Fan stall test service

Fan Stall Test Service – Accredited Assessment of Aerodynamic Stability, Surge Margin, and Performance Degradation for Industrial and HVAC Fans

For Belgian manufacturers, plant operators, energy managers, and quality engineers in the HVAC, power generation, chemical, and process industries, the aerodynamic stability of centrifugal and axial fans is a critical factor for operational reliability, energy efficiency, and equipment longevity. Fan stall – the sudden breakdown of smooth airflow due to excessive backpressure or flow obstruction – can cause severe vibrations, increased noise, motor overload, and even catastrophic impeller failure. Our ISO/IEC 17025 accredited laboratory offers a specialised fan stall test service that quantifies the stall onset point, the performance degradation, the surge behaviour, and the dynamic response of fans under controlled inlet and outlet conditions. With a custom‑built fan test rig, high‑speed pressure sensors, torque meters, and vibration analysers, we provide the data needed for safe operation, control system tuning, and design optimisation. Our BELAC‑accredited reports are recognised by the Belgian Federal Public Service (FOD Economie), notified bodies, and authorities under the Machinery Directive (2006/42/EC), the Energy‑related Products Directive (2009/125/EC), and national energy efficiency regulations.

Fans and Equipment We Regularly Test

We accept a wide range of fan types and sizes, from small axial fans (diameters below 200 mm) to large industrial centrifugal fans (diameters up to 2,000 mm). Our test rig is designed to handle various flow rates, pressures, and temperatures, and we can test both bare fans and complete fan assemblies with drives, inlet boxes, and outlet ducts. Common specimens include:

Centrifugal fans – forward‑curved, backward‑curved, radial‑blade, and aerofoil types.
Axial fans – fixed‑pitch, variable‑pitch, and vane‑axial configurations.
Mixed‑flow and diagonal fans – for medium‑pressure applications.
High‑pressure industrial fans – for pneumatic conveying and combustion air.
Exhaust and ventilation fans – for building services and tunnel ventilation.
Fan assemblies with silencers, dampers, and diffusers – to evaluate system effects.
Variable‑speed drive (VSD) fan systems – to study stall behaviour at different rotational speeds.
Multi‑stage fan units – for high‑pressure applications.

Performance Curve Measurement – Mapping the Flow‑Pressure Characteristic

The foundation of stall assessment is the accurate measurement of the fan's performance curve (volume flow versus pressure rise). Our fan stall test service follows the most recognised international and European standards to generate reliable performance data, including the unstable region beyond the stall point:

Performance test according to ISO 5801 (Industrial fans – performance testing using standardized airways) and AMCA 210, with Belgian NBN implementation – We install the fan in a test duct equipped with flow straighteners, settling screens, and a throttling device (a variable‑area cone or damper) to control the system resistance. We measure the volume flow using a calibrated nozzle or an orifice plate (ISO 5167), the static and total pressure rise across the fan using pressure tappings and precision manometers, the shaft torque and speed (with a torque meter and tachometer), and the electrical power input. We record data over a range of flow rates, from fully open (free delivery) to completely closed (shut‑off). The performance curve (flow vs. pressure, efficiency, and power) is plotted, and the stall point is identified as the peak of the pressure curve (the point where further reduction in flow causes a drop in pressure).
High‑resolution testing near the stall region – we take more data points in the vicinity of the expected stall point (typically 5‑10% of the peak pressure) to define the stall boundary precisely – We use small, incremental changes in the throttling device to capture the sharp transition between the stable and unstable regions.
Forward and backward sweep of the throttle – to detect hysteresis and to distinguish between the stall onset pressure and the recovery pressure – The stall point may be different when approaching from the high‑flow side compared to the low‑flow side. We perform both forward (decreasing flow) and backward (increasing flow) sweeps to identify any hysteresis loop.
Performance at different speeds – to evaluate the effect of rotational speed on the stall margin (fan laws) – We repeat the performance test at multiple speeds (typically 3‑5 speeds within the operating range) to generate a family of performance curves and to determine the speed‑dependent stall boundary.
Measurement of sound and vibration – in parallel with the performance test – to correlate stall with acoustic and mechanical indicators – We record sound pressure levels (dB(A), one‑third octave bands) and vibration levels (velocity, displacement) to identify the characteristic signatures of incipient stall.

Stall and Surge Detection – Dynamic Pressure and Flow Measurements

Stall and surge are dynamic phenomena characterised by rapid fluctuations in pressure and flow. Our advanced instrumentation captures these transient events with high fidelity, enabling precise stall identification:

High‑frequency pressure transducers (piezo‑resistive, response time < 5 ms) – installed at the fan inlet, outlet, and in the duct – to measure the unsteady pressure during stall – We sample pressure at rates up to 10 kHz and analyse the signal for characteristic stall signatures: periodic pressure pulsations (rotating stall) or large‑amplitude, low‑frequency oscillations (surge).
Hot‑wire anemometry and fast‑response flow visualisation – to detect flow reversal and recirculation at the impeller inlet – We use a hot‑wire probe to measure the instantaneous velocity at the inlet plane; the onset of stall is marked by a sudden drop in velocity and the appearance of reversed flow.
Fast‑response torque and power measurement – to detect the sudden change in aerodynamic load during stall – The shaft torque and motor power will drop sharply when the fan transitions from stable operation to stall. We record the torque and power simultaneously with pressure and flow, enabling correlation of the aerodynamic and mechanical responses.
Surge detection – by monitoring the pressure oscillations and flow reversals that occur when the fan operates in the deep stall region – Surge is characterised by violent, low‑frequency pressure pulsations (typically 1‑10 Hz) that can cause severe mechanical damage. We identify the surge boundary and provide the surge margin (the percentage difference between the operating point and the surge line).
Visualisation of rotating stall – using high‑speed pressure transducers arranged circumferentially around the inlet – to detect the propagation of stall cells – We place multiple sensors around the inlet circumference to measure the pressure field and to detect the rotating stall cells. The number of cells and their rotational speed are determined.

Stall Margin and Surge Margin Calculation – Defining the Safe Operating Envelope

The stall margin and surge margin are key parameters for control system design and operational safety. Our service provides these critical values, enabling you to establish safe operating limits:

Stall margin – defined as the difference between the actual pressure rise and the pressure rise at stall, expressed as a percentage of the stall pressure (or as a ratio of flow rates) – We calculate the stall margin for the design operating point using the measured performance curve and the stall boundary. A typical target for industrial fans is a stall margin of at least 10‑15%.
Surge margin – defined as the difference between the operating pressure and the surge pressure at the same flow, or as the distance between the operating point and the surge line on the performance map – We determine the surge line from the measured pressure‑flow data (the locus of points where the pressure oscillations become unstable) and calculate the surge margin for your specific operating conditions.
System line and operating point – we plot the measured fan performance curve together with the system resistance curve (based on your ductwork and fittings) to identify the actual operating point – If the system line intersects the fan curve near or beyond the stall point, we will advise on corrective measures (e.g., speed reduction, inlet guide vanes, or system modification).
Margin at variable speeds – for variable‑speed drives, we calculate the stall and surge margins across the entire speed range and identify the speeds where the margins become critical – We generate a 3D performance map (flow, pressure, speed) and highlight the safe operating envelope.

Dynamic Stability and Control System Validation

Fan stall is often triggered by rapid changes in system resistance (e.g., filter clogging, damper closure, or process variations). Our testing includes dynamic scenarios that simulate these transient events to validate control system response:

Transient stall test – we simulate a sudden increase in system resistance (by fast closure of the throttle valve) and record the fan's pressure, flow, torque, and speed response over time – We measure the time to stall, the amplitude of the pressure transient, and the recovery time when the resistance is restored. This data is used to set the control system response time and to evaluate the effectiveness of anti‑surge control algorithms.
Load‑rejection test – we simulate the loss of downstream flow (e.g., by opening a bypass valve) to assess the fan's response to a rapid decrease in load – This test is relevant for fans in parallel operation, where a sudden trip of one fan can cause a surge in the other.
Controller tuning support – we provide the measured dynamic data (pressure‑time, flow‑time, torque‑time) to assist in the tuning of PID controllers and anti‑surge systems – We can also recommend set‑point adjustments and alarm limits based on the test results.
Stall warning and protection – we evaluate the performance of stall detection sensors (e.g., pressure transmitters, vibration sensors) and the associated alarms and shutdown logic – We simulate stall events (by introducing a blockage or by throttling) and verify that the protection system activates within the required time.

Mechanical and Structural Effects – Vibration, Noise, and Stress

Stall and surge are not only aerodynamic events; they also impose significant mechanical loads on the fan structure, bearings, and motor. Our test service includes a comprehensive mechanical characterisation to assess the potential for damage:

Vibration measurement (ISO 10816, ISO 20816) – we measure the vibration velocity and displacement at the bearing housings and the fan casing during the performance test and stall test – We record the vibration spectrum (FFT) to identify the frequency components associated with stall (e.g., the blade‑passing frequency sidebands, the rotating stall cell frequency). A significant increase in vibration levels during stall indicates a risk of bearing damage or shaft fatigue.
Noise measurement (ISO 3744, ISO 3746) – we measure the sound power level (in dB) and the frequency spectrum to correlate stall with increased broadband noise – Stall is often accompanied by a distinct noise change (a roaring or pulsing sound). We quantify this and provide data for acoustic design.
Torque and stress analysis – we record the instantaneous torque and, if applicable, the blade bending moment (using strain gauges on the blade or shaft) to assess the fatigue loading during stall – The repeated torque spikes during surge can cause fatigue failure of the shaft or coupling. We provide a fatigue life estimate based on the measured load spectrum.
Transient speed measurement – we monitor the fan speed during stall and surge to detect fluctuations that could affect motor loading – Speed variations during surge can cause motor overheating and electrical instability.
Thermal monitoring – we measure the bearing temperature and the motor winding temperature during the stall test to ensure that the fan does not overheat under the increased aerodynamic load – Prolonged operation in stall can cause excessive heating and damage to the motor.

Environmental and Operational Conditioning

To reflect real‑world operating conditions, we offer the option to condition the test fluid (air) or to modify the intake and exhaust configurations:

Temperature conditioning – we heat or cool the inlet air to simulate the effects of ambient temperature on air density and fan performance – Changes in air density affect the pressure and power; we test at different inlet temperatures (e.g., 5°C, 25°C, 50°C) to provide performance data for seasonal variations.
Altitude simulation – we test with low‑density air (using a suction chamber) to simulate fan performance at high altitudes – The stall margin may change with altitude; our test rig can simulate atmospheric pressures down to 70 kPa.
Inlet and outlet configurations – we test the fan with different inlet elbows, dampers, and discharge conditions to evaluate the effect of installation geometry on stall behaviour – System effects (e.g., uneven flow distribution at the inlet) can trigger early stall. We provide recommendations for optimising the inlet and outlet conditions.
Dust and particulate loading – for fans in dirty environments, we introduce a controlled dust feed to study the effect of contaminant accumulation on the stall characteristics – The change in blade surface roughness and the build‑up of deposits can reduce stall margin; we quantify these effects.

Calibration, Accuracy, and Quality Assurance

All tests are performed under our ISO/IEC 17025:2017 accredited quality system, with full traceability of pressure, flow, torque, speed, and temperature measurements:

Calibration of pressure transducers, manometers, and flow measuring devices (nozzles, orifice plates) – according to ISO 5167 and ISO 17025 – We use certified reference pressure gauges and flow standards to achieve measurement uncertainties < 0.5% for pressure and < 1% for flow.
Calibration of torque and speed sensors – with traceable reference standards (ASTM E74, ISO 7500‑1) – The torque meter is calibrated with certified weights and a calibration arm; the speed sensor is verified with a calibrated tachometer.
Calibration of vibration and noise measurement systems – with reference shakers and acoustic calibrators (ISO 16063, IEC 60942) – We use a known vibration source and a sound level calibrator to ensure accurate readings.
Verification with reference fans – we regularly test a reference fan with well‑documented performance to validate the test rig and the measurement procedures – The reference fan results are compared with the manufacturer's data and with previous tests to confirm repeatability.
Interlaboratory comparison (ILC) – we participate in proficiency testing programmes for fan performance testing – Our results are regularly compared with those of other accredited laboratories to ensure consistency.

Compliance with Belgian and European Regulations

Our fan stall testing services support your conformity assessment under the relevant European directives and Belgian regulations for machinery, energy efficiency, and safety:

Machinery Directive (2006/42/EC) – for industrial fans and ventilation systems – The stall test provides essential data for the risk assessment, ensuring that the fan will not operate in an unstable regime that could cause hazardous mechanical failure. Our reports are accepted by Belgian notified bodies.
Energy‑related Products Directive (ErP, 2009/125/EC) – for the energy efficiency of fans – The performance curves obtained from the test, including the stall region, are used to determine the fan efficiency and the compliance with the EU regulation 327/2011 (fan efficiency requirements).
ATEX Directive (2014/34/EU) – for fans used in potentially explosive atmospheres – Stall can cause friction, sparks, or overheating; our test data helps verify that the fan can be operated safely under all flow conditions.
Belgian environmental and building regulations – for ventilation and air conditioning systems in buildings – The proper characterisation of the fan's operating range, including the stall margin, ensures that the fan can meet the required flow and pressure under all operating conditions.
ARAB (General Regulation on Occupational Safety) – for the safe operation of fans in industrial installations – Our test results help define safe operating limits and protect workers from the effects of fan failure.

Reporting and Accreditation

All fan stall tests are performed under our ISO/IEC 17025:2017 accredited quality system, with full traceability of all measurement chains. Our BELAC‑accredited reports are recognised by the FOD Economie, Belgian notified bodies, and European authorities. Each report includes:

A complete description of the fan, the test setup, and the test conditions.
The performance curve (flow vs. pressure, efficiency, and power) for the full operating range.
The identified stall point (pressure and flow) and the stall margin.
The surge boundary and surge margin.
The dynamic pressure and flow data during stall (pressure‑time, flow‑time).
Vibration and noise measurements during stable operation and during stall.
Torque and power data – for mechanical load assessment.
Statistical summary of repeated tests (if applicable).
Calibration certificates for all instruments.
A professional conclusion on the aerodynamic stability of the fan and recommendations for the safe operating range, control system settings, and any necessary design modifications.

Our reports provide the confidence you need to certify your fans, optimise their operation, and ensure safe and reliable performance.

Why Choose Our Fan Stall Test Service?

We understand that fan stall is often a hidden risk that can cause significant downtime, damage, and energy inefficiency. Our service provides not only the stall point but also the entire performance map, enabling you to select the right fan for your system, to set appropriate control parameters, and to avoid the costly consequences of operation near the unstable region. Our team offers rapid scheduling, flexible test programmes (from simple single‑speed tests to complex multi‑speed and transient studies), and clear, actionable interpretation of results – we do not simply deliver a pressure‑flow curve; we explain the aerodynamic and mechanical implications, we highlight the safe operating margins, and we provide practical recommendations for improving stability and efficiency. We work closely with your fan manufacturers, system designers, and plant operators to tailor the test programme to your specific application and operational needs. With state‑of‑the‑art test rigs, high‑speed instrumentation, and extensive experience in fan aerodynamics, our fan stall test service delivers the accuracy, reliability, and regulatory acceptance you need to ensure the stable and efficient operation of your fans in the Belgian and European industrial landscape. Contact us to discuss your fan types, operating conditions, and test objectives – we will develop a tailored test plan that provides the definitive assessment of your fan's aerodynamic stability.