Blending and decanting

[adamr]

Ok so I should know how to do this.... but I dont

Can anyone tell me the formula to calculate the mix I will get if I decant air into my twinset?

An example :- I will have a 32% mix for saturdays dive and will take a 15l filled with 200bar air. How do I calculate the new twinset pressure and also the new diluted mix?? I know I will have to do this calc at the end of the first dive when I know my twinset end pressure.

Cheers

Adam

[Simon TW]

don't bother, just decant and then analyse the gas, the mix and the pressure will both depend on what your starting pressure is.

[Scuby]

Have a search for Nigel H on here, and his Blender application. Very easy to use.

Alternatively, if you have Excel (or a pen and a bit of paper) then you can work it out from basic principles - just break down the gas into the separate O2 and N2 components and go from there.

Alternatively, if you're just topping up a mix, you could always go with the approach of just seing what you come out with, as you'll presumably always want to get the strongest mix possible anyway - just top it up and see what comes out.

As a slight side question, is this twin 12's or something smaller? Can't think of many dives you'd do using 32% (so necessarily not that deep) where you'd need a top-up for the second dive - should easily get two hour long dives out of twin 12's, and then you're keeping the best mix for the 2nd dive too.

David

[stevechesh]

Originally Posted by adamr

Ok so I should know how to do this.... but I dont

Can anyone tell me the formula to calculate the mix I will get if I decant air into my twinset?

An example :- I will have a 32% mix for saturdays dive and will take a 15l filled with 200bar air. How do I calculate the new twinset pressure and also the new diluted mix?? I know I will have to do this calc at the end of the first dive when I know my twinset end pressure.

Cheers

Adam

Adam,

As Simon said, there isn't enough info to calculate, however, have a look here: nitrox filling tables

and download the file that Gobfish posted. There is some useful info on there

[Colin Marriott]

Originally Posted by adamr

Ok so I should know how to do this.... but I dont

Can anyone tell me the formula to calculate the mix I will get if I decant air into my twinset?

An example :- I will have a 32% mix for saturdays dive and will take a 15l filled with 200bar air. How do I calculate the new twinset pressure and also the new diluted mix?? I know I will have to do this calc at the end of the first dive when I know my twinset end pressure.

Cheers

Adam

You'll add together all the litres of gas you've got, and divide by the summed cylinder volumes.

e.g.
Lets say the twinset is 12ltrs, and has 100bar in it. Thats 1200ltrs of gas.
There's 3000ltrs of gas in you're 15l.
These will be added together when you decant to give a total of 4200ltrs, but this is distributed across 27ltrs of cylinders giving a pressure of 4200/27 = 155.5bar

You can do the same with the oxygen
Twinset will have 384ltrs of O2, 15l will have 630ltrs
giving a total of 1014ltrs O2
therefore the O2 % will be 1014/ 4200 * 100 = 24%

ColinM

[Simon TW]

Bollocks, I just spent ages typing a PM with it all on.

[Simon TW]

Originally Posted by Colin Marriott

Lets say the twinset is 12ltrs, and has 100bar in it. Thats 1200ltrs of gas.

Is it twin 6s

[colinicky]

Originally Posted by Simon TW

Is it twin 6s

ROFLMAO

[Colin Marriott]

Originally Posted by Simon TW

Is it twin 6s

In my example . . . yes!

He might dive twinned 6ltrs . . . we don't know . . . . do we


ColinM

[stevechesh]

If you don't have an analyser, top your twins up from the 15 and dive them on air tables, and don't go below the MOD of 32%.... Easy, sorted, and no maths involved.......