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October 2020 / 35 vary the system's static pressure and airflow. A damper is a valve or plate that regulates airflow inside a duct or other air-handling equipment by opening and closing. A dust collection system has one damper per fan, and in some cases, more than one fan is used. One option to alter the airflow is to manually adjust the damper. When the filters are new, the damper can tor's resistance to airflow, referred to as pressure drop or static pressure, changes over time according to how loaded the cartridge filters are with dust. This relation- ship is seen in Figure 2. As you can see in Figure 2, the new filters are able to easily pass through more airflow while keeping a lower static pressure when compared to aged filters, which have difficulty passing more air through due to the dust buildup on the cartridge filters. Without any intervention, the fan will move more air than needed in the filters' early stages of life when the static pressure across the filters is low. This consumes unnecessary energy and also causes high-velocity air to hit the filters, which reduces filter life. In the late stages of the filters' life when the fil- ter media is loaded with dust particles, the airflow through the media becomes restricted, and the fan motor has to work harder to keep the airflow high enough to capture the dust particles in the filter. This increases the static pressure, which is measured in inches water gauge. When the static pressure increases, the airflow needs to be adjusted to avoid excessive energy usage. This can be accomplished manually or by installing a variable-frequency drive (VFD). Manual airflow adjustment. Dust collectors typ- ically use a damper at the fan's outlet to mechanically FIGURE 2 Airflow and pressure drop (static pressure) in new versus aged cartridge filters 1 Aged filters New filters Static pressure Pressure drop Airflow (cfm) WWW.POWDERBULK.COM/SUBSCRIBE