The fan industry has a trade association called Air Movement and Control Association International, or AMCA, which produces several standards and methods of testing. AMCA Standard 99-10 addresses drive configurations for different types of fans. This blog post will not address fans designed for motors to be remotely mounted (specifically, AMCA Arrangements 1, 3, or 7). Rather, here we will address common freestanding drive arrangements for fans with factory mounted motors.
This AMCA standard for centrifugal fans is also recognized as an ISO standard (ISO 13349). Your choices for direct drive centrifugal fans are Arrangement 4, 5, or 8. These arrangements are all Single Width Single Inlet (SWSI).
With Arrangement 4, the impeller is overhung on the motor shaft and there are no bearings on the fans. The motor is actually mounted to a motor mounting pedestal, which is part of the fan assembly.
Arrangement 5 is similar to Arrangement 4, but the fan has a C-Face motor. The impeller is overhung on the motor shaft and there are no bearings on the fan, but the motor is flange mounted to the fan casing.
Arrangement 8 is actually a couple driven fan. In this case, the impeller is overhung on a shaft and there are two bearings mounted to a bearing pedestal base. The motor is mounted to a motor pedestal. The fan casing, bearing pedestal, and motor pedestal are all assembled together and the motor shaft is connected to the fan drive shaft through a coupling which must be properly aligned.
Tubular Centrifugal Fans
For tubular centrifugal fans with factory mounted motors, you have Arrangement 4. Arrangement 4 is direct drive, where the impeller is overhung on the motor shaft. The motor is supported within the fan casing. These fans are typically available for either horizontal or vertical mount configurations.
For belt drive tubular centrifugal fans, you have Arrangement 9. This is where the impeller is overhung on a shaft supported by bearings mounted within the casing. This fan is also designed for mounting in either a horizontal or vertical orientation. The motor on this Arrangement 9 fan is mounted external to the fan casing.
Like the centrifugal fans, the AMCA standard addressing axial fan drive arrangements is also an ISO standard (ISO 13349). The choice for direct drive axial flow fans is Arrangement 4.
Arrangement 4 is direct drive where the impeller is overhung on the motor shaft. There are no bearings on the fan and the motor is mounted on a base or integrally mounted to the fan housing.
Axial Belt Drive Fans
For axial flow belt drive, your definition is Arrangement 9. In this arrangement, the impeller is overhung on a shaft with two bearings mounted either upstream or downstream of the impeller. The motor is mounted to the fan casing or on a base that is integral to the fan casing.