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2000 Fire Door-Fan Manual updated 2002-05-28 Page 20 of 58
Select Blower Range
Principles of Infiltrometer Air Flow Measurement
The Infiltrometer can accurately measure airflow between 18 CFM and 6500 CFM. However, in order to
measure accurately over this wide range, the range must be changed as described in the following section.
The Infiltrometer fan blade pushes air out the back of the fan creating a negative pressure in front of the
blades. This negative pressure pulls air through the fan's rounded (venturi) shaped inlet. More negative
pressure, more flow. The Infiltrometer has been calibrated so for each size of inlet opening and for each
negative pressure (Flow Pressure) the flow rate in cubic feet per minute (CFM) is known. As flow decreases the
Flow Pressure decreases eventually to the point that it becomes too low to read accurately.
By reducing the size of the inlet with the restrictor plate a given amount of air is forced to enter the blower at
a higher velocity, resulting in a much higher flow pressure. (The fan speed must be increased in order to pull
the same quantity of air through the blower with the restrictor plate in place.)
Therefore, as the flow rate requirement decreases, such as in tighter buildings, the size of the blower inlet
must decrease to maintain a high and accurately readable Flow Pressure. Each inlet size has a pre-established
configuration or range. Ranges are somewhat analogous to gears in a standard transmission car. The slower
you go the lower the gear.
Changing Ranges
The Retrotec 2000 Series Infiltrometer blower has 7 flow ranges for the greatest possible accuracy and
versatility.
Range 22 (wide open with no restrictor plate installed) is the most powerful and most commonly used range. It
is used to test buildings with ELA's greater than approximately two square feet.
To use range 22, remove all the restrictor plates.
Range A (1st restrictor ring attached) is the next most commonly used range. It is used to test House/Rooms
with ELA's between approximately one and three square feet.
Range B (2nd restrictor ring attached) is used to test House/Rooms with ELA's less than one square foot.
Ranges C8 requires the installation of the plate with 8 holes open, on top of the motor. Ranges C4 down to C1
require plugging some of the holes. Put plugs in the exact positions as shown - others will produce erroneous
results. These very restrictive ranges are needed when testing very small rooms.
Each plug must be gently worked into the hole, but be careful you do not push the Panels right out of the
doorway. (If the blower is ever turned around for reverse measurement, ensure none of the plugs have fallen
out by peeking through the screen.)