This is perhaps the most common arrangement for industrial and other applications. It is available in SISW and usually belt driven. Two bearings are mounted on a pedestal and the wheel is overhung to one side. The bearing pedestals are internal on axial fans.
This arrangement is similar to arrangement 1 except the bearing pedestal is supported by the fan housing. Two separate bearings may be used although at one time it was more common to see this arrangement with the 2 bearings races in a common bearing housing. A/2 is usually belt driven.
This arrangement is available in both SISW and DIDW. A bearing is bracket mounted on each side of the housing . . . or on axial fans, on each side of the wheel. This results in a compact unit. Since one or both of the bearings are in the airstream, A/3 is usually not used in application where dirt and/or heat will run through the fan. The bearing bracket supports can make it difficult to add ductwork to the inlet or inlets of the fan. A/3 is usually belt driven.
In this arrangement, the wheel is directly mounted on the motor's shaft (& bearings). The fan itself does not have a shaft or bearings. This arrangement is more common in axial or smaller centrifugal fans where proportions allow the motor shaft to reach the wheel hub. However, some manufactures offer A/4 centrifugals up to 200 HP as standard. Due to the close coupling of the motor, Arrgt. 4 fans are normally restricted to a maximum temperature limit of 200°-F or less and it is common to add some type of volume control to the fan since variable speed motors are often not economically available.
An arrangement 7 fan is an arrangement 3 fan with a motor base attached to the drive side. It is designed to be direct driven through a flexible coupling, with the motor (or turbine) mounted on the attached base. The same cautions that apply to arrangement 3 fans apply to arrangement 7. A very practical use is in large mechanical draft fans which use inlet boxes. In that case, it eliminates the need for separate independent bearing pedestals which can simplify installation. Arrangement 7 is available in SISW and DIDW.
This arrangement is similar to an arrangement 1 fan. A smaller "outrigger" motor or turbine base is customer provided, or shipped attached to the bearing pedestal, for direct connection through a coupling. It is most often used where V-belt drives are not appropriate, as with very high horsepower's.
This is an arrangement 1 belt driven fan with the motor mounted on the fan rather than on the "floor". It allows factory assembly of the motor and drives. On higher horsepower fans, the industry sometimes refers to arrangement "9H". In this modification of arrangement 9 the motor is mounted on the structural steel base that is furnished by the fan manufacture. It also allows factory assembly of the motor and drives.
This SISW arrangement is similar to an arrangement 9 fan except the motor is mounted inside of the bearing pedestal. This offers some degree of weather protection to the motor however it restricts the motor size. It is most important to provide adequate ventilation to the motor in A/10.
Air Movement and Control Association (AMCA) standards include the option of either belt drive or direct drive for most arrangements. Rare and often impractical drive options have been omitted.