No Joke

[boulderjohn]

It accomplishes avoiding the scenario where the valve might be open slightly resulting in an OOA situation at depth?

So does shutting off the valve, which the diver intended to do. It's not like this happens every time, you know. It is a rare oversight.

 

[Landlocked123]

I have a buddy who is a service tech. He confirms there is absolutely no need to do the 1/4 turn back towards closed after fully open. I also heard a very valid argument from e techie guy that in case of an emergency having the knob turning both ways can, in a moment of high stress, cause one to lose track of which direction to turn. If the valve is fully open and secured then there is only one way to turn it which is closed. That argument made total sens to me. Why add more variables and cognitive stress in an emergency situation.

 

[kelemvor]

I think you're confusing issues. The quarter turn back instead of 100% on has been pretty thoroughly debunked here in other threads. Apparently it was a carryover from older welding valves or something.

Boulderjohn's scenario involved just turning your tank on a little bit for about 3 seconds because that's all you need at the time. I've done it that way myself. However, I don't do it that way anymore. I've gotten into the habit of turning the tank on 100% as soon as I connect my regs and leaving it on until my dive is over. That means it's on during the boat ride to the site, during tests etc. I guess if there was an undetected leak I could be spoiling my dive. So far that hasn't happened. I always hook up before we leave the dock because it's much harder to obtain a replacement tank out in the ocean .

Also, I don't really understand how someone could take 2 breaths off a regulator and not notice the valve was closed - even if it's been pre charged. I've tried doing that on purpose. I get much less than 1/2 a breath from air remaining inside my regulators/hoses. Maybe it would work if I had four hoses and one of them was a 6' long hose or something? Maybe different regulators have a larger interior volume that could hold more gas combined with someone having a super tiny sac?

 

[Wookie]

I think you're confusing issues. The quarter turn back instead of 100% on has been pretty thoroughly debunked here in other threads. Apparently it was a carryover from older welding valves or something.

It isn't debunked, it just isn't necessary for this design and use.

Has no one really explained the reason for the 1/4 turn back?

Valves in steam plants are designed with a front seat as well as a back seat. They are designed like that so that in the event of a packing rupture, you can backseat the valve and repair the valve packing without closing the valve. But you don't want to leave the valve on the back seat because the steam will condense between the disc and the packing and leave a little water at the bast of the packing. When the valve is closed, the valve would come off the back seat, the water would flash to steam, and the packing, packing gland, packing gland follower, and packing gland bolts might fail, shooting bits of valve and steam throughout the space and causing general mayhem. Everyone in the entire United States Navy is trained to open a valve fully and then back it off a 1/4 turn.

Guess who the first scuba instructors were. Right, Navy guys. They brought their inappropriate for the use knowledge with them.

The 1/4 turn back isn't debunked, and if you think it was, you don't understand the word. It was inappropriately applied and isn't necessary for a valve that wasn't designed for a backseat.

 

[kelemvor]

It isn't debunked, it just isn't necessary for this design and use.

Has no one really explained the reason for the 1/4 turn back?

Valves in steam plants are designed with a front seat as well as a back seat. They are designed like that so that in the event of a packing rupture, you can backseat the valve and repair the valve packing without closing the valve. But you don't want to leave the valve on the back seat because the steam will condense between the disc and the packing and leave a little water at the bast of the packing. When the valve is closed, the valve would come off the back seat, the water would flash to steam, and the packing, packing gland, packing gland follower, and packing gland bolts might fail, shooting bits of valve and steam throughout the space and causing general mayhem. Everyone in the entire United States Navy is trained to open a valve fully and then back it off a 1/4 turn.

Guess who the first scuba instructors were. Right, Navy guys. They brought their inappropriate for the use knowledge with them.

The 1/4 turn back isn't debunked, and if you think it was, you don't understand the word. It was inappropriately applied and isn't necessary for a valve that wasn't designed for a backseat.

I think you're splitting hairs on the wording. Debunked with regards to doing it on scuba valves.

I guess I did remember wrong, I thought it was a carryover from welding. Apparently it's a carryover from steam valves. That doesn't change the fact that you don't need to do it on a scuba tank does it?

According to meriam webster it's "
: to expose the sham (see 1sham 2) or falseness of

I thought I used debunk correctly; although I could have explicitly said "on scuba valves". I thought it was a safe assumption on scubaboard, when discussing turning valves on scuba tanks.

 

[Wookie]

I think you're splitting hairs on the wording. Debunked with regards to doing it on scuba valves.

I guess I did remember wrong, I thought it was a carryover from welding. Apparently it's a carryover from steam valves. That doesn't change the fact that you don't need to do it on a scuba tank does it?

According to meriam webster it's "
: to expose the sham (see 1sham 2) or falseness of

I thought I used debunk correctly; although I could have explicitly said "on scuba valves". I thought it was a safe assumption on scubaboard, when discussing turning valves on scuba tanks.

Perhaps. Not worth quibbling over. I would think that debunked meant that it was at one time thought to be necessary. Although it isn't, as a Navy trained steam plant mechanic, I still do it. I use my blinkers in Florida too, and that has been totally debunked....

 

[Joneill]

Alec Peirce talks about the origin of the “open and close 1/4 turn” for scuba tanks (and why it is not necessary today) here (at 5:07 in):

 

[wetb4igetinthewater]

It isn't debunked, it just isn't necessary for this design and use.

Has no one really explained the reason for the 1/4 turn back?

Valves in steam plants are designed with a front seat as well as a back seat. They are designed like that so that in the event of a packing rupture, you can backseat the valve and repair the valve packing without closing the valve. But you don't want to leave the valve on the back seat because the steam will condense between the disc and the packing and leave a little water at the bast of the packing. When the valve is closed, the valve would come off the back seat, the water would flash to steam, and the packing, packing gland, packing gland follower, and packing gland bolts might fail, shooting bits of valve and steam throughout the space and causing general mayhem. Everyone in the entire United States Navy is trained to open a valve fully and then back it off a 1/4 turn.

Guess who the first scuba instructors were. Right, Navy guys. They brought their inappropriate for the use knowledge with them.

The 1/4 turn back isn't debunked, and if you think it was, you don't understand the word. It was inappropriately applied and isn't necessary for a valve that wasn't designed for a backseat.

Thanks for explaining all that Frank. Mind if I quote you elsewhere?

 

[Wookie]

Yeah, sure. It's all true, I swear.

 

[Rooster59]

I use my blinkers in Florida too, and that has been totally debunked....

Awesome