Subways and tunnels are enclosed spaces with high population density. In the event of a fire, smoke spreads extremely rapidly. Ventilation systems must be reliable, pressure-resistant, fireproof, and efficiently installed. Spiral ducts have become the preferred choice for these large-scale infrastructure projects precisely because of the following key advantages:
I. Four core advantages of spiral ducts
| Advantages | Value to subways/tunnels |
| High circumferential stiffness | Withstand piston wind pressure, and prevent collapse under negative pressure during smoke exhaust |
| Spiral reinforcement | Resist bending along its length and does not deform when suspended |
| Welding/flange connection | Good sealing performance, air leakage rate ≤1% |
| Circular cross-section | Low resistance, lower energy consumption for the same airflow |
II. Why not use rectangular ducts or ordinary welded round ducts?
• Rectangular ducts: Stress concentration at corners, prone to bulging under high pressure; large on-site fabrication volume, difficult to control quality.
• Ordinary welded round ducts: No spiral reinforcement, prone to bending over long distances; numerous welds, high risk of leakage.
• Spiral ducts: One-piece spiral forming, no longitudinal weld seams; built-in reinforcing ribs, good rigidity; factory prefabricated, only connection needed on-site.
III. Special requirements for ducts in subways/tunnels & responses of spiral ducts
| Requirements | Responses of spiral ducts |
| Pressure resistance ≥2000 Pa (piston air) | High circumferential stiffness, suitable for plates with a thickness of 1.2–1.5 mm |
| Fire prevention | Galvanized sheet or stainless steel, non-combustible Class A |
| Corrosion resistance | Optional galvanized coating Z275 or 304 stainless steel |
| Fast installation speed | Spiral duct sections are 2-3 meters long, with flange/socket connections, several times faster than on-site welding |
| Easy to maintain | The inner wall is smooth and resistant to dust accumulation, and can be rinsed |
IV. Real case data
A city’s subway environmental control system uses BYFO spiral ducts:
• Diameter: Φ600-1400mm
• Thickness: 1.2mm galvanized sheet, enhanced type flange
• Test pressure: 2500Pa, deformation <0.5%
• Installation efficiency: 150 meters per shift per day
• 5 years of operation: No air leakage, no deformation complaints
V. What can BYFO provide?
• Heavy-duty spiral duct machine: Processing thickness can up to 1.5mm, diameter can up to 1600mm
• Enhanced type flange machine: Adaptable to high-pressure systems, flange strength increased by 30%
• Fixed-length flying cut: Smooth duct ends, error ±1mm
• Material optional: Galvanized sheet, 304/316 stainless steel, aluminum sheet
In short: If your tunnel or subway requires durable ventilation ducts, spiral ducts are the answer.
Need to select a model based on specific duct diameter and pressure?Contact BYFO technical team, provide parameters, and we’ll provide a solution within 24 hours.
