Tank Size Question

Ok, a question on tank size and pressure:

Lets take two aluminum tanks, both 80 CuFt. One is rated 3000 psi
Service Pressure and the other tank rated 3300 psi Service Pressure. What
exactly is the difference here in performance between 3000 psi and 3300 psi?

The amount of air a tank can hold is based on the cubic foot, right? So
if both tanks are 80CuFt, then why would I want one rated for 3300psi?

When your filling tanks, and the psi on the tank says 3000, then that
means when the pressure gauge on the compressor read 3000 then your tank is
filled, right?

What about the 3300 tank? Do you have to fill it to 3300 psi to fill it
up for use? If so, wouldn't that mean you have more air in the tank to
breath? With 3300 psi, aren't you shoving more air into the tank than the
3000 psi tank?

Please explain.

Thanks

In article <3pd_c.2524$N4.1562@newsread3.news.pas.earthlink.n et>, Von
Fourche <monaco8292@hotmail.com> wrote:

€ Please explain.

You got ripped off in you cert class.

Just like everyone else.

--
"We're going to rush the hijackers."
-Jeremy Glick, aboard United Airlines flight 93, September 11, 2001

On Sat, 04 Sep 2004 06:37:51 GMT, "Von Fourche"
<monaco8292@hotmail.com> wrote:

> When your filling tanks, and the psi on the tank says 3000, then that
>means when the pressure gauge on the compressor read 3000 then your tank is
>filled, right?
>
> What about the 3300 tank? Do you have to fill it to 3300 psi to fill it
>up for use? If so, wouldn't that mean you have more air in the tank to
>breath? With 3300 psi, aren't you shoving more air into the tank than the
>3000 psi tank?

The 3300psi tank will have a slightly smaller internal volume. You
have to pump it to a higher pressure, but you still only pump 80cf
into it.

The 3000psi tank will also still contain roughly 13.3cf at 500psi.
The 3300psi tank will contain roughly 12cf at 500psi, which means that
the ONLY positive effect of the higher pressure cylinder is that it
gives you 1cf more air to use before the DM bitches at you.

IOTW, there is no reason to select the 3300 over the 3000.

80cf is 80cf, no matter the starting pressure.



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

"Rich Lockyer" wrote

> The 3000psi tank will also still contain roughly 13.3cf at 500psi.
> The 3300psi tank will contain roughly 12cf at 500psi, which means that
> the ONLY positive effect of the higher pressure cylinder is that it
> gives you 1cf more air to use before the DM bitches at you.

Not true. Depending on the brand, there is a size difference, and it is
signficant to some, and a buoyancy difference, enough to be significant to
everybody.

> IOTW, there is no reason to select the 3300 over the 3000.

That is entirely a matter of opinion. My opinion differs from yours. All
of my 80 cubic foot tanks are Catalina Compact 80s. They're about an inch
shorter than the standard 80, making it possible for me to carry them
without bending my elbows, ie making them easier to carry, and their about 4
lbs less buoyant, allowing me to dive my steel plate and wing, in warm
water, with no lead at all. I'd say those are a couple of pretty good
reasons to select the 3,300 over the 3,000.

Lee

"Von Fourche" <monaco8292@hotmail.com> wrote:

> Ok, a question on tank size and pressure:

> The amount of air a tank can hold is based on the cubic foot, right? So
> if both tanks are 80CuFt, then why would I want one rated for 3300psi?

I'm still trying to figure that one out myself


> When your filling tanks, and the psi on the tank says 3000, then that
> means when the pressure gauge on the compressor read 3000 then your tank is
> filled, right?

Ignoring "hot fills", yes.


> What about the 3300 tank? Do you have to fill it to 3300 psi to fill it
> up for use?

When it is filled to 3300psi, it has 80ft^3.

But what this also means is that at 3000psi, its only 3000/3300 = 90%
full: it will have 3000/3300 of 80ft^2, or roughly only 72ft^3.



> If so, wouldn't that mean you have more air in the tank to breath?

No. Its confusing because in the USA we refer to a tank by its capacity
when it is filled to its operating pressure, instead of by its actual
"dry" volume.


> With 3300 psi, aren't you shoving more air into the tank than the
> 3000 psi tank?

You're not really shoving in "more" air. What happens is because the
higher psi tank is physically smaller, you have to shove harder to get
it in there...

Think of taking the same amount of clothing on a trip, but packing it
all into a smaller suitcase...you don't end up with more clothes.

For two tanks of the same "size" rating, the one with the higher
pressure will be a physically smaller tank internally.

Externally, the tank _should_ also be smaller, but you do need more
"meat" to the tank to withstand the higher operating pressure, plus the
manufacturer may choose to do some other stuff too. For the 10%
difference between an 80ft at 3000psi versus 3300psi, some people won't
be able to eyeball the difference.


For any group of tanks that all each rated at 80ft^3, all you're really
doing is playing around with the formula:

PV = constant

Here, its (3000psi)(691in^3) = (3300psi)(628in^3) = "80ft^3"


Just watch your units.


-hh

"Rich Lockyer" <rlockyer@linkline.DONTSPAMME.com> wrote in message
news:tnrij0dctkig2lg7p5j5gqskh6tjkercvc@4ax.com...
> The 3000psi tank will also still contain roughly 13.3cf at 500psi.
> The 3300psi tank will contain roughly 12cf at 500psi, which means that
> the ONLY positive effect of the higher pressure cylinder is that it
> gives you 1cf more air to use before the DM bitches at you.

Funny way of looking at performance instead of reserve. BTW this is only
true if the shop fill monkey actually fills the tank 3300 tank to 3300. If
he stops at 3000 then there is 6cf LESS usable gas compared to the standard
3000psi AL80. (Based on true size of AL80 and delta pressure of 2500psi with
service pressures of 3300 and 3000 )

Von Fourche wrote:
> Ok, a question on tank size and pressure:
>
> Lets take two aluminum tanks, both 80 CuFt. One is rated 3000 psi
> Service Pressure and the other tank rated 3300 psi Service Pressure. What
> exactly is the difference here in performance between 3000 psi and 3300 psi?
>
> The amount of air a tank can hold is based on the cubic foot, right? So
> if both tanks are 80CuFt, then why would I want one rated for 3300psi?
>
> When your filling tanks, and the psi on the tank says 3000, then that
> means when the pressure gauge on the compressor read 3000 then your tank is
> filled, right?
>
> What about the 3300 tank? Do you have to fill it to 3300 psi to fill it
> up for use? If so, wouldn't that mean you have more air in the tank to
> breath? With 3300 psi, aren't you shoving more air into the tank than the
> 3000 psi tank?
>
> Please explain.
>
> Thanks
>
>


If you take 80 cubic feet of air and put it into a cylinder
the size of a phone booth (remember those?), you would have
about 15 PSI (ambient). Now take that same air and shove it
into a coke can and the pressure would be tremendous!

Your 3300 PSI 80 is just a little smaller than the 3000 PSI
80. I once got to see an experimental Russian titanium 80
that was just a little bigger than a football. Of course,
no regular dive shop could fill it. 6000 PSI is my
recollection of what it took to fill to 80 cubic feet.

Just my $.02
--

Ray Contreras
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Webmonkey for:
http://www.ossystems.com
http://members.aol.com/gaspast
http://www.rayzplace.com


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"Lee Bell" <leebell@ix.remove.netcom.com> wrote in message
news:4th_c.5331$Vl5.4644@newsread2.news.atl.earthl ink.net...
> "Rich Lockyer" wrote
>
> > The 3000psi tank will also still contain roughly 13.3cf at 500psi.
> > The 3300psi tank will contain roughly 12cf at 500psi, which means that
> > the ONLY positive effect of the higher pressure cylinder is that it
> > gives you 1cf more air to use before the DM bitches at you.
>
> Not true. Depending on the brand, there is a size difference, and it is
> signficant to some, and a buoyancy difference, enough to be significant to
> everybody.
>
> > IOTW, there is no reason to select the 3300 over the 3000.
>
> That is entirely a matter of opinion. My opinion differs from yours. All
> of my 80 cubic foot tanks are Catalina Compact 80s. They're about an inch
> shorter than the standard 80, making it possible for me to carry them
> without bending my elbows, ie making them easier to carry, and their about
4
> lbs less buoyant, allowing me to dive my steel plate and wing, in warm
> water, with no lead at all. I'd say those are a couple of pretty good
> reasons to select the 3,300 over the 3,000.



I was told at my dive class the aluminum 80 3000 psi was the most
popular and standard use tank in the U.S. and Caribbean and general dive
industry. Is this true? What about Australia and the Pacific Islands?

I asked my instructor why he uses all aluminum, he said they don't rust
as bad, and cheaper too. But aren't steel tanks supposed to last longer
than aluminum? And if you have to get an internal inspection every year for
rust, what difference does it make anyway? As long as you end all dives
with at least 500psi in your tanks then why worry about water getting in?
And don't steel tanks load to lower psi than aluminum? Isn't this easier on
compressors? Instead of constantly filling tanks up to 3000 they could be
filling tanks up to 2600psi or whatever, and the compressor wouldn't have to
work as hard.

Von Fourche wrote:
<snip>
>
>
> I was told at my dive class the aluminum 80 3000 psi was the most
> popular and standard use tank in the U.S. and Caribbean and general dive
> industry. Is this true? What about Australia and the Pacific Islands?
>
> I asked my instructor why he uses all aluminum, he said they don't rust
> as bad, and cheaper too. But aren't steel tanks supposed to last longer
> than aluminum? And if you have to get an internal inspection every year for
> rust, what difference does it make anyway? As long as you end all dives
> with at least 500psi in your tanks then why worry about water getting in?
> And don't steel tanks load to lower psi than aluminum? Isn't this easier on
> compressors? Instead of constantly filling tanks up to 3000 they could be
> filling tanks up to 2600psi or whatever, and the compressor wouldn't have to
> work as hard.
>

they don't rust at all! but they can corrode the 'paint' will lift off
and be replaced by a white crust - not dangerous however. Al tanks
aren't inspected for rust - they are inspected for cracks. Al tanks,
when they do fail, tend to fail explosively. Al is more prone to stress
fracture than steel. there is also the buoyancy question - a steel tank
will often be more negative than Al ( the other advantage to a 3300psi
Al bottle over a 3000psi Al one ) the "standard" Al 3000psi tank is ~ 4
lbs positive empty - thats 4 lbs of lead you need to wear. A comparable
steel bottle will be ~neutral empty. there is also reg wear to consider
a higher pressure in the tank causes more wear on the HP seat in the reg.

H. Huntzinger wrote:
>
> "Von Fourche" <monaco8292@hotmail.com> wrote:
>

> > With 3300 psi, aren't you shoving more air into the tank than the
> > 3000 psi tank?
>
> You're not really shoving in "more" air. What happens is because the
> higher psi tank is physically smaller, you have to shove harder to get
> it in there...
>
> Think of taking the same amount of clothing on a trip, but packing it
> all into a smaller suitcase...you don't end up with more clothes.
>
> For two tanks of the same "size" rating, the one with the higher
> pressure will be a physically smaller tank internally.

really well put!


>
> -hh