KEVOS® MAKEOS · Pneumatics
Compressed Air Pipe Pressure Drop
What pressure drop does this compressed air flow cause in this pipe?
Pressure drop in a compressed air line from free-air flow, line pressure, pipe size and length, using the Darcy–Weisbach method with air density at line pressure and a Colebrook friction factor.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Air flow (free air delivery) | m³/min | Flow of free air (at inlet conditions) through the pipe. |
| Pipe inside diameter | mm | Inside diameter of the pipe. |
| Equivalent pipe length (including fittings) | m | Straight length plus equivalent length of fittings and valves. |
| Line pressure (gauge) | bar | Pressure at the start of the pipe. |
| Air temperature | °C | Temperature of the compressed air. |
| Pipe roughness | mm | Roughness: about 0.045 mm for steel, 0.0015 mm for aluminium or plastic air pipe. |
Method and formulas
- Line density ρ = 1.204 × (p_abs ÷ 1.01325) × (293.15 ÷ T); actual flow = free air flow × (1.01325 ÷ p_abs) × (T ÷ 293.15).
- Re = ρ v d ÷ μ (μ ≈ 1.81 × 10⁻⁵ Pa·s); Colebrook friction factor.
- Δp = f (L ÷ d) ρ v² ÷ 2.
- Example: 5 m³/min at 7 bar g through 100 m of 40 mm pipe drops about 0.18438 bar.
Limitations
- Valid while the drop is a small share of the line pressure (under about 10%); otherwise calculate in sections.
- Equivalent lengths of fittings must be estimated from fittings data.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size compressed air mains and drops
- Check pressure at a remote user
- Find savings from a larger main
Who it is for
- Maintenance engineers
- Energy and utilities managers
- Design engineers
What you get
- Air velocity and Reynolds number
- Friction factor
- Pressure drop and percentage of line pressure
Interpreting the result
- A common design aim is under 0.1–0.3 bar drop from compressor to the furthest user.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3036–3041, 3024–3027. Topic reference; no source tables or recommended settings are reproduced.
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