Newly serviced regs break on third dive

[Puffer Fish]

Where are you getting your info? According to Parker, EPDM is a almost as good or equal to viton for O2 resistance, equal for weather resistance, and better in most mechanical properties like abrasion and tear resistance which is where viton really falls down. And better with cold. Several Parker reps have told me never recommend viton when they can avoid it, because they have so much trouble with it. About all EPDM is really bad at is oil resistance - but then you really shouldn't be using oil in your regulator.

As far as color, just about any O-ring can be made in any color you like. This is not a unique feature to EPDM. Scubapro used to use nitrile O-rings color coded to the location, and most of us have seen black, brown, red and green viton.

Since most reg manufacturers have gone over to EPDM O-rings as nitrox becomes commonplace, one assumes they must have some reasons.

Your comments are right out of the hand book, regarding the difference between EPDM and Viton. But we were talking about a static, high pressure O-ring. In this case, almost as good for O2 is not the same as better. There is no weathering issue, no abrasion issue. Tear resistance could be an issue, but that is one of the reasons that the normal durometer is slightly higher for Viton.

The one place you could make a fairly strong argument is the cold resistance (usually shown as -15C for viton), but viton has a nasty charactoristic of going into a glass phase as it gets even close to that temperature, and can shatter. Never heard of it doing that in a scuba system, but the space shuttle is a different story.

It should be noted that EPDM is a much cheaper material than Viton (depending on grade and Viton family), and what is a few pennies to me could be very big dollars to a large user of O-rings.

Viton, and EPDM are not one compound, but families of compounds. Viton does have one that is fairly low temperature resistant product line (down to -30C), in Viton A, but most O-rings are not made with this. But it can be obtained.

Last I knew, Parker is the largest user of Viton in the world, will check tomorrow.

There is this tendency to assume all viton is the same and all EPDM is the same. Viton comes in, that I know of, A-F families. Looking at the Exxon data(they are the largest maker of EPDM), there appears to be an even larger selection.


Someone can remove the carbon in Viton and replace it with Red Iron oxide, and you get a red O-ring. You no longer have quite the same physical properties when you do that. It is not that you can't, it is that you shouldn't. In addition, even when black, they can vary considerably. When you buy an O-ring, most of the time you don't actually know what the real physical properties are, unless it has some sort of certification (since the Viton issue with the space shuttle), all aerospace certified ones have durometer values tested for each lot. Milspec also do. Everyone else, it is around the stated value, usually by some unknown amount.

Note: The space shuttle o-rings are still viton, just to a tighter specification, and tested

I'm not a fan of EPDM, because I worked on a job using the product, and found out how hard it is to make the product repeatable. If it is to specification, it is very good, and it does take different pigments far better. We were blending and extruding EPDM for golf grips, and could not get durometer repeatability within +/- 5. The material we were using was the identical product being used by several major O-ring makers. It is possible something has changed in the last 3 years, but if so, it has been done very quietly.

Actually, I tend to use the specific versions of viton (and several other long life vesions of Kalrez or Chemraz), which is why I did not list sites to buy the things. There is also a great Urethane o-ring (not the same properties as listed in most reference guides)

Reality is, that 99.99% of the time one can use almost any O-ring and it will work. Buta-N can be used with Nitrox, for example and it will last more than a year. Every so often, just buying some O-ring will cause a major issue, this thread was started because of one of those. As this is a free country, anyone who feels comfortable in buying their own O-rings has the right to do so. If one of them fails on a dive, that was a choice they made. When someone tells someone to buy a specific item from a specific supplier, they are now part of that decision.

 

[Scuba]

Since better is a relative term, I wonder if the experts can agree on the following points or state arguments in support of their position.

Neutral:


EPDM and Viton have about equal resistance to O2.


EPDM advantages:


EPDM is more resistant to sunlight than Viton.

EPDM is significantly more resistant to abrasion than Viton.

EPDM is significantly more resistant to tear than Viton.

EPDM is more resistant to cold than Viton.


Viton advantages:


Viton is significantly more resistant to oil than EPDM.

Viton is harder than EPDM.

Viton is significantly less elastic than EPDM.

Viton's production quality is more consistent than EPDM's.

If you are going to buy generic, I would suggest buy certified ones, yes, they cost slightly more, but they at least have some proven physical performance characteristics. Not that any would not work.

Are these certified o-rings individually tested? How do I know if an o-ring is certified? Will you please expand on this issue.

 

[Scuba]

Actually, I tend to use the specific versions of viton (and several other long life vesions of Kalrez or Chemraz), which is why I did not list sites to buy the things. There is also a great Urethane o-ring (not the same properties as listed in most reference guides)

You beat me to post by a few minutes. At any rate, I appreciate everyone's input.

Do you believe there is a better O-ring available today for SCUBA gear application than those being used today for this purpose? What are the superior attributes? How significant? Any significant drawbacks? Sources to purchase and obtain further info?

Your willingness to share your expertise is appreciated and it's perfectly natural and healthy that other knowledgeable sources would question and discuss any assertions made, something that is also appreciated. Please keep in mind this is a discussion forum, so don't be concerned with discussing, we can all make up our own minds, for better or worse. If we restrict our discussion due to the fact someone will always misinterpret and misapply what is said, than there is hardly any point to discussing much of anything. Please continue to provide information for the discussion, and let everyone make their own decisions. Hopefully a more informed, better decision.

 

[angryguy777]

my head hurts haha...

At least I'm learning something.

-Z

 

[Puffer Fish]

Do you believe there is a better O-ring available today for SCUBA gear application than those being used today for this purpose? What are the superior attributes? How significant? Any significant drawbacks? Sources to purchase and obtain further info?

Your willingness to share your expertise is appreciated and it's perfectly natural and healthy that other knowledgeable sources would question and discuss any assertions made, something that is also appreciated. Please keep in mind this is a discussion forum, so don't be concerned with discussing, we can all make up our own minds, for better or worse. If we restrict our discussion due to the fact someone will always misinterpret and misapply what is said, than there is hardly any point to discussing much of anything. Please continue to provide information for the discussion, and let everyone make their own decisions. Hopefully a more informed, better decision.

http://www.oringsusa.com/html/online_store.html

http://www.marcorubber.com/viton.htm

http://www.parker.com/ead/cm2.asp?cmid=5386

I put the above links in the wrong order, you should first look at the Parker site first, then the marco and finally the oringsusa.

One of the advantages of Viton is it's resistant to compression set, which is much better than EPDM. Regarding temperature, if you look down the list of viton specifications, you will notice that there are several with very low temperature ratings (Viton A is much better, for example than other Vitons).

By buying to a specification, you know what you are actually getting.

The marco site does a great job of showing what happens when one puts color in a viton O-ring. It does not make a better O-ring. If you go to the EPDM data from the same site, notice that there is no color data, because it is not an issue.

I have not bought from Marco, so don't know their pricing, but they are a great example of the type of source to buy from.

I have bought from Oringsusa. You can get excellent, clearly defined O-rings from them and several others (I'm not at my home computer, so cannot give the complete list). Actually, if you check their price on EPDM O-rings, they make .03 look expensive.

What would I use? I would use one of the low temperature rated Viton's, in black, with a Durometer of 74 - 76 for all high pressure o-rings. The higher durometer improves the physicals that would make EPDM better. I would used EPDM on the outside, exposed to the world O-ring, or Viton, and toss it after 6 months.

I've seen hundreds of high pressure o-ring failures (still a really, really small percentage) and never even heard of one using the correct size and the above material.

They don't test individual o-rings, they cert the batch. There is an exception to this for aerospace and nucleair rated ones, but the cost gets silly, even for me (like over $10.00 per O-ring).

If you go the EPDM route, then make sure you toss the O-ring every time the item is taken apart. Viton will usually last 3 to 5 years, as long as not in a wear situation (but not forever)

Urethane (some) for wear locations, but one has to be very picky about source. Will send as soon as I can find it.

Hope this makes sense.

 

[WarmWaterDiver]

Your post on using Buta-n for nitrox, what maximum O2 percentage and differential pressure are you putting as the envelope for that? There have been industry reports of 'smoking an o-ring' from (semi)adiabatic heat of compression when the first stage is first pressured up. Consider the Eupopean tanks of 300 barg as the highest pressure case, then drop down to 3500, 3000, 2400, and 1800 PSIG if you could, to cover the more common / typical scuba tank operting pressures in the USA.

 

[Puffer Fish]

(semi)adiabatic heat of compression

Wow - I have not heard that expression for over 30 years

If we are talking about static pressure O-rings, properly installed and the proper size (not a metric equalivalent put in a english setting or the other way around), and they were lubed with a fluorpolymer grease, then they would be usable to the limits of recreational Nitrox and 3500 psi. I would suggest HNBR would be better, but either would work. I don't believe that there would be an issue even above this pressure, but have no experience.

Heat of compression on a properly fitted static O-ring is just not that much (at most it would be is around 10 C), but get anything off, and it will get ugly fast. The beginning of the extrusion process can generate a lot of heat, and I would suspect that is what people are seeing. But the heat is from compression of the O-ring through the seal and not from simple air compression.

The extrusion process sometimes does not blow out the O-ring, just pushing small amounts of O-ring material into the seam. This can and does make a lot of heat.

It might be possible to have this happen with a poor fitting O-ring, deformed to fit during compression. It would be very difficult to do any math on this, because the number of possible options is rather staggering. Never seen this one.

If we go to any other use, other than static, there are a lot more concerns. If the regulator is a piston design, the piston O-ring is different subject.

 

[oxyhacker]

Wow - I have not heard that expression for over 30 years

You must not be doing much gas handling!

Re your O-ring comments, there is a parallel O-ring thread in General Scuba, where I have made some comments on O ring selection so I won't repeat them, except to comment that my approach on selecting O-rings is to assume that the engineers who design regs are not dumb, and so I try, when using generics, to come as close as I can to what they originally supplied and resist the urge to second guess them looking for something better. Since even nitrile will usually last for 5+ years in a regulator, ultimate life does is not a major concern for me. Viton went through a brief fad in the early days of nitrox, but most manufacturers are now using other compounds so I can't share your enthusiam for it.

One good point you make, which I have made many times here, is that nitrile, viton and EPDM are not uniform, standard products - there are low end and high end formulations, cheap imports, good imports, and good domestic versions. So all these statements one hears comparing compounds are only generalizations. The cheap ones are to be avoided, and the expensive ones too expensive to be cost effective. So one wants to look for reliable products in the middle.

 

[Puffer Fish]

You must not be doing much gas handling!

Re your O-ring comments, there is a parallel O-ring thread in General Scuba, where I have made some comments on O ring selection so I won't repeat them, except to comment that my approach on selecting O-rings is to assume that the engineers who design regs are not dumb, and so I try, when using generics, to come as close as I can to what they originally supplied and resist the urge to second guess them looking for something better. Since even nitrile will usually last for 5+ years in a regulator, ultimate life does is not a major concern for me. Viton went through a brief fad in the early days of nitrox, but most manufacturers are now using other compounds so I can't share your enthusiam for it.

One good point you make, which I have made many times here, is that nitrile, viton and EPDM are not uniform, standard products - there are low end and high end formulations, cheap imports, good imports, and good domestic versions. So all these statements one hears comparing compounds are only generalizations. The cheap ones are to be avoided, and the expensive ones too expensive to be cost effective. So one wants to look for reliable products in the middle.

I could not agree more!!! Most of my work is in correcting problems and some are under very high pressure and temperature. Your advice is far better than any I could give, because I live in a world where I do material specifications. my approach is to identify the absolute best cost/ performance. Ask me why something failed and how to prevent it, I'm your man. Ask me something simple, and I will guarantee, my approach is way to detailed for most people.

This thread is about a static, high pressure O-ring failure. That application and that application only is best suited for high quality Viton A. Ask about the O-ring in the first stage piston design, and you would get a completely different answer. Most equipment companies tend to buy O-rings from mostly the same material, so when they change, they change everything. You are not going to go far wrong in using their guidelines and you know it will work.

My first big usage regulator was the first Poseiden. I would have to replace the main O-ring after every 200 dives or so, until I replaced it with teflon (pfa, if memory servers me correctly) encapsulated viton. It not only breathed easier, it lasted over 1,000 dives without any noticable wear (I gave it away at that point). That is one expensive O-ring, and one that no equipment maker would normally use, because of the cost, but it is also one remarkable piece of technology. So, every so often, using special technology has a value, but most of the time one just gets zero defects, which is what you should expect from using original equipment specifications.

 

[WarmWaterDiver]

The 'hydraulic hammer' is a well known event when first opening the tank valve - the unsteady-state condition, often overlooked by folks used to dealing with steady-state, is commonly the area where problems crop up. The space shuttle event you referenced is a good example of this. This is where making recommendations for fitness for service may not be interpreted by all as 'only for static o-rings', etc. from the context of the post.

My general objection is the term 'adiabatic' is used too much in this sport - the gas handling systems never get to a 100% adiabatic approach, and in reality, such systems are designed to attempt the best approach possible to isothermal operation - but inhaling and exhaling don't occur simultaneously, tank pressure is not constant unless you're not breating for a significant period of time and you shouldn't ever hold your breath while on SCUBA, the time when you prep the equipment for use and break down the equipment after use are dynamic environments, etc. Hence my choice of (semi)adiabatic as best representation, and demonstration that SCUBA is never well modeled by 'steady state' representation. The extremes of 'worst case condition' such as initial pressurization (greatest differential pressure), low tank pressure (lowest differential pressure), etc. all need careful consideration when performing evaluations.

The biggest question of any "What If" study is either "What if I didn't ask enough What If questions to cover all eventualities for evaluation?" or "What if the evaluation didn't cover all situations?". The remainder of the evaluation is risk assessment, but if something's not put into the front end, it can't get assessed.