Thinner 'O' rings ?

[Externet]

Greetings.
Always remember/identify/used to the size of "O" rings in the tank valves just by looking at them. Now got to play with a valve branded 'Ocean Dynamics' and noticed smaller thinner (yellow) rings. Is there two sizes for CGA850 ?
Removed, compared with my spares, and yes, they are different.

 

[happy-diver]

tic tac toe with an extra toe

 

[Pearlman]

I have a similar issue. I ordered a spare set of DIN O-Rings for a save-a-dive kit and I got thinner O-Rings than what my Scubapro service kits give. In the pic below the original is the 01-050-428 White O-Ring while the spare ones I got look softer and thinner. The white appears to be Viton I think? I am now confused if I should ever use them or share them with a fellow diver on a boat. Somebody help me understand how DIN O-rings can be thinner than the OEM ones and safety issues involved?

 

[Pearlman]

—duplicate post deleted —

 

[Tanks A Lot]

The white one you see is made from EU (Polyether-urethane), often just called Polyurethane in the diving industry. This elastomer has the best mechanical properties of most elastomers commonly used. It's downside is its horrendous compression set, which is irrelevant in this area.

The original 01.050.428 O-ring from ScubaPro is a BS1806 111 (2.62mm x 10.77mm) in 85 Shore A. I can't comment as to what you have ordered, as the color of an O-ring is meaningless. However, you are likely to get away with using what you have ordered, but it won't perform, meaning last as long, as the original EU O-ring. If you ask me, I would not toss that original EU O-ring, these usually last for several years. In any case they will outlast a NBR or FKM O-ring by a long shot.

There are standards in place which stipulate which O-ring should be used, but few manufacturers care. CGA V-1 calls for a 2.5mm x 11.00mm O-ring of unspecified hardness, while ISO12209 calls for a 2.65mm x 11.20mm O-ring, also of unspecified hardness. You find a plethora of O-rings on manufacturers equipment, most are either a BS1806 111 (2.62mm x 10.77mm) or a BS1806 112 (2.62mm x 12.73mm) and very few use what the standards call for.

 

[Pearlman]

There are standards in place which stipulate which O-ring should be used, but few manufacturers care. CGA V-1 calls for a 2.5mm x 11.00mm O-ring of unspecified hardness, while ISO12209 calls for a 2.65mm x 11.20mm O-ring, also of unspecified hardness. You find a plethora of O-rings on manufacturers equipment, most are either a BS1806 111 (2.62mm x 10.77mm) or a BS1806 112 (2.62mm x 12.73mm) and very few use what the standards call for.

Thank you for the very informative post! So did I understand it correctly that differences in c.s and hence o.d of <1mm are inconsequential to proper sealing and safety aspects?

In the example above the difference between 111 and 112 is quite large - 12.73 - 10.77 =1.96! And that’s the i.d looks like…
As a newbie to Scuba gear maintenance I am worried about using the wrong O-ring because of very tiny differences in dimensions of O-Rings not perceptive to the human eye and easily mistaken for each other causing safety issues and a sealing failure on a dive…

 

[Tanks A Lot]

In the example above the difference between 111 and 112 is quite large - 12.73 - 10.77 =1.96! And that’s the i.d looks like…

I have worded this poorly, apologies. Let me rephrase it a bit.

The mentioned standards set out the withdrawal connectors and their dimensions. However, they are not a law, merely industry standards. Hence, manufacturers are free to alter this design. All of the ones I know stick to most of the design parameters, especially the threading. However, most manufacturers decided to use different O-rings than what the standards call for. The reason is, I guess, availability. So while CGA V-1 calls for a 2.5mm x 11.00mm (A metric O-ring, can you believe it?!) and ISO12209 calls for a 2.65mm x 11.20mm (A non standard) O-ring, this is not what you end up finding in a lot of SCUBA gear. You MAY find these exact dimensions, but may very well have slightly different values.
In the end, the correct O-ring is what the manufacturer says it is. If they designed their withdrawal connector around a BS1806-111, than that is the correct size. If they designed it around a BS1806-112, than that is what you should use. The BS1806-111 and BS1806-112 are not interchangeable, as their dimensions are too far apart from each other.
A lot of manufacturers chose a gland that fits the BS1806-111 O-ring in a 85 Shore A hardness. This is close to what the ISO standard calls for, but not exactly what it says.

As a newbie to Scuba gear maintenance I am worried about using the wrong O-ring because of very tiny differences in dimensions of O-Rings not perceptive to the human eye and easily mistaken for each other causing safety issues and a sealing failure on a dive…

While I said the correct O-ring is what the manufacturer says it is, you should not worry all too much. Especially for the part you are working on, an ever so slightly different sized O-ring won't make a difference and work just fine. Especially if you can't discern a difference by eye on this rather large O-ring. Material selection and Shore A rating are key though, so stick to something 85 Shore A and above.

Elastomer quality can differ vastly from source to source. The O-rings from a supermarket "quality-saver-jumbo-extra" pack won't cut it.