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1.6 FRESH AIR MAKEUP VENT
The purpose of the vent is to provide ventilation for
commodities that require fresh air circulation and
must
be closed
when transporting frozen foods.
Air exchange depends on static pressure differential
which will vary depending on the container and how the
container is loaded. The chart below gives air exchange
values for an empty container. Higher values can be
expected for a fully loaded container.
0
30
60
90
120
150
180
210
240
0
10 20 30 40 50 60 70 80 90 100
AIR
FLOW
(CMH)
1-
!
/
2
”
PERCENT OPEN
69NT40 FRESH AIR MAKEUP
T-BAR
2-
%
/
8
”
3”
T-BAR
T-BAR
ZERO EXTERNAL STATIC 50HZ
For 60HZ operation multiply curves by 1.2
a. Full Open or Closed Positions
Maximum air flow is achieved by loosening the wing
nuts and moving the cover to the maximum open position
(100% position). The closed position is 0% air flow
position.
The operator may also adjust the opening to increase
or decrease the air flow volume to meet the required air
flow.
b. Air Sampling for Carbon Dioxide (CO
2
) Level
Loosen wing nuts and move cover until the arrow on
the cover is aligned with the “atmosphere sampling port”
label. Tighten wing nuts and attach a 3/8 tube to the
sampling tube.
If the internal atmosphere content has reached an
unacceptable level, the operator may adjust the cover
opening to meet the required air flow volume to ventilate
the container.
c. Reduced Flow for Fresh Air Makeup
On some models the air slide is supplied with two
adjustable air control disks. The fresh air makeup can be
adjusted for (15, 35, 50 or 75) cubic meters per hour
(CMH). The air flow has been established at 60HZ power
and 2 1/2 inch T bar and with 15mm (.6 inch) H
2
O
external static above free blow.
Loosen the hex nut and adjust each disk to the
required air flow and tighten hex nut.
NOTE
The main air slide is in the fully closed position
during reduced air flow operation.
NOTE
Model 69NT40-454 has a special air makeup
cover with a maximum air flow (100% open) of
80CMH (47CFM).
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