roll-off vs gas loss, during catastrophic failure

[Mako Mark]

There was a recent discussion about valves and the quarter turn back technique on the instructor forum, but it brought up the question of how it applies to tec, so here goes, I will ask the question again in a different context:


All formal tec training has told me to have manifold valves all the way open, I cant help thinking that valves turned on four full turns are shut down far more quickly and easily than those that are open fourteen. During repeated valve shutdown drills, I often find the excersize tires the forearms to the point of cramping.

How much gas can you lose/save in 10 extra turns of the valve?? And how high up the list of "badness" is the problem of rolloff in comparison to ten extra seconds of gas loss during catastrophic failure??

I personally have never experienced roll-off while using doubles, and dont consider it a hugely life threatening situation as it can be readily monitored. I do consider slow response shutting down valves during catastrophic air loss a serious problem that should be prioritized much higher than roll off.

Opinions please.......

 

[J1M1]

There was a recent discussion about valves and the quarter turn back technique on the instructor forum, but it brought up the question of how it applies to tec, so here goes, I will ask the question again in a different context:


All formal tec training has told me to have manifold valves all the way open, I cant help thinking that valves turned on four full turns are shut down far more quickly and easily than those that are open fourteen. During repeated valve shutdown drills, I often find the excersize tires the forearms to the point of cramping.

How much gas can you lose/save in 10 extra turns of the valve?? And how high up the list of "badness" is the problem of rolloff in comparison to ten extra seconds of gas loss during catastrophic failure??

I personally have never experienced roll-off while using doubles, and dont consider it a hugely life threatening situation as it can be readily monitored. I do consider slow response shutting down valves during catastrophic air loss a serious problem that should be prioritized much higher than roll off.

Opinions please.......

I guess if you are worried about your left post rolling off from forward movement you could open that post about 4 turns to be sure that you could shut it down quicker if that post needed to be shut down...I dont know if valves deliver more gas when only partially open..If that is the case then you are sacrificing the amount of breathing gas delivered..However i can get to my valves and shut the offending post in less then 10 seconds.I know some peole who loosten up the isolator knob to help facilitate shutting it faster. Some also only partially open the isolator...I guess this argument would then have no need for discussing the right post being partially open since it will roll into the on position if it were rolled at all...JD

 

[MikeFerrara]

the valves on my manifolds go full of to full on in about 1 1/2 turns.

 

[Mako Mark]

the valves on my manifolds go full of to full on in about 1 1/2 turns.

My diverites go in about 10 - 14 that is why I asked the question. What brand are we talking about here, cause that makes a hell of a lot of sence to me!

 

[japan-diver]

Which dive-rite do you have? My DiveRite manifolds tale 2 1/2to 3 turns from full on to full off?

 

[Pez de Diablo]

My Halcyon and my dive rite manifolds all turn off from full in under 3 turns. It takes me less than 3 seconds to turn off a valve.

I keep em turned all the way open, that way I am not fooling around opening a valve when I should have closed a valve. When turned all the way, you know what is going to happen when you turn the valve.

 

[Curt Bowen]

I personally have never experienced roll-off while using doubles, and dont consider it a hugely life threatening situation as it can be readily monitored. I do consider slow response shutting down valves during catastrophic air loss a serious problem that should be prioritized much higher than roll off.

Opinions please.......

I have only had one roll off and that happened at Twin Dees solution tube. If you have never dove Twin Dee's the entrance is a small virtical tub just big enough to squirm down with your arms streached out infront of you. If you pull your elbow back, your stuck.

Good thing I had my secondary right there attached by my neck, I had to grab it with my teeth.

As for 4 turns, I know with extreme deep dives not opening the valve could restrict gas volume flow.

Of course all I dive now is the right way Sidemount LOL

Fire away DIR guys

 

[chickdiver]

Valves should be full open. If the valve is only partially opened, there can be resultant confusion during the shutdown procedure predicated by stress (IE opening the valve when you think you are closing it). Valves should also be given regular maintenance (an issue many people ignore with doubles, since it is time consuming and a pain to break them down) as proper lubrication of the valves makes all the difference in the world with valve shutdowns.

 

[MikeFerrara]

My diverites go in about 10 - 14 that is why I asked the question. What brand are we talking about here, cause that makes a hell of a lot of sence to me!

I have one of the older Halcyon manifolds. I think they've change sources since though.

We have some diverite's that require more turns (maybe 3?)but not as many as yours.

I've also had diverite manifolds come new with gummed up o-rings that were comming apart. They sealed but it took two men and a boy to turn them especially when the tanks were full.

 

[Mako Mark]

Of course all I dive now is the right way Sidemount LOL

My aching back seems to agree with you and I am pretty sure I am heading that way. Any advice on rigs?