Newly serviced regs break on third dive

[Puffer Fish]

"Going to a higher duro o-ring and a little extra torque might stop it from extruding"

Great point and good understanding of what the failure was.

But before throwing away your regulator, consider the following (pardon the engineering/geek talk in this):

1. AWAP is absolutely correct - this should not have happened. I don't know the margin or error involved in the design specfication, but it would at least be 30% higher than the stated value.

2. The o-ring, as AWAP pointed out, was extruded (is this a common word in the dive industry?) through the little tiny openning. But why is not that easy to determine.

3. The following are likely causes:

a. The design of the seat/compression area is faulty, either by design or by wear (actually fairly unlikely in this case, but it could be)
b. The O-ring was slightly smaller than the design specification. Smaller could be the diameter of the ring (inside or outside), or the diameter of the material.
c. The O-ring was slightly bigger than the design specification. Blah, Blah.... as above.
d. The durometer of the material was too soft. Actually, there are 5 or 6 common measurements of material hardness, but this is one of the most common. Hardness is always a trade-off between it and flexibility/compressability. This is actually a very common issues with high pressure static O-rings.
e. The O-ring is not made with the correct material. With a given material, hardness and flexibility are clear opposites. Change materials and all bets are off. I would bet I can get at least 50 different types of "rubber" looking material in an O-ring.

Because this started with you getting service done, my bet is on the o-ring. That it happened twice is actually a good sign (in a strange, twisted sort of way), because it means that the o-rings were replaced. The only problem is that they (the o-rings) don't seem to be quite up to the job.

If it were me, I would just test the o-rings for fit and hardness. But if you don't have a micrometer and a hand held durometer, I would suggest getting some O-rings from a different source, and try those.

As a note, in my business, every o-ring has a size, allowable tolerances, material and hardness specifications. I have never seen this in the dive equipmentment world. Doesn't mean they don't have it, just never seen it.

By the way, using a slightly harder, better material O-ring is always a good idea with this type of design.

I did a quick check and getting a 70 duro Buta-N o-ring (lowest cost) versus a 75 duro viton (fluorocarbon) increases the cost per o-ring by 5 times - from 2 cents to 10 cents. A lot if one is making thousands, but hardly anything to an individual.

Also, Viton is FDA approved and has an almost infinite life span when setting around, which is not true with Buta-N (except the FDA part).

 

[ZzzKing]

"Going to a higher duro o-ring and a little extra torque might stop it from extruding"

Great point and good understanding of what the failure was.

But before throwing away your regulator, consider the following (pardon the engineering/geek talk in this):

1. AWAP is absolutely correct - this should not have happend. I don't know the margin or error involved ...

Very impressive geekspeak! Very informative, too.

 

[angryguy777]

Thanks for the geek speak, it sounds like the o-ring is the culprit. However, it had been several years since I dove my regs before I got it serviced, but the problem never happened until I got it serviced here in Australia.

When the leak happened the second time, the o-ring was extruded enough that the boat handler could see it. He loosened it up and tightened it on the spot, which was a good temporary fix because once the o-ring gets seated, you're good to go. However, I'm guessing this is a temporary fix only?

-Zak

Liveaboard trip is comin up soon, this crap better not happen again.

 

[Puffer Fish]

Thanks for the geek speak, it sounds like the o-ring is the culprit. However, it had been several years since I dove my regs before I got it serviced, but the problem never happened until I got it serviced here in Australia.

When the leak happened the second time, the o-ring was extruded enough that the boat handler could see it. He loosened it up and tightened it on the spot, which was a good temporary fix because once the o-ring gets seated, you're good to go. However, I'm guessing this is a temporary fix only?

-Zak

Liveaboard trip is comin up soon, this crap better not happen again.

Zak - After the above comments - please keep in mind the following:

1. Once the O-ring was damaged by the extrusion event, it needs to be replaced.

2. It should not have been possible to tighten the connection and have it not leak, unless the connection was slightly loose to start with. or the tank pressure was lower.

3. Since your original post, just for information sake, I checked what a couple of regulator makers are using, and what one could easily buy. Seems that Buta-n and Viton are very common materials. Buta-n can be attacked by O, so Viton is fairly common in Nitrox regulators. Buta-n is most common in 70, while Viton is common in 75 (firmer).

4. There are two other interesting aspects of this -

a. U.S.A O-rings are english specified, with metric equalivalant also shown. European O-rings are metric, with english equalivalant shown. They are close, but not the same, even though they have the same listed specification. I don't have a clue as to what was originally in your reg, or what is commonly available in Australia.

b. It is easy to get lower cost o-ring kits (check out SCUBA.Com), that are roughly the right size, but may be slightly different, and or slightly softer or harder than what was originally. Most of time these would work, but beware high pressure applications.

My suggestion would now be to 1. Use viton, they are normally firmer and will last longer. 2. Make sure the size is correct, and make sure the fitting is tight.

You should be good to go for a long time.

 

[angryguy777]

You brought up some very good points regarding the different measurement systems, after all, that problem almost killed the Hubble telescope. I bought the regs (oceanic first stage, Genesis SPG) from my LDS in the states, no problems there. I got them serviced by a licensed Oceanic repairtech here in Australia, then the problems start.

I'll definitely replace the O-ring before I dive again.

When I had the problem last time, I didn't even take my BC off to fix it. The boat handler fixed it while I was wearing my gear so I couldn't actually see it. See if you can make sense of this:

He tried to unscrew the HP hose with some needle nose pliers, but couldn't get it to move. Then he got a better pair of pliers and was able to loosen it. When he did this, I recall him saying something to the effect that it "was loose", but I attributed it to his efforts with the needle-nose pliers. However, it may have been loose but he just couldn't get a good grip with the first set of pliers. The o-ring was extruded during all this. He then took off the hose, reseated the o-ring and screwed it back in. Then he turned on the tank and presto, it worked fine.

I never thought about it being loose because I personally watched the repair tech tighten it after the first incident. I think it was a possibility but I can't be sure. As I understand it, when attaching hoses to the first stage, it should be hand tight, then tightened a little more with a wrench, correct? I saw the repair tech do this but I guess its possible it was loose. Strange...

Well I'm going diving in 2 weeks. I'll order some o-rings when I get back to the states because this trip will probably be my last here in Oz and I'll make do with what I have here.

-Zak

PS- I'm guessing you studied material science? That's some scary stuff haha

 

[WarmWaterDiver]

A number of companies are using EPDM in lieu of Viton for higher O2 services now as well.

My wife had a weird o-ring extrusion event when we were on our Flower Gardens NMS trip in September - but I take a complete extra reg, and it occurred when turning the tank on, so no damage or loss of dives due to the event. We reviewed this with our tech diving instructor who was also the last person to perform reg maintenance on the rig - looking at the cutaway drawings, it appeared there was a sudden and extreme failure of the o-ring that was internal to the first stage DIN fitting resulting in the o-ring being extruded through the fitting and out the top. Like I said, weird.

The o-ring was one of the purple EPDM ones. I have heard there were some quality control concerns with the purple EPDM o-rings. Just FYI.

 

[Puffer Fish]

PS- I'm guessing you studied material science? That's some scary stuff haha

Actually I studied Biochemistry, but I play an organic coating engineer in every day life. Most of what I do is cosmetic stuff, but every so often one gets to do functional coating (those that really matter). Things you might know: The hinges on the space shuttle bay doors, the starter motor shafts on the Boing 777 and the coating on the magnets in GM car fuel pumps. Every system I design has hundreds of O-rings in them, some with very odd chemicals and frequently under very high pressure. O-ring faulures in my business vary in important from a trivial air leak, to taking out a plant(and all of the people) the size of city block. Pays to understand material science issues.

WarmWaterDiver has brought up another material that appears to be used. EPDM has two reasons for existing as an o-ring material -

1. It has great UV light resistance, so would be good anywhere that an o-ring could be exposed to sun light.

2. It can be made in nice colors. Nothing to do with performance, just looks cool.

Compared to Viton, it is not more resistent to 02 and has several other attributes that make it a bad choice for a high pressure O-ring, but it looks cool - never underestimate the importance of that. Nice choice for a Quick Disconnect o-ring that could lay out in the sun, but it is softer, far to elastic (easier to extrude under pressure) and tends to vary in production. Did I mention that it can be made in nice colors?

Regarding tighting pressure, if everything was the correct size and material, and there was no seat damage, finger tight would hold (please don't try that). There is a real world issue with tighting two threaded objects together, their flat surfaces will never line up exactly correctly (I know, seem like you should be able to, but I lived through a really ugly experience with just this issue).

The miss fit is due to the necessary play in the two objects threads, which results in some very small deflection when one gets to the initial point of contact. How much tighter one has to go to deform the threads depends on all the math of the threads and the surfaces. If you tighten something down to make it flush, you are distorting the threads, which will increase the amount of force needed the next time.

So the correct answer is that you should tighten the fitting no more than is necessary, so that it does not leak, and with time, this will need to be increased. As that answer is, in reality, really stupid - I would suggest that you go a bit more than lightly tight, something that cannot come unscrewed by accident.

I hope that it is obvious, at this point, that your o-ring failures are not helping with this issue.

Use the correct size Viton and you should be good.

As a side note, I see you can get generic Viton replacement o-rings for around $1.00 or more from several dive shops. A pack of 50 really, really high grade one's (aerospace/medical grade) costs around $.10 each, but you end up with 50 o-rings (they get cheaper, the more you buy, so 10,000 is really cheap). As this is a standard O-ring, that everyone uses, if you belong to a dive club, a dollar a person will get 5 people 10 O-rings, that will last close to forever as replacements (until used).

 

[captain]

Good source for O rings.

http://www.air-oil.com/oringsonlinefset.htm

 

[kb2ehj]

Captain,

The prices on that web site look good. This may sound funny but what size do I need for a 'standard' yoke valve or as I see on their site, dash size?

Thanks in advance

 

[Puffer Fish]

Captain,

The prices on that web site look good. This may sound funny but what size do I need for a 'standard' yoke valve or as I see on their site, dash size?

Thanks in advance

I small suggestion -Never, never buy something that your life may depend on at the suggest of someone on a forum.

Discussion is great, but if you have to ask what size is needed, you are most likely not a candidate for buying your own O-rings.

If the following link makes perfect sense to you, then you have more than enough skill to make your own decision:

http://www.allorings.com/pressure_vs_clearance_gap.htm

It would appear that the Captain is comfortable with buying his own, which is fine for him. Remember, this can be a very important issue. If you don't know, it would be best to get O-rings from the equipment maker.

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.