Collapse Margin
Fan static pressure, diameter and duct length determine how much radial support is needed. Larger diameters or stronger suction may require a tighter pitch, heavier wire or shorter sections.
Flexible Extraction Duct Systems
Negative Pressure / Spiral Ventilation Duct
Custom wire-supported flexible ducting for mine and tunnel extraction, dust collection, fume removal, portable blowers and industrial exhaust routes. DERFLEX coordinates the coated textile body, helix reinforcement, wear protection, connection and suspension as one finished assembly.
Finished Product, Not Fabric Only
Duct wall, helix support, wear strip, end cuff and suspension details are configured for the intended airflow route.
A Flexible Exhaust Route Built Around the Fan, Contaminant and Installation
A negative pressure ventilation duct carries contaminated or unwanted air toward an extraction fan, dust collector, filtration unit or discharge point. Typical media include dust-laden air, welding fumes, smoke, diesel exhaust, heat and process vapors. Because the pressure inside the duct is lower than the surrounding atmosphere, an unsupported textile tube can flatten and restrict airflow.
A spiral ventilation duct addresses this problem with a continuous steel helix or closely spaced support structure. The reinforcement keeps the cross-section open, while a flexible PVC-coated textile wall provides an airtight passage that can follow temporary or changing routes. The selection is not based on diameter alone: suction level, total run, bends, air temperature, contaminants, movement frequency and acceptable pressure loss all affect the finished construction.
DERFLEX approaches each order as a duct assembly rather than a roll-material transaction. Material grade, wire diameter, pitch, external abrasion strip, seam method, suspension and coupling geometry are reviewed together. This supports more consistent fit-up at the fan, easier section replacement and clearer repeat-order specifications for contractors, equipment builders, distributors and industrial users.
Start With System Data
Four Decisions That Shape a Reliable Spiral Exhaust Duct
These decisions should be confirmed before fabric weight, color or packaging is finalized.
Pressure-Loss Control
Sharp bends, compressed sections, undersized diameters and poorly matched cuffs add resistance. Route planning and internal smoothness matter to airflow as much as nominal duct size.
Contaminant Compatibility
Dust, moisture, oil mist, fumes, temperature and chemical exposure influence coating formulation, cleanability, seam choice and optional surface treatments.
Field Handling
A suspended line, floor-laid hose and frequently relocated duct do not wear in the same way. Contact zones, lifting points and section lengths should match actual site practice.
← AIR
Material & Construction
Every Layer Has a Different Job
Coated Textile Body
High-tenacity polyester with a PVC coating forms a flexible, weldable and cleanable air barrier. Fabric weight and coating formulation are selected according to pressure, wear and environmental exposure.
Helix Reinforcement
Continuous spring-steel support maintains the duct opening under suction. Wire gauge and pitch influence collapse resistance, bend radius, compressed length, handling weight and cost.
Wear Protection
An external strip can cover the wire path or reinforce identified contact zones. This is useful where the duct touches tunnel walls, floors, machinery or repeated lifting points.
Connection & Suspension
Zipper, hook-and-loop, ring, clamp or soft-cuff systems are coordinated with the airflow direction and equipment connection. Suspension may use single or double lines, tabs, loops or eyelets.
Reference Specification
Custom Negative Pressure Spiral Ventilation Duct Options
The table is a quotation guide rather than a universal rating. Final values are confirmed against the fan curve, route and required test criteria.
| Item | Reference Options | Selection Consideration |
|---|---|---|
| Product Form | Finished flexible suction / exhaust duct with formed body, spiral support, suspension and specified end connections | Clarify whether the inquiry is for a complete duct or PVC duct fabric by the roll. |
| Body Material | PVC-coated high-tenacity polyester textile; application-specific coating and surface finish | Match to pressure, abrasion, humidity, contaminants, temperature and cleaning method. |
| Material Weight | Approximately 450–800 g/m2 reference range for selected ventilation fabric constructions | Weight alone does not define suction performance; reinforcement and finished assembly design are equally important. |
| Nominal Diameter | 300–3000 mm project reference range | Final availability depends on negative pressure, wire design, section length, transport and handling requirements. |
| Section Length | Custom; 5 m and 10 m are commonly requested, with other lengths reviewed by project | Shorter sections simplify routing and replacement; longer sections can reduce connection count. |
| Spiral Support | Continuous spring-steel wire; wire diameter and pitch configured to duty | Tighter pitch increases support but can increase stiffness and weight. Wider pitch improves flexibility but provides less support per metre. |
| Coupling Options | Zipper, hook-and-loop cuff, ring-to-ring, clamp cuff, soft cuff or equipment-specific connection | Review installation speed, leakage control, airflow direction, fan outlet and replacement practice. |
| Suspension | Single or double line; reinforced tabs, loops, eyelets or project hardware | Diameter, section weight, route geometry and site support spacing influence the design. |
| Wear Protection | Optional external strip over the helix path and local reinforcement at cuffs or contact zones | Recommended for floor contact, dragging, wall contact or frequent relocation. |
| Color & Marking | Orange, yellow, black and project colors; OEM logo, direction arrows, section ID and packing marks | Availability depends on material grade, order quantity and confirmed artwork. |
| Optional Treatments | Flame-retardant, antistatic, anti-cold, anti-mildew, anti-UV or selected chemical-resistance formulations | State the exact standard, test method, acceptance value and required documentation before sampling. |
| Pressure Rating | Confirmed by project rather than represented by one generic value | Provide fan static pressure, airflow, total run, bends, temperature and duct orientation. |
Engineering note: the listed values are reference configuration ranges and do not constitute a performance guarantee. Production specifications, tolerances, test methods and documentation should be confirmed in the approved sample or order contract.
Procurement Guide
Match the Construction to the Extraction Route
A useful RFQ describes the system duty and installation, not only the required diameter.
Construction Logic by Site Condition
| Higher suction or larger diameter | Review tighter wire pitch, higher radial support, shorter sections and more robust suspension. |
| Frequent relocation | Balance support with compressibility; add wear protection and define lifting or dragging points. |
| Multiple bends | Use shorter sections where practical and avoid excessive compression that reduces the effective internal area. |
| Dust-heavy extraction | Prioritize smooth inner surfaces, cleanable construction, leakage control and replaceable sections near collection points. |
| Underground or hazardous zone | Confirm flame-retardant and antistatic requirements using named standards and acceptance criteria. |
| Equipment integration | Provide fan outlet diameter, flange or clamp geometry, photos and allowance for vibration or movement. |
Applications
Extraction Ducting for Underground, Industrial and Mobile Systems
Each application is configured around the fan, contaminant, route and handling conditions.
Mine Heading Exhaust
Local extraction of dust, diesel emissions, blasting fumes and heat from development headings or changing work zones.
Tunnel Construction
Temporary negative-pressure routes connected to fans, filtration equipment or dust collectors during excavation and lining work.
Dust Collection
Flexible connections for crushing, drilling, cutting, sanding and material-handling processes where rigid ducting is impractical.
Welding & Fume Extraction
Move smoke and process fumes from temporary workstations, tanks, fabrication areas and confined industrial spaces.
Portable Fan Systems
Collapsible hose assemblies for maintenance, emergency ventilation, equipment cooling and mobile extraction packages.
Shipyard & Confined Space
Temporary suction or supply lines for holds, tanks, engine spaces and enclosed work areas, subject to the required material and safety specification.
Product & Site Views
DERFLEX Ventilation Duct References
Actual DERFLEX product and application images are used below. Final construction is based on the confirmed project specification.
Manufacturing & Quality
Control the Details That Affect Fit, Leakage and Repeat Orders
Quality requirements should be written into the approved specification so inspection is based on measurable criteria.
Material Verification
Confirm fabric grade, coating, color, weight, finish and any specified flame or antistatic treatment.
Dimension Check
Measure diameter, section length, wire pitch, cuff size and suspension spacing against the order drawing.
Seam & Reinforcement
Inspect welded seams, wear-strip placement, support continuity and local reinforcement at high-stress zones.
Coupling Fit
Check zipper, ring, clamp or soft-cuff geometry against mating sections and equipment-side dimensions.
Order Traceability
Record approved artwork, packing, test requirements and critical configuration details for repeat production.
Related DERFLEX Resources
Continue From Exhaust-Duct Selection to Material and System Planning
Six related pages connect the finished duct with underground ventilation, fabric selection and alternative airflow configurations.
Finished Duct
Spiral Wire-Reinforced Ventilation Duct
Review the broader positive, negative and reversible-duty finished duct configuration.
Mine & Tunnel
PVC Flexible Ventilation Ducting
See a finished-product overview for mine and tunnel airflow applications.
System Formats
Mine and Tunnel Ventilation Ducting
Compare high-pressure, low-headroom and wire-reinforced duct concepts.
Material Engineering
PVC Fabric for Tunnel Ventilation Duct
Understand fabric structure, airtightness, abrasion and processing requirements.
Fabric Supply
Mine Ventilation Ducting Material
Review coated-fabric characteristics for underground ventilation production.
Selection Guide
Choosing PVC Fabric for Mining Ventilation
Compare the performance factors that influence a mine-duct material specification.
FAQ
Negative Pressure Spiral Ventilation Duct Questions
Answers for project engineers, mine and tunnel contractors, distributors and ventilation equipment manufacturers.
What is the difference between a negative pressure duct and a positive pressure duct?
A positive-pressure layflat duct is inflated by air pushed from a fan. A negative-pressure duct carries air toward an extraction fan, so atmospheric pressure pushes inward on the wall. Spiral or ring reinforcement is therefore used to resist collapse and preserve the airflow passage.
Why does a spiral ventilation duct need steel-wire reinforcement?
The helix provides radial support along the duct length. Without that support, a flexible textile wall may flatten under suction. Wire diameter and pitch are selected according to pressure, duct diameter, bend requirements, handling and section length.
Can one spiral duct be used for both suction and forced-air ventilation?
Some project-configured spiral ducts can operate in both directions, but the complete system must be reviewed. Fan pressure, couplings, seams, suspension and the possibility of airflow reversal should be confirmed before production.
How should the duct diameter and wire pitch be selected?
Diameter is chosen from required airflow, velocity, total run, bends and allowable pressure loss. Wire pitch is then matched to suction level, diameter and flexibility needs. A tighter pitch generally increases support and stiffness; a wider pitch improves flexibility but provides less support per metre.
Are flame-retardant and antistatic versions available?
Optional flame-retardant and antistatic material grades can be reviewed. The inquiry should state the required standard, test method, acceptance value and documentation so DERFLEX can confirm a suitable construction and testing plan.
What information is required for a quotation?
Please provide fan model or fan curve, airflow direction, static pressure, duct diameter, total run, section length, bends, temperature, extracted contaminant, installation method, coupling preference and any required safety standard. Connection photos or drawings are useful.
Configure a Negative Pressure Duct Around Your Extraction System
Send DERFLEX the fan data, route sketch, operating environment and connection dimensions. The team can review material, wire support, section length, coupling, suspension and OEM details for a project-specific quotation.
Recommended RFQ Attachment
Fan datasheet or curve, route sketch, duct diameter, required section length, equipment connection photos and named test standard.
Request A Quote from DERFLEX
Product configurations, reference ranges and performance statements are subject to final technical review, approved samples, production tolerances and confirmed order specifications.