TANK QUESTION

On Sat, 02 Aug 2003 03:44:26 GMT, "Firewalker"
<firewalker2222@hotmail.com> wrote:

>
>"Rich Lockyer" <rlockyer@linkline.DONTSPAMME.com> wrote in message
>news:dkbmivod4cql7dal2n6n0fm3ktsg3kh9c1@4ax.com.. .
>> On 1 Aug 2003 14:56:14 -0700, markrstephen@hotmail.com (Mark Stephen)
>> wrote:
>>
>> >Standard low pressure steel 80 tanks are usually designed to hold
>> >2400psi (or 2640 with a plus rating) and filling them to 3300psi could
>>
>> Actually, my LDS has a series of steel 80s that are 3000psi tanks.
>> I think they're PST, but not positive.
>
>probably a little negative......

(rimshot)


--- Rich
http://richlockyer.tripod.com/

Paul A. Henry wrote

> I currently use an 80 aluminim tank and always run out of air before
> my son. I was looking at buying a 100 Aluminum but the dealer
> suggested I go with a steel 80 that can be used with my existing
> ScubaPro MK@ primary "without" needing a std DIN fitting and I could
> fill it to 3300 PSI to get the same net air as an 80 Aluminum tank. I
> checked with another dealer and they suggested that this was a bad
> idea as the standard yoke (did not look at mine) is not designed to
> handle 3300 PSI and that I needed to change to a higher pressure DIN
> style yoke.

There's all kinds of thing wrong with the words above, making it hard to
sort what you meant from other things, but here's some input. Hope it
helps.

If you run out of gas before your son using a standard 80, why would you
want a steel 80, pumped to hold as much gas as an aluminum 80? Did you
perhaps mean an aluminum 100?

Catalina has long made, and Luxfer recently started making aluminum tanks,
with A clamp valves, designed for 3,300 psi. The Catalinas are called
Compact and the Luxfers are normally referred to as neutral buoyant. I've
been using the Catalina version for years with no problem. The statement
that your A clamp would have to be changed is bogus, at least it is if
you've got a Scuba Pro Mk anything.

As I see it, you have several choices relative to tank size:
1. Buy a bigger tank, one large enough to allow you time comparable to those
you dive with. The choice between a 3,000 aluminum or a 3,300 psi aluminum
is mostly a matter of buoyancy preference. The 3,300 psi tanks are neutral
when empty versus the 3,000 psi tanks that are around 4 lbs buoyant when
empty (i.e. they're about 4 lbs less buoyant regardless of the gas in them.)
2. Buy a high pressure steel tank. To the best of my knowledge, there are
no steel tanks rated for 3,300 psi. in the U.S. They are either 3,000 or
less, which are available with either a yoke or DIN valve, or they are
3,500, available only with a DIN valve. These tanks tend to be noticably
les buoyant than even the higher pressure aluminum tanks I mentioned above.
My PST steel tanks are rated for 3,500 psi and 100 cubic feet. They are
slightly smaller than my 3,300 psi aluminum tanks and slightly less buoyant.
The big advantage of these tanks is size. The cost is that they are a bit
more negative and that steel tanks need a little different and a little more
careful care to protect against internal rust.
3. Buy a low pressure steel tank and fill it to higher than rated pressures.
Personally, I do not favor this option, but there are a lot of people doing
it. The low pressure steel tanks, apparently, are stronger than what DOT
rates them for. According to those who use them, their buoyancy
characteristics are more desirable than other options that provide the same
amount of gas. Personally, I think these tanks have all the disadvantages
of the hp steel tanks without any noticable offsetting benefits. It could
just be my ignorance.

Whatever you chose for a tank, there's going to be a trade off in size,
availability of fills (for high pressure and over rated pressure options)
and, most significantly, buoyancy. Be sure that whatever you chose suits
your needs in all respects. For example, at 5'8", I really can't
comfortably use a tank noticably longer than a standard 80.

Non tank related options include:
1. Your son may need to understand that he is half a buddy team and that
being a buddy sometimes means being inconvenienced.
2. Your son and you may need to decide whether it's OK for him to continue
solo after you've run out of gas. It's not a decision to be taken lightly,
but it is one that many of us here have made.
3. Learn to relax in the water, getting your consumption rate closer to your
son's. The best way to do this is to dive . . . a lot. Relaxation is the
key.

Lee

In article <50eaa9b7.0308011356.7a410d3f@posting.google.com >,
markrstephen@hotmail.com (Mark Stephen) writes:

>Standard low pressure steel 80 tanks are usually designed to hold
>2400psi (or 2640 with a plus rating) and filling them to 3300psi could
>be a very bad idea. ...

Not quite right, Mark. They are actually "designed" to hole a higher
prssure -- often/usually 4000PSI. They are de-rated by DOT to 2400/2640
to provide a large safety factor for tanks that may be miss-used or abused
in commercial service. Although much or the recreational SCUBA industry
chooses conservatively to keep to the DOT standards, well maintained
LP steel tanks can be and routinely are pressurized to 3500-4000 psi.

A well maintained LP steel 72 pressurized to 3300 PSI will deliver
about 90 CuFt, and will be within the design pressure of standard
yoke valves. For many situations you will find it a better combination
of weight and bouyancy, too. The only problem is that many air fill
facilities will not fill it to 3300. {sigh}

N.B.! While I believe that the safety of filling well maintained LP steel
tanks beyond there DOT ratings is will established, I do not beliee that
this is the case for AL tanks. Therefore I do NOT recommend filling
AL tanks beyond their DOT rated pressure maximums.

--
Charlie Hammond -- Hewlett-Packard Company -- Ft Lauderdale FL USA
(hammond@not@peek.ssr.hp.com -- remove "@not" when replying)
All opinions expressed are my own and not necessarily my employer's.

Interesting, I did not know that...

I would still be hesitant to fill a 2400psi lp steel tank to much past
a 20% overfill, unless it is a new or relatively new tank, but that is
just me...

Mark.

hammond@not@peek.ssr.hp.com (Charlie Hammond) wrote in message news:<x%tXa.1351$Bp1.1314@news.cpqcorp.net>...
> In article <50eaa9b7.0308011356.7a410d3f@posting.google.com >,
> markrstephen@hotmail.com (Mark Stephen) writes:
>
> >Standard low pressure steel 80 tanks are usually designed to hold
> >2400psi (or 2640 with a plus rating) and filling them to 3300psi could
> >be a very bad idea. ...
>
> Not quite right, Mark. They are actually "designed" to hole a higher
> prssure -- often/usually 4000PSI. They are de-rated by DOT to 2400/2640
> to provide a large safety factor for tanks that may be miss-used or abused
> in commercial service. Although much or the recreational SCUBA industry
> chooses conservatively to keep to the DOT standards, well maintained
> LP steel tanks can be and routinely are pressurized to 3500-4000 psi.
>
> A well maintained LP steel 72 pressurized to 3300 PSI will deliver
> about 90 CuFt, and will be within the design pressure of standard
> yoke valves. For many situations you will find it a better combination
> of weight and bouyancy, too. The only problem is that many air fill
> facilities will not fill it to 3300. {sigh}
>
> N.B.! While I believe that the safety of filling well maintained LP steel
> tanks beyond there DOT ratings is will established, I do not beliee that
> this is the case for AL tanks. Therefore I do NOT recommend filling
> AL tanks beyond their DOT rated pressure maximums.

In article <50eaa9b7.0308051015.3fd191fd@posting.google.com >, markrstephen@hotmail.com (Mark Stephen) writes:
>Interesting, I did not know that...
>
>I would still be hesitant to fill a 2400psi lp steel tank to much past
>a 20% overfill, unless it is a new or relatively new tank, but that is
>just me...

Your choice, Mark.
Much of the recreational dive industry agrees with you.

RE: "relatively new" -- One could argue that if a tank has passed
a DOT hyrdo test within the past five years -- which is standard
pratice -- then it can be considered to be "relatively new".
Baring obvious damage, heavy rusting, etc.

--
Charlie Hammond -- Hewlett-Packard Company -- Ft Lauderdale FL USA
(hammond@not@peek.ssr.hp.com -- remove "@not" when replying)
All opinions expressed are my own and not necessarily my employer's.