Nitrox and orings?

[Octopusprime]

I'm new to nitrox and just have a couple questions. My local shop has banked 32% enriched air. I do not plan on blending in the near future.

I know that when partial filling and blending due to 100% o2 everything would have to be cleaned and no silicone can be used. However I saw a O Ring set that said they were Nitrox O Rings. Is their a difference in rings?

 

[decompression]

There are a couple different types of O rings, buna which is a standard rubber and Viton, which is O2 compatable..


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[Peter69_56]

From Dive Gear Express site;

Acrylonitrile-Butadine Copolymers (NBR or Nitrile)	Most O-rings used in SCUBA are made from Nitrile, a hydrocarbon based synthetic rubber. Nitrile offers excellent resistance to many oils and acids and has good physical properties. However, Nitrile is not a very oxygen resistant material and is not considered oxygen compatible. Nitrile is also often referred to as Buna-N.
Fluorocarbon Elastomers (FKM)	O-rings made of FKM have been the preferred choice for oxygen and nitrox compatibility in SCUBA diving applications. FKM is an elastomer with excellent oil and oxygen resistance at high and low temperatures, very good chemical resistance. Even for use with ordinary air, most experts agree that FKM O-rings outperform common Nitrile O-rings.
Polyurethane (PUR)	The milky white O-ring occasionally seen in the face of K-valves, sometimes called a 10,000 psi O-ring, is made of Polyurethane. Polyurethane is very abrasion-resistant, but it is sensitive to UV light (sunlight).
Ethylene Propylene Diene Monomer (EPDM)	EPDM O-rings are becoming more common in SCUBA because some people feel it's a safer material for use in breathing air systems. EPDM is a elastomer with excellent weatherability, heat resistance, dielectric qualities and odor-free characteristics. However, EPDM is less resilient and is not recommended for use with petroleum derivatives.

Hardness -- O-rings are normally available with a hardness rating, as measured by an ASTM type-A durometer, of 70 (the "soft" kind) or more rarely a rating of 90 (the "stiff" kind). The O-rings sold on this page are 90-duro (except for the -003 & -006 O-rings), and well suited for the SCUBA applications we describe. The soft O-rings are appropriate for dynamic applications where the O-ring is providing a seal with a constantly moving part, such as inside regulators. The stiff O-rings are more durable in static applications where the O-ring is providing a seal with stationary or occasionally moving parts, such as a valve.
Color -- O-rings are available in nearly any color, although most commonly seen in black. Most Viton O-rings are black. The Viton O-rings sold on this page are brown, simply to make them easily distinguishable from Nitrile O-rings which are usually black and EPDM O-rings which are often purple. Just to be clear, the COLOR of the O-ring is MEANINGLESS. Some people believe there is a difference in quality based on color, but that is more likely attributed to unknowingly using soft dynamic O-rings in static applications. Our O-ring manufacturer states there is little difference in quality for O-rings based on color alone, and independent testing supports that statement. Some people also incorrectly believe a Viton O-ring can be distinguished from a Nitrile O-ring by the surface appearance. Nitrile O-rings are said to have a shiny surface, and Viton O-rings are said to have a matte surface. This is not a reliable indicator, and certainly not true if the O-ring has been lubricated.

---------- Post added May 2nd, 2015 at 02:08 PM ----------

Nitrile has a lower flash point thus a greater fire risk compared to O2 compatible O rings, and also if exposed continually to high levels of O2 go soft.

Often if Nitrile is used in tank valve neck seals with the tanks containing high levels of O2, they can be found to be deformed into the shape of the groove, rather than remaining a O ring shape.

 

[hroark2112]

If your shop has 32% banked your o-rings will never see 100% O2.

 

[Rhone Man]

To summarise the forgoing (in slightly less scuba geek terms):

For highly enriched oxygen mixtures you should use different o-rings (made of viton). You should also use different lubricants. Some people like to use viton o-rings as standard, but I'd advise against it as they wear out faster (and hence are more prone to leak) than conventional o-rings. In terms of lubricants, the only significant variability is cost (but it is significant).

However, if your dive shop is pumping banked EAN32, you don't need to worry. Only when you get to about 50% do you really need to start fussing.

 

[kwinter]

Keep in mind that the use of Viton o-rings and oxygen safe lubricants is for high pressure oxygen. There is no danger for low pressure applications. So o-rings for tank necks and valve outlets and the ones used in servicing regulators matter. Others like the ones for low pressure ports and hoses can use simple buna and silicone.

 

[chrisch]

There are no fully O2 compatible O rings. Viton are no better in the real world than ordinary ones. More a triumph of marketing over fact. If you look at the regulator manufacturers many (all now??) have stopped using Viton, not least as there are some safety issues with it in the very very very unlikely event it did ever combust.

 

[Peter69_56]

There are no fully O2 compatible O rings. Viton are no better in the real world than ordinary ones. More a triumph of marketing over fact. If you look at the regulator manufacturers many (all now??) have stopped using Viton, not least as there are some safety issues with it in the very very very unlikely event it did ever combust.

As in giving off toxic fumes (Hydrogen Fluoride) ???????????

I think however a small O ring giving off toxic fumes might be the least of your worries if your regulator/cylinder catches fire. I would be more worried about the ensuing fire and the waiting for it to consume all the oxygen before putting out the remains of the tanks, house and probably myself.

I think the instructions for dealing with an oxygen fire is;
Turn off the oxygen supply if possible, then hose down remaining fire
IF NOT THEN RUN
Wait until all the oxygen is consumed
Then hose down whats left and hope the cylinder and/or dive gear is all that has burnt

---------- Post added May 2nd, 2015 at 08:25 PM ----------

Extract from Wikapedia;

Applications[edit]

The performance of fluoroelastomers in aggressive chemicals depends on the nature of the base polymer and the compounding ingredients used for molding the final products (e.g. O-rings). This performance can vary significantly when end-users purchase Viton polymer containing rubber goods from different sources. Viton is generally compatible with hydrocarbons, but incompatible with ketones such as acetone, and organic acids such as acetic acid. O-rings made of Viton are typically color-coded as black, but new gaskets, seals and O-rings should be green FKM or black FKM, but with a green mark on the outer edge.
Viton O-rings have been used safely for some time in SCUBA diving by divers using gas blends referred to as Nitrox. Viton is used because it has a lower probability of catching fire, even with the increased percentages of oxygen found in Nitrox. It is also less susceptible to decay under increased oxygen conditions.

Precautions
At high temperatures or in a fire, fluoroelastomers decompose, and may release hydrogen fluoride. Any residue must be handled using protective equipment.

 

[tbone1004]

Even if they were PP blending, the only O-rings you'd have to worry about are the neck o-ring and if a yoke valve, the yoke O-ring. The whole valve would have to be O2 clean obviously, but for your regulators it wouldn't matter.

This is obviously not kosher, but my second stages are rarely O2 clean, even for my O2 bottle. I am very careful with the valves, and very careful with the first stages due to the 180* hairpin in the valve and the 90* in quite a few first stages. That said, my backgas bottles have viton in them because that's what the parts kits call for, but if the DIN o-ring needs to be replaced, it gets replaced with nitrile since they're much cheaper. Only the O2 bottle gets viton all the time.

 

[Belzelbub]

The o-ring part has pretty much been answered. The O2 compatible o-rings are usually viton, and would appear more brown than the black buna n o-rings. This is only required at the tank, or if you exceed 40% O2.

The other part is that the tank should be O2 cleaned. On the initial cleaning, the tank will be tumbled, and the o-rings replaced with viton. A VIP will be done and a sticker affixed indicating that the tank is O2 clean. On subsequent VIPs, the cleaning process is not required so long as the tank was only filled with EAN or O2 compatible air. The point of this is that most shops will require the O2 clean sticker to fill with EAN, even if a bank fill.