Units of Measure in Diving?

[peterbj7]

This is a unique take on American standards. Not true.

An AL80 pumped to 3000 psi will have 77 cu ft of air.
AL tanks do not use the "+" marks, nor do most of the newer steel tanks.

I'm interested to know what's not true, in any part of what I said but especially in the substantive part.

I have owned over 500 "standard" aluminum scuba tanks of three different makes, together with other sizes in aluminum and some 100 steel tanks of various sizes. The rated pressure for the aluminum tanks varies with manufacturer, so they cannot contain the same amount of air when pumped to the same pressure. And the "+" sign appears on many of these tanks, both aluminum and steel. Now, I haven't bought any tanks in the past six years, so if things have changed since then I may not be aware of it. But most tanks in service are at least that old.

Do note that my example of 3300 was just to illustrate the logic - I didn't say that that number appears on any of my tanks.

 

[Herk_Man]

LOL! Yes, but even in binary, you still must assign units of measurement. However, I do have a t-shirt that says:

There are 10 kinds of people: Those who understand binary and those who don't.

My wife bought me that shirt!

 

[GrumpyOldGuy]

I'm interested to know what's not true, in any part of what I said but especially in the substantive part.

I have owned over 500 "standard" aluminum scuba tanks of three different makes, together with other sizes in aluminum and some 100 steel tanks of various sizes. The rated pressure for the aluminum tanks varies with manufacturer, so they cannot contain the same amount of air when pumped to the same pressure. And the "+" sign appears on many of these tanks, both aluminum and steel. Now, I haven't bought any tanks in the past six years, so if things have changed since then I may not be aware of it. But most tanks in service are at least that old.

Do note that my example of 3300 was just to illustrate the logic - I didn't say that that number appears on any of my tanks.

I think you tried to over simplify the US system and choose poor illustrations.

Here is my list per your request:

1) The "+" is not used on AL tanks in the US.

2) The 3300 rated pressure you mentioned is for a 100cu ft AL tank (not 80 cu ft).

3) The same tank achieves is capacity at 3300PSI, not 3630PSI.

4) Only some steel tanks are allowed a + rating
- Those that do are as you stated (capacity is at 110%)
- Those the do not achieve their capacity at 100% pressure rating

5) The variations in rated pressure for AL tanks are much less than steel. Most are 3000 with a couple of 3200/3300 rating for some oddball sizes. Steel tank pressures vary tremendously from 1800 to 3500PSI.

 

[goonsquad]

I only use American units for the same reason the French only speak French, I'm too lazy to care to learn anything else.

 

[SailNaked]

OK
I have a 15L filled at 230 bar and I breathe at 15L/min in surface.
So i can breathe 15*230/15 equals 230 min

give me the same calculation in imperials to demonstrate me the facility.
with a S100 at 3000psi

My Sac is .5F3/m so at 33F with an AL 80 I should have 2*.5=1 80/1=80 min.

or more likely at 99ft .5*4=2 with AL80 = 40 min.


Il serait si facile de le faire dans n'importe quelle langue dont le français.

 

[DuboisP]

My Sac is .5F3/m so at 33F with an AL 80 I should have 2*.5=1 80/1=80 min.

or more likely at 99ft .5*4=2 with AL80 = 40 min.

Il serait si facile de le faire dans n'importe quelle langue dont le français.

i would prefer the reverse calculation
calculate the time knowing the tank, the depth and the SAC

Félicitations pour cette phrase en français.

 

[DuboisP]

I only use American units for the same reason the French only speak French, I'm too lazy to care to learn anything else.

false
a lot of french people speak english, correspondingly more than US people speaking french or anything else.

 

[Blackwood]

A far more useful system would have been a base of 12, but that didn't come about because we only have 10 fingers (the binary system used by computers is of even less value to us in our everyday lives).

Hey, you've got two arms, don't you? You can count to 3!

in metrics, it's easier
by saying 11.1L beginning at 160 bar, it doesnt' matter if it is a low pressure (200-230 bar or a high pressure (300 bar)

That has nothing to with the metric system. It's simply a way of characterizing cylinders (in their 1ATM condition rather than their pressurized condition).

but it just seems to make more sense to talk about a tank in terms of its capacity at rated pressure - because that's what we're using it for

Not really. Technically, the rated volume is how much volume would come out (less 1ATM worth) if emptied at the surface. We typically breathe them under pressure.

 

[Blackwood]

i would prefer the reverse calculation
calculate the time knowing the tank, the depth and the SAC

The math is the same in metric units as it is in english units.


(Pressure Used)/time * (Volume/Pressure) = Volume/time.

Total Volume/(Volume/time)/Ambient Pressure = how long it lasts.


For "imperial" cylinders, that Volume/Pressure = Rated Volume/Rated Pressure (e.g. 100CF/3442PSI).
For "metric" cylinders, that Volume/Pressure = Volume/Liter (e.g. 11L/BAR).
Ambient Pressure is absolute (e.g. BAR or ATM).

 

[DuboisP]

Ambient Pressure is absolute (e.g. BAR or ATM).

may be i'm wrong, sorry...

so you also use bar or atm to characterize the pressure ?

I didn't remark this unit when I'was looking the weather reports on TV.