Randy,

While I can relate to the intrinsic desire to
mechanically create things, being of like
inclination, this idea is still very flawed.

Precisely the "Tapered" threads are why most any
knowledgeable and reputable fill station operator
will refuse to service these type cylinders and
recommend their destruction.

The taper acts as a wedge applying "Lateral"
force across the crown opening from the outside
while gas pressure is doing the same thing
internally.  With standard type valves having
straight threads, the lateral force across the
crown is limited to internal and only "Axial"
against the valve itself.  This means the
internal gas pressure is pushing only against the
thread bearing surfaces and the underside of the
crown.  

With 1/2 inch "Tapered" valves such ingenious
inventions as "Teflon Tape" add further to this
lateral force.  Add to this the fact I have never
seen a "Crescent" wrench with Torque increments
to facilitate uniform tightening, and the idea of
technicians with varying strength levels.  Even
then, the amount of torgue would change with each
subsequent installation because of the previous
wedging of the opening.  Thus, the opening is
constantly being opened wider and wider
increasing the future likelihood of a
catastrophic vessel failure.

One is still best advised to make them mail
boxes, bells, wind chimes, etc. as opposed to
using them for diving.  To really appreciate how
dangerous these things are one should see the
result of a cylinder explosion.

Sincerely

William




--- Underwater Applications <randy@mi*.co*>
wrote:
> Glad to see you decided against the idea. The
> old 72s don't have enough
> "meat" to thread to 3/4 NGS. I have rethreaded
> 1/2 British Tapered Pipe to
> 1/2 NPT. This is not much of a change at all
> (slight difference in the taper
> degree and in the thread angle itself, threads
> per inch and nominal OD are
> the same), but I found it to be quite
> difficult. It worked, but did me
> little good, because I can't get the British
> tanks hydroed here in the US
> (no DOT stamp). This is the type of thing you
> do because you enjoy the metal
> working (I'm an amateur machinist -- I'll make
> one or two of anything), not
> to save money.
> 
> Sincerely,
> C. Randy Bohrer
> Underwater Applications Corp
> voicemail/fax: (707) 222-7528
> randy@mi*.co*
> www.mixedgas.com
> 
> 
> 
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