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Backward Curved Centrifugal - Motorised Impeller


External rotor motors are usually contained within the depth of the fan impeller, thus saving the space normally occupied by a standard motor. They are located in the air stream, so temperature is limited, and are generally of protection class IP44, so the air needs to be clean and dry to avoid motor contamination.

Backward-curved motorised impellers develop pressure within the envelope of the impeller and do not therefore rely on a scroll housing for this purpose. They are of relatively low cost and can be simply and cheaply housed. Air is drawn through a radiussed inlet ring, which minimises pressure losses and air leakage, and is discharged at 90° to the inlet axis. The impeller has a 'non-overloading' characteristic in that it draws maximum power near the centre of its pressure/volume flow curve.

Low cost speed control is possible by supply voltage variation, either by electronic (triac) method or by transformer.


Air filtration, fume control, electronic cabinet cooling, lamp cooling, solarium equipment, roof extract units, in-line duct fans, high pressure coils, air conditioning cassettes, refrigeration equipment.

Technical Specification

Specification Description
Motor Type

External rotor motor, in the airstream


Single and three phase models

Protection IP44

Backward curved steel, aluminium and plastic


Space saving short axial length. Low cost speed control


Motor backplate. Versions pre-assembled to inlet ring

Pressure Medium
Speed Control Voltage Variation

Ø180 to 710 impeller

Flow Rate

17000m³/h range maximum


1100 Pascals range maximum

Size (in-line duct)

Inlet/discharge spigots Ø100 to 355

Flow rate (in-line duct)

2250m³/h range maximum


900 Pascals maximum