Partial-pressure fill answers how do I fill this cylinder to the mix I want? It takes what the cylinder holds now and the mix and pressure you want, and returns the fill as numbered additions in bar. It is the only tool in the Blending group.
Partial-pressure fill
How do I fill this cylinder to the mix I want?
EAN32
232 bar, 32% O₂/He2 steps from Air at 50 bar. Analyse the mix before you dive it.
- Add Oxygen+32 bar
Add 32 bar of oxygen. Tank pressure → 82 bar Then 52% at 82 bar.
- Add Air+150 bar
Fill with air to 232 bar. Add 150 bar Then 32% at 232 bar.
Ideal-gas partial pressures, filled in the usual order: oxygen, then helium, then top-up with air. Mixes above 40 % oxygen need oxygen-clean equipment.
What you enter
- In the cylinder now: Oxygen (%), Helium (%) and Pressure (bar) of the gas already in it. Enter 0 bar for an empty cylinder.
- Target: Oxygen (%), Helium (%) and Pressure (bar) of the finished fill.
Reading the result
- Fill to: the finished mix by name, EAN32 or Trimix 21/35, with its pressure and composition underneath.
- The steps: one numbered row per addition, in the order it goes in: oxygen, then helium, then a top-up with air. Each row gives the action, the amount to add in bar, a line of instruction, and the mix and pressure the cylinder holds after it. The helium step is left out when the target has no helium.
The verdict counts the steps and always ends Analyse the mix before you dive it. When the cylinder already holds the target, the steps read The cylinder already holds this mix. Nothing to add.
The method note carries two conditions of its own: the figures are ideal-gas partial pressures, and mixes above 40 % oxygen need oxygen-clean equipment.
When the fill cannot work
- The cylinder is already at or above the target pressure. The verdict turns amber and asks you to lower the start pressure or raise the target.
- The cylinder is richer than the target. If it holds more oxygen or helium than the finished mix needs, the steps do not produce the target. Drain the cylinder and start again.
- Real gas and temperature. Oxygen and helium depart from ideal behaviour at fill pressures, and a cylinder filled fast reads high until it cools. Put the analysed mix into a plan, not the target.
The steps assume an unlimited bank behind each addition. To fill by decanting from your own cylinders, use the blending calculator in the planner.