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11.Airflow × Static Pressure × Duct Diameter Chart: A Complete Selection & Piping Guide (2025 Edition)

1｜Understand the Three Key Parameters: Q, ΔP, and D

Airflow (Q, CMM = m³/min) — the total air volume moved.

QCMM=Vf(m/s)×A(m2)×60Q_{CMM}

  • Recommended conveying velocity (to prevent settling):

    • General dust: 14–18 m/s

    • Metal chips: 18–22 m/s

    • Fragile particles: 8–12 m/s

Static Pressure (ΔP, Pa / kPa) — total system resistance from duct friction, fittings (equivalent length), and internal components (hoods, filters, HEPA, silencers).

Duct Diameter (D, mm) — increasing D reduces friction loss and static pressure but requires more space and cost; smaller D stabilizes vacuum and suits small hoses and hand tools.

2｜Airflow × Static Pressure × Duct Diameter Reference Table

Duct Dia. (mm)

Recommended Velocity (m/s)

Airflow (CMM) @16 m/s

ΔP / 10 m @16 m/s (approx.)

Application Guide

32

18–22

≈ 7.7

5,000–6,000 Pa

High-vacuum for hand tools / long hoses

38

18–22

≈ 10.9

3,500–5,000 Pa

High-vacuum, small nozzle / long reach

50

16–22

≈ 18.8

2,500–3,500 Pa

Transition between high & medium vacuum

63

16–20

≈ 29.8

1,800–2,500 Pa

Medium pressure, mid-distance with bends

76

14–18

≈ 42.6

1,200–1,800 Pa

Borderline between medium & low pressure

100

14–18

≈ 74.3

900–1,300 Pa

Low-pressure, high-volume, short-mid range

125

14–18

≈ 116.0

700–1,000 Pa

Low-pressure, large hood areas

150

14–18

≈ 167.8

500–800 Pa

Main low-pressure duct

200

14–18

≈ 298.1

400–600 Pa

Large low-pressure main line

Pressure drop is estimated; actual design requires correction for duct roughness, fittings, and throttling components.

3｜Quick Reference: Equivalent Lengths for Common Fittings

Fitting Type

Equivalent Length

90° Standard Elbow

30–50 D (use 40 D)

90° Long Radius Elbow

20–30 D (use 25 D)

Tee – Straight Path

20–40 D (use 25 D)

Tee – Branch

60–100 D (use 80 D)

Damper / Butterfly Valve (open)

10–20 D (use 15 D)

Flexible Hose

1 m ≈ 2–3 m straight duct (use 2.5 ×)

4｜Step-by-Step: Sizing & Duct Layout in One Table

  1. List all suction points and face velocities → calculate Q for each.

  2. Multiply by simultaneous-use coefficient (e.g. 0.7) and add 10–20 % safety margin → get total Q.

  3. Sketch the longest / worst-case branch → compute equivalent length using table above.

  4. Select D from chart to maintain target duct velocity (14–18 m/s; metal = 18–22 m/s).

  5. Estimate ΔP:

    ΔPline≈R×v2×Leq\Delta P_{line} \approx R \times v^2 \times L_{eq}ΔPline​≈R×v2×Leq​

    (R coefficient provided in downloadable table).

  6. Add internal losses (hood + filter + HEPA + silencer) = ΔP total.

  7. Determine system class:

    • ΔP < 3 kPa → Low Pressure

    • 3–10 kPa → Medium Pressure

    • 10 kPa → High Vacuum

  8. Compare your Q × ΔP point on the fan curve to the system curve — fine-tune duct size, velocity, or branch layout accordingly.

5｜Three Practical Sizing Examples (2025)

A｜Small-Diameter Long-Distance (Tool Extraction / Central Cleaning)

Two × Ø38 mm hoses (10 m each) + Ø76 mm floor nozzle (5 m, 0.7 coefficient).
→ Verdict: High vacuum for stable suction; main duct ≥ Ø63 mm recommended to lower loss.

B｜Batching Station with Multiple Bends

Four weighing hoods (0.6 × 0.5 m @ 0.6 m/s) + one dumping port (18 CMM).
→ Verdict: Medium pressure cartridge collector + ePTFE filter (A/C 0.8–1.2 m/min) + ΔP-triggered pulse cleaning.

C｜Large Open Hood (Woodworking / Grinding)

Multiple open hoods across machines.
→ Verdict: Low-pressure high-volume system with large main duct; add spark arrestor + explosion vent for combustible dusts.

6｜Frequently Asked Questions

Q1: Why is suction weak with Ø50 mm duct?
→ Equivalent length and friction too high; enlarge to Ø63/76 mm or reduce bends / hose length to cut ΔP.

Q2: Is high vacuum always stronger?
→ Not necessarily. High vacuum = small flow / high head — great for small nozzles and long hoses, not for large hoods.

Q3: Do I need HEPA? Where should it be?
→ Yes for indoor return, fine dust, or sensitive products. Sequence: Main Filter → Fan → HEPA, then perform PAO/DOP integrity test and monitor ΔP up/downstream.

Q4: How to choose the R coefficient?
→ Engineering rule: Small dia = 2.0; Medium = 1.0; Large = 0.6 (Pa/(m·(m/s)²)). Refine using duct roughness, Re number, and fitting type.

Q5: What about combustible dust?
→ Use antistatic filter media / hoses, full grounding and equipotential bonding, flame isolation valves, explosion vents or chemical suppression, and certified Zone electrical equipment.

7｜Top 8 Design Pitfalls to Avoid

  1. Focusing on motor HP instead of fan curve vs system curve.

  2. Undersized ducts — high velocity but insufficient Q.

  3. Ignoring the worst-case branch → airflow collapse during operation.

  4. Excessive A/C ratio → high ΔP and filter blinding.

  5. Using high-vacuum small-flow setup for large hoods.

  6. No ΔP baseline or alarm thresholds (e.g., Alert ≥ 1700 Pa; Action ≥ 2000 Pa).

  7. Incorrect HEPA placement or no PAO/DOP testing.

  8. Treating explosion safety as just “antistatic filters” — no isolation, venting, or grounding.

8｜From Engineering to Procurement

Explore our [Project References] for real-world examples of duct sizing, central dust collection layouts, and high-vacuum performance data.

Contact us to learn more about [Central Dust Collection System Design & Ducting Solutions] — from main / branch diameter selection, worst-case branch calculation, to damper balancing and system optimization.