Changing the Filters
The pre-filter, located at the bottom of the unit, is designed to keep the unit’s interior and the
HEPA filters free of dust and large particulates. Frequent changing of the pre-filter (see Pre-
Filter Replacement) will serve to keep the unit running smoothly and will substantially
extend the life of the HEPA filters.
Typically, the pre-filter should be changed monthly, but in certain situations it should be
changed more frequently. A periodic inspection should provide an indication of how often to
replace the filter.
If properly maintained, the HEPA filters should last 12 months or more in normal use.
The magnehelic gauge, as described previously, is designed to measure and display the
pressure differential between the plenum (inside the unit) and the atmospheric (room) air
pressure. As the HEPA filters age and become dirty, they present a higher resistance to the
airflow and thus a higher pressure inside the unit develops, which is represented by higher
readings on the gauge.
The standard filters used in the Recirculator II are an extruded aluminum frame, enhanced
performance HEPA filter designed to provide approximately 575 cfm when new, at a
pressure differential of about 0.60-0.65 inches w.c. When the pressure differential increases
to about 0.85-0.90 inches w.c., indicated by the dividing line between red and green on the
magnehelic gauge, the airflow has decreased about 25% to approximately 400 cfm. As above
referenced, it is at this point the manufacturer recommends HEPA filter replacement, in order
to maintain adequate minimum airflow.
NOTE: However, before changing the HEPA filters, check or replace the pre-filter to
ensure it is not loaded or is in any way obstructing the airflow, thereby causing a
reduction in efficiency. If the magnehelic gauge still indicates a high pressure
differential after replacement of the pre-filter, proceed with replacement of the HEPA
filters according to the following instructions This will ensure that the unit continues to
change and purify the air effectively.
Filters should be handled with caution during inspection and changing, although they need
not be classified as medical or hazardous waste. Your facility has developed safety
regulations regarding the changing of HEPA filters. Please consult the appropriate staff
members for guidelines.
