TL;DR — Direct answer: A tunnelling and TBM site runs on compressed air at the face, where the machine is advancing, and the air must travel through a tunnel that lengthens every day: face tools, shotcrete spraying, ventilation support and dust suppression all draw on it, while dust, heat, humidity and vibration punish any system that was sized for a fixed workshop. The working system sizes on face demand at the longest tunnel length the drive will reach, protects intakes against tunnel dust, keeps ventilation and safety air separate from production peaks, and advances its distribution as the TBM advances, because pressure at the face is the only pressure that counts.
A tunnel drive is a factory that moves. The TBM or the drill-and-blast face advances metres every day, the ventilation duct lengthens behind it, shotcrete follows the excavation, and the compressor plant — usually on surface or at the portal — must push air further down the tunnel with every advance. A system that held pressure at the face in month one can sag in month six simply because the tunnel is longer, and the face crew feels that sag as slow drilling, weak shotcrete spraying and sluggish tools.
QiAir, a Chinese manufacturer and supplier of screw air compressors, sizes tunnelling air from the face equipment list and the planned drive length, because a machine quoted for the portal will not hold pressure at a face kilometres down the tunnel. The sections below start at the face and work back to the portal.
Face air, shotcrete and TBM auxiliaries
Face air is the governing load, and it is high-flow and bursty. Drilling, bolting, segment handling, TBM auxiliaries and shotcrete spraying all draw together during an advance cycle, typically at 7 bar or more at the tool, and the sizing sheet must list every face machine, its rated consumption at working pressure, and which machines truly run together during a full advance and lining cycle. A system sized on average face demand will starve the face whenever drilling and shotcrete overlap, and shotcrete that sprays weakly because header pressure sagged produces a lining defect that is expensive to repair and difficult to inspect.
Distribution down a lengthening tunnel is the harder problem. Pressure loss grows with tunnel length, bends, moisture and leaks, so the design needs a main sized for the final drive length, not the first month, receivers near the face to absorb cycle peaks, drops sized for the largest tool at peak, and pressure checks at the face repeated as the drive advances. Wet air is a second problem: moisture in face air accelerates tool wear and causes problems in cold tunnel sections, so drying and drainage at the portal plant and at face receivers must handle the real water load, and the tunnel main needs drainage at low points.
Ventilation support, dust and the tunnel environment
Ventilation support air must not be allowed to compete with face production air. Ventilation doors, regulators, dust-suppression sprays and monitoring equipment need stable, lower-flow air that arrives even when face tools peak, so the design should separate or prioritise ventilation and safety air from drilling and shotcrete peaks. A ventilation control that fails because a shotcrete burst starved the header is a ventilation failure, not a minor pressure event, and the tunnel ventilation plan should name which air users are safety-critical and what pressure they must hold during a face peak.
Tunnel dust, heat and humidity punish equipment that would last years on surface. Rock dust is abrasive and coats cooler fins and intake filters, heat and humidity load dryers and raise discharge temperatures, and vibration from blasting and TBM operation loosens fittings. Portal compressor rooms need intake air drawn from the cleanest available location, pre-filtration where dust levels are high, and cooler cleaning tied to advance rate rather than to the calendar. Tunnel receivers and drops need drainage, corrosion protection and inspection access, because a receiver that cannot be drained or inspected in a tunnel will corrode quietly until it becomes a safety finding.
- Size face air for the final drive length, not the first month.
- Separate or prioritise ventilation and safety air from face peaks.
- Recheck face pressure as the drive advances; tunnel length is pressure loss.
Reliability, advancing distribution and the export buying check
Reliability on a tunnelling site is measured in advance rate, because a surface compressor failure stops the face, the shotcrete crew and the lining operation at once. That argues for duty-and-standby capacity at the portal plant with automatic changeover, a service arrangement measured in hours, and spares on site covering filters, separators, drains and service kits. Changeover should be tested monthly under load, and the site should hold a written plan for which face operations keep running and which pause if one machine is lost, so a failure becomes a managed reduction rather than a full stop.
Before ordering from China, a tunnelling buyer should document the face equipment list with coincident demand, the planned drive length and tunnel layout, the ventilation and safety air list, required pressure at the farthest face, dust and humidity conditions, and voltage and frequency. QiAir sizes export tunnelling orders from that sheet, and confirms whether any equipment sited in the tunnel or near hazardous areas needs special certification. Get the face list and the drive length in writing, and the plant that arrives holds pressure at the face for the whole drive, not just the first month.
Frequently asked questions
Why does tunnelling air sag as the drive advances?
Pressure loss grows with tunnel length, bends, moisture and leaks, so a system sized for the portal or the first month starves the face as the tunnel lengthens.
What pressure do face tools and shotcrete need?
Typically 7 bar or more at the tool. Size on coincident drilling, bolting and shotcrete demand, with pressure confirmed at the face during a full advance cycle.
Should ventilation air share the face header?
Only with separation or priority: ventilation and safety air must hold pressure even during face peaks, or a tool burst becomes a ventilation failure.
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QiAir is a Chinese manufacturer and supplier of screw air compressors. If you are sourcing a screw compressor from China — for a factory, a textile mill, a construction site or a new production line — contact QiAir for a sized quotation, documented performance data and export support.