QIYUE FAN · TECHNICAL ARTICLES
Industrial Fan Airflow And Pressure Explained
Two Impeller Flow Directions
These descriptions distinguish the flow through the impeller. They do not compare pressure capability, airflow capacity or efficiency.
Centrifugal
Inlet: toward the impeller eye, generally along the shaft axisImpeller: flow turns outwardDischarge from the impeller: radial, away from the shaft axis
The casing then collects and directs the flow. The final casing outlet direction is not the same thing as the flow direction at the impeller exit.
Axial
Inlet: generally along the shaft axisImpeller: air passes through the blade rowDischarge from the impeller: generally along the shaft axis
“Axial” describes the general through-flow direction. It does not imply that the discharge has no swirl or that every axial fan has the same performance.
In This Guide
Selection Basics
Four Values That Must Be Read Together
Airflow, pressure, operating point and motor power are not independent values. They are part of the same fan-selection decision.
01 · Airflow
How Much Air Must Move
Usually expressed in m³/h, m³/s or CFM. It must match the ventilation, cooling, combustion or dust-capture demand.
02 · Pressure
Resistance the Fan Must Overcome
Ducts, elbows, filters, collectors, silencers, dampers and outlets create resistance.
03 · Operating Point
Airflow + Pressure Together
State airflow and pressure together, such as 18,000 m³/h at 2,400 Pa, then check every required operating case and the permitted range.
04 · Motor Power
Confirmed After Fan Curve
Motor power is checked after duty point, fan speed, efficiency and suitable margin are established.
Basic Definition
What Does Airflow Mean in Industrial Fan Selection?
Airflow is gas volume per unit time. State whether the value is actual volume at the fan inlet condition or a reference-condition volume; record temperature, pressure and gas composition needed to relate the bases. In industrial projects, airflow may be required for workshop ventilation, dust extraction, boiler combustion air, drying ovens, cooling systems, tunnel ventilation or chemical exhaust.
Airflow should be calculated from the process demand instead of simply choosing the largest fan. Too little airflow may fail to remove dust, heat or gas. Too much airflow may increase noise, power consumption, duct velocity and filter load.
Typical Units
m³/h · m³/s · CFM
Workshop ventilation
Often derived from air-change or process demand.
Dust extraction
Based on capture velocity and hood/process demand.
Boiler / process air
Based on combustion or production requirements.
Pressure Definition
What Does Fan Pressure Mean?
Fan pressure describes pressure rise across defined fan boundaries. Ducts and connected equipment contribute losses; compare the system requirement and fan rating using the same pressure definition and installation boundary.
Static Pressure
Fan Static Pressure
Fan total pressure minus fan outlet velocity pressure. It is not simply the difference between inlet and outlet static readings.
Velocity Pressure
Air-Speed Component
Related to air velocity in the duct or outlet and changes with duct area.
Total Pressure
Static + Velocity Pressure
At one section, total pressure combines static and velocity pressure. Fan total pressure is outlet total pressure minus inlet total pressure; do not confuse a section value with the rise across the fan.
Need the exact terminology? Read Static Pressure vs Total Pressure. If no pressure value is available yet, continue with Static Pressure Unknown.
Selection Rule
Airflow and Pressure Must Be Matched at the Same Operating Point
Maximum airflow and maximum pressure are not a usable duty pair. For a stated configuration, speed and gas density, a steady operating point is found from the fan and system curves on consistent bases, within the permitted stable range. Changing speed, controls or system conditions changes this review.
01
Required Airflow
m³/h or CFM demand
02
System Resistance
duct + filter + outlet
03
Fan Curve
model + speed + pressure
04
Working Point
real airflow and pressure
Example: 18,000 m³/h at 2,400 Pa is one operating point. It is not enough to check 18,000 m³/h alone. Use the Fan Performance Curve guide to confirm the actual working point.
Application Review
Different Systems Need Different Airflow and Pressure Balance
The same airflow can lead to a different fan direction when duct resistance, filtration, temperature or process equipment changes.
Swipe the table sideways to view all columns.
| Application | Airflow Focus | Pressure Focus | Fan / Selection Path |
|---|---|---|---|
| Workshop Ventilation | Large air exchange volume | Low to medium resistance | Axial Flow Fans |
| Dust Collection | Capture airflow at hoods | Duct + filter resistance | Dust Collection Fans |
| Baghouse System | Stable capture airflow | Loaded-filter pressure drop | Baghouse Fan Selection |
| Boiler Draft | Combustion air or flue-gas volume | Furnace and flue resistance | Boiler Fans |
| Long Duct System | Process airflow requirement | Higher friction and elbow loss | Centrifugal Fans |
Common Mistakes
Common Airflow and Pressure Mistakes
Mistake 01
Selecting by Maximum Airflow
Maximum airflow is usually measured at very low resistance and does not represent real duct operation.
Mistake 02
Ignoring Filter Resistance
Dust collectors, bag filters and scrubbers can dominate total system resistance.
Mistake 03
Mixing Static and Total Pressure
The project pressure basis and fan curve pressure basis must be confirmed before model comparison.
Technical Next Steps
Continue by Selection Topic
Move from basic airflow and pressure understanding into pressure basis, operating point, motor power and full project review.
Main Selection Route
Industrial Fan Selection Center →
Organize airflow, pressure, medium, temperature, installation and electrical data.
Pressure Basis
Static Pressure vs Total Pressure
Avoid mixing pressure definitions in fan selection.
Missing Data
Static Pressure Unknown
Continue from duct, equipment and resistance information when pressure is missing.
Power
Industrial Fan Power Calculation
Estimate shaft and motor power after the duty point is established.
FAQ
FAQ About Industrial Fan Airflow and Pressure
Can I select a fan by airflow only?
No. Airflow must be matched with pressure at the same operating point. A fan with enough airflow at low pressure may fail in a high-resistance duct system.
Why does airflow drop after installation?
A common reason is underestimated system resistance. Long ducts, elbows, dampers, filters, dust collectors or outlet stacks can reduce the actual airflow.
Is static pressure the same as total pressure?
No. At a duct section, total pressure is static plus velocity pressure. Across a fan, fan total pressure is the difference in total pressure, while fan static pressure is fan total pressure minus fan outlet velocity pressure. Match the project and rating definitions.
Should baghouse filter resistance be included?
Yes. For baghouse dust collection systems, filter resistance and loaded-filter pressure drop should be included in the pressure review.
Which fan is better for high pressure?
Centrifugal fans are commonly reviewed for duct systems, dust collectors and higher-resistance applications. Axial fans are usually used for larger airflow and lower pressure ventilation.
What information should I send to QIYUE FAN?
Send airflow, static pressure or total pressure, duct layout, filter resistance, working medium, temperature, dust or corrosion condition, voltage, frequency, outlet angle and quantity.
Technical reference: ASHRAE Handbook, Fans: terminology and pressure definitions. The conceptual diagram is not a performance rating.
Send Your Operating Conditions
Airflow, pressure, gas medium, temperature, voltage and quantity.