TM 5-3805-291-23-1
THEORY OF OPERATION - CONTINUED
0003 00
BRAKE AND HYDRAULIC FAN SYSTEM - CONTINUED
(1)
Hydraulic fan system is used to meet cooling requirements by reducing horsepower driving hydraulic fan
in a cooler condition or light application. Hydraulic fan system controls fan speed through use of a piston
pump which drives a fixed displacement gear motor.
(2)
Piston pump is mounted to front engine housing on left side of machine. Piston pump draws oil from
hydraulic oil tank through pump inlet. High-pressure oil then flows to control manifold, which directs oil
to either braking system or hydraulic fan motor. Braking system has priority. When oil is not required by
braking system, oil is directed to hydraulic fan motor, located at rear of machine between radiator and
engine. Pressurized oil from control manifold flows into hydraulic fan motor inlet, causing hydraulic fan
motor to rotate fan blades. Fan rotation forces cool air to flow through cooling package.
(3)
After hydraulic oil exits hydraulic fan motor, it flows through a hydraulic oil line to hydraulic oil cooler.
When engine is first started and hydraulic oil is cold, oil from piston motor can not flow easily through
hydraulic oil cooler. Oil pressure will increase in hydraulic oil cooler and hydraulic oil cooler bypass valve
will open. Valve limits maximum oil pressure in hydraulic oil cooler to 65 psi (450 kPa). Case drain oil
from piston pump and hydraulic fan motor flows through a hydraulic oil line to hydraulic oil tank, where it
is filtered through a screen.
0003 00-103
