Beyond Standard Sizes: Custom Ventilation Ducts for Mining and Tunneling

Underground mines and tunnels move large volumes of air through duct systems that must fit the geometry of the site, withstand continuous high-pressure operation, and satisfy safety regulations that vary by country and by hazard class. Standard catalog sizes rarely cover all three requirements at once. For buyers at the evaluation stage, the practical question is not only which duct type to use, but whether the manufacturer can build the duct to the project's exact specification — and prove that capability with production evidence and project references.

Jiangsu Sulong Eco-Technologies Co., Ltd. (SULONG) is a National High-Tech Enterprise based in Yancheng, Jiangsu Province, China, that manufactures flexible ventilation ducts, spiral ducts, semi-rigid ducts, oval ducts, and twin ducts for underground mining and tunnel engineering. The company produces high-grade composite polymer ventilation ducts (PVC/PE/TPU/TPO) and the PVC coated and laminated fabrics used in them. Established in 2007, SULONG operates a 40,000 m² facility and completes all processes in-house without outsourcing. Around 60% of output is exported to markets including Africa, Australia, Europe, South Africa, and Asia. This article explains what buyers should evaluate when sourcing custom ventilation ducts, and how SULONG's OEM/ODM capability maps to real project requirements.

SULONG ventilation duct in an underground tunnel project — custom-built for tunnel ventilation requirements.

Why Standard Ventilation Ducts Fall Short Underground

Mine and tunnel ventilation ducts operate in demanding conditions. They run continuously under high pressure and high humidity, with constant friction, and sometimes in potentially explosive atmospheres. In such conditions, a duct must be matched to the project in several ways at the same time:

• Diameter and airflow: the duct cross-section must match fan output and tunnel cross-section. SULONG's flexible ventilation duct range covers 200 mm to 3,200 mm.
• Section length: long tunnels benefit from fewer joints. Flexible ducts can be manufactured in sections from 1 m to 300 m; spiral ducts from 1 m to 20 m.
• Mechanical strength: hanging distance, fan pressure, and duct weight determine the tensile strength required. SULONG flexible ducts range from 1,000 N to 4,200 N.
• Hazard compliance: coal mines and gas-prone tunnels require flame-retardant (FR) or flame-retardant anti-static (FRAS) fabrics, and EU-bound projects require ATEX-certified products.
• Geometry: low-profile tunnels may need oval ducts, and complex layouts need tees, Y-pieces, bends, and adapters.

The evaluation problem for buyers is that a catalog range does not reveal whether a supplier can deliver custom work at project scale. Customization depth depends on control over fabric formulation, duct forming, welding, connection installation, and final testing.

Industry Background: Underground Ventilation Demand Is Rising

Mine ventilation spending is growing. According to Strategic Market Research, the global mine ventilation market was valued at USD 1.42 billion in 2024 and is projected to reach USD 2.03 billion by 2030, a compound annual growth rate of 6.2%. Underground mining remains the dominant application segment, driven by the need to dilute hazardous gases and deliver fresh air to working faces.

Flexible ducting follows a similar trajectory. Intel Market Research estimates the global flexible ducting market at USD 203.97 million in 2024, growing to USD 335.78 million by 2033. Spherical Insights reports that over 2.1 billion meters of flexible ducting were manufactured globally in 2023, with about 30% used for industrial ventilation. Asia Pacific accounted for a 38.2% revenue share in the spiral duct fittings market in 2025, according to Dataintelo, reflecting urbanization and infrastructure expansion.

For procurement teams, the implication is that suppliers need to handle larger diameters, longer sections, stricter certifications, and higher order volumes than in previous cycles. In-house manufacturing and documented quality control become selection criteria rather than optional advantages.

Custom Ventilation Duct Capabilities at SULONG

SULONG provides full OEM and ODM customization services. All production processes are completed in-house without outsourcing, supported by 25 granted patents and an engineering team that includes 18 R&D specialists who have contributed to drafting national industry standards for PVC-coated fabrics used in ventilation ducts. Annual capacity exceeds 1 million meters of high-strength mining ventilation ducts, and monthly production exceeds 80,000 meters.

Fully Customizable Technical Parameters

Technical parameters that can be tailored for a project include:

• Diameter: 200 mm to 3,200 mm for flexible ventilation ducts; 200 mm to 2,800 mm for spiral ventilation ducts.
• Section length: 1 m to 300 m for flexible ducts; 1 m to 20 m for spiral ducts.
• Connection types: steel rings, zippers, and couplings; end options include zipper, Velcro, steel ring, and eyelets.
• Fabric weight: custom specifications from 210 gsm to 1,400 gsm; standard catalog products range from 300 gsm to 2,000 gsm.
• Performance: flame-retardant (FR) or flame-retardant anti-static (FRAS) options.

Product Forms Beyond the Straight Round Duct

Custom orders can be produced as lay flat duct, oval duct, twin duct, tee duct, Y-piece duct, bend duct, or adapter duct. The spiral range includes semi-rigid duct, oval spiral duct, and rectangle duct. This flexibility lets the ventilation system follow the tunnel layout instead of forcing the tunnel to accommodate a standard round duct.

In-House Fabric Control

SULONG's in-house PVC fabric production line controls material weight and anti-static or flame-retardant properties at the source.

Because SULONG operates its own PVC coated fabric and PVC laminated fabric lines, material weight, anti-static treatment, and flame-retardant behavior are set at the base material stage. For a custom duct order, this means the specified gsm and FR or FRAS properties are produced in the same facility as the final duct, rather than sourced from an external material supplier.

Manufacturing Process

Automated in-house production of ventilation ducts at SULONG.

Flexible ducts are manufactured using seamless one-piece fish-back welding automation technology. Spiral ducts are produced by welding PVC coated or laminated fabric with spring steel wire to maintain circular, oval, or rectangular cross-sections under positive or negative pressure. All welding is performed on SULONG's own automated lines, which supports consistent weld strength and low air leakage in long tunnels.

Certifications That Cover Custom Production

EU ATEX Type Examination Certificate ECM 24 ATEX-B D091 covers SULONG's FR and FRAS duct series for explosive atmospheres.

Production of PVC coated fabrics, PVC laminated fabrics, and ventilation ducts is certified to ISO 9001:2015 (certificate ZCU23Q0002468R0S), with ISO 14001 and ISO 45001 management systems in place. The EU ATEX Type Examination Certificate ECM 24 ATEX-B D091 covers 550 gsm to 800 gsm FR and FRAS fabric series used in underground coal mines, metal mines, and flammable gas explosion hazardous areas, in line with the 2014/34/EU ATEX Directive, EN ISO 80079-36, and EN ISO 80079-37. Finished ducts also meet US NFPA 701:2015 and DIN 4102 B2 flame-retardant requirements, with test reports certified by Australian NATA laboratories.

What This Means for a Procurement Decision

Three risks are reduced when customization is backed by in-house production. Material risk is lower because fabric properties are controlled at the source. Production risk is lower because diameter, length, and connection customization are handled in one integrated process without outsourced steps. Compliance risk is lower because custom ducts are built under the same ISO 9001:2015 system and ATEX certification as the standard range, making documentation easier to trace to the delivered product.

How a Custom Ventilation Duct Order Moves Through SULONG

The workflow below is what buyers should expect when moving from evaluation to execution.

1. Define the specification. The buyer provides diameter, section length, connection type, fabric weight, FR/FRAS or anti-static requirements, and duct form. Custom non-standard fabric specifications are discussed against minimum raw material batch sizes, and trial and prototype orders carry zero MOQ for specification validation.
2. Produce the fabric. Fabric is manufactured in-house at the specified gsm, with anti-static and flame-retardant properties added during coating or lamination.
3. Form and weld the duct. Flexible ducts are fabricated with seamless one-piece fish-back welding automation; spiral ducts are welded with spring steel wire for circular, oval, or rectangular cross-sections.
4. Install connections and end finishes. Zipper, Velcro, steel ring, or eyelet ends are fitted according to the site connection plan and the chosen connection type (steel rings, zippers, couplings).
5. Apply three-level quality control. SULONG implements 100% inspection in accordance with ISO 9001:2015: batch IQC checks on incoming materials, IPQC patrol inspections every two hours during production, and 100% FQC physical performance testing before shipment.
6. Complete pre-delivery inspection and documentation. Every batch is subject to 100% pre-delivery inspection; third-party inspections such as SGS and on-site acceptance checks are supported. Each batch ships with traceability documentation, Mill Test Certificates (MTC), and quality conformity labels.
7. Deliver and support. FOB, CIF, or DAP (door-to-mine-site) delivery terms are available. After-sales support includes 24/7 customer service, video-based technical diagnosis by specialists within 2 hours, global on-site engineer dispatch, bilingual installation and training manuals, and free replacement for production defects within the 12-month warranty period.

Use Cases: Custom Ducts in Real Underground Projects

The following project references show how customization and in-house production translate into project outcomes. Figures come from SULONG's project records.

Primary Forced Ventilation at the Buriticá Gold Mine

A global tier-1 mining conglomerate and EPC contractor uses SULONG ducts for primary forced ventilation and hazardous gas dilution at the Buriticá Gold Mine. The project includes an annual supply of 20 kilometers of ventilation ducting over 3 years. The 700 g/m² high-strength flame-retardant series features zero-leakage seamless construction and complies with SGS, ATEX, and NFPA 701 standards. The reported result was 100% stable, continuous operation with a zero defect and rejection rate.

Xi'an–Chengdu High-Speed Railway

For the Xi'an–Chengdu Railway Project, undertaken by China Railway 2nd Engineering Group and a key part of the national "Eight Vertical and Eight Horizontal" high-speed rail network, SULONG supplied 20 km of ventilation duct over 4 years. The project is one of the group's longest and most technically demanding tunnels at 19.68 kilometers, and the critical duct requirement was long-tunnel performance with a low air leakage rate.

Melbourne Metro Rail Project, Australia

1,500 mm diameter SULONG ventilation duct supplied for the Melbourne Metro Rail project.

The Melbourne Metro Rail Project includes a 9 km tunnel connecting the Sunbury and Dandenong railway route in Melbourne, Australia. SULONG has supplied 1,500 mm diameter ventilation ducts since 2019. The project required high flame retardancy, easy installation, and flexible large-diameter ducting that meets strict safety requirements for underground tunnel projects.

Trunk Road T2 Tunnel, Hong Kong

The Trunk Road T2 Tunnel is a key undersea road tunnel project on Hong Kong Route 6, approximately 3.4 kilometers long including about 2.1 kilometers of undersea tunnel, built with tunnel boring machines. SULONG supplied 5 km of flexible and spiral ventilation duct for temporary ventilation during construction. The project was completed within 2 years.

Guangxi Beibu Gulf Water Conservancy Project

A large-scale national water conservancy project in the Beibu Gulf region of Guangxi, undertaken by China Water Resources and Hydropower 14th Engineering Co., Ltd., used 30 km of SULONG ventilation duct over 3 years. The tunnels were driven with slurry balance shield tunneling machines to manage the region's water-rich and complex geology.

Comparison: Flexible vs. Spiral Ventilation Duct Customization

The table below compares the two main product families in SULONG's custom ventilation duct range, based on manufacturer specification data.

Tensile strength for flexible ducts ranges from 1,000 N to 4,200 N, a key parameter for long suspended lines where the fabric must carry its own weight plus airflow pressure.

FAQ: Custom Ventilation Duct Procurement

What certifications cover SULONG's custom ventilation ducts?

SULONG's production of PVC coated fabrics, PVC laminated fabrics, and ventilation ducts is ISO 9001:2015 certified (certificate ZCU23Q0002468R0S). The company also holds ISO 14001 and ISO 45001 management system certifications, CE marking, US NFPA 701:2015 and DIN 4102 B2 flame-retardant compliance, and test reports certified by Australian NATA laboratories. For explosive atmospheres, the EU ATEX Type Examination Certificate ECM 24 ATEX-B D091 covers 550 gsm to 800 gsm FR and FRAS fabric series used in underground coal mines, metal mines, and flammable gas explosion hazardous areas, in accordance with the 2014/34/EU ATEX Directive, EN ISO 80079-36, and EN ISO 80079-37.

Which ventilation duct specifications can be customized?

Diameter, section length, connection type, fabric weight, and performance properties can all be customized. Flexible ventilation ducts can be built from 200 mm to 3,200 mm in diameter with section lengths from 1 m to 300 m; spiral and semi-rigid ducts range from 200 mm to 2,800 mm with sections from 1 m to 20 m. Connection options include steel rings, zippers, and couplings, and end finishes include zipper, Velcro, steel ring, and eyelets. Custom fabric weight ranges from 210 gsm to 1,400 gsm, with FR or FRAS performance available. Duct forms include lay flat, oval, twin, tee, Y-piece, bend, adapter, semi-rigid, oval spiral, and rectangle.

What is the MOQ for custom ventilation duct orders?

SULONG applies flexible MOQ terms. There are no strict quantity restrictions for standard stock products or mining trial orders, and trial and prototype orders carry zero MOQ. Fully customized non-standard fabric specifications can be negotiated based on the minimum raw material batch sizes. Payment milestones, such as a 30/70 split, and volume-based tiered pricing can be aligned to the official purchase order requirements.

Can buyers request a sample or trial order before full production?

Yes. Trial and prototype orders carry zero MOQ, so project teams can validate fabric weight, connection fit, and flame-retardant, anti-static, or FRAS performance before committing to full production. SULONG also supports third-party inspections such as SGS and provides Mill Test Certificates and quality conformity labels with every batch. To request a sample or obtain a project-specific quotation, contact SULONG with your duct specification.

What is the lead time for custom ventilation ducts?

Standard custom orders require a lead time of 15 to 30 days. Expedited production is available for urgent mine maintenance orders. Monthly capacity exceeds 80,000 meters, and delivery terms include FOB, CIF, and DAP (door-to-mine-site). For time-critical projects, confirm current production slots with the SULONG team before finalizing the order.

Conclusion: Evaluate Custom Capability Before You Order

Custom ventilation ducts are more than longer or wider versions of catalog products. They require control over fabric formulation, welding quality, connection design, and compliance documentation, and that control depends on in-house manufacturing capability.

For buyers moving from evaluation to execution, the practical checklist is: confirm the customization range (diameter, length, fabric weight, connections), verify that production is in-house, check that certifications cover custom builds, and confirm MOQ and lead time against the project schedule. SULONG's in-house model — from PVC fabric to finished duct — is designed to meet these criteria, with project references in gold mines, high-speed rail, metro rail, undersea road tunnels, and water conservancy tunnels.

If your project requires a non-standard ventilation duct specification, the next step is to validate it against SULONG's production capabilities.

Request a quote, sample, or custom specification review.

Download the SULONG Ventilation Duct Catalog to review the product range, or contact Autumn Cui for a project-specific quotation.

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Tel: +86-18251952515 | Email: autumn@js-sulong.com | SULONG, No.9 Filter Material Industry Park, Funing, Yancheng, Jiangsu Province, China