Left post rolloff.

[Bombay High]

I know there is concern in overhead environments of having your left post roll off in contact with an overhead obstruction, which is what dictates the primary hose coming off the right post.
Would it not be relatively simple to have the left post valve machined with reverse threads, so that it would not roll shut in contact with an overhead ?

 

[aquaregia]

I don't think such manifolds are readily available, and I suspect having less than 100% acceptance on something like that would cause mad deaths.

Have you read this? “Ideal” Manifolds… Not So Ideal?

 

[TSandM]

I've seen this discussed somewhere before. One of the problems is that we learn very early that counterclockwise is open, and clockwise is closed (righty tighty, lefty loosey). Changing the threads on the left post violates that. I suppose one could learn to do it differently with practice -- we can learn almost anything. But it's critically important that this be standard within a team, because when someone comes over to help you with a catastrophic failure, they MUST know whether the valve is currently in the open or closed position, because it changes everything. So, unless you could get the whole DIR world to change simultaneously, you'd have a real problem with mixed teams with different directional valves.

It's not a big deal, the left post roll-off. Although it's rather sobering to see how far the valve can turn with ceiling contact, it's easy to do a flow check and put it back right after each "clonk". If you are sharing gas and roll off, you just reach up and turn the valve back on. (It should never get that far, because you are to do a flow check after each ceiling impact.)

 

[kwinter]

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.

 

[TSandM]

Valve cages are an equipment solution to a technique problem . . . first, we learn precise buoyancy control, to avoid ceiling contact. Then we learn to be very facile with valve manipulation, to do flow checks when ceiling contact occurs, either through error or because it was unavoidable. Valve cages can interfere with reaching valves for shutdowns, and they simply aren't necessary, if the diver has learnt his other lessons well. (Remember, this is the DIR forum.)

 

[kwinter]

Valve cages are an equipment solution to a technique problem . . . first, we learn precise buoyancy control, to avoid ceiling contact. Then we learn to be very facile with valve manipulation, to do flow checks when ceiling contact occurs, either through error or because it was unavoidable. Valve cages can interfere with reaching valves for shutdowns, and they simply aren't necessary, if the diver has learnt his other lessons well. (Remember, this is the DIR forum.)

Of course. I was being facetious.

 

[TSandM]

Hey -- I did say we could learn to do it differently! But yes, when GUE at least makes changes, they put out a bulletin on the website, and we are all supposed to make the changes at the same time. As JJ said in his recent interview in Diver magazine, the biggest strength of the system is its standardization -- not even as much WHAT we standardize upon, but that we standardize upon SOMETHING.

I have read all the IRAP threads on the CDF forum. There are several stories of left post rolloffs. In all of them, the diver was unaware of the issue until he had to breathe the backup reg (or, IIRC, in one case the diver had his gear configured to have his primary on the left post). This just won't happen if you follow your training and do flow checks after cave or wreck contact. It just isn't a big deal. I just spent a week in MX and I dove some pretty small cave, and yes, I hit the ceiling from time to time. A quick hand up to the left post ensures that all is as it should be. It's not that hard!

 

[rongoodman]

I just spent a week in MX and I dove some pretty small cave, and yes, I hit the ceiling from time to time.

Sounds interesting--anything I should be putting on my list for the next trip?

 

[tbone1004]

yeah so one of the things you should do from time to time is breathe off of that octo to ensure that it's working. Part of the check gear before you set it up, after you set it up, before you get in the water, after you get in the water, before you descent, after you finish descent and constantly throughout the dive. That being said, you can replace the left knob with a metal one which won't spin, and to fully turn off a post is difficult to do. Partially turn off sure, but any time you feel yourself hit the ceiling you should reach back and check that and the manifold to make sure you didn't bust it. You can get hard plastic knobs without a whole lot of grip that will be more difficult to spin off as well. Redoing the threads on the valves would be a potential solution, but that would be a problem.
Thorndikes learning laws, law of primacy. We first learn right tighty left loosey. instinct says to do that when we turn valves and having to turn them both forward or both back would be problematic. Could be done, but then you'd have to get all new manifolds, have to deal with one normal and one backwards etc etc. Not saying it's a bad idea, but it's not practical by any means and would cause more problems than the very rare roll-off. It's far simpler to get divers to say "self, i just hit the ceiling, i should probably check my left post" If you are too tasked to think about that you have no business being in a cave or diving doubles, sorry. That's just a very simple thing that no amount of task loading should cover.

 

[PfcAJ]

Metal knobs can dent and jam, and the hard plastic ones break. A roll off (correctable) is significantly better than a break off (uncorrectable) or a dent and jam (uncorrectable).

Just reach back there and check it on occasion and whenever you contact the ceiling.