Manifolds on Twins: It's an open and shut case

[Dominic]

operating the isolator valve does not stress the manifold

The manifold itself, no - but the isolator valve itself..? It's got a pressure imablance acting on it throughout most of the dive, and then you're turning it continually through the dive so the O-rings are getting worn...

Plus we've all, I'm sure, seen an a-clamp O-ring blow when the cylinder was pressurised, but have you ever seen one go bang during a dive? It's the sudden pressurisation that makes it go pop. Apply that to an isolator, and the parallel is that an open isolator is very unlikely to blow a seal, but one that's reguarly closed and opened is much more likely to go pop.

...

The only way I could keep less air in the suit is by not putting any IN on descent - I leave the dump wide open throughout the dive...

Wasn't a problem with my crappy old Apeks dump, but the SiTech one dumps at the drop of a hat..

[Padowan]

Originally Posted by Dominic

Wasn't a problem with my crappy old Apeks dump, but the SiTech one dumps at the drop of a hat..

I also find that the old, hi-profile Apeks auto dump is far superior to the low profile one, or the SI-Tech I had on my old suit...

[wreckweasel]

Originally Posted by Dominic

Apply that to an isolator, and the parallel is that an open isolator is very unlikely to blow a seal, but one that's reguarly closed and opened is much more likely to go pop.

Heres one you'll all like that I SAW first hand (ie not a rumour, or something I heard from a mate).

A twinset at a well known inland site was RAPIDLY filled. The rapid filling dislodged the valve seat from the isolation slug. This resulted in the diver being unable to achieve an open manifold (the twirly bit twirled, but the slug was still holding the manifold shut). We turned the dive early and stripped the lot down, only to discover the problem. All I can think is that the venturi effect caused by the speed of gas flow created reduced pressure which effectively 'sucked' the seat out of the slug.

So, personally, if I equalise tanks now, I do it sloooooowly.

My reply was the "1 turn open", because of this, speed of shutdown and the fact that I like the way my tanks are still immaculate inside.

I dont do the fully open lark, simply because I know *exactly* which way to turn that valve.

As for inverts, Im not even going there


/Z

[DALESDIVER]

Fully open is the safest way to dive the set.

You should know which way to turn it but, as an instructor, I regularly see people who don't know which way to turn off a tap; they claim to know and then open them fully when told it's gone wrong....

So go for the safe way: it's far better than being a donor to fill a black bag.....

[Bob Cooper]

Keeping an isolator fully open has nothing to do with helping to "remember" which way is open and which way is shut. It is done that way to mitigate the risks of having a high O2 content in one cylinder during a pp fill. The isolator should be fully open at all times (in fact, like with all valves, it should be fully open and backed off a fraction).

You shouldn't touch valves during a dive. If you want to practice shutdowns, do it in 3m of water after the dive has finished.

There seems to be a great deal of paranoia about shutdowns and how quickly people can reach and close their isolator. Why?

You are far more likely to want to close your right post in a hurry, so why all the fuss about having an isolator that you can close in a tenth of a second?

[divegyrl]

Originally Posted by Padowan

I also find that the old, hi-profile Apeks auto dump is far superior to the low profile one, or the SI-Tech I had on my old suit...

I hate the new hi profile Apeks dump that they put in my suit at the last service!

Blanaid

[turbanator]

All the way open.

I 'know' which way is off at any angle, but just in case, there is ony one way to go like this.

It does not take long to shut down the isolator, granted it will be a bit longer if the valve is open AND you turn the correct way to start, but this have not been an issue since the dive is only going one way at this point.

I've seen a couple of instances where people have only had 1/2 a twinset filled because the isolator was off, but I don't really think that is a problem during the dive as it should alway be checked before entering the water, esecially as one of those instances was where the set was handed in with the isolator open and it was closed at the filling station.

Perhaps there is an argument here for a balanced 1/4 turn valve??

r
Paul

[Digger]

Bob, I've wondered this for a while. A lot of people have told me to do this throughout my training "all the way open and back half a turn" but recently I heard from a mate who I usually turn to for reasonably good advice that it wasn't necessary with balanced valves, and it's just a legacy from the old vertical pillar valves which could stick open if left all the way open.

I can see that you don't want to jam the thing open when you do it, but up to the stop should be ok shouldn't it?

Just wanted to get it straight, thanks in advance.

Digs.

[Tim Ingmire]

I'm with Bob and both Andy's on this. Worryingly, I also hogloop, wear my torch canister on my waist strap, have my stage on the left and have just bought 2 GUE books.

Is this a worrying trend? Ah, but I still have bungeed wings so all is not lost

[daz]

Originally Posted by Dominic

The only way I could keep less air in the suit is by not putting any IN on descent - I leave the dump wide open throughout the dive...

Wasn't a problem with my crappy old Apeks dump, but the SiTech one dumps at the drop of a hat..

Yeah they are bastards for that

There is no pleasing some people! I actually close mine a few clicks and it is better but I know what you mean. You gotta love em though.

Daz