mixpsi

Nitrox calculator

Calculation notes

Cylinder preset

Tank preset

Starting gas

Target blend

Settings

Changes apply to your fill plan immediately.

Cylinders, source & pressure

Use the cylinder’s stamped rating.

Top-up gas is fixed at 21% air. Use the analyzed source percentage.

Settled pressure shortcuts. Custom PSI can be entered in Target blend.

Enter gas temperatures. Gas can be hotter than the room during filling.

Custom cylinders

Save cylinders in this browser for future sessions.

    Fill temperature
    Fill temperature method
    Temperature estimate settings

    Assumes continuous filling with both sources at the entered temperature.

    Cylinder & heat transfer

    Aluminum. Catalina S80 specifications. Edit for your cylinder.

    Heat-transfer coefficients are starting assumptions for filling in air, not measured values. A water bath needs different settings.

    Fill plan

    Ideal-gas estimate

    Catalina S80

    32%oxygen
    3,000PSI at 80°F

    Pressure checkpoints

    Stop at, gauge PSI

    Read addition pressures after the gas settles at 80°F.

    1. Keep the existing gas

      500 PSI

      21% oxygen, measured at 80°F.

    2. Add 36% nitrox to

      2,711 PSI

      Add 2,211 PSI equivalent at 80°F.

    3. Top with 21% air to

      3,000 PSI

      Add 289 PSI equivalent at 80°F.

    Allow for cooling

    Estimated 119°F3,218 PSIEquivalent hot pressure
    At 80°F3,000 PSISettled target

    10 min continuous fill. Uncalibrated heat-transfer estimate.

    Estimated peak pressure: 3,218 PSI, above the 3,000 PSI rating. Do not fill to this pressure. Allow cooling and follow approved top-up procedures.

    Verify this ideal-gas estimate and analyze the finished mix.

    Calculations and limits

    Oxygen balance

    The calculation accounts for oxygen in the remaining gas and both fill gases. It retains the most existing gas that allows you to reach the target mix and pressure.

    Cylinder volume cancels out for a single rigid tank. Check the selected pressure preset against your cylinder’s stamped rating.

    Before filling

    Have a qualified gas-blending professional review this prototype before using it for a real fill. Verify the cylinder’s rating and equipment compatibility. Stay within rated pressure during filling, including when the gas is hot. Follow approved filling procedures and analyze the finished mix.

    Fill temperature

    The estimate balances energy carried in by the gas with heat absorbed by the cylinder and lost to its surroundings. It uses fill duration, inlet temperature, water capacity, cylinder mass and material, and editable heat-transfer coefficients.

    It assumes a continuous fill at constant molar flow, with the gas and wall starting at the current gas temperature after any bleed-down. Cooling pauses between gases are not simulated. Checkpoints use settled readings unless cooling correction is enabled with entered gas temperatures for each addition stage. Bleed readings always use the starting temperature.

    Heat-transfer values are uncalibrated assumptions. The model uses ideal diatomic gas properties and excludes real-gas compressibility, source-bank limits, and temperature gradients. Neither a model estimate nor a cylinder-surface reading establishes the actual bulk gas temperature.

    If the gas were at 119°F when the gauge reached 3,000 PSI, the fixed-quantity ideal-gas correction gives 2,797 PSI after cooling to 80°F. This does not simulate stopping early at the rating.

    For fixed gas quantity, pressure correction uses PSI + 14.7 and °F + 459.67. Zero gauge pressure still contains atmospheric gas.

    Model reference: pressure-vessel energy balances. The equations apply here; hydrogen-specific coefficients from that study are not used.