The by-pass fume hood is much the same as the constant volume fume hood whereas the exhaust is constant but the sash can fully close. With the sash in any position less than twelve inches the air intake is from below the sash and at the upper section of the fume hood. As the sash opening decreases so does the amount of air below the sash with increased flow at the upper section to a point where a majority of the intake air will enter at the top section of the fume hood. As with the constant volume, fume hood the sash operating position is twelve inches. The counterbalanced sash moves vertically beyond the twelve inch operating height to allow increased opening clearance. Increasing sash opening decreases face velocity. Construction of the standard fume hood is mainly from highly chemical resistant white stress relieved polypropylene seal welded construction. Standard fume hood features include: cool white fluorescent lighting, vented base storage cabinet with hinged door(s), adjustable levelers, top mounted exhaust duct and three back wall mounted banks of adjustable zone exhaust panels.
