The blending calculator takes what is in the cylinder now, the mix you want and the pressure you want it at, and returns the fill as an ordered list of additions in bar. It opens from a gas already in the plan, so the target composition is known before you start.
Current & Target Conditions. Enter the Current Gas in Tank as O₂ % and
He %, with the Current Pressure (bar). Nitrogen shows as N₂ % (auto).
The target composition is read-only; you set only the Target Pressure.
When the inputs are workable the panel reads Ready to calculate blending requirements. Continue.
Blending Instructions. Step through the additions one at a time. Each card shows the action, the amount in bar, and the mix and pressure before and after it.
The sequence
Three additions, always in this order: Add Oxygen, Add Helium, Add Air. Helium is the helium the finished mix needs less what the cylinder already holds. Air is the only source of nitrogen, so the air fill is sized by the nitrogen the mix needs. Air also brings oxygen, about a fifth of every bar, and the oxygen step is reduced by exactly that amount: an empty cylinder filled to EAN32 at 200 bar takes 28 bar of oxygen, then 172 bar of air. The helium step is skipped when the target carries no helium.
Amounts are shown as whole bar, the resolution a fill whip and a gauge work at, but the pressure after each step is not rounded, so errors do not accumulate. Any addition of 0.5 bar or less is left out entirely.
Filling from source cylinders
Each addition normally assumes an unlimited bank behind the whip. If you are decanting from your own cylinders instead, tick Decant Supply on the conditions screen and describe them:
- Target Cylinder Size (L): the water capacity of the cylinder being filled.
- Oxygen, Helium, Air Top-up: one group per supply gas. Add Cylinder attaches a source, up to two per gas; a group left empty reads Unlimited bank and behaves as before.
- Size (L) and Pressure (bar): each source’s water capacity and starting pressure.
Decanting is equalisation. Connect a source to your cylinder and gas flows until the two pressures meet, so a fill stage stops at equalisation or at the step’s target, whichever comes first, and a source can never lift your cylinder above its own pressure. With two sources the calculator drains the lower-pressure one first, then the higher, whatever order you entered them in.
As you type, the panel answers Fill achievable from configured sources or Fill not achievable from configured sources. Each instruction card then shows the transfer from each source: bar added, litres moved, and the pressure left in that source. A step that cannot reach its target says how short it falls and what pressure decanting does reach. The final screen lists Source Cylinders After Fill: what remains in each source and what it delivered.
When the fill cannot be made as asked
Three conditions stop the sequence. Each is reported on the conditions screen in place of Ready to calculate blending requirements, and Next stays disabled until the inputs change.
- Current pressure at or above the target: Current pressure must be less than target pressure. There is nothing to add.
- The cylinder already holds too much of a gas: Bleed the cylinder from 100 bar down to 75 bar first: it already holds more of one gas than this mix allows, with your own pressures. Adding gas cannot dilute what is there. Bleed to the pressure given, enter it as the current pressure, and the sequence is computed from there. 100 bar of EAN50 to EAN32 at 200 bar bleeds to 75 bar and then takes a single air fill of 124 bar; the oxygen in the air makes up the 32 %.
- The mix cannot be made from oxygen, helium and air: This mix cannot be made by adding oxygen, helium and air to this cylinder. A target with less oxygen for its nitrogen than air has (18 % nitrox, say) needs a leaner nitrogen source than air, and no bleed-down helps.
Partial-pressure blending assumes ideal gas behaviour, and real oxygen and helium deviate from that at fill pressures. The calculator does not model temperature: a cylinder filled fast is hot and reads high until it settles. The third step is air, not nitrox and not a banked mix.
The calculator says so itself: always follow proper gas blending safety procedures and verify final mix with analyzer. Put what your analyser read into the gas, not what you asked the blender for.
Next
- Breathing rates is the next step of the plan.
- Depth limits checks the gas that came out of the cylinder.