Centrifugal Fan Drive Arrangements Explained: A, B, C, D, E and F Types
Drive arrangement defines how the motor, impeller, shaft, bearings and transmission are assembled. This guide explains A–F centrifugal fan drive and support types, while also introducing commonly referenced numbered fan arrangements such as Arrangement 1, 3, 4, 7, 8, 9 and 10.
Get Fan Selection Support View Centrifugal FansThese systems are related, but they are not automatically interchangeable. Always confirm the approved fan drawing before production.
What Does Centrifugal Fan Drive Arrangement Mean?
In a centrifugal fan, the drive arrangement describes how the motor drives the impeller and how the shaft, bearings, pulleys or coupling are positioned. Two fans may have similar airflow and pressure but require different mechanical structures because of speed, temperature, dust loading, motor power, foundation and maintenance conditions.
For example, a model such as 4-72 No.10D may use a letter to indicate a drive form. Numbered terms such as Arrangement 1, Arrangement 3 or Arrangement 10 describe another type of mechanical-layout classification. The exact structure should always be confirmed with the fan series and approved general arrangement drawing.
Belt ratios can adjust fan speed, while direct and coupling layouts are more closely related to motor and fan shaft speed.
Overhung and center-hung wheel arrangements create different shaft, bearing, vibration and foundation requirements.
Belts, bearings, couplings and motors require different inspection, adjustment and removal space.
Motor position, duct direction, outlet angle and base dimensions must fit the installation site.
Quick Comparison of A, B, C, D, E and F Types
In this guide, A–F are used as manufacturer or fan-series terminology for mechanical drive and support features, not airflow direction. They should not be treated as universal AMCA numbered arrangement codes. Exact meanings can vary between fan series, so the following descriptions are practical selection references rather than a substitute for an approved drawing.
A–F drive terminology is only one part of centrifugal fan arrangement selection. Numbered arrangements such as Arrangement 1, 3, 4, 7, 8, 9 and 10 describe mechanical and bearing configurations using another classification system.
Common Centrifugal Fan Arrangements 1, 3, 4, 7, 8, 9 and 10
Centrifugal fan arrangements are also frequently described using numbered mechanical layouts. These numbers help identify the relationship between the wheel, shaft, bearings, motor and transmission. They are useful when comparing replacement fans, bearing configurations and industrial fan drawings.
Important terminology note: numbered centrifugal fan arrangements and A–F manufacturer drive codes should not be treated as a direct one-to-one conversion. Use the model drawing, bearing layout and supplier standard as the final reference.
Arrangement 1 Fan – Overhung Wheel
Arrangement 1 normally uses an overhung wheel mounted on a separate fan shaft supported by bearings. A belt-driven configuration is common, with the motor installed separately from the fan bearing pedestal. Final bearing and pulley positions depend on the fan design.
Arrangement 3 Fan Bearing Configuration
In an Arrangement 3 fan bearing configuration, the centrifugal fan wheel is generally positioned between two bearings. This center-hung support provides shaft stability and is commonly considered for larger wheels, higher mechanical loads or applications requiring robust bearing support.
Arrangement 4 Fan – Direct Motor Drive
Arrangement 4 commonly places the centrifugal fan wheel directly on the motor shaft. The compact layout eliminates a separate fan shaft and external fan bearings, but motor speed, shaft loading, temperature and maintenance access must be considered carefully.
Arrangement 7 Fan Bearing and Coupling Layout
Arrangement 7 generally uses an overhung fan wheel with independent fan bearings and a direct connection between the fan shaft and motor through a coupling. Shaft alignment, coupling guard, bearing position and base rigidity are important design checks.
Arrangement 8 Fan Bearing Configuration
Arrangement 8 is another independently supported centrifugal fan configuration in which the fan shaft and bearings are separated from the motor. A direct coupling is typically used between the motor and fan shaft, while the exact arrangement 8 fan bearing layout should be confirmed from the approved drawing.
Arrangement 9 Fan Bearing and Motor Base Layout
Arrangement 9 generally uses an overhung fan wheel and independent fan bearings with a belt drive. The motor is commonly mounted as part of the fan assembly, creating a more integrated installation while retaining adjustable fan speed through pulleys.
Arrangement 10 Fan Bearing and Belt Layout
Arrangement 10 also uses an overhung fan wheel, independent fan shaft and bearing support with belt transmission. Compared with Arrangement 9, the motor mounting and support configuration differ. The arrangement 10 fan bearing positions, motor base, pulley alignment and maintenance space should be verified from the manufacturer's general arrangement drawing.
This A–F drive-arrangement page provides a practical overview of numbered arrangements because both terminology systems appear frequently in industrial fan specifications. For detailed wheel position, shaft support, bearing configuration, SWSI/DWDI layouts and arrangement-by-arrangement selection notes, use the dedicated guide.
Full Arrangement 1, 3, 4, 7, 8, 9 & 10 Guide →What to Confirm Before Selecting a Fan Arrangement
There is no single best drive arrangement for every centrifugal fan. The correct choice depends on the duty point, fan size, operating speed, motor power, working medium, temperature, dust loading and installation conditions.
Use the Industrial Fan Selection Guide together with the fan series, performance curve and approved drawing.
Information Required for Arrangement Confirmation
For quotation, replacement or drawing approval, provide as much of the following information as possible:
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Frequently Asked Questions About Centrifugal Fan Arrangements
What do A–F codes mean in a centrifugal fan?
A–F codes describe manufacturer or fan-series drive and support arrangements involving the motor, impeller, fan shaft, bearings, belt drive or coupling. Exact definitions should be checked against the applicable fan model and approved drawing.
What is an Arrangement 3 fan bearing configuration?
An Arrangement 3 fan bearing configuration generally places the centrifugal fan wheel between two bearings, giving the fan shaft support on both sides of the wheel. For detailed shaft, bearing and motor-layout information, see the complete numbered centrifugal fan arrangement guide .
What is an Arrangement 8 fan bearing layout?
Arrangement 8 generally uses an independently supported fan shaft and bearings with the motor connected through a coupling. The exact Arrangement 8 fan bearing positions and shaft layout should be confirmed from the manufacturer's drawing.
What is the difference between Arrangement 9 and Arrangement 10?
Both are commonly belt-driven arrangements using an independently supported fan shaft and bearings, but the motor mounting and support configuration differ. The motor base, pulley position, arrangement 9 or arrangement 10 fan bearing layout and maintenance clearance should be checked on the final drawing.
Are A–F codes the same as Arrangement 1, 3, 4, 7, 8, 9 and 10?
No. They are related mechanical-layout terminology but should not be converted directly from one system to the other. A–F meanings can depend on the fan series or manufacturer, while numbered arrangements describe standardized mechanical relationships in another classification system.
What does A mean in an A–F centrifugal fan drive arrangement?
A commonly refers to a direct-drive layout with the impeller mounted directly on the motor shaft. Motor frame, fan speed, shaft compatibility, operating temperature and service access must be confirmed for the selected fan series.
What is the difference between B, C and E?
B and C are commonly used for belt-drive forms whose exact shaft and bearing layouts depend on the fan series. E generally indicates a double-support belt-drive form. Pulley position, belt guard, bearing seats, shaft load and maintenance clearance should be confirmed from the approved drawing.
What is the difference between D and F?
D commonly refers to a coupling-drive layout. F generally refers to a double-support coupling-drive form. Coupling type, bearing span, alignment, foundation and service space must be confirmed for the actual fan series.
Can a centrifugal fan arrangement be selected from airflow and pressure only?
No. Airflow and pressure define the aerodynamic duty, but arrangement selection also requires fan speed, motor power, working temperature, gas condition, shaft and bearing layout, rotation, outlet angle, foundation, maintenance space and fan series.
Need Help Confirming a Centrifugal Fan Arrangement?
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