Twinset Configurations - A novices guide

[Ant P]

Originally Posted by Gareth J

Ant

The problem with fitting a non-isolated manifold is that manifolds interface below the cylinder valve - so if you close the cylinder valve the manifold is still accessing gas from that cylinder, even though the cylinder valve is closed.
If the manifold fails, you dump all the gas from both cylinders.
With an isolator you can shut off the damaged manifold from at least one of the cylinders, thus preserving the gas in the other cylinder.

Adding the isolator adds a new failure point on the high pressure side, fitting the manifold reduces the impact of this potential failure.

Isolated manifolds ensure that you can isolate each half of the configuration, worst gas a manifold failure will only dump gas from one of the cylinders not both if a isolator is fitted. In the event of a first stage failure the manifold allows you to access gas from the effected cylinder via the isolator.


Gareth

Sure I agree with all this - which is why I said that if it is a problem with the manifold then it is a different kettle of fish. However if there is a problem with the reg such as a freeflow then you can just shut the post down and bob's yer uncle - and a reg problem is surely more common that a manifold one.

plus if you have a damged manifold - such as by whacking it against something chances are you damage both side of the manifold and yer isolotor won't help you then.


Cheers, a

[Bardo]

Originally Posted by Ant P

plus if you have a damged manifold - such as by whacking it against something chances are you damage both side of the manifold and yer isolotor won't help you then.

Which is why a barrel-style manifold (ie. AGIR, Halcyon, Scubatec etc) is preferable to a facing o-ring style (ie. MDE) as the manifold can take a 'whack' without affecting the integrity of the manifold as it'll simply turn as it obsorbs the energy from the impact. That said, you'd have to whack it pretty damned hard which isn't unheard of if you're scootering...

[Gareth J]

Ant

I agree that more often it's a regulator problem causing a shutdown. With an isolator it is normally open 1/4 of a turn. To shut down takes a fraction of time. With a cylinder valve it is normally fullyopen, this takes a reasonable time to shutdown.

If you have a catastrophic first stage failure, you can empty a 12l cylinder through a firststage in a remarkably short time.

The usual procedure is to shut the isolator prior to shutting off the cylinder, This way you shut off the escaping gas much faster than by just shutting off the cylinder. If the isolator is not fitted to the manifold there is a very high risk that you will have run out of gas totally by the time that the cylinder is shut down.

This is why, generally speaking, thos doing deep dives either dive independents or with isolated manifolds.

Gareth

[Ant P]

Originally Posted by Gareth J

Ant

I agree that more often it's a regulator problem causing a shutdown. With an isolator it is normally open 1/4 of a turn. To shut down takes a fraction of time. With a cylinder valve it is normally fullyopen, this takes a reasonable time to shutdown.

If you have a catastrophic first stage failure, you can empty a 12l cylinder through a firststage in a remarkably short time.

The usual procedure is to shut the isolator prior to shutting off the cylinder, This way you shut off the escaping gas much faster than by just shutting off the cylinder. If the isolator is not fitted to the manifold there is a very high risk that you will have run out of gas totally by the time that the cylinder is shut down.

This is why, generally speaking, thos doing deep dives either dive independents or with isolated manifolds.

Gareth

Not everybody dives with the isolator only open a 1/4 of a turn or even shuts the isolator first even if they have one Anyway, don't get me wrong - I am not advocating not diving with an isolator, just that your reasoning is not entirely correct You could even argue that having the isolator adds another failure point

Cheers, ant

[stevechesh]

Originally Posted by Bardo

Which is why a barrel-style manifold (ie. AGIR, Halcyon, Scubatec etc) is preferable to a facing o-ring style (ie. MDE) as the manifold can take a 'whack' without affecting the integrity of the manifold as it'll simply turn as it obsorbs the energy from the impact. That said, you'd have to whack it pretty damned hard which isn't unheard of if you're scootering...

If whacking a manifold is a problem with scootering, then there are 2 options.
1. Be more careful
or
2. Use a guard. . . .

[milldog]

Originally Posted by Bardo

Which is why a barrel-style manifold (ie. AGIR, Halcyon, Scubatec etc) is preferable to a facing o-ring style (ie. MDE) as the manifold can take a 'whack' without affecting the integrity of the manifold as it'll simply turn as it obsorbs the energy from the impact. That said, you'd have to whack it pretty damned hard which isn't unheard of if you're scootering...

I think that if you were to hit something then the protruding knob would hit first and roll back as mentioned but on an un-isolated manifold there is no knob to catch and therefore wouldn't get as damaged i have seen a barrel O ring set up fail when caught up in a net where the barrel turns forcing the seals break

Graham

[Steve S]

Originally Posted by stevechesh

If whacking a manifold is a problem with scootering, then there are 2 options.
1. Be more careful
or
2. Use a guard. . . .

Actually 3 mate....inverted twins, and if you leave the cylinder boots on it will stop the bottoms from getting scratched

Safe diving,
Steve

[stevechesh]

Originally Posted by Steve S

Actually 3 mate....inverted twins, and if you leave the cylinder boots on it will stop the bottoms from getting scratched

Safe diving,
Steve

yeah yeah, smarty pants

[Sipadan]

Originally Posted by Woz

I tend to not be quite as anal in worrying about shutdowns- just dive with the isolator closed and swap regs. If you need to scavenge the gas then open the isolator at your leisure rather than having to keep practising all the bloody time at being slick when you really don't have to.

i'm much happier doing this too, especially with twin 7s. can't see any disadvantages apart from the extra spg. wonder why this method isn't more popular?

[Sparky750]

Originally Posted by Woz

When diving indies or twins my configuration is identical:

Right post:
FSR 1st stage with-
Main TX40 reg (yellow cover) on 2m hose. Hose down wing loops.
SPG
Wing inflator

Left post:
FSR 1st stage with-
Necklaced ATX100 (black)
SPG
Drysuit inflator

I tend to not be quite as anal in worrying about shutdowns- just dive with the isolator closed and swap regs. If you need to scavenge the gas then open the isolator at your leisure rather than having to keep practising all the bloody time at being slick when you really don't have to.

I think this is the way i'm going to start off at first seems to make more sense to me in my novice opinion