7.2.4   Fresh air
When transporting fruit and vegetables, i.e. respiring cargo (respiration processes, biotic activity), the carbon dioxide and ethylene produced by the goods must be removed from the container (except of course when using CA). To do this, the containers have fresh air flaps through which fresh air is admitted into the container and air can escape from the container. This exchange of fresh air is caused by the pressure differential between the circulating fans, i.e. fresh air is drawn in on the suction side of the fans and dissipated on the pressure side. The quantity of fresh air supplied is no greater than approximately double the container volume per hour, but depends to a large extent on the pressure differential of the fan and thus on the way the cargo is stowed in the container.
Figure 16 shows the fresh air flap of a container. The discs used to fine control the fresh air supply were specially fitted for the shipping company. The small hose connection at the bottom is the "atmosphere sampling point". This enables the gas composition in the container to be measured even if the fresh air flap is closed.
Figure 16: Fresh air flap on a container. The discs used to fine control the fresh air are special equipment.


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