COVER 7S8420 - Caterpillar

Illustration 1 g06040990
Variable pitch fan system
(1) Fan hub
(2) 24V solenoid valve
(3) Air pump
(A) High-pressure air
(B) Intake airThe optional variable pitch fan system consists of an indexing fan assembly in place of the standard fan unit. An air pump and 24V solenoid valve are located at the right rear of the machine. The optional variable pitch fan system periodically changes the pitch of the fan blades in order to clear the cooling system of debris. Air pump (3) draws filtered air from the engine air intake. The air pump compresses the air to 760 kPa (110 psi). Valve (2) allows the compressed air to flow to fan hub (1). The compressed air moves a piston inside the fan hub. The movement of the piston causes the fan blades to swivel by 90 degrees. This movement will reverse the flow of air through the cooling system.In this position, the fan blades will purge the cooling system of debris. During the purge operation, the fan is automatically increased to maximum speed to maximize reverse air flow. The default duration of the purge is 20 seconds. When the purge ends, the pump and the valve shut off. When the pump shuts off, the pressure in the fan hub will vent through a vent port on the valve. The fan blades will return to the normal position. The fan will continue to operate in normal mode until the next purge. The default setting for the duration between two purges is 20 minutes. This purge cycle interval can be adjusted from 3 minutes to 60 minutes by using Electronic Technician. Then, another purge cycle will be initiated. The duration of the purge cycle can also be adjusted using ET.The purge cycle may be initiated manually through the graphical display. Select the "Purge" icon under the "Settings" - > "Functions" section. The minimum time between purge cycles is 3 minutes. If the switch is activated within 3 minutes of the previous cycle, the purge cycle will be delayed until the 3 minutes have passed. Automatic operation will resume after the manual purge is complete.