the major types of particulate air cleaners include fabric filter devices such as bag houses the electrostatic precipitators and cyclone separators gases and vapors are often removed from the air stream by scrubbers remember to provide protection for those handling materials collected from the air cleaner most users install monitors on the air cleaner to warn when the air cleaner is not cleaner is not functioning property when choosing a fan be sure to select one which will provide the necessary steady pressure and volume flow rate remember though the volume flow rate is always determined by a mission control requirement at the hood the fan is to serve the hood need not vice versa fans are divided into two main classifications centrifugal in which the airflow is at right angles to the axis of rotation of the roter