90 degree elbow on second stage

[Flotsam]

I bought an elbow to add to my second stage to see if it helps with some jaw pain. It didn't come with any o-rings. I know the second stage has an o ring where the male LP connector attaches, but shouldn't the elbow fitting have an o ring between it and the LP hose?

 

[Flotsam]

Never mind, I figured it out!!

 

[tbone1004]

the second stage shouldn't have any visible o-rings at the hose connection. There is one o-ring on the hose side that should be visible at the swivel, but that's it. Should be on the elbow as well, it's barely visible below. SOME second stages may have a vibration damping o-ring, and you can see the groove cut out for it on the hose side of the elbow, but it's not required and very few regulators use it

 

[John C. Ratliff]

If you are having jaw pain, check also the mouthpiece. You may need a different one.

While the 90 degree elbow can be helpful with jaw pain, realize that putting a 90 degree change in air flow will affect breathing performance (respiratory work of breathing, due to air turbulence set up in the hose/regulator connection) when at depth and high exertion rates.

SeaRat

 

[tbone1004]

If you are having jaw pain, check also the mouthpiece. You may need a different one.

While the 90 degree elbow can be helpful with jaw pain, realize that putting a 90 degree change in air flow will affect breathing performance (respiratory work of breathing, due to air turbulence set up in the hose/regulator connection) when at depth and high exertion rates.

SeaRat

Please show ANSTI graphs demonstrating proof of this phenomenon. I have yet to witness any noticeable WoB differences in my regulators due to addition or subtraction of an elbow or ball swivel

 

[emoreira]

I bought an elbow to add to my second stage to see if it helps with some jaw pain.

I think that a fixed 90 degrees elbow will improve your comfort but there is a better option. I added a swivel to the hose connection in my second stage reg. This allows a more comfortable routing of the hose and lower effort when turning my head.
360 Degree Swivel for 2nd Stages

 

[Akimbo]

Please show ANSTI graphs demonstrating proof of this phenomenon.

Calculate it for yourself: Pressure Loss from Fittings – Equivalent Length Method – Neutrium

I doubt it would be significant unless you were deep and working hard, but restrictions do matter.

 

[tbone1004]

Calculate it for yourself: Pressure Loss from Fittings – Equivalent Length Method – Neutrium

I doubt would be significant unless you were deep and working hard, but restrictions do matter.

Using that math, and worst case scenario of a 60x factor for the elbow and a 1/4" regulator hose diameter, an elbow effectively adds 15" to the hose length for pressure drop. You can't tell a WoB difference based on hose length because the pressure drop isn't really relevant for how we want this valve to work. No amount of theoretical math will mean anything unless you produce the ANSTI results, and I don't think hose length has ever really been a factor in that testing. I sure as hell can't tell a difference in my short hose *22"* vs my long hose *108"* in my cave diving rig, so adding an extra 15" of effective length won't do anything at the gas densities and pressure differentials we are dealing with

 

[Bob DBF]

I use the 70 degree swivel (also called 110 degree, or even 20 degree, swivel by some) which I found to be better for me on a 40" hose.

Dive Rite Adaptor Second Stage-High Flow Angle
(Couldn't get a picture to post right)

Bob

 

[Akimbo]

No amount of theoretical math will mean anything unless you produce the ANSTI results, and I don't think hose length has ever really been a factor in that testing.

True, but the theoretical math almost always understates the problem in the real world. I was very tangentially involved with development of the first breathing machine at NEDU (US Navy Experimental Diving Unit) in the early 1970s (predecessor to the ANSTI machines). They discovered that the fluid dynamics calculations consistently underestimated actual system performance because it wasn't practical to model or anticipate all the variables at the time. The breathing machine was necessary for developing the US Navy Scuba Regulator evaluation program. We also discovered the hard way that it was desperately needed on for
deep saturation diving.

Another sailor and I were locked out a little shy of 950' using the US Divers version of the Kirby Morgan Band Mask with some field mods approved by Washington. All the wetpot testing at NEDU came back with divers saying it was just fine. The two of us dangling below the bell proved them to be wrong. We were fine until we started heading back to the bell and working much harder. The umbilicals were hung outside the bell on those days and were negative as heck (not the exact word we used). We had to use the freeflow valve on the mask to keep from passing out.

Bottom line, diver's perceptions of breathing resistance are useless, heavy work loads change everything, and small changes can multiply and bite you in the butt. Until a breathing machine establishes the safe working limits of elbows it is reckless to imply otherwise -- especially since thousands of people can read this thread over time and one of them could use one to exceed the undetermined limits. @John C. Ratliff's advisory statement was correct and prudent.