O-Ring and Lubricant

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pscottbaker

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Location
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I found that my SPG hose was ever so lightly leaking at the first stage during a recent dive trip. I've disconnected the hose from the first stage and it looks like the o-ring is a bit dry so I thought I would replace it and while researching the process I found a few options and would like some feedback and guidance. I typically dive nitrox and from what I've read viton is the appropriate o-ring material as compared to nitrile. Any thoughts on my selectin of viton for the o-ring material? My next question is if I should use a lubricant? I've read everything from - don't use a lubricant, use spit and use an O2 compatible lubricant. Any suggestions would be appreciated.
 
If you're an occasional O-ring changer, then the simplest solution is the best. Stop by the hardware store or a dive shop. Grab a 2 - 012 nitrile O-ring, spit on it and snug up your hose.
But since there are 3 materials, 2 durometers, and 4 possible sizes, 3X2X4 equals 24 opinions.
I'll elaborate below.
 
Size: Most manufacturers specify a 2 - 012 0-ring. Some specify 2 - 011. Either will work, for different reasons. A 011 will expand slightly as tank pressure is applied and jam into the corner between the reg body and the hose. For most regulators, a 012 is slightly oversized and will scrunch into place and seal just as well. This is the preferred mechanism, but you don't want the O-ring to wrinkle microscopically, hence a little lube.
EDIT: See more info in post #10 below!

Lube: This o-ring is a static o-ring. There is no movement once it's snugged up. Therefore there's no need for lubrication since the O-ring or the part doesn't slide. But you don't want it to catch microscopically on the fittings when it's first installed. A little lube helps there but doesn't help the seal. For nitrox you don't need an 02-compatible lubricant, or for that matter, any lube at all, if it seals.

Material: Viton has the highest Ignition temperature and is commonly used in oxygen environments. Nitrox doesn't count here. So what else is important? Viton is the poorest at taking a set. It will indent permanently, sooner than the other two. But that's more a theoretical concern than a real one if you use a 012 o-ring. If you use a 011, then it might have slightly more significance. In other words, I wouldn't use 2-011 viton here.
Between EPDM and Nitrile, the only significance is shelf life. If you grab a hardware store nitrile o-ring, it might have come from China with high carbon black content and already be ready to crack. From a reputable manufacturer, it's a great and inexpensive choice.
EPDM lasts longer and has great flexibility. Many manufacturers use EPDM in their service kits.

Durometer: As a high pressure seal, the standard would be to use a duro 90 for this hose. That said, I've seen many manufacturer service kits where the high pressure hose O-ring is definitely softer than that. A Duro 70 will seal better, but extrude easily if your hose unscrews even a hair.

So after all that, what's best? In my mind, a duro 90 EPDM 2 - 012 o-ring with a wisp of lube on it. If that means a special trip or special order, then just drop by the hardware store with wet lips.

And don't snug that hose too tightly. Remember, the reg body is just brass.

The definitive answer lies in @Akimbo 's
 
Alternatively, buy a 4 or 5 spare SPG spools (o-rings included) from Dive Gear Express. They cost $1.50 each. Keep them with your save a dive kit. You'll make plenty of friends on dive trips as they find their SPG's bubbling away, and you can give them a quick fix with a new spool.

I've removed plenty of leaky spools for often the o-rings have split and the spool itself if crusty. So a new spool is the best field repair. Change the o-rings when you are at home and have time to clean it properly. Put the clean spool with new o-rings back into your save a dive kit for the next friend.
 
Alternatively, buy a 4 or 5 spare SPG spools (o-rings included) from Dive Gear Express. They cost $1.50 each. Keep them with your save a dive kit. You'll make plenty of friends on dive trips as they find their SPG's bubbling away, and you can give them a quick fix with a new spool.

I've removed plenty of leaky spools for often the o-rings have split and the spool itself if crusty. So a new spool is the best field repair. Change the o-rings when you are at home and have time to clean it properly. Put the clean spool with new o-rings back into your save a dive kit for the next friend.
It is leaking at the first stage, not the SPG.
 
Just to clarify,
The hose to 1st stage is a static O-ring
The hose to gauge (the pair of O-rings on the spool) is a dynamic O-ring.
 
Alternatively, buy a 4 or 5 spare SPG spools (o-rings included) from Dive Gear Express. They cost $1.50 each. Keep them with your save a dive kit. You'll make plenty of friends on dive trips as they find their SPG's bubbling away, and you can give them a quick fix with a new spool.

I've removed plenty of leaky spools for often the o-rings have split and the spool itself if crusty. So a new spool is the best field repair. Change the o-rings when you are at home and have time to clean it properly. Put the clean spool with new o-rings back into your save a dive kit for the next friend.
Changing the SPG spool at the dive site can only be done if you have an SPG without the hard rubber protection or a SPG with a soft rubber casing. Most of the console rubbers are stiff enough to inhibit the change of the spg's spool without hot water or a hot gun.
 
Changing the SPG spool at the dive site can only be done if you have an SPG without the hard rubber protection or a SPG with a soft rubber casing. Most of the console rubbers are stiff enough to inhibit the change of the spg's spool without hot water or a hot gun.
ER Shears make short work of those boots.
 
Thanks everyone, the information definitely helps and I feel confident I can make the fix successfully now.
 
Well, I learn something every day!
One of our long-time contributors and mechanical wizards, @herman remarked to me that the optimum o-rings for these ports are actually 3-903 & 3-904, from SAE Port specification J19126-1. One is a shade thinner, and one is a shade thicker than the AS538 spec.
Screenshot_20220702-103116_Adobe Acrobat.jpg

And indeed, companies like Aqualung and Poseidon don't have 11's & 12's in their kits.
Just goes to show you how forgiving this static seal is, when what is commonly used by techs all over the world is not what was specified when the port was designed!

Thank you, @herman !!! :wavesmiley:
 

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