CONFIGURING EQUIPMENT1
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The second step is to configure the equipment.  The distance from the source(s) to the collector is key.  Will one collector serve multiple hoods?  If so, duct losses will increase, and the airflow required for efficient collection will rise.

The capture velocities required to collect the material and the sizing of the ducts transporting the material relate to the development of static pressure, the airflow required with the proper horsepower to achieve proper draw.  This is the most critical calculation, and the single most important reason why filtration is generally not a simple do-it-yourself project.

The annual Industrial Ventilation Conference has a course that covers hood design, hood sizing and its relation to ductwork, the conversion of velocity pressure to CFM, and other factors.  Many community colleges have similar programs.  Probably the best reference book in the industry is the Industrial Ventilation manual.  It can be obtained by attending the conference or through the American Conference of Governmental Industrial Hygienists in Cincinnati, OH.

It was recommended earlier that shops consider future requirements right from the start.  The reason is that any addition of equipment, or increase in the distance between system components, necessitates revision of the design. Systems designed with a fan operating at a given RPM will produce a given cfm against a given static pressure.  Change any element of this equation and you change everything else.  The airflow required to achieve a given result rises or falls based on static pressure which, in turn, is based on the length and diameters of the ductwork and the size of the hoods.

ıPhil Weber, Welding Processes Pose Tough Challenge for Fume Filtration, (Welding Design and Fabrication) 9/03
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