The operation of a recirculating system is similar to that of a single pass unit. With this system the air is recirculated through a perforated work deck to a rear-mounted return air duct. This returns the air to the blower intake where it is forced through the HEPA filter again and returned back to the clean zone

SINGLE PASS SYSTEM

Ambient air enters the pre-filter area and is forced through a HEPA filter, affording downward laminar flow through the clean zone. The air is then exhausted out the front of the unit. If necessary, the work deck can be perforated to allow air to pass directly through the unit and then out below the work deck.

CLEAN FUME HOOD-EXHAUST

The design of the Clean Fume Hood-Exhaust includes a perforated work deck. Ambient air enters the system at the top, pressurizes the blower plenum and then the clean air is forced through the HEPA filter with 99.99% effectiveness. The air travels in a laminar flow down through the perforated work surface into the plenum area below and exhausts through the rear mounted exhaust duct to the outside of the central exhaust system as determined by the design.

VARIABLE EXHAUST

The Variable Exhaust unit affords the flexibility of exhausting a portion of the returned air (0% to 100%) resulting in a savings of ambient air conditioning and extending the life of the HEPA filter. The variable exhaust system may be appropriate where a negligible fume situation exists.