Which cylinder factor is used in the duration calculation for E-tanks?

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Understanding how long an E-tank lasts comes down to turning the pressure in the cylinder into a usable gas volume, then linking that volume to the intended flow rate.

The cylinder factor is the amount of gas released per unit pressure for a given cylinder size. For an E-tank, this factor is 0.28 L per psi. That means every psi of pressure corresponds to about 0.28 liters of gas available. So you can estimate total gas by multiplying the gauge pressure (in psig) by 0.28, giving you liters of gas, then divide by the flow rate (L/min) to get duration in minutes. If you account for a residual pressure, use (pressure minus residual) times the factor.

For example, at 2000 psig and a flow of 2 L/min, duration is roughly (2000 × 0.28) / 2 ≈ 280 minutes (ignoring residual). If you subtract a residual of 200 psi, it becomes (1800 × 0.28) / 2 ≈ 252 minutes.

The value 0.28 is the standard cylinder factor for E-tanks; the other numbers don’t serve as the conversion factor for this purpose (they’re not the gas-conversion factor used here).