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SRX3400 Services Gateway Fan Tray


The cooling system consists of a fan tray containing four fans and an air filter. These components work together to keep all services gateway components within the acceptable temperature range. The SRX3400 Services Gateway has one fan tray located in the rear of the services gateway that installs vertically to the right of the card cage. The fan tray is hot-insertable and hot-removable.

Figure 1: Fan Tray
Fan Tray

From the front of the chassis, there is a single air intake on the left side of the services gateway. Air is pushed from the fan tray through the air filter and then to the card cage. The air is exhausted out the right of the system. Figure 2 illustrates the air flow from the top of the chassis and the front of the chassis.

Figure 2: Airflow Through the Chassis
Airflow Through the Chassis

At startup, the Routing Engine runs the fans at full speed until it can obtain reliable temperature data from its temperature sensors. After it finishes booting and has reliable temperature data, the Routing Engine monitors the temperature of certain critical services gateway components and adjusts the speed of the fans accordingly.

The fans have three speeds: low, intermediate, and high. Table 1 shows the correlations between fan speed and critical component temperature. Note that there is hysteresis built into the correlation, so that the fans are not subject to spurious speed changes. Also, if one of the fans in the fan tray fails, the speeds of the remaining fans are automatically adjusted to keep the temperature within the acceptable range.

Table 1: Critical Component Temperatures and Fan Speed Transitions

Critical Component Temperature

Fan Speed Response

Increase to 60°C

Increase from Low to Medium

Increase to 75°C

Increase from Medium to High

Decrease to 65°C

Decrease from High to Medium

Decrease to 55°C

Decrease from Medium to Low

If the maximum internal temperature specification is exceeded and the system cannot be adequately cooled, the Routing Engine shuts down the system by disabling output power from each power supply.