# Two more rebreather patches

Tue Oct 28 05:45:36 PDT 2014

```On Tue, Oct 28, 2014 at 9:36 AM, Paul Sargent <paul.lionseye at icloud.com> wrote:
>
> On 27 Oct 2014, at 17:56, Rodrigo Severo <rodrigo at fabricadeideias.com> wrote:
>
>>> For example: A one hour dive should be 20bar (60 litres) out of a standard 3
>>> litre cylinder - just calculating 1 litre a minute. That's just way off. I
>>> always use about ~50 bar on a ~40 metre dive, so I tend to make sure I've
>>> got at least 100 bar when I jump in.
>>>
>>> (or have a missed a different method of calculating things in the various
>>> mails?)
>>
>> The method of calculation is just that but, as I see things, it would
>> happen the other way around:
>>
>> After this dive Subsurface would show you that your oxygen SAC is 2,5
>> l/min (50 bar of a 3 l cylinder used on an hour dive). So on your next
>> planning you should use 2,5 l/min for oxygen and not the usual 1
>> l/min.
>
> The problem here is that going from a one hour to a two hour dive doesn’t double my O2 use. I might go from 50 bar to 70 bar (i.e. Same use for the ascent aspects, another 20 bar for the extra hour).
>
> To me it sounds to me like we’d need a SAC component (litres/min) and an ascent component (litres/metre.bar). Diluent would just have a descent component (litres/metre.bar). In the example above reasonable figure might be:
>
>     - O2 SAC: 1 litre/min
>     - O2 Ascent:
>            30bar * 3l = 90l
>            90l / 40 metres = 2.25 litres/metre
>            2.25l / 2.5 bar (Avg. Pressure during ascent) = 0.9l / metre.bar

I don't understand way the ascent component has a bar in it (and why
you divided the average consumption per meter by the average
pressure).

Shouldn't the ascent component just be 2.25 litres/metre here?

>     - Diluent Descent:
>            50bar * 3l = 150l
>            150l / 40 metres = 3.75l / metre
>            3.75l / 2.5 bar (Avg. Pressure during descent) = 1.5l / metre.bar

Here again I don't understand why getting a litre/metre*bar. Why not
jsut litre/metre?

Rodrigo
```