Pneumatic Pipe Size Advisor
Minimum pipe ID for a given airflow and length
Airflow और pipe length से minimum safe inside diameter
Compressed air pipe sizing balances two concerns: keeping pressure drop below ~0.3 bar over the whole run and keeping air velocity below ~6 m/s in main lines (20 m/s in branches). Under-sized pipes cause pressure drop and high velocity, which increases turbulence, noise, and moisture precipitation. The simplified velocity-based formula is: minimum pipe inside diameter D (mm) = √(4 × Q / (π × v)) × 1000, where Q is the actual airflow in m³/s at working pressure, and v is the target velocity (6 m/s for mains). For free air Q in NL/min at gauge pressure P bar, actual flow is Q × 1.013 / (P + 1.013) / 60000 in m³/s. So a 1000 NL/min (35 CFM) line at 6 bar needs an inside diameter of at least 14 mm — a G1/2 (12 sut) pipe with ~16 mm inside diameter works comfortably. For shorter branches (≤5 metres) and peaky flow, higher velocity up to 20 m/s is acceptable, so smaller pipes like G1/4 (2 sut) can feed individual tools or cylinders.
Calculator
Calculated minimum ID: 19.5 mm. Target velocity: 6 m/s (main line). Actual flow at 7 bar: 1.79 L/s (normalised free air: 850NL/min). For pipe runs > 50 m also verify explicit pressure drop (target < 0.3 bar).
ƒFormula
D_min (mm) = √(4 × Q_actual / (π × v)) × 1000 where Q_actual = Q_NL_min × 1.013 / ((P_gauge + 1.013) × 60000)Q_NL_min is free airflow in normal litres per minute. P_gauge is line working pressure in bar. Q_actual is the compressed volume flow at working pressure (in m³/s). v is target velocity — 6 m/s for mains, 20 m/s for branches. D_min is minimum inside diameter in mm. This is a velocity-based sizing that avoids pressure drop in runs up to ~50 metres. For longer runs (>100 m), also run an explicit pressure-drop calculation (Harris formula).
Units: Diameter: millimetre (mm) · Flow: NL/min or CFM · Length: metre · Pressure: bar gauge
Air pipe ki size kaise decide karein?
Compressed air pipe design mein do cheezein balance karni padti hain: (1) pressure drop — pure run mein 0.3 bar se zyada nahi girna chahiye, aur (2) air velocity — mains mein 6 m/s se kam, branch lines mein 20 m/s tak acceptable. Chhoti pipe use karne se velocity badh jaati hai, pressure drop hota hai, moisture separate hoti hai, aur noise + turbulence hoti hai. Formula velocity-based: D (mm) ≥ √(4 × Q / (π × v)) × 1000. 1000 NL/min (35 CFM) line 6 bar pe chalne ke liye minimum 14 mm inside diameter chahiye — G1/2 (4 sut) pipe sufficient hai (ID ~16 mm). Short branch lines ke liye chhoti pipe OK — G1/4 (2 sut) ek tool ya cylinder ko feed kar sakti hai.
Worked Examples
Main factory air line
Problem: 50 m run from compressor room to the main factory floor. Peak flow 30 CFM at 7 bar gauge.
Solution: Q_actual = 30 × 28.317 / 60 × 1.013 / 8.013 = 1.79 L/s = 0.00179 m³/s. D_min (at 6 m/s) = 19.5 mm. Pick G3/4 pipe (ID ~21 mm) — gives 5.2 m/s velocity, well within limits. Also adequate for future 20% demand growth.
Short branch to an air drill
Problem: A 3-metre branch feeding an air drill that consumes 12 CFM at 6 bar.
Solution: Q_actual = 12 × 28.317 / 60 × 1.013 / 7.013 = 0.82 L/s = 0.00082 m³/s. For branch at 20 m/s target, D_min = √(4 × 0.00082 / (π × 20)) × 1000 = 7.2 mm. G1/4 BSP (ID ~13 mm, 2 sut) is comfortably sufficient.
Multi-tool distribution line
Problem: Workshop distribution to 5 air tools, each 8 CFM at 7 bar, 20 m pipe run. Diversity 60% (not all running at once).
Solution: Total theoretical: 40 CFM × 0.60 diversity = 24 CFM. Q_actual = 24 × 28.317 / 60 × 1.013 / 8.013 = 1.43 L/s. D_min (main 6 m/s) = 17.4 mm. Pick G1/2 (ID ~16 mm, 4 sut) — gives 7.1 m/s, slightly above target but acceptable. For peace of mind upgrade to G3/4.
Recommended Pipe Size — BSP × Airflow × Line Type
| BSP size | Sut | ID (mm approx) | Max flow @ 6 m/s (CFM) | Max flow @ 20 m/s (CFM) |
|---|---|---|---|---|
| G1/8 | 1 | 8 | 0.7 | 2.3 |
| G1/4 | 2 | 13 | 1.8 | 6.1 |
| G3/8 | 3 | 16 | 2.7 | 9.1 |
| G1/2 | 4 | 16 | 2.7 | 9.1 |
| G3/4 | 6 | 21 | 4.7 | 15.7 |
| G1 | 8 | 27 | 7.8 | 26 |
| G1-1/4 | 10 | 36 | 13.8 | 46 |
| G1-1/2 | 12 | 41 | 17.9 | 59.8 |
| G2 | 16 | 52 | 28.7 | 96 |
| G2-1/2 | 20 | 68 | 49 | 164 |
Flow values at 7 bar gauge. Scale approximately for other pressures: multiply by (7.013 / (P+1.013)) for actual flow equivalence. For runs > 50 m, always run an explicit pressure-drop check; this velocity-based sizing is a first-pass estimate.
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