From: "Jon Wallace" <jon@psubs.org>
Reply-To: personal_submersibles@psubs.org
To: <personal_submersibles@psubs.org>
Subject: RE: [PSUBS-MAILIST] psub convention in Raystown
Date: Tue, 4 Jul 2006 06:53:46 -0400
Notwithstanding the technical benefits of using scuba air, using scuba
services can be a hinderance to someone that does not have a diving
license.
At least around my area you can't get tanks filled without showing your
dive
card. Even though we usually highly recommend that psubbers get their
diving license first, what is a non-diver to do? Assuming a non-diver can
order a tank via mail-order, you might consider checking with your local
fire department. I always assumed our FD sent their air tanks out for
filling and was surprised to see an air filling unit at the station one
day.
Seems they go through enough air just with training that it was worthwhile
investing in their own filling station. They told me that they fill tanks
for local divers upon request.
Jon
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]On Behalf Of Jay K. Jeffries
Sent: Monday, July 03, 2006 11:09 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] psub convention in Raystown
Let me clarify several of the points that Alec was making:
1. While the standards for scuba air require almost no oil, a very
minimal is allowed. Only Class "E" air used in the mixing of NITROX is no
oil allowed. Small amounts of oil will accelerate the deterioration of the
LP and HP flexible hoses associated with a SCUBA regulator.
2. There are two primary reasons for NO moisture in the air finally
compressed into the SCUBA cylinders:
a. On swift release of air from a SCUBA tank as in blowing ballast at
depth in an emergency instead of motoring to near the surface, the
adiabatic
cooling will occur within the tank resulting in condensation. This
moisture
does not subsequently become revaporized when the tank is later refilled.
The accumulated moisture will cause a hastened corrosion of the tank
interior resulting in a failed hydro or tank failure.
b. If the gas expansion occurs under low temperature ambient
conditions, the moisture can freeze in the 1st or 2nd stages of the
regulator that is surrounded by air resulting in an uncontrollable free
flow
condition which can result in rapid loss of tank pressure.
3. SCUBA tanks available from AGA are rated to 4,400 psi.
4. Studies conducted in the 70s at the University of Rhode Island
from
that 99.9% of SCUBA tank failures due to corrosion were "soft" and not
explosive (i.e., the air slow leaked out of a pin hole). A catastrophic
failure of a SCUBA tank releases the energy equivalent to 10 pounds of
dynamite. Aluminum tanks have a variety of other reasons for catastrophic
failure such as overheating and brittle fractures forming in the neck due
to
poor forming methods to name a few.
Respectfully,
Jay K. Jeffries
Ocean Engineer
Andros Is., Bahamas