Info O-rings for Divers

1: O-rings for Divers​

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Question:

“ I'm a recreational diver. Why should I care about O-rings? ”

Answer:

“ For starters, an O-ring failure could empty your Scuba tank in about a minute. ”

(Table Reprinted by permission)
This table appeared in Life Ending Seconds, 3000 to Zero in 72 Seconds, Advanced Diver Magazine by Curt Bowen

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“ Don’t worry. Catastrophic O-ring failures are extremely rare, as long as you know what you're doing. ”

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However, O-ring leaks aren't unusual at all, and can prematurely abort your dive or detract from an expensive vacation. Fortunately, understanding them is easy and will dramatically reduce failures. Many O-rings can be safely replaced in the field with minimal skill and are part of most Save-a-Dive kits.

You can repair most leaks with some spare O-rings, a removal tool kit, a wrench or two, and some lubricant.

What is an O-ring?​

O-rings are "resilient" toroids (doughnuts) made from a variety of materials and are primarily used for liquid and gas tight pressure seals.

Literally billions of O-rings are made every year. They come in an enormous variety of materials, sizes, colors, and shapes.

Where are O-rings Used?​

Most divers are wearing about 50 O-Rings. Here are a few of the diving-related products that depend on them:

• Cylinder valves
• Regulators
• SPGs (Submersible Pressure Gauges)
• Dive Computers
• BCDs
• Underwater lights and camera housings
• High Pressure Compressors, Nitrox mixing systems, etc
• Machinery and fittings on boats
• Commercial diving equipment — like almost everything we use

O-ring Types​

O-ring applications are divided into two broad categories; Static and Dynamic. There are so many creative applications that some can be seen as hybrids. Static simply means that the sealing surfaces are not moving under pressure while dynamic do. For example:

Static​

• Scuba cylinder to valve seals
• Scuba valve to first stage seals, DIN and Yoke
• Hose connections on first stage Scuba regulators
• The lens seal on metal-body SPGs
• Port and door seals on underwater camera housings
• Door and port seals on decompression chambers

The first O-ring that divers learn to use is usually the stage regulator connection to the cylinder valve. This image is of a DIN connector

The first O-ring that divers learn to service is often the hose to first stage regulator connections

O-ring grooves don't have to be round. This image of is an underwater camera housing. This is classified as a static pressure-seating face seal O-ring.

Pressure-seated O-rings like this one don't require robust clamping mechanisms because the pressure does the work. The four small spring-loaded latches are all it takes to compress the O-ring enough to make the initial seal.

This PLB (Personal Locator Beacon) housing has threaded caps at both ends with static piston seal O-rings. You can see the compression of the O-rings through the clear plastic tube.

Sectional view of a conical Acrylic pressure-seating viewport for a deep submersible rated for 1,000 M or 3,281' working depth. Similar ports are used for decompression chambers. The O-Ring only functions at very shallow depths, enough for the pressure to create a metal to plastic seal. ​

Dynamic​

• Cylinder valve stems
• Hose connections on second stage Scuba regulators and swivels
• Hose to SPGs and dive computer connections
• Button and rotary controls on underwater camera and light housings
• Power inflator quick disconnects on BCs (sort of a hybrid but they are allowed to rotate)
• Hydraulic and pneumatic pistons including counterbalance pistons on hatch-back cars

Hose connector to the second stage regulator is a dynamic seal. Look closely and you can see the brown O-ring in the groove under the lock nut.

The standard HP (High Pressure) hose connection that was originally designed for SPGs are also used for AI (Air Integrated) dive computer adapters and wireless transmitters for AI wrist-mounted computers. Note the different style "spools" with a separate O-ring for the hose and the mating device.​

Table of Contents for O-rings for Divers
Post 1: O-rings for Divers (this post)
[URL='https://www.scubaboard.com/community/threads/o-rings-for-divers.553724/']O-rings for Divers[/URL]

Why should I care?​

What is an O-ring?​

Where are O-rings Used?​

O-ring Types​

Post 2: How do O-rings Work?
[URL='https://www.scubaboard.com/community/threads/o-rings-for-divers.553724/#post-8116451']How do O-rings Work?[/URL]
Post 3: O-Ring Materials, Lubrication, and Maintenance
[URL='https://www.scubaboard.com/community/threads/o-rings-for-divers.553724/#post-8116452']O-Ring Materials, Lubrication, and Maintenance[/URL]

O-Ring Installation​

Material​

Lubrication​

Oxygen Cleaning and Compatibility​

Oxygen Cleaning in the Real World​

Post 4: O-Rings Buying Guide
[URL='https://www.scubaboard.com/community/threads/o-rings-for-divers.553724/#post-8116453']O-Rings Buying Guide[/URL]

Measurements​

Material​

Durometer​

Making Custom O-rings​

Pro Tips​

Post 5: O-ring History
[URL='https://www.scubaboard.com/community/threads/o-rings-for-divers.553724/#post-8116454']O-ring History[/URL]

Patents​

Enabling Technologies​

Post 6: DIY O-rings for Divers
[URL='https://www.scubaboard.com/community/threads/o-rings-for-divers.553724/#post-8116455']DIY O-rings for Divers[/URL]

Underwater Housings​

High Pressure Gas Systems​

Custom Gas Manifolds​

Custom Scuba Cylinder Manifolds​

Special thanks to the Scubaboard Moderators that helped me with this thread and XS Scuba for their technical assistance.

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Continued in the next post

 

[chillyinCanada]

It's tough, going against the grain. Christolube MCG-111 is the 800lb gorilla, and Tribolube has had a tough sell.
That said, Christolube absolutely dries in place. It is a real beast to clean, and most of us just leave the residual layer of PTFE in place and lube over it. I don't see that as a problem.
In contrast, T71 just doesn't seem to dry. While Tribolube 66 is favored by many DIY'ers because it's even cheaper than T71, Tribolube 66 does seem to separate out the oil carrier from the PTFE. It's certainly true in the 1lb tubs that I buy. But then, so does Christolube. Additionally, T66 doesn't have quite the temp spread that T71 has, so I don't use it to pack Atomic sealed pistons despite the added cost. I don't think it's quite as responsive (sl. more viscous).

I'll be quite honest: I like T71 for how it feels in my fingertips compared with MCG-111 as I lube orings. It's a subtle thing, but it's real. Between that, the price and its non-drying characteristics, I don't EVER use Christolube unless the manufacturer won't allow a substitute. Add in its suitability for oxygen service at high pressure and it's a slam dunk.
It's maybe $400/lb for T71 and $325 for T66, vs $400/lb for Christolube. Obviously, smaller quantities get huge markups.

Then there's silicone. It's a GREAT non-drying lube! But it is not compatible with oxygen service. For me, the deal breaker is that, plus the fact that you can not clean it off a reg. You can wipe it, but there's no reliable solvent. You can use detergent, but it doesn't emulsify. In other words, if you want to convert that old Mk5 to a deco reg for your 20ft bottle, you can do it yourself. I won't take the risk. Yeah, after a dozen cleanings and droplet or shaken test tube tests it might pass. But at that point you've expended enough labor that you might as well have bought a new O2-clean first stage. But for non-O2 uses, it's perfect. My JJ-CCR specifies it!
I just can't do anything with it near my other tools for reg service.

Bottom line for me? I'm not cheap enough to use T66 to save 30%. I'm not happy with how it separates from the carrier oil (just like Christolube). I pretty much use T71 for everything except my breather and port plug/hose orings. It doesn't dry, which is critical for the threads where salt water infiltrates under pressure (yoke and DIN bolts). Now we can argue about using lube on threads that are "supposed" to be dry-threaded, lol!

If folks would like an alternative source for 10cc of T71 in a syringe with a blunt plastic needle, PM me. Between my Trident account and $4.50 USPS postage, I can probably save you a few bucks. Not too many of you, though. It's a PITA to package.

Finally, an anecdote. Years ago, when I was working with Rudy Mola of Diving Technologies Int'l, Tribolube had just come out, and he was asked to help evaluate it. We did this test together, which is not very scientific, but I've never forgotten it. We took a pencil eraser sized dollop each of T71 and Christolube. We put both in the blue flame zone of a propane torch and just let them sit. Maybe 60-120sec. At the end of the test, the T71 was just gray ash on the end of the spatula. It didn't smoke. It just sat there. The Christolube didn't smoke either, after all that time. But in the middle of the spatula sat a tiny red ember. I've never forgotten it. Does that mean anything? Dunno.

It explains your slight bias, so that means something

 

[markmud]

Wow! Just Wow! I am blown away by the detailed responses and links that @Akimbo, @rsingler, and @couv responded with.

"Now we can argue about using lube on threads that are "supposed" to be dry-threaded, lol!" (Post #44)
I am not a fan of dry threaded connections in the marine environment! That method works great for throw-away, or one'n'done products.

Thanks so much,
m

 

[Schwob]

"Now we can argue about using lube on threads that are "supposed" to be dry-threaded, lol!" (Post #44)

Please do!

DIN first stage threads:
I read about it in the past, came away thinking I should leave them dry, but still wonder about the wisdom behind it. It still seems to me I might be inviting trouble.
So far, I left them dry, in my case just the DIN first stage in the valve or, possibly quite worse, the DIN first stage in the yoke adapter. Why possibly worse? Because on i.e. this trip (salt water) with occassional dives only, the first stage and yoke stay (lazy bum) connected (during rinses, during drying, during storing while doing other touristy things…)
What could possibly go wrong?
What would be better if I had lubed the DIN threads with what? (strictly below 40% O2)
Should I really separate the yoke adapter from the first stage all the time anyway, even if I were to add lube?

 

[rsingler]

The problem with lubing threads that are engineered for dry threading is axial load on the threads/reg body.
As the graph below shows, applying the same torque to a lightly lubed thread can increase axial load by 40% or more.

The consequence can be catastrophic thread failure.
The problem is that you have little guide to selecting the new "correct" torque setting if you choose to lube the yoke bolt. The starting forces are not insubstantial (20-30 ft-lb, depending upon manufacturer). And then you have all the ScubaBoard stories of loosened bolts on a dive boat with loud hissing when the tank is turned on. "Gee, maybe I should honk this sucker down a bit more. "
If you're going to try to go longer than the specified service interval because your IP is rock steady, you have to compensate somehow for the crystallization of salt in the threads of your yoke or DIN bolt. Four years from now, you may not be able to disassemble your reg from all the verdigris locked between the bolt and reg body, no matter how pristine your reg is inside the air path.

I choose to lightly lube. I always use a torque wrench. And I set my torque below the dry spec (note: some mfrs DO specify bolt lube).
Between lube and a lower torque setting, I am more at risk for loosening, for any given axial load specification for the threads. But over time, that risk decreases, since lube does not stay where you put it. If you measure assembly vs disassembly torque values three months apart, it is often harder to disassemble than the torque value you fastened with. That doesn't mean the axial load increased all by itself. It is just a function of increased friction as lube is displaced, or verdigris corrosion forms.
Recognizing that I'm more at risk for loosening, I try not to do knucklehead maneuvers like adjusting the angle of my first stage after the tank is turned on. I don't carry my tank using the reg body as a handle. The HP oring seal between the yoke bolt and the reg body is independent of torque. Lightly kissing metal-to-metal is all you need to prevent gas loss. The seal is made by displacement of the ring against the crack between the two parts, and more torque doesn't improve that. The only thing torque does is make it more likely that the parts will stay together for the service interval.

But what lube does, is allow me to run a longer time between services and still get my toy apart. Or make disassembly easy at a standard service interval. A film of lube is good temporary chrome protection for threads you want to last 30 years.

Should I really separate the yoke adapter from the first stage all the time anyway, even if I were to add lube?

I can no longer count the number of DIN bolts that have unscrewed from the reg body as I was trying to loosen the adapter from the DIN fitting on a set in for service. You can do the math: unscrewing force "X" applied to a DIN adapter whose connection is ~15mm diameter, while the underlying bolt connection to the reg is only ~9mm diam. Guess which one lets go first...

Yeah, I know. Lube attracts sand and grit.

 

[SlugLife]

Can someone recommend a good source for bulk-kit of odd-sizes of o-rings, such as the ones you're likely to find inside a 1st & 2nd stage. A standard bulk oring-kit seems to cover nearly everything for normal scuba uses, but missing a lot of the ones that go inside regulators.

Sure, I can find these same o-rings packaged individually, but that adds up real quick.

 

[Kupu]

I have made a few bulk purchases from Orings and More, The Oring Store LLC, and also McMaster-Carr.

@couv mentioned a couple sources in post #27.

 

[Capt. Bas]

Perfect for regulator parts

Yeah toluene works similarly to xylene, they slightly thin and get between the silicone and the material you are cleaning. Okay so it lubricates the silicone as it thins the stuff so the silicone slides off leaving no visible residue
I use a brush and mechanically brush it off takes a few seconds to work then throw it in some detergentised hot
water, do some more parts before plopping it all in the the ultrasonic, no other dechemicalising or prep required

But most definitely I do toluene over xylene due to less residual odour, I think a cleaner surface and I like it better

Xylene reminds me of turps yuck!


Hey methyl ethyl ketone and isopropyl alcohol works but that stuff really kills you even out in the open
Look at some plumbers and drunks

To be honest, you're picking the wrong solvents as the bad ones, Toluene and Xylene are both more toxic than IPA and MEK.
If Xylene remembers you of Turp, thats very likely as it is one of the main components in old fashioned lacquer thinners (the grade above white spirit)
Toluene is considered bad for your health at least in Europe. Smells very nice by the way, but the same goes for Benzene and thats considered very unhealty at the moment.

 

[Akimbo]

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Selected for the ScubaBoard Knowledge Base.

This thread was selected for the ScubaBoard Knowledge Base on 26 September 2021. Special rules discouraging off-topic and counterproductive replies apply after this date. A link was left in the original forum

Don't be confused if you suddenly find yourself in the Knowledge Base forum.​

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[BlueTrin]

If you blow the o-ring on a DIN first stage and need to replace it.

Is it a standard o-ring or for example it could be different between an Apeks and SP first stage?

 

[rsingler]

If you blow the o-ring on a DIN first stage and need to replace it.

Is it a standard o-ring or for example it could be different between an Apeks and SP first stage?

If we are just talking DIN, the inner and face sealing orings are one of only two standard AS-538 sizes: 2-111 or 2-112. The Durometer should be 90, and you can make your choice of materials using the excellent discussion by @Akimbo above. Manufacturers commonly supply all of EPDM, Viton and polyurethane in their kits. I do not see Buna-N nitrile in kits any more for these high pressure seals.