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Jim,

I confess I know little about the engineering issues on much of the
equipment I dive compared to many on these lists.  I suspect, however, that
ball joints are not used in isolators for the same reason they are not used
in tank valves.  Why I do not know.  Ball joints sound like a good idea, but
I know they are not recommended for use in O2 blending systems, probably due
to the very rapid acceleration of gas they could cause.

I have not heard of a diver citing confusion as a problem on which way to
turn the isolator when a shutdown was necessary.  I have heard from one
diver cite two occassions when *he* believed that the 1/2-2 turn approach
saved his life.  Can we take this to the bank, probably not.  But since the
number of incidences concerning the alternative number zero from everything
that I have read,  I would prefer to dive the same config as other teammates
for the sake of uniformity.

The issue of 1/2-2 turns or full open in my opinion is not an issue to
invoke rule #1.  Diving with someone keeping it closed would be on the other
hand.

We do get poor vis on occassion down here, but usually on the shallower
wrecks and reefs in which case I'm usually in a single 80.  We had less than
10' in Puss Lagoon last week in the Keys.  On the other hand many of our
wrecks do not share the same historical significance as those up in your
neck of the woods.  I will be working out of Cape Hatteras this summer for 6
weeks and hope to enjoy some of those good sites, some of which I hear have
less than great vis.

Do you do any diving with Mike Hillier and the Miss Lindsey?

Regards, John



-----Original Message-----
From: Jim Cobb 
To: John Chluski 
Cc: Techdiver List 
Date: Saturday, March 28, 1998 1:09 PM
Subject: Re: seeking opinions on isolator valves


>John-
>
>If I look at this in a "likelyhood of failure" point of view, I see the
>isolator as an item which is very rarely used, but when you need it, it
>has to be there. If speed of shutdown was such a big issue then why isn't
>the isolator a ball valve?
>
>IMHO, I think that it is best to leave it fully open to avoid it's
>turning into a potential liability.
>
>BTW, you are having one hell of a Virginia Beach, Va. dive if you have
>30' of vis!
>
> Jim
>

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