Cross Bar on doubles?

[Aquamaniac]

I have been teaching tech diving for 8 years and have not yet seen a diver here in cold water who can do a complete valve drill in 10 seconds
More like 30 and on a high performance regulator that equals more like 40-50 cuft.
But no argument with the rest of your post.

All your doing is lifting your arm to your shoulder and turning a valve 1.5-3 times.
10 seconds should be a doddle. I can do it in 6 ;-)

 

[elan]

I have been teaching tech diving for 8 years and have not yet seen a diver here in cold water who can do a complete valve drill in 10 seconds
More like 30 and on a high performance regulator that equals more like 40-50 cuft.
But no argument with the rest of your post.

There is no problem doing 2 valve shutdowns in less than 10 secs with 2 hands

why would you want to do the complete valve drill , can you explain ?

 

[elan]

At the end one can always sling an AL80 "pony" and get the best of both worlds

 

[halocline]

Why not leave the isolator almost closed; the gas flow between the tanks only needs to be very slow, and shutting it is simply a 1/4 turn (or thereabout).

Isolator failure, such that gas leaks out uncontrollably through the isolator, has to my knowledge only occurred in these incessant 'manifold vs independent doubles' threads. Not in the real world of actual diving.

 

[Jeff Toorish]

I've done it both ways --for a while I preferred keeping my backmount doubles independent. I dive side mount a lot, so switching between regulators is second nature to me. There are only two reasons I can think of for diving isolated backmounted doubles; for convenience if you are often breaking down your doubles to two single tanks and to eliminate the several failure points on the manifold.

If you are diving isolated doubles, you most definately would not want to breath the first tank down to 1500 psi (assuming 3000 starting psi). You would want to breath down by about 500 psi to 2500. Then switch and breath the second tank down by about 1000 to 2000 psi. That would be thirds right there, if you are in an overhead environment. At that point, you would switch to the first tank and take it down to about 1500 and then go in 500 psi increments.

You really want to keep the tanks within about 500 psi of each other just for trim sake and to ensure both tanks have an adequate air supply in case of a catastrophic failure in one of them.

Having said all that, I eventually decided that a manifold really makes things easier and even with all those failure points, staticstically manifolds don't seem to fail very often.

Jeff

 

[DaleC]

Just curious, did Bam mention he wanted to go cave diving?

 

[elan]

Why not leave the isolator almost closed;

IMHO the risk of accidentally closing the isolator is not worth the solution for an imaginary problem

 

[Aquamaniac]

Why not leave the isolator almost closed; the gas flow between the tanks only needs to be very slow, and shutting it is simply a 1/4 turn (or thereabout).

Isolator failure, such that gas leaks out uncontrollably through the isolator, has to my knowledge only occurred in these incessant 'manifold vs independent doubles' threads. Not in the real world of actual diving.

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


If you recall, there was a horrific incident at Eagles nest a few years ago because a diver had left an isolator closed whilst mixing gas. Ever since then, I am anal about keeping mine all the way open all the time. This is not the blame of the manifold, but worth remembering.

 

[PfcAJ]

There is no problem doing 2 valve shutdowns in less than 10 secs with 2 hands

why would you want to do the complete valve drill , can you explain ?

Lol, sure, lets shut down ALL out gas. Shut down both posts with both hands, come on... Its a leak, not the end of the world. Shut down the offending post, see if it can be fixed, and if not, you go home.

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.

The best move in regards to valve manipulation is not convolutions such as closed isolator, partially open isolator, double valve shut downs (lol), or any other shenanigans. PRACTICE till you're able to do it in trim and with good buoyancy, then go dive and keep your skills sharp.

 

[elan]

Lol, sure, lets shut down ALL out gas. Shut down both posts with both hands, come on... Its a leak, not the end of the world. Shut down the offending post, see if it can be fixed, and if not, you go home.

There are 3 valves on the manifold, think again and guess which 2 I meant :shocked2: No one told you before not to put words in people mouths ? Yeah now tell me that closing the manifold is called isolating...