New Bug Reports/Feature Requests

[Rick Walsh]

On 26 February 2016 at 06:59, Linus Torvalds <torvalds at linux-foundation.org>
wrote:

> On Wed, Feb 24, 2016 at 6:25 PM, Linus Torvalds
> <torvalds at linux-foundation.org> wrote:
> >
> > And this time, if you actually put in 15.3 liter, with subsurface you
> > get a nominal size of 127 cuft, and a "actual" size of 119.6. So this
> > time the "120" in the "HP120" is the actual size.
> >
> > But it's almost impossible to tell ahead of time. Is it the nominal or
> > the actual size? Who can tell.
>
> Ok, I went back and tried to look at a number of cylinders. Not all
> that many, because quite frankly, it's painful to try to look things
> up, but I tried to find a pattern.
>
> The most common cylinder size in recreational scuba is AL80, and
> everybody seems to do that by nominal size (so 77.4 actual).
>
> The other sizes are really all across the map. The Luxfer AL72 and
> AL50 is also nominal (real: 69.9 and 48.4).
>
> But then the Luxfer and Catalina AL53 and AL63 look to be by actual size.
>
> And then there's a Luxfer AL19/27 that says that the real size is
> actually 19.9/27.9 cuft. Everybody else rounds to nearest, or rounds
> up.
>
> There's a Luxfer AL92 that claims a 3200 psi working pressure (crazy),
> and has a real size of 90.3. That doesn't make sense in *any* model.
> At 3200 psi, if the real size is 90.3, the nominal size should be
> around 95. In no case does "92" make sense.
>
> Most of the *steel* cylinders seem to be "actual size", although I
> found one LP80 by Faber that seemed to take the Aluminum approach and
> was just 78 (which is odd - since it's an LP cylinder, that's neither
> actual _nor_ nominal, because at 2400+10% the air compressibility
> hasn't become an issue yet.
>
> But for the steel cylinders, there's the issue of some of them using
> the plus-size (pretty much all LP, but also a lot of the HP ones). I
> didn't do the math.
>
> And the X8-119 that we looked at is claimed to be "real" 119, but as
> mentioned earlier, when I take the claimed metric size, I don't
> actually get that. But there might be rounding issues going on, so who
> knows.
>
> And I don't actually know how trustworthy the list I found is. It's
> here, in case somebody cares:
>
>
> http://www.indianvalleyscuba.com/services%20page/Tank%20Inspection/information/CYLINDER%20SPECIFICATIONS.pdf
>
> but on the whole I don't really find anything in there that changes my
> opinion that "Imperial sizes are not reliable". Even when you find
> spec sheets like this, they leave you wondering how accurate they
> really are. Where did the numbers come from? Some manufacturers are
> better than others in actually giving those things, it may be that
> parts of those numbers in that table are just "we don't know, so we'll
> just assume the name is according to real volume".
>
>
Just in case that all sounds too simple, in Australia, at least the cooler
waters of Victoria, we let to have a bet each way and end up with the worst
of both worlds - we use metric sizes, except when we don't.

The most common cylinder here for recreational and OC tech is a steel 12
litre Faber cylinder with 232 bar working pressure.  But unlike European 12
l cylinders, the volume is actually 12.2 l, which is suspiciously close to
being an American HP100 with an Australian Standards stamp (NB working
pressure is 232 vs 237 bar).  The second most common cylinder is a Faber 10
l (actually 10.5 l) steel with 232 bar working pressure.

When it comes to aluminium cylinders, we refer to them according to their
imperial capacity - usually Luxfer or Catalina AL80 or AL40.  Gas calcs are
done in metric units, so anyone doing the calcs would be aware of their
volume in litres but would usually refer to an 80 rather than 11.1 l
cylinder.
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