O-ring blew up after 3 dives - bad luck or I messed up?

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Was it a buna or viton o-ring? From reading some posts by rsingler, viton o-rings are more prone to damage.

-Z

I too have experienced that Viton (yes I was buying genuine FMK Viton brand) o-rings are more prone to damage. I don't know if there is scientific truth to back this but just based on my own personal experience I find that Viton does not last as long. I also find that it swells when under pressure for long periods of time. As in the o-ring literally swells up larger. I actually stopped using Viton DIN o-rings on my deco regs/O2 CCR regs because of this as it was just annoying to keep changing them.
 
I have found that FKM has a lower tensile strength than Nitrile (by a factor of 2:1 in my last pull test), and has poorer long term set capabilities. Static Viton o-rings in high pressure applications soon develop the shape of the land, and lose some of the elasticity that helps an oring displace and seal.
I have not noted swelling, but they clearly change shape.
Sudden fracture of both FKM and Nitrile o-rings may be more a function of fillers than the quality of the o-ring compound. Imported o-rings seem to be particularly prone to this, and I see it not infrequently.
While extrusion and o-ring failure due to a loose fitting is indeed a risk, overtightening won't hurt the oring in a hose connection, though it may indeed damage soft brass threads.
But I've seen what you've seen: sudden unexpected failure where the o-ring simply fractures. As suggested above, there may have been too much filler with resulting brittleness, or perhaps a small flex crack that propagated after pressurization due to mishandling of a stiff duro 90 oring during installation, especially if it was installed when cold.

In any case, no big deal. Carry some in your save-a-dive kit and replace it on the spot. O-ring sourcing is a very variable phenomenon. Don't blame yourself.
 
Just for 100% clarification your talking about the actual 012 o-ring that goes on the male 7/16" HP hose end that screws into your first stage? and not the the little 003 o-rings that go on the spool between the HP hose and SPG?
Yes correct
Was it a buna or viton o-ring? From reading some posts by rsingler, viton o-rings are more prone to damage.

-Z
No idea.

I'm completely new to this, I've always rented my gear before. I'm discovering that there are different types of o-rings / brands etc.

I didn't trust the random o-ring they gave me at the shop so I went ahead and bought some new ones, a dozen for LP ports, a dozen for HP ports (so at least I know they're the right type/size) + some silicon grease.

Out of curiosity, when I opened my tank, the flow was very high with the broken o-ring. If that happens underwater, and my tank runs out of air and salt water starts getting in, how much damage am I looking at? Both SPG and the first stage will have to be cleaned/serviced? Or not really a big deal?
 
Out of curiosity, when I opened my tank, the flow was very high with the broken o-ring. If that happens underwater, and my tank runs out of air and salt water starts getting in, how much damage am I looking at? Both SPG and the first stage will have to be cleaned/serviced? Or not really a big deal?
The HP port should be flow-limited, so that the tank takes at least 15-20 minutes before becoming fully empty.
So it is expected that you are back on the boat before the air finishes.
If the failure affects an LP port, instead, the air flow can be really huge, emptying your tank in a couple of minutes.
After the tank is empty, some water can flow in, requiring at least a proper cleaning of the reg.
 
Wait, am I missing something?
HP "pushes through" a lot of air, LP pushes through a very low flow of air, no?
If my LP port fails it would be equivalent to having a free flowing regulator, which leaves me a lot of time to empty a tank.
But HP should be much faster to empty the tank no? What you describe seems to be the opposite.
 
While the pressure of the the hose where you connect your console to is much higher than on the other ports, e.g. 207 bar to 10 bar, the opening that the gas has to rush through is tiny on the high pressure side.

  • High pressure side: High pressure + tiny tiny aperture = Very small loss of gas.
  • Low pressure side: Low pressure + huge aperture = Huge loss of gas.

I have in my head that EN250 stipulates that a burst HP hose shall not leak more gas than 29L per minute. However I cannot find that reference in EN250, so I'm not sure where I got this number from. Looking at this number, it seems a bit on the low end as well. Somewhere between 90L and 120L seems more reasonable.

A ruptured LP hose will be limited by how much your cylinder valve and/or regulator can pass through (And yes, how much can pass through a single port...). A ScubaPro MK25 EVO can flow 8500 liters of air per minute at 200bar for example.

Curt Bowen did an interesting Test on this. The HP hose failure took 22 minutes to empty the cylinder. The LP hose failure took around 80 seconds to empty the cylinder.
 
Wait, am I missing something?
HP "pushes through" a lot of air, LP pushes through a very low flow of air, no?
If my LP port fails it would be equivalent to having a free flowing regulator, which leaves me a lot of time to empty a tank.
But HP should be much faster to empty the tank no? What you describe seems to be the opposite.
Although the quality is poor this video demonstrates HP hose lose takes over 30 min to drain tank, but LP less than 2 min. Here. Just be patient they get round to it.
 
Oh I didn't think that through, I wrongfully assumed that they were the same diameter.

Thanks for the clarification guys, learning a lot :)

Since we're on this topic and I'm starting to realize there's a lot I should know and I don't - are there any other areas of concerns I need to worry about except my LP and HP orings? (aside from regular rinsing + servicing by a pro every year)
 
Wait, am I missing something?
HP "pushes through" a lot of air, LP pushes through a very low flow of air, no?
If my LP port fails it would be equivalent to having a free flowing regulator, which leaves me a lot of time to empty a tank.
But HP should be much faster to empty the tank no? What you describe seems to be the opposite.
It is the opposite. The HP port is designed for a pressure gauge, which requires substantially no flow, so the port has just a very tiny hole for air passage.
An LP port instead is designed for allowing a massive air flow. So the tank will be emptied much faster through an LP port than through the HP port.
 
Since we're on this topic and I'm starting to realize there's a lot I should know and I don't - are there any other areas of concerns I need to worry about except my LP and HP orings? (aside from regular rinsing + servicing by a pro every year)
Well, serviced by a pro WHEN NEEDED, not every year.
Some sealed first stages are rebuilt typically every 5 years.
Most balanced second stages need servicing (a new seat) every 2-3 years.
You should buy an IP gauge, indeed, and learn how to evaluate yourself if the reg is operating properly or is needing service.
 

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