Carrier 69NT40-489-100 Series, Руководство по эксплуатации и обслуживанию

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96 T-305
8.4 CONTROLLED ATMOSPHERE (CA) FLOW
CIRCUIT
Starting at the right-hand side access panel (see Item 1,
Figure 56, page 89), the air intake filter (Figure 62,
page 97 item 2) filters dust from the air. A compressor
suction air accumulator (see Figure 62, page 97, item
3) collects moisture from the compressor inlet air
stream. The condensate is collected in the water
separator tank and drained to the front of the unit. The
air is then compressed in the compressor.The
pressurized air then passes through the condensing line
(item 5), located under the refrigeration evaporator coil,
which condenses the moisture in the air. This
pressurized air is then passed through an air filter
assembly (item 9) to remove dirt and moisture. The
moisture is discharged every one-half hour by two
normally closed drain solenoids (items 10 & 11) to an
area outside of the container. The pressurized filtered
air is heated by the air heater (item 13), allowing the
nitrogen membrane separator (item 15) to work more
efficiently. The CA Controller ensures this efficiency by
using the membrane temperature sensor (item 16) to
maintain the temperature of the compressed air
entering the nitrogen membrane separator. The high air
temperature switch (item 14) is a safety device that
protects the membrane from being overheated.
When the heated, pressurized air enters the nitrogen
membrane separator the nitrogen (N
2
) is separated and
delivered to the inside of the container. The rate of
nitrogen separated is determined by the flow of air
through the membrane. The flow rate is established by a
two stage solenoid valve called the nitrogen purity valve
(NPV) (item 17). When de-energized, the NPV allows a
very pure stream of nitrogen to pass into the container
(used to decrease the amount of oxygen).
To decrease the amount of CO
2
in the container, the
NPV is energized. When energized, the NPV introduces
a higher flow rate of less-pure nitrogen that purges the
excess CO
2
. Other gases that have been separated
from the air during this process are passed to an outlet
that delivers these gases to a point outside of the
container.
To increase the level of oxygen in the container, a
normally closed oxygen solenoid valve (item 23, OSV) is
energized. This allows pressurized, filtered air to
bypass the membrane and flow directly into the
container.
The CA Controller monitors the amount of oxygen (O
2
)
and carbon dioxide (CO
2
) inside the container by using
carbon dioxide and oxygen sensors (items 25 & 26).
A sample of the container air to be sensed is drawn in
through a normally closed sample air solenoid valve
(item 21) and passed through the sensor filter assembly
(item 24). The oxygen sensor (item 26) and carbon
dioxide sensor (item 25) need to be calibrated, refer to
section 9.1, page 99 for a more detailed explanation.
The CA Controller uses solenoid valves (items 19, 20 &
22) for calibration and monitoring system
performances, refer to section 9.1.7, page 106 for a
more detailed explanation.
In some instances, a high level of carbon dioxide (CO
2
)
is needed to transport particular products. In order to
achieve this, CO
2
charge ports have been added to the
container inside the bulkhead wall, as well as on the
outside of the unit. Once the CO
2
source (item 30) has
been connected and the CA Controller initiated, the
carbon dioxide solenoid valve (item 29) energizes when
a higher concentration of carbon dioxide is required.