Left post rolloff.

[lamont]

*** MOD NOTE ***

Keep in mind that this is the DIR forum, and that this question has been asked and answered correctly (and the DIR answer in this case agrees with the IUCCR one and with the rest of the industry).

 

[Bombay High]

Any post that uses the words "simple" and "machined" in the same sentence can't really be serious. Easier to build a valve cage so the left post never comes in contact with the ceiling.

Maybe my mistake was to put this in the DIR forum, because I know that there are specific rules of what may or may not be discussed here.

Kwinter, please understand, that in the industry that I come from, machining reverse threads is no big deal. We do machining and welding work at depths that you likely have not been to and likely will never be to.

My question is genuine. It is not such a difficult thing to develop the muscle memory to turn your left post off one way and your right the other, because when you think of the direction of movement, they will correspond. I understand that for people used to doing valve drills one way, this will involve unlearning.

But if a rolloff is a genuine concern to the point that it governs equipment configuration, why has this not been something that has been even thought off.

If it has been thought off and been discarded, then I would love to know why.

But to say that machining and simple dont go together reveals an incredible level of ignorance. Most great machining is also incredibly simple. And I do not mean a DIY job, but something undertaken by Halcyon or one of the other reputable manufacturers that make DIR standard equipment.

Warm regards

(seriously)
BH

PS - My question was for the DIR forum, because it was a genuine. In commercial diving we protect our valves by inverting our cylinders.

 

[boulderjohn]

As has been said, a roll off is easily preventable, but even if it happens, it should be easily fixable. During my training for general technical diving certifications, one of the instructor tricks was to shut down your left post while you are engaged in some activity and won't notice. Then he would put your buddy OOA so you have to donate your primary. When that happens you get nothing when you inhale from your alternate, so you reach back and are breathing just fine in a couple of seconds.

 

[PfcAJ]

There are some things in DIR diving that were built around what was the standard at the time (regs feeding right to left and scootering with the right hand are easy examples). This valve turn direction you're noticing isn't any different.

I agree with you that it makes sense to have a reverse threaded left post. Unfortunately, all the manifolds doubles in the entire world are righty tighty. All of them. It would be I'll advised to introduce a few oddballs into the mix. A far more simple solution is to stick to the proven procedure.

 

[Bombay High]

There are some things in DIR diving that were built around what was the standard at the time (regs feeding right to left and scootering with the right hand are easy examples). This valve turn direction you're noticing isn't any different.

I agree with you that it makes sense to have a reverse threaded left post. Unfortunately, all the manifolds doubles in the entire world are righty tighty. All of them. It would be I'll advised to introduce a few oddballs into the mix. A far more simple solution is to stick to the proven procedure.

I agree with you totally. I also do not think that a complete roll off - roll shut is a real world possibility. Also, if you are diving the kind of dives that would involve this scenario, I would imagine you would have the prescence of mind and ability to reopen a shut valve in an emergency, without freaking out.
My question was asked only because this was obviously a big concern, that warranted a mandatory gear configuration.

I know that throwing oddball lefty tighty valves into the mix is ill advised now, but why was this not made standard years ago ?

 

[robertarak]

But if a rolloff is a genuine concern to the point that it governs equipment configuration, why has this not been something that has been even thought off.
QUOTE]

I think you may considering this more of an issue then it is. When the early creators and adopters of the DIR style of diving had to consider which side to place the primary and which to place the back up a decision had to be made. It would be my guess (just a guess) that there was no reason they could think of NOT to put the primary on the right and a very very small chance of left valve roll-off, so they chose the right for the primary. I do not believe that it is such a major concern that the entire system revolves around that one issue. Just the best choice when creating a standardized approach.

 

[PfcAJ]

Left post roll off is a real thing, I've done it many times. If you're sharing gas while passing a restriction and it rolls off, it could be fatal for your buddy if your long hose is on the left post.

 

[aquaregia]

I was just thinking, from a human factors perspective, reversing the threads on the left post could cause confusion about the thread direction of the manifold. Probably not a real-world problem, but it's interesting to think about.

 

[TSandM]

It constrains gear configuration because in one setting, it's a trivial problem, and in another, it's a potential fatality. IF you are sharing gas through a restriction, and the post that the diver in front (the recipient) is breathing rolls off, he can neither get to your tanks to fix it, nor may he even be able to communicate the problem to you. (We were in a few situations last week where it might have been pretty dicey.) On the other hand, if you roll your OWN post off, you just reach up and fix it.

It's enough of a potential issue to mandate a hose configuration, but with the hoses configured so, it's really a non-issue.

 

[lamont]

look, this is really simple:

- a left post rolloff killed at least one experienced cave diver (someone with a better memory should be able to find this in iuccr).

- the proposed solution of using reverse threads has been thought of, e.g. post #2.

- why weren't they built this way originally? probably didn't seem like the biggest issue that needed solving at the time.

- why don't we all change? the fear is that confusion over which way the left valve turns will lead to more incidents than it prevents and it will do more harm than good.

you can debate that last point till you are blue in the face that the reverse threaded way is 'obviously better' and that everyone should change for the betterment of humankind, but you're going to get a lot of divers who don't sign on and there's almost certainly going to be some collateral damage along the way.

- its easy to fix, reach back and turn it back on. practice, practice, practice.

that is the DIR answer. period.

you can try to assert that eliminating pilot error and fixing it to be more perfect is worth is, but that's just an assertion, not really an argument. the actual argument is fuzzy. the argument gets resolved in this forum by the competing assertion that you just need to practice, and that the risks of switching are believed to outweigh the benefits.

so, its been thought about, the arguments are actually blatantly obvious. the reasons for the decision and the work-around is also obvious -- and since the guy who heads the GUE training agency could very easily get his other company to start machining manifolds with reverse threads, i'm assuming this issue was actually considered at one point and rejected and not rejected entirely capriciously. i'm also positive that it wasn't made as some kind of vast conspiracy.