Flexible air duct purchase must ask 7 questions: engineers will not tell you screening logic
2025-03-04
Why do professional buyers screen suppliers by these 7 questions?
There is a serious information asymmetry in the performance parameters of flexible ducts:
- Similar products claimed to be “high temperature resistant 120℃”, but deformed at 60℃ in the actual test.
- “CE marking” may only refer to the compliance of packaging materials, not the duct itself.
- Confusing fire rating labeling (BS 476? EN 13501? NFPA 260?).
This article provides a questioning system validated by ASTM/ISO test methodology to help you get to the real performance of your product.
Essential Question 1: How is the temperature range verified? Look at the TGA curve or manufacturer's dictation?
Technical Analysis
Key Indicators:
- Glass transition temperature (Tg): the critical point at which the material starts to soften
- Temperature of heat loss (Td₅%): the temperature at which 5% of the mass is lost (measured value should be > nominal temperature resistance)
Validation Methods:
- Require manufacturers to provide TGA (Thermogravimetric Analysis) report, compared to the ASTM E1131 standard curve.
- Be wary of the “instantaneous temperature resistance” word game, need to clarify the continuous operating temperature range.
Essential Question 2: What international standards do the fire ratings correspond to? How to convert?
Global Mainstream Standards Comparison Table
| Area | Standard | Grade Definition | Equivalent conversion formula |
| European Union | EN 13501-1 | A2-s1,d0 (highest grade) | s1=Smoke density ≤ 50% |
| North America | UL 94 | V-0 (self-extinguishing within 2 seconds from fire) | Correlation test with UL 723 radiant flux |
| China | GB 8624 | B1 (flame retardant) | Additional rating for smoke production toxicity |
Pit Avoidance Guide: Requirement of SBI (Single-Body-Ignition Test) Reports from Third-Party Laboratories
Essential Question 3: What are the hidden terms behind the certification mark?
In-depth interpretation of the certificate highlights
Global Mainstream Standards Comparison Table
| Type of Certification | Key Test Items | Overlooked qualifications |
| UL 181 | Flame spread ≤25 | Only for pipe diameter ≤254mm |
| CE CPR | Continuous burning ≤150mm | Evaluation of joints is not included |
| FMVSS 302 | Burning rate ≤100mm/min | Tested in horizontal position only |
Recommendation for action: Require vendors to provide a scanned copy of the “Scope of Application” page of the certification.
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