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

[Pyndle]

Hi,

I got a new set of DST/XTX50 and after 3 dives, when I was about to do the 4th one (there was a few days of travelling in the middle), my O-ring was broken as soon as I turned on the air. I'm talking about the small o-ring that sits between the Regulator and the HP hose for my SPG. O ring looked clean, just snapped in 2.

I'm assuming this is not common and I messed something up - would over-tightening the nut be the most likely cause of that?
Or more likely something else like big changes of temperature during the travelling (freezing AC to 40 degrees outside sitting in a suitcase back to freezing AC)?

Thanks!

 

[stiebs]

Did you attach the SPG hose yourself? If so, and it's not something you've done a lot before there are a few common mistakes that you may have made.

Number one, as you suggested, is overtightening it. The oring is what makes the seal, and really only needs to be hand tightened then snubbed no more than ⅛ of a turn. Too tight will definitely stress the oring.

Another thing to watch out for is if you put the oring on yourself, it's possible to damage it by pushing or turning it over the threads.

 

[Imla]

Also. While this is a stationary o-ring and not sealing parts in motion, installation will cause friction. So if the o-ring wasn't slightly lubricated when installing hose on 1st stage, friction/pulling forces could damage the o-ring. (And of course, It could be just bad luck. o-rings are usables. always keep them on hand)

 

[happy-diver]

The hose was inadequately tightened

 

[BoltSnap]

The hose was inadequately tightened

As in loose, not tight enough.

 

[broncobowsher]

Too loose will blow before too tight in that application. The HP hose will bottom out mechanically without damaging the O-ring. But loose, high pressure air will find a path and take it, blowing out the O-ring in the process.

The fitting won't back out while under pressure. Air pressure will press on the threads all but locking them in place. So it backed out between dives. Would never really have been an issue during a dive.

Now that several people are telling you it was too loose, don't go around and over-tighten everything either. These threads are made of soft metals. I use a 2-finger pull on a wrench about 3" off the hex. Roughly a dozen in-pounds of torque.

Dry O-rings can catch and distort as they are tightened as well. While lube isn't needed (not a dynamic O-ring) a hint of lube so the rubber will slide into place. Just enough that the O-ring has a gloss to it with no apparent lube applied.

 

[Eric Sedletzky]

You can’t really over tighten a hose as it relates to the o-ring because the fitting will bottom out metal to metal first before the O-ring gets smashed out. But over-tightening will stress the threads and there is no reason to over snug it. All it needs is a gentle snug just enough so you know it won’t loosen.
Also, make sure you use the correct O-ring. Anything exposed to full tank pressure needs to be duro 90 or it could extrude. Squeeze on it side ways, it should be stiffer than standard duro 70 O-rings.
I’m not sure if they include the proper durometer O-rings in save-a-dive kits. You might have to buy a few over the counter from your dive shop.

 

[Pyndle]

Thanks for the replies. That makes sense - I did attach it myself and have no clue what I was doing. I will try to find someone who knows what they're doing to learn how tight it should be / will also look

 

[GF99/99]

Hi,

I got a new set of DST/XTX50 and after 3 dives, when I was about to do the 4th one (there was a few days of travelling in the middle), my O-ring was broken as soon as I turned on the air. I'm talking about the small o-ring that sits between the Regulator and the HP hose for my SPG. O ring looked clean, just snapped in 2.

I'm assuming this is not common and I messed something up - would over-tightening the nut be the most likely cause of that?
Or more likely something else like big changes of temperature during the travelling (freezing AC to 40 degrees outside sitting in a suitcase back to freezing AC)?

Thanks!

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?

 

[Zef]

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

-Z