Alternate Air Inflator & DIR

[android]

Would the isolator usually be open or closed? The valve would just turns off the left tank right, Not the 1st stage mounted on the left post?

 

[Soggy]

Would the isolator usually be open or closed? The valve would just turns off the left tank right, Not the 1st stage mounted on the left post?

The isolator is always open, unless one of your tanks blew a burst disk or oring. The isolator isolates the left and right tanks, so in the event of a burst disk blowing, you can save the contents of at least one tank. It is not attached to a regulator. The left and right posts control the valves to the regulators. You can shut down a post and still have access to the gas in both tanks, also.

 

[BCS]

Please excuse my ignorance. What is the DIR position on Alternate Air inflators? I know the alternate around neck with tubing is right where you need it, but isn't the inflator pretty close as well? There is a point where tubing can be used to help hold the reg in the mouth in case of unconsiousness. Any other reasons?

besides allof what has been posted as to why not an AAI, the fact that when you have a malfunction like an inflator free flow into your wing and you disconnect it, well you've left yourself w/o a backup reg and the need for oral inflate of your wing as well...plus the AAI mechainism itself is a bit more complex than either one just by itself....meaning seperately (back up 2nd stage and wing inflator) they are simpler and work very well, but combine the two and the result is a bot more complex, prone to more failures/malfunctions and they tend to breath like crap....which is just what one does not want in an emergency....basically, it's not optimal for all the reasons listed, and the only "up" side is the reduction of a hose of a hose....

just another $0.02 worth...

dive safe!---b.

 

[android]

I'm not familiar with doubles, so let me ask one more question. There are three connections to the post,

1) the tank
2) the regulator 1st stage
3) the isolator

Is the valve between the regulator and isolator meaning if the left valve is off the left 1st stage is off?

or

Is the valve between the tank and the isolator meaning that if the left valve is off and the isolator is open you can breath air on the left side that came from the tank on the right side?

The latter would seem the better arrangement. If you blow a burst disk, you can close a valve and still breath from both sides. If you blew a reg O ring, you would have to isolate, but you guys all use DINs so that should be infrequent.

Which blows more often DIN O rings or tank burst disks?

 

[Spectre]

Would the isolator usually be open or closed? The valve would just turns off the left tank right, Not the 1st stage mounted on the left post?

No. Completely incorrect. The valves shutdown the posts above the T to the crossover, not below it. When you turn off a post, you just shut down that post, you don't turn off the tank. With the left post off, you still have access to both tanks of gas.

In other words the valve turns off the 1st stage on the left post. NOT the left tank. If the left tank fails at the tank neck, you will still loose all your gas if you just shut down the left post. You have to then isolate. The isolater shuts off the crossover between the two tanks, and the posts shut down the outlets to the first stages.

Wouldn't you have to very carefully roll the valve handle along an overhead surface like a kid pushing a toy car?

Ask any overhead diver what their first reaction is after they bump a ceiling, and judge if they aren't concerned about the left post being rolled off. [Hint. First reaction is to check that your valves didn't turn at all]

 

[Spectre]

Which blows more often DIN O rings or tank burst disks?

It's not just DIN O-rings to worry about. It's any o-ring in the first stage, in your second stages, in your SPG, any cuts in your hose. And that's not even covering the more common failures like freeflows. Not many will be able to recite stories of tank neck o-ring failures, or burst disk failures. Not many will -not- be able to recite a story of a blown 1st stage o-ring, or hose o-ring, or SPG o-ring, or leaking hose, etc, etc, etc....

 

[android]

Thanks, now I get it.

 

[kidspot]

Hey Android -

Thanks for asking - I was about to ask the same question.

as Dr. Kent Hovind puts it "Ignorance can be fixed . . . stupid is forever"

 

[Dan Gibson]

It happened to me in Cave 1. Almost, but not a complete shutdown. It happened during a lights our air share in the Peanut Tunel at Peacock. I felt a little resistance and decided to stop my buddy (I was the donner and man behind). I backed up and immediately saw light as my instructor thought I rolled completely off and came in quickly. It happens very quickly. I just reached up after backing off a little and turned it back on completely and gave the instructor the ok. We then proceeded to finish the drill.

I believe there was another member on the list who did it in the Eye at Ginnie.

OK, the explanation about the left and right valves seems reasonable, yet rather improbable.

Wouldn't you have to very carefully roll the valve handle along an overhead surface like a kid pushing a toy car? A valve handle has a diameter of about 1.5in, so the circumference is about 4.7in. Usually it about 5 or 6 full turns to go all the way from open to closed, so that's about 2ft of rolling. So you have to roll for 2ft while avoiding contact with the tank which actually protrudes higher without noticing it.

Is there a recorded instance of this actually happening? Wouldn't the much more like event be that someone just rams the valve into something solid straight on and it breaks off?

Also, could not some foreign object become wedged on the bottom of the valve between the tank and the diver thus rolling it the other way?

 

[Soggy]

I'm not familiar with doubles, so let me ask one more question. There are three connections to the post,

Here's a picture of my doubles rig....maybe that will help you understand better.
http://soggy.thedecostophosting.com/gallery/displayimage.php?album=16&pos=16