Air and Time Calculation

[Guillotine]

Let say that we have an example here:

I have a 12l cylinder with 3000psi and as I know so far that the average person consumes 20l per minute. So, if I want to calculate how much I can stay with that cylinder under the depth of 10miters. Would it be?

3000psi / 14.7 = 200Bars
200Bars * 12l = 2400 <-- Air?
2400??? / 20l = 120 <-- Minutes?

Does that mean I can stay for nearly 2 hours on that depth? I’m not sure, appreciate your help.

 

[Quarrior]

http://home.flash.net/~table/gasses/sac.htm
http://home.austin.rr.com/thefirewolf/SAC Rates2.xls

 

[DareDevil]

Let say that we have an example here:

I have a 12l cylinder with 3000psi and as I know so far that the average person consumes 20l per minute. So, if I want to calculate how much I can stay with that cylinder under the depth of 10miters. Would it be?

3000psi / 14.7 = 200Bars
200Bars * 12l = 2400 <-- Air?
2400??? / 20l = 120 <-- Minutes?

Does that mean I can stay for nearly 2 hours on that depth? I’m not sure, appreciate your help.

No, it is slightly different. The 20 l/min should be read as 20 l/(min * atm), meaning that the amount of air you need will increase as you go deeper.

Look:

1) A 12l cylinder filled at 200 atm provides 2.400 l*atm. This is your air amount
2) At 10 meters the pressure is equal to (1 + 10/10) atm = 2 atm
3) Air consumed according to pressure: 2 atm * 20 l / (min*atm) = 40 l / min
4) Divide the air amount by the air consumed: 2.400 l*atm / 40 l/min = 60 min

The formula:

time = 10 * (tank pressure) * (tank size) / (air used) * (10 + depth)

where:
time is expressed in minutes
tank pressure is expressed in atmospheres
tank size is expressed in liters
air used is expressed in liters (usually 20 liters)

But I would not use 20 liters, it may be too optimistic: 25-30 liters may be a better value according to many factors: your shape, currents, etc...

Paolo

 

[Guillotine]

So my calculation is fit but on the surface? Which means on surface the tank will give me 2 hours of air on that rate of 20l/minute. At the depth of 10m the tank should give me around the half, which equals 1 hour on that depth. Correct?

Based on the formula:
Time= 10 * (200) * (12) / (20) * (20) = 24000 <----what does this indicates?

Appreciate you help.

 

[DareDevil]

So my calculation is fit but on the surface? Which means on surface the tank will give me 2 hours of air on that rate of 20l/minute. At the depth of 10m the tank should give me around the half, which equals 1 hour on that depth. Correct?

Based on the formula:
Time= 10 * (200) * (12) / (20) * (20) = 24000 <----what does this indicates?

Appreciate you help.

Yes, your computation is correct only at surface level. At any different depth, you have to adjust the 20 liters value according to the pressure because you will breath denser air: you will need 20 liters a 0 meters, 40 liters at 10 meters, 60 liters at 20 meters and so on...

The number 24000 does not indicate anything because it is wrong . I forgot to tell you have to compute the product of all the factors before the division ("/") sign and then divide by the product of all the factors after the division ("/") sign.

The formula is:

Time = 10 * (200) * (12) / (20) * (20)
Time = 24000 / 400
Time = 60

60 is the number of minutes you may stay at the depth of 10 meters, with a 12 liters tank filled at 200 atm assuming a 20 liters/minutes air rate.

You may want to use Excel to build a table according to your tank size that can be used to quickly check how much time you have, then print it out and make it waterproof: it will help to check quickly how much time you have.

Of course this is not needed if you have a computer with an air probe, but computers may break so it is something handy, just like diving tables.

Paolo

 

[Guillotine]

Thank you so much Paolo, You made it clear

I have 1 more question please, is it the same if you express 200 atm as 200 Bars?

Thanks again, really appreciate you help.

/salute

 

[DareDevil]

Thank you so much Paolo, You made it clear

I have 1 more question please, is it the same if you express 200 atm as 200 Bars?

Thanks again, really appreciate you help.

/salute

Not exactly, but almost. 1 bar = 0.99 atm, therefore 200 bars = 197.39 atm.

Paolo

 

[Guillotine]

Got it, thanks