Duct connections must also be as tight as possible to prevent a reduction in air velocity at the hood because of leaks at joints. Figure 6 illustrates some basic duct design principles. Air Cleaners Air cleaning devices on ventilation systems are sometimes necessary to capture large amounts of dust. In some instances, they may be required by air pollution regulations. The type of air cleaner depends on the type of contaminant being removed, its concentration in the air, the amount of contaminant that must be removed, and other factors.
Dust filters are the most common type of air cleaners found in industry.
Other types of air cleaners remove gases and vapors. Local air pollution regulations dictate the type of air cleaner required. The cost and extra resistance that these air cleaners add to an exhaust ventilation system must be considered in the design. For more information on air pollution regulations and requirements, contact the local air pollution control authority for your locality. Fans Fans are the workhorses of exhaust ventilation systems.