Air flow resistance test

Professional Air Flow Resistance Testing Services – Accredited to ISO/IEC 17025

Air flow resistance, often expressed as pressure drop or differential pressure, is a critical performance parameter for filtration media, ventilating grilles, porous ceramics, and other air‑handling components. Our laboratory offers comprehensive air flow resistance testing under controlled conditions, covering a wide range of materials and complete assemblies. All tests are conducted in accordance with internationally recognised standards and are covered by our ISO/IEC 17025 accreditation (CNAS‑approved). Whether you are a manufacturer, importer, or end‑user, our precise measurements help you optimise product design, verify compliance with local and export regulations, and ensure energy‑efficient operation in heating, ventilation, and air conditioning (HVAC) systems, cleanrooms, and industrial exhaust networks.

Product Samples We Regularly Test

Our laboratory accepts a diverse array of products for air flow resistance evaluation. Typical samples submitted by our clients include:

• Fibrous filter media – non‑woven fabrics, glass fibre papers, melt‑blown polypropylene, and electrospun nanofibre layers, both flat sheets and pleated configurations.
• Rigid porous materials – sintered metal filters, ceramic foam filters, porous plastic sheets, and honeycomb monoliths.
• Complete filter assemblies – panel filters, bag filters, V‑bank filters, HEPA/ULPA filters, and carbon‑impregnated gas‑phase filters.
• Ventilation and exhaust components – louvres, grilles, diffusers, duct silencers, and demister pads.
• Protective masks and respirator elements – melt‑blown layers for personal protective equipment (PPE).
• Automotive cabin filters and engine intake filters – both dry and wet‑type (oil‑soaked) filters.

Core Testing Methods for Fibrous Filter Media and Flat Sheets

For flat or pleated media samples, we measure the relationship between face velocity and pressure drop using a custom‑built test rig. The following parameters and standards apply:

• Pressure drop versus face velocity curve – tested over a velocity range from 0.1 to 5.0 m/s (or as specified). The differential pressure is measured using a precision capacitance manometer (±0.25% full scale) according to ISO 16890‑2 (Air filters for general ventilation – Part 2: Measurement of fractional efficiency and air flow resistance). We report the initial resistance at rated flow (e.g., 0.5 m/s) and provide polynomial curve‑fitting coefficients for engineering design.
• Resistance after dust loading (clogging test) – synthetic dust (e.g., ISO 12103‑1 A2 fine test dust) is fed into the upstream airstream at a controlled rate; the pressure drop is continuously recorded until a predefined final resistance (typically 2× or 3× initial resistance) is reached. The test follows ASHRAE Standard 52.2 or ISO 16890‑4 for general ventilation filters, and we report the dust‑holding capacity and the evolution of resistance.
• Effect of temperature and humidity – the test chamber is equipped with heaters and a humidifier to evaluate resistance changes under hot or moist conditions (up to 70°C and 95% RH). Measurements are taken per ISO 5221 and internal procedures, with results corrected to standard atmospheric conditions (20°C, 101.3 kPa).
• Anisotropy assessment – for non‑woven media, we test resistance in both the machine direction (MD) and cross direction (CD) to detect directional variability; tests are performed on multiple specimens using a circular clamp fixture with an exposed area of 100 cm².

Core Testing Methods for Complete Filter Assemblies and Ducted Components

For installed filters, housings, and grilles, we perform air flow resistance tests in a full‑scale wind tunnel that simulates actual operating conditions. The following procedures are applied:

• Overall pressure drop at nominal flow rate – the filter is mounted in a standard duct section (rectangular or circular) with straight lengths upstream and downstream to ensure fully developed flow. The differential pressure between upstream and downstream static pressure tappings is measured using a multi‑channel pressure scanner. We follow EN 1822‑5 (for HEPA/ULPA) or ISO 16890‑3 (for general ventilation) to determine the resistance at the filter’s rated airflow (m³/h) and at 50%, 75%, and 125% of that rate.
• Leakage and bypass check – using a tracer gas (SF₆) or aerosol photometer, we verify that the measured resistance is not affected by internal bypass leaks. This is particularly important for bag filters and rigid cartridge filters, as per ISO 29461‑1 (Air intake filters for rotary machinery).
• Resistance uniformity across the face area – for large filters, we traverse the upstream and downstream planes with a Pitot probe array (according to ISO 3966) to check velocity distribution; non‑uniform flow can cause misleading pressure drop readings. We report the velocity uniformity index and correct the measured resistance if needed.
• Dynamic resistance under pulsating flow – for engine air filters and pulse‑jet cleaned filters, we apply cyclic flow (frequency up to 10 Hz) using a controlled fan with a variable‑speed drive, measuring instantaneous pressure drop with high‑speed transducers (1 kHz sampling) to evaluate the damping characteristics and average resistance, in line with ISO 5011 (for air cleaners for internal combustion engines).

Core Testing Methods for Porous Rigid Materials and Specialty Components

For ceramic foams, sintered metals, and honeycomb structures used in high‑temperature or corrosive environments, we adapt our test rig with appropriate seals and heating elements. Key test items include:

• Darcy permeability and Forchheimer coefficient – by measuring pressure drop across the sample at multiple flow rates (ranging from laminar to turbulent regimes), we fit the data to the Darcy‑Forchheimer equation. The test is conducted per ASTM D6539 (Standard Test Method for Measurement of Pneumatic Permeability of Partially Saturated Porous Materials) and ISO 17312 (for ceramic filters). We report both viscous and inertial resistance parameters.
• Thermal resistance variation – for samples intended for hot gas filtration (e.g., diesel particulate filters), we perform measurements at temperatures up to 300°C, with the test section enclosed in an electrically heated oven. Pressure drop is recorded at each temperature after thermal stabilisation, following guidelines from ISO 15579 (for metallic porous materials).
• Compressibility effect – for soft porous materials, we apply different clamping torques and measure the corresponding resistance change, thus providing a correction factor for installation conditions. This is done in accordance with ISO 4003 (for bubble point and porosity) adapted for resistance.
• Chemical ageing impact on resistance – after exposure to acid, alkaline, or solvent aerosols, we re‑measure the air flow resistance to assess structural degradation, using our standard resistance protocol as a before‑after comparison.

Report Accreditation and Regulatory Compliance

All air flow resistance tests described above are performed within the scope of our ISO/IEC 17025 accreditation, with full traceability to national and international reference standards (including NIST‑traceable pressure calibrations). Our test reports provide detailed raw data tables, graphical curves, calculated resistance coefficients, and a clear statement of conformity to the specified acceptance criteria. The reports are accepted by regulatory bodies worldwide, including the US EPA, EU CE marking authorities, and national standards agencies such as ANSI, BSI, and DIN, as well as by procurement departments in the HVAC, automotive, and cleanroom industries. We also support clients with product certification under Eurovent 4/11, ASHRAE 52.2, and ISO 16890 energy labelling requirements. For export shipments to Latin American markets, including Chile, our reports are recognised by the local import authorities when accompanied by a Spanish translation and official accreditation certificate, which we provide upon request. Every test is backed by a rigorous quality management system, ensuring that your products meet the highest performance and safety standards.