Bypass Cooling A type of motor cooling design which incorporates a separate airflow through the motor to cool it. The main airflow, which picks up the dirt travels through the suction fan or fans but bypasses the motor itself. This prevents residual dirt or moisture in the main airflow from coming in contact with the armature, field, carbon brushes, etc. Bypass cooling is always incorporate din wet/dry vacuum cleaners as well as the traditional “dirty air” uprights. A motor is either a bypass cooled type or a flow through cooled type.