HEAD 0545547 - Caterpillar

The AFFF fire extinguishing system is activated by an actuator, usually a cartridge (5) that sends CO2 gas under pressure to a pneumatic actuator (9) on the valve assembly (10). The valve (10) is opened by the pneumatic actuator (9) to release the stored pressure in the retardant cylinder (11). In addition to the CO2 gas cartridge, some models may be equipped with a manual actuator located on the retardant cylinder or with an electric actuator that can be activated when using a radio control system.The retardant cylinder (11) is filled with a water/foam fire retardant solution and is pressurised by nitrogen to a pressure of 1200 kPa (175 psi). Valve (10) holds the pressure in the cylinder.When the pneumatic actuator (9) is triggered, (by pneumatic, manual or electrical means) a plunger in actuator (9) trips a trigger in valve assembly (10), which allows the valve to open. Stored pressure in retardant cylinder (11) forces retardant into siphon tube (12) and on through valve assembly (10) to the nozzle lines group which supplies the nozzles (13).Nozzles (13) spray retardant onto targeted danger areas in the engine compartment. Targeted danger areas would typically include the turbocharger, the fuel injection pump, the electric starter motor, and each end of the diesel engine. The nozzles will continue to spray retardant until retardant cylinder is exhausted.