What pipe diameter do you need?
Find the required internal diameter from flow, length and permitted pressure drop.
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How we calculate
Method: Darcy–Weisbach, isothermal compressible gas: p₂² = p₁² − (λL/D + ΣK) ṁ²RT/A². λ: 64/Re for laminar flow, Colebrook for turbulent flow; the conservatively higher value in transition. Smooth-pipe roughness of 0.0015 mm and steel roughness of 0.045 mm are indicative, not material guarantees. Viscosity follows Sutherland's relation. We numerically find the smallest diameter meeting the pressure-loss limit and a maximum velocity of 20 m/s.
Assumptions and limitations: Dry air, steady flow, constant temperature, no elevation difference. Validity is limited to a pressure drop of 10% of absolute inlet pressure and velocity up to 20 m/s. Does not model networks or transients. The result is the internal diameter, not DN or a commercial size.
Method references- CAGI Compressed Air & Gas Handbook, chapter 4, 2021 – system design, storage and pressure losses.
- Spirax Sarco: Pipes and Pipe Sizing – Darcy–Weisbach; Colebrook equation for friction resistance.
Method version 1.0. Standard references verified in the ISO catalogue; the physical balances are not calculations prescribed by ISO. Before final design, we will verify actual operating and catalogue data.