Stage/deco/BO reg with inline shutoff

[stuartv]

I searched on this subject and found a thread from 10 years ago. There, the consensus was that stage regs should not have an inline shutoff. But, nobody in that thread talked about the reason that I was given for why to use one. So, I'm resurrecting the discussion, but in its own thread, instead of continuing one from 10 years ago.

My tech instructor/mentor suggested to use an inline shutoff on my deco regs. I believe he was taught to do so by his tech instructor/mentor. His tech instructor is a very well-respected crusty old diver, expedition-level deep wreck diver, tech instructor, cave instructor, and CCR instructor. I'm not going to get into names because I think the practice should stand on its own merits, not the credentials of the person recommending it.

The recommendation to me was to add an OPV to the 1st stage and an inline shutoff to the 2nd stage on each of my deco/BO regs. Then dive with them all with the cylinder valve open and the inline shutoff turned off.

I'll explain the reason given by using an example. I was helping my tech instructor teach an AN/DP class and the reason he gave actually happened for real to one of the students. So, this reason is not just hypothetical.

The student did not have an inline shutoff setup. He started the dive with his deco reg charged and the valve off. During the dive, he must have occasionally bumped the purge on the 2nd stage of the deco reg. It wasn't leaking, but he bumped i enough to depressurize the line. Once the line was depressurized, the 1st stage turned in the valve a little.

When the student turned the deco cylinder valve on, as part of his normal gas switch, an explosion of bubbles came pouring out of the valve because the 1st stage had turned just enough to allow it to leak (a LOT) around the DIN O-ring.

In this case, the student was able to turn the valve off, tighten the DIN wheel on the 1st stage and re-open the valve. It did not extrude the O-ring and ruin its ability to seal. But, it certainly seems like on another occasion, that absolutely COULD happen.

My instructors point about using an inline shutoff was totally borne out by this incident in real life. If the student were diving with an inline shutoff (turned off) and the valve turned on the whole time, then accidentally bumping the purge on the 2nd could not have depressurized the line. Therefore, the 1st stage would not have had an opportunity to get loose.

There are some obvious cons to using the inline shutoff.

You can forget to turn your cylinder valve on and panic yourself when you open the inline shutoff, try to breathe, and get no gas.

You can forget to shut the inline valve and get none of the planned benefit (i.e. still bump the purge and accidentally depressurize the line).

You can forget the shutoff is there and panic yourself trying to breathe with it closed.

You can have debris that makes the inline shutoff become unable to open. The old thread had an example where the diver got a piece of shell stuck in just the right spot to block opening of the inline shutoff.

The inline shutoff adds 2 more O-rings to your LP gas supply to the 2nd stage, so 2 more opportunities for a failure.

Am I missing any of the cons?

Thoughts on the reason I was told for being in favor of using an inline shutoff?

 

[grantctobin]

I searched on this subject and found a thread from 10 years ago. There, the consensus was that stage regs should not have an inline shutoff. But, nobody in that thread talked about the reason that I was given for why to use one. So, I'm resurrecting the discussion, but in its own thread, instead of continuing one from 10 years ago.

My tech instructor/mentor suggested to use an inline shutoff on my deco regs. I believe he was taught to do so by his tech instructor/mentor. His tech instructor is a very well-respected crusty old diver, expedition-level deep wreck diver, tech instructor, cave instructor, and CCR instructor. I'm not going to get into names because I think the practice should stand on its own merits, not the credentials of the person recommending it.

The recommendation to me was to add an OPV to the 1st stage and an inline shutoff to the 2nd stage on each of my deco/BO regs. Then dive with them all with the cylinder valve open and the inline shutoff turned off.

I'll explain the reason given by using an example. I was helping my tech instructor teach an AN/DP class and the reason he gave actually happened for real to one of the students. So, this reason is not just hypothetical.

The student did not have an inline shutoff setup. He started the dive with his deco reg charged and the valve off. During the dive, he must have occasionally bumped the purge on the 2nd stage of the deco reg. It wasn't leaking, but he bumped i enough to depressurize the line. Once the line was depressurized, the 1st stage turned in the valve a little.

When the student turned the deco cylinder valve on, as part of his normal gas switch, an explosion of bubbles came pouring out of the valve because the 1st stage had turned just enough to allow it to leak (a LOT) around the DIN O-ring.

In this case, the student was able to turn the valve off, tighten the DIN wheel on the 1st stage and re-open the valve. It did not extrude the O-ring and ruin its ability to seal. But, it certainly seems like on another occasion, that absolutely COULD happen.

My instructors point about using an inline shutoff was totally borne out by this incident in real life. If the student were diving with an inline shutoff (turned off) and the valve turned on the whole time, then accidentally bumping the purge on the 2nd could not have depressurized the line. Therefore, the 1st stage would not have had an opportunity to get loose.

There are some obvious cons to using the inline shutoff.

You can forget to turn your cylinder valve on and panic yourself when you open the inline shutoff, try to breathe, and get no gas.

You can forget to shut the inline valve and get none of the planned benefit (i.e. still bump the purge and accidentally depressurize the line).

You can forget the shutoff is there and panic yourself trying to breathe with it closed.

You can have debris that makes the inline shutoff become unable to open. The old thread had an example where the diver got a piece of shell stuck in just the right spot to block opening of the inline shutoff.

The inline shutoff adds 2 more O-rings to your LP gas supply to the 2nd stage, so 2 more opportunities for a failure.

Am I missing any of the cons?

Thoughts on the reason I was told for being in favor of using an inline shutoff?

I’m pretty opposed to them, especially on bailout bottles. If you want a nice rant, Dave Slutton wrote a great one in one of the CCRX FB discussion groups.

I’d wager/I fear your instructor was taught by Sotis, one of the few former rogue proponents of such things. Happy to be mistaken on that.

Cons that are missing:
-OPVs suck. The rebuildable XS Scuba are 20% better and still suck.
-One more step between you and gas when you desperately need it.
-Unconventional, nobody in a mixed team will have ever used one/not expecting it when a reg is handed to them.
-Shutoffs can and do fail.

These, in addition to the cons you listed, render them a non starter. The only community I’ve actively seen them used is among REVO divers (ignoring their unfortunate use on mCCRs oxygen lines).

 

[JonG1]

I prefer simple on bailout and deco, I check for a de-pressurised line regularly just in case you do bump it empty.

Adding an opv that could leak and a shut off valve that could fail seem like too much of a risk, personally.

More steps, more stuff on checklists, more servicing too.

I think there may be a similar relatively recent thread in TDF.

 

[rjack321]

In this case, the student was able to turn the valve off, tighten the DIN wheel on the 1st stage and re-open the valve. It did not extrude the O-ring and ruin its ability to seal. But, it certainly seems like on another occasion, that absolutely COULD happen.

This doesn't happen unless the reg DIN actually unscrews, a bump and leak does not create enough of a gap to extrude the o-ring (there isn't really anyplace for it to go)

Shutoffs are a bad idea on deco bottles and especially on BOs. OPVs fail waaayyyy more often than you will ever extrude a DIN oring (basically never). Keep it simple, when you or a buddy is "that close" to panicking the shut off is going to make your day go from salvageable to f*cked.

 

[Pressurehead]

I’m pretty opposed to them, especially on bailout bottles. If you want a nice rant, Dave Slutton wrote a great one in one of the CCRX FB discussion groups

Cons that are missing:
-OPVs suck. The rebuildable XS Scuba are 20% better and still suck.
-One more step between you and gas when you desperately need it.
-Unconventional, nobody in a mixed team will have ever used one/not expecting it when a reg is handed to them.
-Shutoffs can and do fail.

).

Just curious, not trying to be contrary, when you say "suck", in which way do they 'suck'?
Thanks.

 

[stuartv]

You've prompted me to realize, I should not use one on a BO, for sure. That should always be turned on and ready to breathe. No point in an inline shutoff on that, as you'd never (should never) turn it off.

So, let's limit this to just deco cylinders. I.e. cylinders that you would normally have charged but turned off. Cylinders that you never want to breathe by accident and that you would normally only be starting to use in very controlled circumstances. I.e. you don't normally switch to a deco gas as an emergency operation.

 

[stuartv]

This doesn't happen unless the reg DIN actually unscrews, a bump and leak does not create enough of a gap to extrude the o-ring (there isn't really anyplace for it to go)

Shutoffs are a bad idea on deco bottoms and especially on BOs. OPVs fail waaayyyy more often than you will ever extrude a DIN oring (basically never). Keep it simple, when you or a buddy is "that close" to panicking the shut off is going to make your day go from salvageable to f*cked.

It does happen that people sometimes go to remove a DIN 1st stage from a tank and can't get the DIN wheel to turn, so they twist the regulator itself, which turns the wheel along with it. Then, they hold the wheel and twist the reg back, then turn it again. I.e. they basically use the 1st stage body to ratchet the DIN wheel until it's open enough to turn by hand.

Now, I KNOW that you shouldn't do that. It's a good way to actually loosen the bolt in the center that is holding the DIN threaded part of the reg on.

But, it seems like it would be possible to accidentally get that same kind of ratcheting action by accident that could loosen the DIN wheel (on a depressurized line) enough to allow the O-ring to extrude. Very unlikely, I'm sure. But, would it ever happen?

I'm not trying to disagree or argue with you. Just understand what you think is possible versus "NEVER have to worry about that happening."

It SOUNDS like the reality is that, yes, with no inline shutoff, you COULD have happen exactly what happened to the student that I described. But, (from what you're saying), that should never be any worse of a problem than it was that day. I.e. see the bubbles starting to come out and shut the valve, tighten the DIN wheel a little bit, and re-open the valve. Worst case is not bad at all, in which case it's not enough of a risk to merit all the other cons of an inline shutoff. Yes?

 

[happy-diver]

Dave Slutton

What's this all about

 

[stuartv]

Just curious, not trying to be contrary, when you say "suck", in which way do they 'suck'?
Thanks.

Good question. If you do the prescribed maintenance on one of the expensive XS Scuba/Highlands ones, like you do the maintenance on your deco regs (which you DO do, right?), what problems are you likely to have?

 

[grantctobin]

Just curious, not trying to be contrary, when you say "suck", in which way do they 'suck'?
Thanks.

They don't last very long in salt water, poor machining tolerances, and frequently bubble. God forbid you have to adjust them ever so slightly tighter and there's salt or sand in the threads you don't see.