2nd-stage swivel failure in Cenote Cristalino, Mexico - 06-Nov-2010

[whodunit68]

I started diving just over 2 years ago on 26-Aug-2008. Today, 06-Nov-2010, was my 353rd dive, 41st since 26-Aug (year anniversary), and 95th of 2010. It was my 90th cave dive after having completed full cave. I have had a couple incidents where I had to assist another diver but this is the first case where I was the one with a fairly significant issue. Perspective.

Today was the last day of 8 days of diving - all guided - here in Mexico caves. It has been a great week of diving including the Blue Abyss via Pet Cemetery, Xunaan Ha, and more - a different cave every day. Today began with my pick-up at 8:15am in Playa del Carmen. We headed out to Cenote Cristalino after picking up the gear and tanks and so on. I'm writing this to share some experience. I don't know if anyone will take anything away from this or not but the hope is that there's at least one little tidbit.

I've been diving sidemount all week to further work on getting comfortable with sidemount. Gabriel of Advanced Diver Mexico has been my guide.

I'll fast-forward ahead to the incident. Gabriel was leading the dive. We completed 2 jumps and were at about 23 minutes into our dive when all of a sudden I heard something "pop." I hear a fairly significant "free-flow" of bubbles on my right and immediately reached to shut off my right tank while signalling to Gabriel (though I later found out he didn't see my signal but heard me coughing). It's a good thing I had so many simulated free-flows during my full cave. The problem got a little worse because the free-flow continued. Gabriel had already reached me (we stayed pretty close to each other in the caves the entire week - it was a good pairing for me) and saw that it was actually my left side having issues. He shut off my left valve. Unfortunately, since I was slightly flustered at this point, I didn't it yet realize it but had 2 regulators I couldn't breathe from - both valves were now off. The visibility was quickly going south due to the percolation caused by the free-flow. We both maintained our buoyancy and both had touch contact with the line. I signalled to Gabriel that I'm out of air and I grabbed one of his regulators. I had already taken in some water (hench the earlier coughing) and admit I started to get a bit nervous. It isn't a good feeling to be taking on water and feel like you have no air 23 minutes inside a cave.

Ok, so now I have Gabriel's reg and he has one and he checks his pressure seeing that he has plenty of air and we both signal thumbs-up and "ok" to exit immediately. After a few metres, he asks again if I'm ok and he maintains touch contact with me (to say "hey buddy, I'm here with you and we're going out together") - this was very good. Then he checks my right regulator/valve and turns it on slowly and pushes the reg at me. I accept cautiously but breathe and all is ok. I had plenty of gas - well over 2,000 psi at 30' with only about 20 minutes to the exit to go. So, I'm with my right tank/regulator again and we make an uneventful, smooth exit cleaning up our jumps and communicating often - as we did all week.

After surfacing, Gabriel told me it was my frickin' 2nd-stage swivel and not a valve, which I originally thought. I looked at it (we're still in the water fully kitted up) and saw the o-ring protruding from the middle of the swivel. He tightened it right there on the surface and It is interesting timing since I saw a recent thread on the swivels. It was a simple matter of the screw loosening a little. It was enough....

So, a few hours later (I deliberately waited), I wonder some things...in my current sidemount configuration, I heard the free-flow on my right side. This could *easily* be confusing since the left bottle 2nd-stage swivel is on my right side and my long-hose 2nd-stage is on my right side. This was the first in the problems here. I switched off right because I heard it on right. Gabriel uses a double short-hose configuration which keeps the 2nd-stages separate. It looks clean and also would have avoided this problem.
Of course I have to think about whether or not I want to continue to use the swivel. I dive fairly often in between my travels and I'm pretty conservative and watch my gear closely. I get it serviced when it's supposed to be and pretty carefully check it when kitting up. It is not possible to systematically check every possible failure point. I understand the desire to remove them when possible. I'm going to think about this for a while but while I'm considering, I'll probably use right angles. Wayne @ Amigos told me that if one of my swivels fails and I die, he doesn't want me coming back there to complain about it. Very Wayne :) ...

There are some things I could have done different. One of the most important things is that we communicated and he responded quickly and calmly. This could have turned into an ugly situation and been a real vacation spoiler.

I have a forced break from caves for a while as I'm flying out tomorrow to New Jersey then back to Brasíl and around South America before going back to the States. I'm not sure if I'll dive in December as planned.

[Kevin Carlisle]

Hey Steve, glad everything worked out and sounds like you did you job well. I love my swivels but have thought about going with phantom hoses to eliminate the need. Glad your ok buddy and hope to see you next time you make it up to Marianna.

[Dsix36]

Glad that everything worked out OK for you. I have been using 90 degree fittings since i am afraid of the same thing.

Thanks for posting about your adventure.

[JCDdiver]

Steve,

Good report. Thank you for sharing your experience. I'm glad you were able to sort it out without any major issues. Let me know when you want to dive. Be safe.

[GLENFWB]

Thank you for telling us this story Steve. I have gotten rid of both my swivels because one of them failed on me a few months back. Fortunate for me it started small with a steady stream of bubbles. I know it could be fixed but I decided right there and then to replace them. Your point about isolating the tank from the direction of the noise is a GREAT lesson, and frankly something I have never thought about. I will learn from your lesson. Thank goodness for your training and a good buddy.

[JCDdiver]

Steve,

Good report. Thank you for sharing your experience. I'm glad you were able to sort it out without any major issues. Let me know when you want to dive. Be safe.

[icestac]

Just out of curiosity, was this an omniswivel branded swivel or a generic one?

Glad you are ok.

Cheers,
Jeff

[whodunit68]

Just out of curiosity, was this an omniswivel branded swivel or a generic one?

Glad you are ok.

Cheers,
Jeff

Thank you, I sincerely appreciate it (and the words from current and potential friends/buddies above.
It's a very good question - it was a generic swivel. To be honest, a quick turn of a screw can probably happen to either so I'm not sure in this case it was dependent on that but I could very easily be wrong.

Gabriel gets big credit for being calm in a tough situation. After further discussion, I learned that by the time he turned and saw me (which was very fast), the free-flow caused such percolation that it was difficult for him to see what was going on. Under different circumstances with a different person, I'm not sure how it would have turned out.
I'm not very interested, especially based on this experience, in finding out what it's like to drown. What I felt then (and feel some now - sore throat and some other things) are not pleasant.
Boy I'm glad this one is over.

[Mark Vlahos]

I am also curious about the design of the swivel. Can you link a picture? I know that some designs appear to be more robust than others.

Mark Vlahos

[whodunit68]

3306

[HeloDriver]

Good lessons to be taken away. Very glad you are ok and thank you for sharing.

[Samantha]

Steve - When I saw your post in FB I was very concerned about what could have gone wrong. Relieved you are alive and well. Thanks for posting.

Give me buzz when you're back in NJ.

[LCF]

Steve, glad you are okay.

In quite a few of my classes, one of the things that could really get one a chewing out from the instructor in the debrief was if you turned off the reg your buddy was breathing. Over and over again, they hammered and hammered that the very first thing you had to do, when you went to assist a buddy with a problem, was verify which reg he had in his mouth, and you were NEVER to shut a valve attached to a reg someone was breathing.

Reading your story, I can really see how having all of your gas turned off raised the stress level enormously. I don't know if it's harder to verify which reg someone is using when they are on sidemount, or if the poor viz was the issue. But you have given me a real-life story to cement the lessons from class -- don't turn off someone's current gas supply, no matter how urgently you feel a valve needs to be closed.

[stairman]

Glad everthing turned out ok. I read in Jills sidemount book the other night ,how its wise to stay away from hemipherical swivels and will not dive them. A 90 degree angle with captured o ring was advised where needed.

[Major Restriction]

Your point about isolating the tank from the direction of the noise is a GREAT lesson, and frankly something I have never thought about.

I use two distinct mouthpieces on my sidemount (and backmount) regulators so I can tell which regulator I have in my mouth by feel. I never have to guess in an emergency situation.

[OneBrightGator]

Thanks for posting this, it's very timely for me.

And I think I'll be going with elbows instead :)

[Slüdge]

A 90 degree angle with captured o ring

??? I think someone is using an incorrect term - you can't have a captured o-ring if it rotates.

[benjamin]

I've had 2 failures with (omniswivel) swivels, one minor and the other serious. I don't use them anymore, I changed over to 70 degree swivels, they work great. Glad things went well for you.

[whodunit68]

once again, thank you for the well wishes and support. I sincerely appreciate it!
Lynne, I have to admit, you got me re-thinking it even further and to be honest, the replay eventually presented some additional insight into how reactions could have been different. I won't yet comment further on it as further reflection is required in order to really have my arms around it.
OneBrightGator - I did see the thread and realize the timing.
Does the screw loosening qualify as a swivel failure? I suppose it does...bottom line for me is that no matter how careful we are, there's always something that can go wrong and we have to know how to deal with the issues.

[whodunit68]

??? I think someone is using an incorrect term - you can't have a captured o-ring if it rotates.

I don't think he was talking about a rotating 90 degree - the right angles I know of don't rotate.

[Slüdge]

the right angles I know of don't rotate.

Every one I've seen does.

[icestac]

I don't think he was talking about a rotating 90 degree - the right angles I know of don't rotate.


Every one I've seen does.

It just allows the second stage to rotate around the "X axis" (if you can call it that) in the same way the second stage can freely rotate when connected to the fitting on most hoses.

All of this talking about rotating swivels really makes my head spin... :rolleyes:

[FW]

This is from the Sidemount forum, but pretty well covers Steve's cause of the swivel trouble.

I've fought these things for years. I have a couple of customers that INSIST on them. Plus, when I did some sidemounting it was the only way to get the fit I wanted. But they started leaking every ten dives or so and had to be reassembled.

Several weeks ago I ran across a service bulletin that says you MUST use Loc-Tite when assembling them. That opens up a whole new window on things. Maybe they're useful after all...

[whodunit68]

This is from the Sidemount forum, but pretty well covers Steve's cause of the swivel trouble.
agreed, thanks Forrest. Unfortunately I saw that afterwards....

[sskasser]

<snip> Ok, so now I have Gabriel's reg and he has one and he checks his pressure seeing that he has plenty of air and we both signal thumbs-up and "ok" to exit immediately. After a few metres, he asks again if I'm ok and he maintains touch contact with me (to say "hey buddy, I'm here with you and we're going out together") - this was very good. ...<snip>....Gabriel uses a double short-hose configuration which keeps the 2nd-stages separate. It looks clean and also would have avoided this problem....<snip>

First off, glad you're ok, Steve!

What issues (or were there any) did you encounter during the airshare with Gabriel using double short-hose configuration? "We've" discussed the theoretical implications ad nauseum, but here's some real data and I'd love to hear how it went.

Thanks for sharing such a great detailed report!

Shirley

[whodunit68]

It just allows the second stage to rotate around the "X axis" (if you can call it that) in the same way the second stage can freely rotate when connected to the fitting on most hoses.
Thanks for explaining!


First off, glad you're ok, Steve!

What issues (or were there any) did you encounter during the airshare with Gabriel using double short-hose configuration? "We've" discussed the theoretical implications ad nauseum, but here's some real data and I'd love to hear how it went.

Thanks for sharing such a great detailed report!

Shirley
Thanks, Shirley. Yes, I can. Interestingly, I asked Gabriel how he does an air share. His answer was that first he tries to match configuration with his dive team. In sidemount, the likelihood of an airshare is very low. However, if a situation arose where he must, he says he would just pass the bottle. At one point during the scenario, it seemed as if he was preparing to do just this (right before my right valve was turned back on).
It was not easy to share with the short hose especially around the back of his neck but we did it. He made it pretty easy to do. We would have made it out of the cave. Frankly, his setup sure looked cleaner and the short hose configuration wasn't all that much different than sharing air with someone in a recreational setup, though it's been simulated eons since I did that.

[BobK]

So I gather that you were diving sidemount, yet when you had a failure you shut down the wrong tank ? I always thought that one of the porported benefits of sidemount diving was that you could easily isolate the tank with the problem, yet this incident shows that is not always true.
Can you explain in more detail why this occured ? I'm really not trying to be adversarial, but this seems to be contrary to one of the main "safety benefits" I have read about sidemounting.

[skip]

My 90-degree angle does not "swivel" or "rotate." It's locked at 90-degrees. However it does rotate after the elbow turn where the second stage screws on (so the second stage rotates).

skip

[skip]

So I gather that you were diving sidemount, yet when you had a failure you shut down the wrong tank ? I always thought that one of the porported benefits of sidemount diving was that you could easily isolate the tank with the problem, yet this incident shows that is not always true.
Can you explain in more detail why this occured ? I'm really not trying to be adversarial, but this seems to be contrary to one of the main "safety benefits" I have read about sidemounting.

I've never seen this benefit. I wear one reg on a necklace, just like backmount and the other one is in my mouth (just like backmount). when a freeflow occurs it's not easy to determine if it's the one in your mouth or the one on your necklace unless you remove the one in your mouth and look at it. if a tank valve goes (or din o-ring?), making the source of freeflow at the tank, then it's a bit easier (i would imagine).

skip

[Slüdge]

My 90-degree angle does not "swivel" or "rotate." It's locked at 90-degrees. However it does rotate after the elbow turn where the second stage screws on (so the second stage rotates).

Yes, they all do.

[CaveBuddy95]

Great you came out unhurt.

Things to bare in mind are the fact that, at all time, you should know what reg you are breathing from. Sidemount is different from BM, as you know and it is essential to know what reg is in your mouth. Having said that, we all went through this drill during cave class. Having the instructor sneak from bellow and purge any reg reg to see if you are 'aware' of what is your breathing source. Be it in basic sidemount or basic backmount, it is fundamental skill.
Basic sidemount regs/house should be set exactly the same as basic backmount. One short bungeed (with 90°elbow - not swivel) and a 7ft. This works great. And on top of that, it makes transition from backmounted doubles to sidemount configuration, a breeze. And it works great until you reach 'real' sidemount cave passage. On top of that, sm short hoses are not that easier to dive with. There are pros and cons.
In a 2 man team, if using sidemount at a basic level, both need to have same regulator configuration, in this case, I suggest basic sidemount reg config. But what do I know really!! :)
Sharing air on long hose is in muscle memory, peace of cake whereas passing over a cylinder needs preparation and practice. If tank is not rigged adequately and the protocol is not reharsed it can lead to disaster or at least not such uneventful exit.
In real sidemount cave it's different. I presume or wrongly assume you were not in SM cave. :roll:
Sidemount is old practice and is under estimated and wrongly seen as some way to sling 2 tanks on our sides and go on but there is more to it than that, specially in cave environment.
Training is important at that level of advanced diving. The value behind good training is that it will give you the right tools from the get go as well as make you aware of others gear configuration - what to do or what not to do.
I just took sidemount cave trianing with Steve Bogaerts and after 50 dives in SM on self-taught rig config. I just got my eyes opened to real sidemount caved diving. Yes, there is huge value in taking training from a guy like Steve Bogaerts. During class we reached the limits of the long-hose use, that is, the cave was getting small, not advanced small but small enough to demonstrate that long hose has its limits. Limits that I will reach after going through a good serie of basic sidemount cave dives and I will go to Steve again to take the advanced sidemount course.

Again, I'm glad you came out unhurt.

Cheers

ps:did I mention that swivels are dangerous? no? so better now that never! SWIVELS HAVE BEEN RECALLED FOR MONTHS NOW - 90° elbows are the future! :)

[whodunit68]

There was not a question in my mind about which reg I was breathing.
You are right, it was not a sidemount-only section of the cave.
Many valve shutdowns during full cave but also discussed were probabilities of the correct valve. The swivel is off to the right and gas exited to the right of that. I heard and felt bubbles on the right so I immediately shut off the right - exactly what I was taught, meanwhile switching to the other reg. If one of his regs or hoses fails, the distinct advantage is that each is very much on its respective side.
He likes the short hose and that's his perogotive and i will have to make my choice...

[CaveBuddy95]

There was not a question in my mind about which reg I was breathing.
You are right, it was not a sidemount-only section of the cave.
Many valve shutdowns during full cave but also discussed were probabilities of the correct valve. The swivel is off to the right and gas exited to the right of that. I heard and felt bubbles on the right so I immediately shut off the right - exactly what I was taught, meanwhile switching to the other reg. If one of his regs or hoses fails, the distinct advantage is that each is very much on its respective side.
He likes the short hose and that's his perogotive and i will have to make my choice...

No more comments :|

[Michael Stroeck]

So, a few hours later (I deliberately waited), I wonder some things...in my current sidemount configuration, I heard the free-flow on my right side. This could *easily* be confusing since the left bottle 2nd-stage swivel is on my right side and my long-hose 2nd-stage is on my right side. This was the first in the problems here. I switched off right because I heard it on right.

For humans, there is no such thing as directional hearing while underwater.

If you get the sensation that something is coming from the right, that might be true or not... But it won't be your ears telling you that. You hear mostly via bone conduction while immersed, and that just is no good for making out the direction of the sound source. You can not rely on hearing to locate a the area where you are losing gas.

If you can not see exactly where the bubbles are coming from is better to ignore your unreliable senses completely and just always methodically go through a well-defined procedure that will catch the offender at some point.

1) Have a pre-determined valve-shutdown procedure.
2) Perform it often and meticulously for training purposes.
3) Follow it to a T in any emergency situation until you can't hear bubbles and are breathing from something other than the shut-off regulator.
4) In stressful situations, do not even think about trying to make critical decisions before you have exhausted all the standard, well-ingrained reactions that you have built up in training.


Many valve shutdowns during full cave but also discussed were probabilities of the correct valve.

Probabilities are fine, as long as you use them to define your procedure which you then always use. I just think its not possible to make judgements based on probabilites while you are actually losing gas back in a cave. IMHO, the chances of messing up, getting even MORE freaked out and then drowning are much higher than making the right judgement.

[limeyx]

For humans, there is no such thing as directional hearing while underwater.

If you get the sensation that something is coming from the right, that might be true or not... But it won't be your ears telling you that. You hear mostly via bone conduction while immersed, and that just is no good for making out the direction of the sound source. You can not rely on hearing to locate a the area where you are losing gas.

If you can not see exactly where the bubbles are coming from is better to ignore your unreliable senses completely and just always methodically go through a well-defined procedure that will catch the offender at some point.



While you might be "technically" correct regarding the hearing (I don't know enough to say), in practice I (and others) don't find what you wrote here to be the case.

I have had many many cases in class where "surprise" bubbles are used to emulate a failure and in every single case, I was able to determine which "side" they were coming from (notwithstanding that bubbles on one side of the body can come from a regulator on the opposite side)

In our last class (CCR), i was also easily able to tell that the slight "clunk" was my left-side quick QC4 being unhooked by our instructor.

That said, in my classes there is a very simple and repeatable process for hunting down and fixing/handling leaks, and the first step for someone "helping" the victim is to make darned certain the regulator that person is (or is attempting to) breathe is fully turned on, regardless of where bubbles are or appear to be coming from.

Nick

[Michael Stroeck]

I have had many many cases in class where "surprise" bubbles are used to emulate a failure and in every single case, I was able to determine which "side" they were coming from (notwithstanding that bubbles on one side of the body can come from a regulator on the opposite side)

In our last class (CCR), i was also easily able to tell that the slight "clunk" was my left-side quick QC4 being unhooked by our instructor.

Hi Nick,

Definitely, you can also feel bubbles, or the act that causes them (unhooking). I was talking about the "hearing" part specifically. The real reason for my post was the "procedure" part, and what to do when you don't actually know what's going on.

[limeyx]

Hi Nick,

Definitely, you can also feel bubbles, or the act that causes them (unhooking). I was talking about the "hearing" part specifically. The real reason for my post was the "procedure" part, and what to do when you don't actually know what's going on.

I do agree for sure with the procedure part. Whether it's hearing, feeling or something else, so far I have found I can make a very good determination where to start looking for a leak (thankfully mostly in classes!)

[Bobby]

Glad that the dive came out OK for you. There are some things to take away from it, that is sure. The swivel issue was the main cause for the problem but I don't believe that it was the root cause.

I am not sure what or why others are teaching the way they are. I have always taught putting a person on my known source of gas before turning anything of theirs off. I have had a number of failures and had others in my team with failures in SM. The need to shut down someone elses cylinders in SM has also never been needed. With the OP's configuration I can see how the wrong cylinder was shut down. The response should have been to turn the shut down cylinder back on before shutting down the other one. Since his team member shut down his cylinder, the team member should have put him on his gas source first.

SM does not have one widely accepted gear configuration yet and may never have it due to the various specialty reasons for using SM. I believe this is a classic example of why people should spend time getting experience with doubles (BM) and honing thier muscle memory before moving to SM. For any advanced technical diving such as SM, CCR, multiple stages, etc. I approach my gear configuration with a solo menatality and the ability to lend assistance for another diver regardless of them being in my team or not. For me that means a long hose on every dive and configuration. I have not yet found cave small enough that I could get through but I could not get a cylinder through that has a long hose on it. If the passage is small enough that a long hose won't help someone then I won't dive it with a teammate that is not comfortable doing the passage solo. Gaining dive time and experience IMHO builds the knowledge on handling configurations, situations, etc..

Bobby

[Greenwood_60]

The bubbles are going to displace water as they move past you. There will be some distance from your body they can pass and you will still feel the movement of the water that they displace. The effects will be much greater an object passing you in air due to the incompressible medium, and the viscosity of the fluid.

The brain will combine cues from multiple senses. You will hear the bubbles, and feel the direction, and your brain will combine that in to a sense of bubbles in a particular direction.

[jcbrown]

For humans, there is no such thing as directional hearing while underwater.

If you only hear in one ear, you can have directional hearing. It is a learned skill.

[Teknadv3x]

Can someone post a picture of the 90 dgree elbow... also who is the OEM

Thanks in advance
Dave

[whodunit68]

Can someone post a picture of the 90 dgree elbow... also who is the OEM

Thanks in advance
Dave
here you go: http://www.piranhadivemfg.com/item/90-Degree-Elbow-524.

[cavedivingwoman]

This is Cave Diving Woman's man posting, so I guess I am Cave Diving Man? I am a design engineer, EE & physicist by occupation when I am not diving, so o-rings and seals are the stuff of my life. Here's the simplified story:

1) All swivels add one or more dynamic seals (typically an o-ring moves against a rigid & hopefully smooth sealing surface), so they are prone to wear out and leak eventually (if you don't periodically lube the o-ring, preferably using silicone or an oxygen compatible grease intended for continual movement, and keep the mating surface clean and polished to prevent corrosion build up and abrasion), but no more than the typical seal at the end of a second stage regulator hose anyway. So the chance of a failure just increases linearly with the number of such seals in line. If/when they do leak they tend to give early warning by bubbling a tiny bit at first which then gets progressively worse over time, so the failure is very rarely catastrophic unless you ignore it and don't do any maintenance even after you get the warnings. Botttom line is if you do not need a swivel don't use one as it is an additional failure point, but if you do need it, e.g. for a short hose feeding from the LHS tank for a right handed second stage in sidemount rig without neck wrapping, then go ahead, but use the right kind.

2) The good: a fixed angle right angle or 45 degree swivel only typically adds one dynamic seal. The other internal seal that is typically employed in the assembly is static and has very low risk. Good (though somewhat difficult to get and rather expensive) examples of this kind of swivel are the Scubapro 45 degree type which are also very compact (or there are more available and lower cost right angle versions available from Trident). I've never seen one of this type fail, and they are used extensively and successfully in technical applications.

3) The ugly: the second class of swivels are very similar to the first but are formed from a solid metal sphere with an oulet union port that screws in to one side either at right angles or 45 degrees from the inlet port. This kind are OK, available and inexpensive, but they are rather bulky and I have seen that the outlet port can come loose (loctite threadlock can fix this problem), so I tend to avoid them. Another even uglier class of swivels are the type more recently found on some second stages that have a ball joint with a limited solid angle cone to swivel through. This type not only rotates the seal but allows it to translate across the surface of the sphere, which is much more likely to result in abrasion of the o-ring, especially if any corrosion occurs, so I recommend against using this type.

4) The bad: this class of swivel look spherical like the previous type and have the apparently attractive feature of swiveling to any angle, but they achieve this by having two internal concentric o-rings sandwiched between two hemispheres held together with a screw through the middle. I warn against using this type. It adds multiple failure points including 3 dynamic seals, but most seriously if the central screw comes loose the failure can be catastrophic as the two hemispheres will separate enough for the o-rings to escape the retention grooves, so instantly you get all leak and no air delivered. If you feel you must use this type make sure the central screw is captured tight and retained in place using loctite/permatite or similar cyanacrylate thread locking adhesive. better still just avoid them.
Neil Benjamin

[JamieZ]

This is Cave Diving Woman's man posting, so I guess I am Cave Diving Man? I am a design engineer, EE & physicist by occupation when I am not diving, so o-rings and seals are the stuff of my life. Here's the simplified story:

1) All swivels add one or more dynamic seals (typically an o-ring moves against a rigid & hopefully smooth sealing surface), so they are prone to wear out and leak eventually (if you don't periodically lube the o-ring, preferably using silicone or an oxygen compatible grease intended for continual movement, and keep the mating surface clean and polished to prevent corrosion build up and abrasion), but no more than the typical seal at the end of a second stage regulator hose anyway. So the chance of a failure just increases linearly with the number of such seals in line. If/when they do leak they tend to give early warning by bubbling a tiny bit at first which then gets progressively worse over time, so the failure is very rarely catastrophic unless you ignore it and don't do any maintenance even after you get the warnings. Botttom line is if you do not need a swivel don't use one as it is an additional failure point, but if you do need it, e.g. for a short hose feeding from the LHS tank for a right handed second stage in sidemount rig without neck wrapping, then go ahead, but use the right kind.

2) The good: a fixed angle right angle or 45 degree swivel only typically adds one dynamic seal. The other internal seal that is typically employed in the assembly is static and has very low risk. Good (though somewhat difficult to get and rather expensive) examples of this kind of swivel are the Scubapro 45 degree type which are also very compact (or there are more available and lower cost right angle versions available from Trident). I've never seen one of this type fail, and they are used extensively and successfully in technical applications.

3) The ugly: the second class of swivels are very similar to the first but are formed from a solid metal sphere with an oulet union port that screws in to one side either at right angles or 45 degrees from the inlet port. This kind are OK, available and inexpensive, but they are rather bulky and I have seen that the outlet port can come loose (loctite threadlock can fix this problem), so I tend to avoid them. Another even uglier class of swivels are the type more recently found on some second stages that have a ball joint with a limited solid angle cone to swivel through. This type not only rotates the seal but allows it to translate across the surface of the sphere, which is much more likely to result in abrasion of the o-ring, especially if any corrosion occurs, so I recommend against using this type.

4) The bad: this class of swivel look spherical like the previous type and have the apparently attractive feature of swiveling to any angle, but they achieve this by having two internal concentric o-rings sandwiched between two hemispheres held together with a screw through the middle. I warn against using this type. It adds multiple failure points including 3 dynamic seals, but most seriously if the central screw comes loose the failure can be catastrophic as the two hemispheres will separate enough for the o-rings to escape the retention grooves, so instantly you get all leak and no air delivered. If you feel you must use this type make sure the central screw is captured tight and retained in place using loctite/permatite or similar cyanacrylate thread locking adhesive. better still just avoid them.
Neil Benjamin
ROTFLMAO, were still talking about swivels and elbows arent we and not the space shuttle.

[FW]

ROTFLMAO, were still talking about swivels and elbows arent we and not the space shuttle.
Makes no difference, the things are dangerous, and shouldn't be trusted in caves. There are plenty of safer ways to get good hose routing. Fixed 90s, or non-handed second stages, are a couple.

[JamieZ]

Makes no difference, the things are dangerous, and shouldn't be trusted in caves. There are plenty of safer ways to get good hose routing. Fixed 90s, or non-handed second stages, are a couple.

Easy killer I wasnt debating anything, just thought the delivery was funny. I agree with your assessment.

[mdax]

couldn't we reduce another point of failure by having the 90/70 degree change built into the hose?
Anyone ever try to have custom reg hoses made that had the bend in them?

[FW]

couldn't we reduce another point of failure by having the 90/70 degree change built into the hose?
Anyone ever try to have custom reg hoses made that had the bend in them?

Not that particular type, but other than getting custom length hose, it is next to impossible to get anything else custom. I have been trying to get someone to make me some hoses with older fittings, and they won't, even if I supply my old fittings.

[gasdiver]

Not that particular type, but other than getting custom length hose, it is next to impossible to get anything else custom. I have been trying to get someone to make me some hoses with older fittings, and they won't, even if I supply my old fittings.

Back in the 80's we found a hydraulics shop in Atlanta that would make LP hoses for us when we supplied the fittings. Of course we never told the guys what we were doing with these hoses, just that they would be used for air.

[FW]

Back in the 80's we found a hydraulics shop in Atlanta that would make LP hoses for us when we supplied the fittings. Of course we never told the guys what we were doing with these hoses, just that they would be used for air.

Yep, I had a few made back then. I just can't find a shop willing to crimp used fittings now.