How do I get 28% from 1000psi 32%

[Dexloy]

Example of method one. This is primarily for situations where a high O2 in a full tank needs a lower O2 but it will work either way. Original tank press 3500 psi. Reduce 32% mix to 28%.

P1 X .32 + P2 X .21 = 3500 X .28
.32 P1 + .21 P2 = 980
P2 = 3500-P1
.32P1 + .21(3500-P1) = 980
.32P1 + 735-.21P1 = 980
.11P1 + 735 = 980
.11P1 = 245
P1 = 2227 psi

Drain the tank to 2227 psi and top off with air.

I have offered two methods and provided two examples. This is the example for method one which is now being included per your request. I hope that these two economical methods work for you.

I think I undedrstand thanks pesky

 

[Dexloy]

A quick excel sheet I made to do the math, Just plug in the numbers you want.

CB Nitrox work sheet.xls - Windows Live SkyDrive

 

[sskasser]

Just keep in mind that oxygen compression is not necessarily linear and a straight math equation won't necessarily give you an exact mix. These will all get you in the range, though. YMMV

 

[pescador775]

Just keep in mind that oxygen compression is not necessarily linear and a straight math equation won't necessarily give you an exact mix. These will all get you in the range, though. YMMV

And you should bear in mind that these equations were developed for blending at atmospheric pressure where compression factors do not come into play. Moreover, running an electronic analyzer after the mix has been compressed is SOP. Finally, the purpose of final gas mixture measurements has nothing to do with compression factors of any of the gases but merely to verify that the fractions contained in the mix were correct to begin with.

 

[Dexloy]

And you should bear in mind that these equations were developed for blending at atmospheric pressure where compression factors do not come into play. Moreover, running an electronic analyzer after the mix has been compressed is SOP. Finally, the purpose of final gas mixture measurements has nothing to do with compression factors of any of the gases but merely to verify that the fractions contained in the mix were correct to begin with.

Correct, this is just to get you in the range without wasting what is in the tank and must be verified after the fill by both the mixer and diver. Using these numbers I have been +- .2 consistently. YMMV