Cross Bar on doubles?

[halocline]

What would be the advantage of a "nearly closed" valve?

Nearly closed means it's still open (cracked open) so that gas can flow between the tanks, but it can be closed more quickly in the event of an emergency. I don't see any downside to this. Leaving the valve all the way open just means it takes longer to close.

 

[halocline]

The 1/4 turn open isolator is a bad idea. Its real easy to be completely closed on accident (myriad of issues with that), and it doesn't provide instant feedback if you accidentally turn it the wrong way in a real situation. Having the isolator open all the way means you can only turn it one way. Closed. Times when you really have to isolate are exceedingly rare.

I really don't see how keeping it slightly open would result in it getting closed by accident. There's no roll off danger with an isolator. Having it cracked open does provide feedback; you turn it a little and it stops, closed. Tank valves are not like volume controls; once it's cracked, plenty of gas will flow between the tanks. I don't understand the advantage of having it several turns open.

But I can understand how some divers might not be comfortable with it. I do agree that needing the isolator is exceedingly rare. I just hear the argument in favor of independent doubles frequently that by the time you close the isolator, half the gas is gone, and it's simply not true.

 

[TSandM]

I do think it isn't unreasonable to realize that shutting valves in a cave in Florida or Mexico, with minimal exposure protection and bare hands, is different from shutting valves in the bottom of Lake Washington, in 41 degree water, with heavy exposure protection and dry gloves. I can twirl a well-maintained valve shut in no time in the former setting, but it does take longer in the latter. My Full Cave instructor even convinced me I could shut a valve AND isolate at the same time -- in warm water gear. I cannot do it in my cold water setup, and I use a Fusion drysuit which is about as mobile as you can get.

That said, the failures that require isolating are sufficiently rare that I don't worry about it. I keep my skills as sharp as I can, and the skill I practice most is staying in touch with my team.

 

[DaleC]

I just hear the argument in favor of independent doubles frequently that by the time you close the isolator, half the gas is gone, and it's simply not true.

I hear the arguement in favor of manifolded doubles that it is critical to have access to all the gas and in many cases that is not true either. Each system has its place.

 

[elan]

My Full Cave instructor even convinced me I could shut a valve AND isolate at the same time -- in warm water gear. I cannot do it in my cold water setup, and I use a Fusion drysuit which is about as mobile as you can get.

If the dry suit and undergarment fit properly you can do it even in cold water. I'm far from being a flexible person and I have off the shelf bare trilam and undergarment (400 g on the torso in total) and I can fairly easy do any combination of the 2 valves (except shutting down the left post with right hand and the other way around). I just practiced it last week in 37F water

I never dove fusion but I have a buddy who had it in the past. He complained about problems with reaching valves in his Fusion. Once he switched to a custom cut Trilam suit that fits him well the problems have gone. My guess is with all the wrinkling and excess material of the inner shell overlapping the suit has to be stretched properly before the dive, I don't know.

 

[DA Aquamaster]

I do think it isn't unreasonable to realize that shutting valves in a cave in Florida or Mexico, with minimal exposure protection and bare hands, is different from shutting valves in the bottom of Lake Washington, in 41 degree water, with heavy exposure protection and dry gloves. I can twirl a well-maintained valve shut in no time in the former setting, but it does take longer in the latter. My Full Cave instructor even convinced me I could shut a valve AND isolate at the same time -- in warm water gear. I cannot do it in my cold water setup, and I use a Fusion drysuit which is about as mobile as you can get.

If the dry suit and undergarment fit properly you can do it even in cold water. I'm far from being a flexible person and I have off the shelf bare trilam and undergarment (400 g on the torso in total) and I can fairly easy do any combination of the 2 valves (except shutting down the left post with right hand and the other way around). I just practiced it last week in 37F water

I never dove fusion but I have a buddy who had it in the past. He complained about problems with reaching valves in his Fusion. Once he switched to a custom cut Trilam suit that fits him well the problems have gone. My guess is with all the wrinkling and excess material of the inner shell overlapping the suit has to be stretched properly before the dive, I don't know.

I'll take the middle ground here as I see both points of view. I also have a Fusion and with my heavy DUI undergarment on after 45 minutes in 39 degree water, a valve drill can be a challenge both from the undergarment aspect but also from a not quite cold but less than warm hands perspective. The result is that I can do a valve drill in full cold water gear after cold soaking awhile, but it does not happen nearly as fast as it does in warm water.

In about 15 years of dry suit diving, I have noted that it is important to arrange each layer before you don the next one to ensure maximum flexibility in the arm and shoulder area if you want maximum flexibility for a valve drill, and that has been true with trilams as well as the Fusion.

I won't argue that a custom cut suit offers great mobility, but when you consider the wide variation in undergarments needed for 35 degree water and 70 degree water, a custom cut suit for cold water is excessively baggy in warm water, and a custom cut suit for 70 degree water is excessively snug in cold water. The Fusion handles both extremes equally well with great moblity and no excess material to cause drag.

My Fusion experience has been very positive in terms of mobility, but then I had to go up one size to offset the skinny cut of the legs issue in the Fusion, so there is more room in the bladder around the shoulders than may be the case for a diver my same overall dimensioons but with skinnier legs and consequently a suit one size smaller.

 

[elan]

I figured out (later confirmed by other divers as well) that the key point for me in eliminating the restriction of the suit was to inflate the suit excessively while still at the surface and stretch in all important directions. Then deflate the suit to the normal state and start the dive. After this even if I heavily squeezed the suit does not limit my hands much and I can reach the valves with no problem. And now I do not even bother with arranging each piece on the surface as I used to do.

 

[RJP]

My Full Cave instructor even convinced me I could shut a valve AND isolate at the same time -- in warm water gear. I cannot do it in my cold water setup, and I use a Fusion drysuit which is about as mobile as you can get.

Yeah, my Tec instructor convinced me I could isolate the manifold and shut down the offending valve at the same time...without warning, at 100fsw, in 50deg water, in a drysuit, dry or 5-7mm gloves, with numb hands, and cramping forearms, 1ft off a silty bottom, in 30sec, without varying more than +/1' or so.

He was quite persuasive... in that you had to be able do it to pass the course. In fact you needed to do it multiple times on each of the 12 dives, or you didn't move from one dive to the next.

Early on in the course you had 45-60sec to get it done, and some more leeway on depth, but by the second half of the class it was under 45sec, and 30sec by end.

 

[RJP]

I figured out (later confirmed by other divers as well) that the key point for me in eliminating the restriction of the suit was to inflate the suit excessively while still at the surface and stretch in all important directions. Then deflate the suit to the normal state and start the dive. After this even if I heavily squeezed the suit does not limit my hands much and I can reach the valves with no problem. And now I do not even bother with arranging each piece on the surface as I used to do.

A quick valve drill at the surface is a great thing.

 

[elan]

RJP you have an impressive post count of Split Fin posts, do you run an application that tracks an existence of Split Fins in topic and posts the responses from the knowledge base ? What programming language is it written in ? Can you share the knowledge base with us ?