HOSE ASSEM. (26.50" long overall) 4D6123 - Caterpillar

Fan Pump and Control Valve
Operation at Maximum Pressure
Illustration 1 g02444546
Fan Pump and Control Valve (Maximum Speed)
(1) Actuator piston
(2) Swashplate
(3) Bias spring
(4) Drive shaft
(5) Fan pump
(6) Piston and barrel assembly
(7) Case drain passage
(8) Output to fan motor
(9) Pin
(10) Plunger
(11) Spring
(12) Solenoid
(13) Adjustment screw
(14) Spring
(15) Orifice
(16) Signal passage
(17) Pump control spool
(18) Pressure control spool
(19) Adjustment screw
(20) Pump control valve
(BB) Cutaway section
(CC) Component surface
(FF) Activated components
(GG) Tank pressure
(JJ) High pressure When maximum fan speed is required, the engine ECM sends minimum signal current to solenoid (12). Plunger (10) blocks signal passage (16). The force of spring (14) plus the signal pressure holds pump control spool (17) downward.When pump control spool (17) is held downward, the passage to actuator piston (1) is open to the case drain. The force of bias spring (3) moves swashplate (2) toward the maximum angle.The pistons travel in and out of the barrel at increasing distances which increase flow and fan motor speed. Fan speed continues to increase until the resistance from the fan drive motor creates enough pressure for the force exerted on pressure control spool (18) to exceed the force from spring (11) or swash plate (2) reaches the maximum angle.Pressure control spool (18) limits the maximum pressure of the oil that flows to the fan motor through output (8). If the output pressure overcomes spring (11), the pressure control spool moves upward. High-pressure oil is allowed to flow to actuator piston (1). The pump destrokes.Operation at Minimum Pressure
Illustration 2 g02444716
Fan Pump and Control Valve (Minimum Fan Speed)
(1) Actuator piston
(2) Swashplate
(3) Bias spring
(4) Drive shaft
(5) Fan pump
(6) Piston and barrel assembly
(7) Case drain passage
(8) Output to fan motor
(9) Pin
(10) Plunger
(11) Spring
(12) Solenoid
(13) Adjustment screw
(14) Spring
(15) Orifice
(16) Signal passage
(17) Pump control spool
(18) Pressure control spool
(19) Adjustment screw
(20) Pump control valve
(BB) Cutaway section
(CC) Component surface
(FF) Activated components
(GG) Tank pressure
(KK) First pressure reduction
(LL) Second pressure reduction When the engine is first started or when the machine is working in a cold climate, the required fan speed for cooling is low. Maximum signal current is sent to solenoid (12).When a slower fan speed is required, the engine ECM increases the signal current to solenoid (12). Pin (9) pushes plunger (10) downward against spring (11). When the plunger moves downward, signal passage (16) is opened to the case drain. The pressure at the top of pump control spool (17) lowers. The pressure at the bottom of the pump control spool overcomes the force of spring (14). The spool shifts upward which allows pressurized oil to flow to actuator piston (1).When oil flows into actuator piston (1), the force of bias spring (3) is overcome. Swashplate (2) moves toward the minimum angle until equilibrium is reached between the pressure in the actuator piston and the force of the bias spring.The pistons travel in and out of the barrel for a shorter distance. The cylinders fill to a smaller amount. A decreased amount of oil flows through output (8) to the fan motor. The decreased amount of oil flow to the fan motor causes