Crossbar and isolator valve: do they help?

[kensuf]

Another thing to consider is how many incidents have occurred that are attributable in some way to the presence of the isolator that would not have occurred in the absence of the isolator. For example, how many people have discovered an isolator that was closed at some point when it shouldn't have been?

There have been at least two fatalities that I am aware of that may possibly have been prevented if the isolator was opened. Both of those should have been caught in a pre-dive check, and at least one of those should have been caught during the dive when the pressure gauge wasn't dropping.

 

[Akimbo]

I figured it was because with that the combo of cylinders and bands would have to position the tanks so the center to center measurement lined up perfectly with the ends of the manifold...

Alignment isn't a problem while assembling them and is less critical because the manifold is so strong. The direction the isolation valve points would be fixed but most point up anyway.

http://www.aqualung.com/militaryandprofessional/product_information/j-k-twin_manual_07-07.pdf

 

[cool_hardware52]

I figured it was because with that the combo of cylinders and bands would have to position the tanks so the center to center measurement lined up perfectly with the ends of the manifold. With the modular approach we actually use, the manifold can be screwed in or out to get the ends lined up with the cylinder centers, even if the bands don't position them perfectly.

With good quality bands designed to the actual tank diameters being twinned and designed for the C to C of a specific manifold the effective C to C of the banded tanks will be quite close.


"Adjustable" manifolds aren't really. The amount of C to C adjustment possible *without* unporting the inner pairs of barrel orings is tiny. "Adjustable" refers to the ability to position the the two post valve orifices in the same direction and to allow "adjustment" of the iso valve relative to the posts.

I did a project for a particular Rebreather application that required designing and fabricating extensions for the Iso bars. That lead me to having several discussions with the engineers at Thermo. (This was before XS acquired them) It was quite interesting to learn what "adjustable" actually means.

Tobin

 

[tbone1004]

Are you talking about the use of thicker/stronger disk, or an actual plug that goes in place of the burst disk plug?

both technically. They're basically thick pieces of metal that go in place of the burst disc that can't burst. You can't tell externally that they're plugged or not which is ideal when visiting other dive shops. You could also machine an actual plug that replaces the whole assembly if you were properly motivated

 

[kensuf]

I may replace mine with a Vindicator someday--I eyed up that option when I ordered the manifold from DGX. But I decided for my first set of doubles, while I'm still learning, I'd just force myself to check more often. I didn't bother asking, but I figured it's probably what the GUE guys would advise.

You may recall your cavern instructor telling you a story about a friend of his that giant strided into Peacock with his valves off. I believe he probably told you to verify your valve is opened by hitting your inflator and breathing the reg before stepping into the water. Same holds true for your isolator.

I like to do a valve check before every dive. Sometimes I make a huge production of it and do a full blown valve drill with my buddy paying attention, but even when I don't do that, I still reach up and verify all valves are open.

 

[Caveeagle]

There have been at least two fatalities that I am aware of that may possibly have been prevented if the isolator was opened. Both of those should have been caught in a pre-dive check, and at least one of those should have been caught during the dive when the pressure gauge wasn't dropping.

Ken, do you require an isolation manifold for your tech training? I recently acquired a set of early 104s with a non-iso manifold. I am swapping over the bands on those tanks and was considering swapping in an Iso-valve at the same time. I understand both sides of the argument, but there seems to be very little actual DATA to sway me to either side of this argument.

Too bad we are not like the FAA with tons of documentation and DATA on failure rates for given components.

 

[tbone1004]

@kensuf hit that nail on the head

equipment checks at the following times
before you leave the house
after you set up the equipment
after you don the equipment
before you get in the water
after you get in the water
on descent

they take less than 30 seconds in doubles to tap your wing inflator, tap your drysuit inflator, take a breath on your primary, take a breath on your secondary, reach back and manipulate the three valves *turn back whatever you can without regripping the knob and then open until you feel it stop to make sure it's all the way open*. Doesn't have to be a full s-drill, but each time you do that, you are validating that everything is open and functioning

 

[kensuf]

Ken, do you require an isolation manifold for your tech training? I recently acquired a set of early 104s with a non-iso manifold. I am swapping over the bands on those tanks and was considering swapping in an Iso-valve at the same time. I understand both sides of the argument, but there seems to be very little actual DATA to sway me to either side of this argument.

Too bad we are not like the FAA with tons of documentation and DATA on failure rates for given components.

Agreed on the data point, I think public shaming has been a cause for the lack of data. If someone posts "I jumped off the back of a boat with my valves off" someone else will say "what an idiot you are"...

I think I know which 104's you got. There were 3 sets for sale and I was really tempted to buy all 3.. The stories those tanks could about the places they've been.. I don't require an isolator. Heck, I dove for years using a yoke manifold (I'm sure you did too!) and there sure as heck wasn't an isolator on them, but I think they're valuable. You can get just the isolator crossbar for the manifold if you choose to add one.

 

[flymolo]

I have vindicator knobs on one of my doubles sets and I don't find them very useful as I can't see them underwater.

I find reaching back and doing a flow check every so often, or whenever my valves come into contact with something, is more comforting.

 

[Lorenzoid]

You may recall your cavern instructor telling you a story about a friend of his that giant strided into Peacock with his valves off. I believe he probably told you to verify your valve is opened by hitting your inflator and breathing the reg before stepping into the water. Same holds true for your isolator.

I like to do a valve check before every dive. Sometimes I make a huge production of it and do a full blown valve drill with my buddy paying attention, but even when I don't do that, I still reach up and verify all valves are open.

The interesting thing about valve checks and breathing both regs is that it won't catch a closed isolator if you're convinced you're turning the isolator in the correct direction. It can happen to a diver who is just starting to learn to use doubles and doesn't yet have the direction burned into muscle memory. (It wasn't me.) And yes, watching the SPG not dropping should be a clue.