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

[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.