1/4 Turn on Valves - What are the various DIR agencies' take on this?

[WhiteSands]

I open my valves all the way, the back them off from fully open by no more than a quarter turn. Reason is two fold. If for some reason my valve gets jammed in an overhead environment AND I have a need to close it down in case of a second stage failure the valve won't be jammed open from said impact. Granted this is very unlikely. Second, if for some reason I have to close a valve in an emergency and I happen to turn it the wrong way, the fact I turned it only a small amount before the handle stops will help remind me to turn it the other way to close it.

In both circumstances, if the valve is fully open and it gets jammed or in a sudden attempt to close it in the even of a leak, there is the possibility for the valve to get jammed open. Which could cause further stress adding to an already bad situation to begin with.

As far as Acetylene tanks go, the reason those get opened a quarter turn is for safety. If your have a fire between you and the tank, like from a failed hose or other connection, it is a simple act to close the valve cutting off the supply of flammable gas as quickly as possible. How that practice made it into scuba I have no clue.

Just my thoughts. B.

Thanks for your feedback. I like understanding the reasons behind doing things, to help me make an informed choice.

 

[DevonDiver]

....help me make an informed choice.

Let that choice be fully informed...

...If for some reason my valve gets jammed in an overhead environment AND I have a need to close it down in case of a second stage failure the valve won't be jammed open from said impact. Granted this is very unlikely.

Exactly how unlikely? I've never seen a modern valve 'jam', regardless of impact or rotational force applied. Where valves have broken (free-floating), it was due to lateral impact...and the initial position of the valve would have been immaterial...

...have to close a valve in an emergency and I happen to turn it the wrong way, the fact I turned it only a small amount before the handle stops will help remind me to turn it the other way to close it.

Which is surely an argument for having the valve fully-opened (no turn-back whatsoever). That provides immediate feedback to the diver and prevents any chance of confusion. The valve can only turn in one direction... and that direction is closed.

In both circumstances,...there is the possibility for the valve to get jammed open.

No offence intended, but is this an assumption?

My experience: in 22 years diving, I've seen no evidence to support such an assumption or possibility.

It's important to question assumptions like this, because the scuba community is really quite credulous and that results in it being absolutely awash with regurgitated nonsense that is passed along from diver-to-diver and instructor-to-student without the slightest concern about whether it is factual or not...