Closed isolation valve during dive.

[Davey Willo]

I was talking to a guy last night who runs his twins manifolded but with the isolation valve closed at all times, he then alternates tanks/regs throughout the dive.

He feels that this is the safest way to go in the event of a free flow or failure as it will retain air in at least one bottle, his thoughts on an isolation and shutdown routine being that it might not go as smoothly as one hoped and therefore the gas loss at depth would be unacceptable.

This guy's approach is, in the event of an incident, shut off the offending first stage, THEN crack open the isolation manifold and decant from both bottles to ascend, but this would be the ONLY time he would ever open it.

Personally, I'd prefer not to have to keep monitoring 2 seperate bottles and changing regs during a dive, but I found his thoughts on the subject very interesting and it appeared to me to be a slightly safer option for those who are used to running independants and are moving to manifolded, or who don't mind treating a manifolded setup as independants with the ability to decant when necessary.

Thoughts?

[Hobby]

There are pros and cons for most things and that's where the problem arises I suppose.I used my twins last as independants having removed the manifold ie.I breathed one down and switched to the other(which I would'nt have needed to do if Bren and I could have found our way around in perfect vis!)This may be frowned upon and questioned as to the procedure if my 2nd cylinder popped a ring,freeflowed etc.However,in this particular case it was'nt an issue,it was'nt particularly deep or restricted(which does'nt make it right)but I beleive that there was less potential failiure in the rig than with the manifold.Look at the RN rig,they don't even have a contents guage and only one (decent)reg.,if it goes pot they manually turn the cylinder on and off to control the supply(using inverts)and they don't seem to have a safety issue with this even in dire conditions.Thoughts,Hobby.

(Edited by Hobby at 1:28 pm on May 22, 2002)

[Ammers]

Have to agree with Hobby on this one, there are indeed pros and cons. It's really down to whether or not you want to work on the concept of independent bottles or not. I have to comment that in the event of an incident you would be adding an associated task load in terms of decanting gas. Dave, we'll talk about this stuff in depth hopefully at St. Abbs. I'm looking forward to hooking up for a few beers and some fun dives.

[JP]

gonna bring this one back to the front again (sorry Dave, keep doing this with your old posts!) Simply because it raises all kinds of issues.

The guy running iso shut...had he heard of thirds?  if he needed to open the iso after a blow out to have enough gas to get out...surely he wasn't running them as independants as far as thirds goes?  (third from one tank then swap over and so on)  Otherwise he should be OK.  seems like he was just increasing fail points in the top of the rig without the benefits.  As for making the shut down work.  Never done one in anger in two years, but I think the adrenalin will make me more not less flexible.

Time taken to shut down against gas lost in that time is interesting.  Read an article about it in Diver a while ago comparing time needed to make it work depending on size of cylinders carried.  Think it was about 6-8 months ago..will hunt it down.

Anyone got experiance of working like this?

JP

brief recommendations was that below 10 litre sets, run them independant or with ISO shut decanting periodically and reclosing the valve...again what's the point?  may as well run thirds on independants.

[Ammers]

Playing devil's advocate - diving on independents makes sure that you are checking both regulators during a dive. How many people check both regs regularly through the dive on a manifold with the isolator open?

Just throwing in my tuppence worth since I'm bored!

[Dominic]

I do.

[Ammers]

Hi Dom. Been a while since we had a ruck.  Fancy having one? What ya fancy rucking about? I'm a bit bored as you can tell.  My latest Ammers ruck is oxygen sensors. Any takers? >:-)

[Dominic]

You should always dive dehydrated.

That way, when you resurface and rehydrate, all the gas has lots of fluid to be dissolved in, and you therefore decrease your risk of getting Bent.

Any takers? ;)

[Dr Stevil]

Ahem, right then...

I like to encourage nervous trainees to have a wee dram or three to steady their nerves before a dive, especially first time out.

next?

PS ;)
PPS RN method, Yes.. can't be that bad can it, still toying with te idea of the invert config  
PPPS Dave - I think you're losing control of your thread - its a mutiny!

(Edited by Steve W at 12:06 pm on Jan. 16, 2003)


(Edited by Steve W at 12:07 pm on Jan. 16, 2003)

[Ammers]

You should always dive drunk. That way, when you finish the dive, you don't have to go to the pub, you can just stay warm in your car while driving home.  <hehe>