Crossbar and isolator valve: do they help?

[helodriver87]

Sure but not enough to be meaningful in this case. While it equalized, no gas was going against the pressure from higher cylinder. None. Any molecular diffusion would have to occur at a scale large enough go thru the manifold, that is not happening fast enough to blend both cylinders. The cylinders are still two distinct vessels with a small connection and without pressure to blend, it is not happening at a rate that will make your doubles safe to dive.

Probably true. I'm curious to try it though. See how long it takes to get a meaningful change.

Regardless, it's really a moot point if you treat a closed isolator in predive checks as an indicator of unsafe doubles until you can validate what you have.

 

[cerich]

Regardless, it's really a moot point if you treat a closed isolator in predive checks as an indicator of unsafe doubles until you can validate what you have.

Aye

 

[rjack321]

Probably true. I'm curious to try it though. See how long it takes to get a meaningful change.

A very long time. This has been "tested" anecdotally over the years. It takes longer than months even with the isolator open and the tanks driving around in the back of a pickup for weeks jostling, heating and cooling. You are more likely to need a hydro before those gases mix to any functional degree.

Unless you know the history of the tanks, the fill and the valve status from dropoff to pickup, E.g. you were watching them fill at EE or cave adventurers etc then analyze both sides.

 

[stuartv]

Probably true. I'm curious to try it though. See how long it takes to get a meaningful change.

Regardless, it's really a moot point if you treat a closed isolator in predive checks as an indicator of unsafe doubles until you can validate what you have.

What's the difference between finding a closed isolator during predive checks and having the blender open the isolator immediately before you see the tanks, when you pick them up from being filled?

As far as I can tell, there is only a difference if you assume that the mixes in the two sides will homogenize during the time between picking them up and when you are doing your pre-dive checks (which has now been strongly asserted that it won't happen).

In other words, it seems to me that you should always treat your tanks the same as if you found a closed isolator during your pre-dive check. Because unless you watched them being filled, you don't actually know any more from finding the isolator open than you would if you found it closed.

 

[helodriver87]

What's the difference between finding a closed isolator during predive checks and having the blender open the isolator immediately before you see the tanks, when you pick them up from being filled?

As far as I can tell, there is only a difference if you assume that the mixes in the two sides will homogenize during the time between picking them up and when you are doing your pre-dive checks (which has now been strongly asserted that it won't happen).

In other words, it seems to me that you should always treat your tanks the same as if you found a closed isolator during your pre-dive check. Because unless you watched them being filled, you don't actually know any more from finding the isolator open than you would if you found it closed.

I'd like to think if a blender did anything other than confirm your isolator position they'd tell you. They have absolutely no reason to turn the thing after filling. Probably optimistic of me to hope for that though. But that gets back to tank history. Like rjack mentioned, analyzing both sides if the tanks left your control is the smart thing.

 

[stuartv]

Probably true. I'm curious to try it though. See how long it takes to get a meaningful change.

Regardless, it's really a moot point if you treat a closed isolator in predive checks as an indicator of unsafe doubles until you can validate what you have.

It is the Brownian motion of the molecules of gas that results in a homogeneous mix in your cylinder. Those molecules are randomly bouncing around and they distribute themselves evenly in relatively little time when you put them into a container that is hugely larger than the size of the molecules.

But, imagine if you took 2 55 gallon drums and you filled one of them halfway with black BBs and the other one halfway with white BBs. And then you connected the 2 drums with a pipe that is 1 inch in diameter. Now, take it up to the Internation Space Station (for zero G) and mount the whole thing on a random orbital vibrator. How long do you think it would take to end up with half of each color BBs in the other drum? I'm thinking it would be a LONG time.

Not a perfect "model", but I think it makes the relevant point. It's not like there is a vacuum of O2 in the other cylinder that is pulling O2 over and pushing N2 back in exchange.

 

[rjack321]

I'd like to think if a blender did anything other than confirm your isolator position they'd tell you. They have absolutely no reason to turn the thing after filling. Probably optimistic of me to hope for that though. But that gets back to tank history. Like rjack mentioned, analyzing both sides if the tanks left your control is the smart thing.

At least around here, tanks in the filling queue are often not out of sight or touch of other customers. I don't trust others idiots or their kids etc in the shop. New or novel things always seem to get messed with.

 

[cerich]

As far as I can tell, there is only a difference if you assume that the mixes in the two sides will homogenize during the time between picking them up and when you are doing your pre-dive checks (which has now been strongly asserted that it won't happen).

that assumption could kill a diver

 

[Joris Vd]

If you are a diver who religiously does his pre-dive checks the manifold is definitely Safer than a manifold without isolator.

But fact is that People make mistakes.
To me unless you're diving overhead i'd say the risk of accidently diving with a closed manifold or getting a half fill is greater than a tank o-ring extruding. There are no Burst discs in Europe, but in that case there's also another added safety with the isolator.

I only got an isolator because it was mandatory for my iantd tek lite class for the valve drills. If I wasn't planning on progressing into overhead environments i'd probably dive without one.

 

[PfcAJ]

If you’re unsure, analyze both sides.