it recurring during the dive.

What could have caused the o-ring to extrude? Something that comes to mind is that I've been swapping hoses around a bit as I don't have dedicated singles/doubles regs yet.

 

[northernone]

I had my gear setup and pressurized. About 5-10 minutes later, I heard air freeflowing out of the first stage. Fortunately we were still on the boat and haven't gone into the water yet.

It turned out that the HP o-ring for my SPG hose extruded out. We removed the hose, inspected the o-ring for damage, and put it back. It pressurized without leaking and I completed the dive without problems, although I did feel a bit nervous about it recurring during the dive.

What could have caused the o-ring to extrude? Something that comes to mind is that I've been swapping hoses around a bit as I don't have dedicated singles/doubles regs yet.

A loose hose will do it. Sometimes they can twist free a couple turns during transportation if they've not been torqued sufficiently. Can extrude without visible damage to the oring.

If it wasn't loose, I'd be shocked it could extrude.

 

[Fibonacci]

Couple of possible causes... the outer diameter of the SPG hose vs the o-ring recess in the first stage.
The most likely cause is someone putting lubricant on the o-ring... seems to make 'em squirt out like a watermelon pip!

 

[guruboy]

The high pressure caused it!

I'm here all night, folks.

 

[rsingler]

@northernone had it right. The o-ring for the HP hose is captured between the end connector for the hose and the recess in the first stage. Properly tightened, there is NO room for an extrusion, lubricated or not.
This happens to me all the time in my shop. I'm testing a reg and twist on a gauge hose by hand with zero wrench work. It usually works just fine for a quick test, but every so often I hear a little hiss, and quickly shut off the tank. Sure enough, the hose has untwisted a hair, and the oring is extruding thru a 1/4 mm gap. I tighten the hose a little and go on with my work. Of course, that o-ring gets replaced before the reg goes out the door.

You can improve your odds by using a 90 duro hard 2-011 o-ring for your HP hose. It's just a LITTLE more resistant to extrusion. But there is a fair amount of variation by manufacturers. Some use a 2-012 and some use a 2-011. My point is, the oring jams into place between the two metal pieces whether it's a shade large or a shade small.
But if there's ANY gap, out it comes. That makes a quick hose twist a good check to add when you're setting up your gear. Any movement, and you've discovered a quick thing to fix before you dive (make sure you carry a thin wrench with you - bicycle wrenches make reasonable lightweight add-ons to your kit - just carry the sizes you need).

Add some hose rings to your Save-a-Dive kit. Easy fix.

 

[herman]

Orings extrude for 3 reasons - excessive space between the 2 mating surfaces, excess pressure or improper durometer (hardness). Odds are the hose was a little loose which introduces excessive space between the mating surfaces but a word of caution. The hoses need to be snug but not excessively tight. Don't be tempted to really crank down on the fitting, that will do no go and possibly do damage if you get too excessive with it
Contrary to popular belief, hose orings should be lubed as well. That does not cause them to extrude but rather is required for them to work properly. They need to slide into place as the hose is installed and to a lesser extent when they become pressurized. If they are dry, the oring can bind creating a gap that will cause it to leak or worse become damaged during installation. Lubing them may make the oring tend to extrude more if excessive space exist between the mating surfaces but this is still excessive space between the mating surfaces and not "caused by" the lube itself.

 

[wKkaY]

Thanks all for the replies! I tighten my hoses with a wrench, slightly more snug than finger tight. I'm aware that the brass is soft so I haven't tightened it harder, I'll up it a little bit from now.

I've been applying lube to the hose o-rings, a habit I carry over from handling torchlights. When screwing the battery cover on dry o-rings there's significant resistance which I feel could compromise the seal.