A gas loss non-emergency

[nimoh]

One or more of you would be bent or dead.

flots

While I understand the point you are trying to make, this isn't true. Diving conservatively means that you could have gone a little further, or taken a little longer to solve an issue...but didn't.

 

[Akimbo]

…Sidebar observation: I'd guess that four out of ten hoses have been overtightened, two out of ten are a little loose, and only 40 percent correctly installed. Hint: It's the oring that makes the seal, not the thread...

It is amazing to me how few people understand how O-rings work. They are intended to move in the groove or recess. The hose fitting only needs to be tight enough to prevent accidentally unscrewing due to normal handling. That will be more than tight enough to prevent extrusion under design pressures. Brass is a very weak material, though ideal for machining. Over tightening can cause the thin cross section of an LP hose to crack… usually where the O-ring is.

Here is an illustration from the Parker O-ring Handbook:

http://www.parker.com/literature/ORD 5700 Parker_O-Ring_Handbook.pdf

 

[flots am]

While I understand the point you are trying to make, this isn't true. Diving conservatively means that you could have gone a little further, or taken a little longer to solve an issue...but didn't.

The plan didn't sound conservative, which is why I mentioned it.

 

[PfcAJ]

seemed pretty conservative to me. There's a lot of flexibility with doubles and a stage. If they plan their gas in a similar manner to what I do (and I think they do), they could have easily exited without the stages at all. The reserve gas is put in the backgas (allowing 2 regs + a long hose), not the stage bottle. Now, I did this math in a hurry, so feel free to double check:

1stage + al80 doubles ~ 230cuft
1/3 of that value is 77cuft
They drop the stage at 1700 (breathing 33cuft), ~ 42cuft left in the bottle
Continuing on backgas for the remaining 44cuft, that gives a turn pressure of ~2200psi
Back at the stage at 1400psi, 70cuft in backgas

Now at this point, they only used 33cuft to get there from the door. Even without the stages, there's 70 cuft (twice the gas needed to get out) in their doubles. Even 15mins of backgas deco is going to use about 10cuft of gas.

The fact that there are two stages in the water almost for sure means that they could get at the gas in the broken stage (if it stayed broken). Diver with the broke stage breaths backgas on exit while the other diver breaths the stage. When diver 2 exhausts the stage (which, btw, should be in OW as stages are used first going in and last coming out) a reg could be moved over to the 'broken' stage bottle, and diver 2 continues on backgas the rest of the way. This is just an option, and totally unnecessary given their gas plan + equipment config.

Bottom line is that a stage bottle really gives a lot of options.

 

[Doppler]

So what's the correct way to tighten a hose?

See postings above... but here's the overview.

Given the orings are the correct specs for the job at hand -- size and harness -- tighten using a torque wrench set at the manufacturer's suggested setting in either inch pounds or milli-Newtons. When in doubt, tighten just enough to make it very hard to loosen the fitting by hand.

 

[kwinter]

Thanks for posting a good lesson. Another option in case the hose had been bad rather than just loose. You could have shut down Peter's secondary post and removed that reg to put on the stage. A lesson I learned the hard way years ago........

 

[Akimbo]

…Given the orings are the correct specs for the job at hand -- size and harness -- tighten using a torque wrench set at the manufacturer's suggested setting in either inch pounds or milli-Newtons...

Seriously, does anyone outside the factory actually use a torque wrench on hoses? Short of putting a Crow’s Foot open-end adapter on a socket-drive torque wrench, which blows any accuracy you might have, where can you get an adjustable open-end torque wrench? I have never seen one under several hundred dollars.

I was taught “by feel” — virtually useless on the Internet and variable over time. I recommend grasping an open-end or 6" adjustable wrench near the open-end and make it “little-girl snug”.

As far as that goes, what are the torque specs for a hose in a first stage?

 

[nimoh]

I use a crowfoot on my torque wrench for tightening hoses. It doesn't change the accuracy or precision of your wrench by any measurable amount, but you do have to account for the extra length the crowfoot adds to the wrench using a simple formula. I tighten my hoses to 40 inch pounds, and set my wrench for 36 inch pounds.

 

[Doppler]

Seriously, does anyone outside the factory actually use a torque wrench on hoses? Short of putting a Crow’s Foot open-end adapter on a socket-drive torque wrench, which blows any accuracy you might have, where can you get an adjustable open-end torque wrench? I have never seen one under several hundred dollars.

I was taught “by feel” — virtually useless on the Internet and variable over time. I recommend grasping an open-end or 6" adjustable wrench near the open-end and make it “little-girl snug”.

As far as that goes, what are the torque specs for a hose in a first stage?

Well, the post did ask what is the correct way! :cool2:

I think the last sentence is the key. And I suspect you and I may use very similar methods in practice.

 

[lowviz]

It is amazing to me how few people understand how O-rings work. They are intended to move in the groove or recess. The hose fitting only needs to be tight enough to prevent accidentally unscrewing due to normal handling. That will be more than tight enough to prevent extrusion under design pressures. ...//...

Also pretty common if your "tank commander" doesn't mate the cylinder and manifold properly after a VIP...