Downdraft tables are self-contained, portable filtration systems that remove harmful particulates and return filtered air. They are indoor air quality devices that draw-down air and do not require external ventilation. Often downdraft tables are used as workstation fume extractors and dust collectors in welding, sanding, grinding, and other finishing applications. They draw dust and fumes down and away from the breathing zones of workers and other personnel. Downdraft tables use highly efficient filters to capture particles as small as .5 microns. Compressed-air, pulse-jet blasts may be used to ensure that filters maintain peak operational efficiency.
There are two basic types of downdraft tables: wet and dry. Wet downdraft tables use a liquid and a standard filter element to capture and collect flammable or explosive metal dusts. Typically, water is the liquid that is used. Features for wet downdraft tables include impellers for water reversal, automatic water level control, after-filtration devices or mist eliminators for the capture of fugitive mists, and sludge collection tubs for the removal of captured metal particles. With metalworking applications, wet downdraft tables are often used to remove aluminum dust, magnesium dust, or titanium dust. Dry downdraft tables are also commonly available. These products do not use a liquid such as water, but still use a standard filter element to capture smoke, fumes, and vapors.
Downdraft tables are designed to accommodate various sizes and types of production equipment. They usually come in standard sizes, but custom configurations are also available. Performance specifications for downdraft tables include airflow, efficiency, and minimum particle size. Airflow is the velocity of the air stream that downdraft tables create. The unit of measure, standard cubic feet per minute (SCFM), is the volumetric flow rate of a gas when corrected to standard conditions of temperature, pressure, and relative humidity. Efficiency measures how well downdraft tables control or eliminates airborne contaminants. Minimum particle size is the size of the smallest particle (in microns) that downdraft tables can collector or capture.
Typically, downdraft tables are used in applications such as welding, woodworking, chemical preparation, grinding, and processing explosive materials. Special features may include spark guards, exhaust chimneys, heavy-duty work surfaces, and easily-accessible or oversized collection bins. Downdraft booths are similar to downdraft tables, but larger.