Selection Guide — AIR VOLUME — OPEN BY-PASS

Open by-pass fume hoods are designed for operation on constant air volume exhaust systems. The air by-pass provides for an alternate route for air to enter the hood as the sash is closed. The size of the by-pass is set so that, as the sash is closed, the velocity of the air increases to no more than three and one half times the velocity with the sash fully open.

Selection Guide — AIR VOLUME — LOW CONSTANT VOLUME

Low Constant Volume fume hoods use a restricted sash opening or a lower face velocity, or both to reduce the exhaust quantity of air, measured in cubic feet per minute (CFM), necessary to contain fumes with a typical face velocity of 80-120 FPM. Traditionally, such fume hoods can reduce the exhaust CFM from 40% to 60% from Open By-pass levels.

Selection Guide — AIR VOLUME — RESTRICTED BY-PASS

Restricted By-pass fume hoods are designed for operation on variable air volume (VAV) exhaust systems when used with a fume hood face velocity controller (not provided with hood). By reducing the amount of air exhausted as the sash is lowered a constant face velocity is mantained, exhausting less air than a Constant Volume hood.

Selection Guide — AIR VOLUME — AUXILIARY AIR

Auxiliary Air fume hoods are Constant volume hoods designed for use when it is not feasible to introduce the required makeup air through the room ventilation system. Up to 70% of the exhaust volume can be supplied through an auxiliary air chamber mounted above the hood. These hoods require a separate ducted fan system for the supply of the auxiliary air.