how much air do you use?

[FreeFloat]

Boogie711 once bubbled...
I don't think PSI per minute is a useful statistic at all. Even if it were adjusted to account for surface atmospheric pressure, it still gives you no idea what your breathing rate is.

When you say "So how many cu.ft are in a steel tank (on average)?" that's the equivalent of saying "How many feet are in a ball of string?"

For example - there are two steel tanks in my office right now. One gives me 100 cf at 3442 psi. One gives me 95 cf at 2640 psi. For mathematics sake, lets say I use one cubic foot of air per minute at the surface - using your math, Im using either 34.42 psi/min OR 27.78.

If you use the example of an E8-149 and a HP80, the number swings from 23.1 psi/min to 43.75 psi/min -- all for the same breathing rate.

Sorry Boogie711, I should have been more specific. I dive steel "72s" filled to around 2400 psi at room temp (so that they end up closer to 2250 by the time they get on-site this time of year)

So a steel 72 holds roughly how many cu.ft....?

 

[Warren_L]

That would be 72 cu ft at it's service pressure.

Boogie's point is that the psi/min measure is only useful as a comparison if you use the same type of tank all the time, which I believe you are. So if it works for you.... no problems.

 

[FreeFloat]

My log book has a spot for recording what size and type of tank I was using as well as start and end pressures (obviously).

I prefer the steel 72s mainly for the size - they're not too tall for me. And now I have the weighting nailed. And with my gas consumption I simply can use a smaller tank, so why not? Where I get my tanks from has limited selection - just steel 72s and AL80s. Actually yesterday the second tank I brought had a J valve.....

 

[FreeFloat]

Just uploaded a new profile pic - see for yourself how big a steel 72 looks on me!

 

[V_D]

FreeFloat once bubbled...
So how many cu.ft are in a steel tank (on average)?

What kind of a question is this?

There is no average cu.ft in steel tanks.

Please don't waste opur time with questions like this.

 

[FreeFloat]

That wasn't very nice, V_D.

Welcome to the board, by the way.

I know I wasn't very specific but my question, if you read my other posts in this thread, arose because someone commented about AL80s holding slightly less than exactly 80 cu.ft.

I'm a recent cert and an still learning things about equipment. For example, only yesterday did I actually get to see & touch a pressed-steel 100 tank. Before that, I thought there were only steel 72s and various sizes of aluminum tanks. So when I referred to steel, I forgot to specify "steel 72". Oops. My bad. So crucify me.

Never intended as a waste of time.

:upset:

 

[Warren_L]

Don't worry about it Freefloat ... this is the New2Scuba area so nothing wrong with asking any questions. It's just some people are not very nice to begin with. Asking questions about something you don't know is never a waste of time.

 

[AquaBob]

V_D once bubbled...


What kind of a question is this?

There is no average cu.ft in steel tanks.

Please don't waste opur time with questions like this.

__________________
It is better to remain silent and look stupid than opening your mouth and removing all doubt

Welcome V_D.

Man, I never thought I would ever say that!

Yopu couldn't have chosen a more appropriate tag line.

---------------

Free float --
So you're here for Crucifiction.... Good... Line on the Left ... One Cross each..... Next....

Sorry... back to the topic...

Even though the 72s and 80s are only ballpark numbers... they are close enough for these kind of speculative calculations. They certainly won't be out by more than a few percent... generally better than our SAC predictions.

 

[FreeFloat]

My SAC - however you calculate it - has risen a bit of late. I attribute it to the water temps. It's up to 29 psi/min or thereabouts.

Any kind of a performance benchmark - whether it's how good your vehicle is on gas, or you are on air consumption - is only useful if the same calculation is performed over and over throughout a range of time. Then, although the numbers you get, in and of themselves, are relatively meaningless (especially to other people) it's the trend that becomes useful.

 

[Charlie99]

FreeFloat once bubbled...
My SAC - however you calculate it - has risen a bit of late. I attribute it to the water temps. It's up to 29 psi/min or thereabouts.

Any kind of a performance benchmark - whether it's how good your vehicle is on gas, or you are on air consumption - is only useful if the same calculation is performed over and over throughout a range of time. Then, although the numbers you get, in and of themselves, are relatively meaningless (especially to other people) it's the trend that becomes useful.

Most people talk about vehicle gas consumption in repeatable, transferable numbers such as mpg or liters/100km.

Talking about scuba air consumption in psi/min is like talking how many mile per tank of gas. On more simple conversion turns the numbers into something that is useful with different size gas (scuba or car) tanks.

This "magic" conversion factor for an AL80 is simply 3000psi/77.4cu ft = 39psi/cu ft. So 29psi/min is 0.75cfm if you are using an AL80 ---- a nice universal number that isn't dependent upon tank type.

Charlie