390D Excavator Hydraulic System Main Hydraulic System Caterpillar

Main Hydraulic Schematic

Illustration 1	g02174314
(1) Bucket cylinder (2) Stick cylinder (3) Boom cylinders (4) Left travel motor (5) Right travel motor (6) Front swing motor (7) Solenoid valve (swing parking brake) (8) Rear swing motor (9) Counterbalance valve (left travel motor) (10) Counterbalance valve (right travel motor) (11) Anti-reaction valve (front swing motor) (12) Swing control valve (13) Swivel (14) Boom drift reduction / regeneration valve (15) Solenoid valve (travel speed) (16) Proportional reducing valve (power shift pressure) (17) Pilot relief valve (18) Valve (hydraulic activation) (19) Solenoid valve (hydraulic lockout solenoid) (20) Accumulator (21) Pilot oil manifold (22) Bypass check valve (23) Load sensing signal reduction valve (24) Main control valve (25) Stick drift reduction / regeneration valve (26) Slow return check valve (27) Pilot filter (28) Return filter (29) Return filter (30) Case drain filter (fan motors, swing motors, and travel motors) (31) Case drain filter (swing pump, front pump, rear pump, and fan pump) (32) Hydraulic oil cooler (33) Fan motor (34) Pilot pump (35) Fan pump (36) Proportional solenoid valve (fan pump control) (37) Pressure sensor for the swing pump (38) Swing pump (39) Pressure sensor for the front pump (40) Front pump (41) Rear pump (42) Hydraulic tank

Hydraulic Pump Flow and Pressure Control System

Illustration 2	g02205804
Pump compartment (34) Pilot pump (35) Fan pump (38) Swing pump (40) Front pump (41) Rear pump

Illustration 3	g02205974
Main control valve (43) Main control valve (boom side) (44) Main control valve (stick side)

This machine is driven and controlled by the following five systems:

• The main hydraulic system controls the cylinders and the travel motors.

• The swing hydraulic system controls the swing motors.

• The pilot hydraulic system supplies oil to the main pump and the control circuits.

• The electronic control system controls the outputs of the engine and pump.

• The separate cooling system supplies oil to the fan motor in order to cool the hydraulic oil.

The main hydraulic system delivers oil flow from front pump (40) and rear pump (41) in order to control the following components: bucket cylinder (1), stick cylinder (2), boom cylinders (3), left travel motor (4) and right travel motor (5) .

Front pump (40) and rear pump (41) are variable displacement piston pumps. The performance of the pumps is equal, and the pumps are arranged in series.

Front pump (40) is directly connected to the engine by a coupling. The front pump delivers oil to the center manifold of main control valve (24) .

Rear pump (41) is connected to the front pump. The rear pump delivers oil to the center manifold of main control valve (24) .

The oil delivery from both pumps is combined at main control valve (24) .

The pilot hydraulic system controls the output flow of the front pump and the rear pump.

Illustration 4	g02205993
Swing (6) Front swing motor (8) Rear swing motor (12) Swing control valve

The swing hydraulic system delivers oil from swing pump (38) to front swing motor (6) and rear swing motor (8) through swing control valve (12). The swing hydraulic system drives both motors simultaneously. Swing pump (38) is mechanically connected to the PTO of the engine.

For more information concerning the operation of the swing hydraulic system, refer to Systems Operation, "Swing Hydraulic System".

Illustration 5	g02206273
Cab (A) Joystick (B) Left travel pedal (C) Right travel pedal (D) Monitor (E) Joystick

The pilot hydraulic system receives oil flow from pilot pump (34). The pilot hydraulic system controls the following functions:

1. The pilot hydraulic system controls the operation of the implement control valves and the swing control valve.

   Pilot oil flows from pilot pump (34) to main control valve (24) through pilot oil manifold (21). When no operation is performed, the pilot oil exerts pressure against both ends of the control valve spools.

   When a joystick or pedal is operated, an electrical signal is sent to the machine ECM. The machine ECM energizes the proportional solenoid valves proportionally to the movement of the joystick. The joystick movement corresponds to a control valve spool in main control valve (24) or swing control valve (12) .

   When a proportional solenoid valve is energized, pilot oil pressure in the end of the control valve spool drains to the hydraulic tank. The pilot pressure oil on the other end of the valve spool forces the control valve spool toward the energized proportional solenoid valve. When the control valve spool shifts, oil is delivered from front pump (40), rear pump (41), and/or swing pump (38) to the cylinders and/or motors.

   In this way, pilot oil drives each circuit of the main control valve and the swing control valve.

2. The pilot hydraulic system also controls the output flow of the main pumps.

   Oil from the pilot pump changes to a signal pressure. This signal pressure is called power shift pressure. The power shift pressure controls the output flow of front pump (40) and rear pump (41) via proportional reducing valve (16). The power shift pressure is sent to the main pump regulators. Power shift pressure adjusts the output flow of the main pumps according to the load on the system.

3. The pressure from the pilot hydraulic system is also used to perform the following operations:

   1. Pilot pressure releases the swing parking brake by using solenoid valve (7) .

   2. Pilot signal pressure automatically changes the travel speed to either HIGH or LOW according to the system load. Solenoid valve (15) controls the displacement change valves in the travel motors.

   3. Pilot signal pressure changes the delivery pressure of the main pump according to the usage of the machine (travel mode or implement mode).

   4. Pilot pressure is supplied to the proportional reducing valve in stick drift reduction/regeneration valve (25). The proportional reducing valve controls the stick regeneration system.

   5. Pilot pressure is supplied to the proportional reducing valve in boom drift reduction/regeneration valve (14). The proportional reducing valve controls the boom regeneration system.

For more information concerning the pilot hydraulic system, refer to Systems Operation, "Pilot Hydraulic System".

Illustration 6	g02206555
Pump compartment (35) Fan pump (36) Proportional reducing valve

Fan pump (35) drives the separate hydraulic motors for the cooling fan. Fan pump (35) is a variable displacement piston pump. When the oil temperature rises, an electrical signal is sent from the machine ECM to proportional reducing valve (36). The operation of the proportional reducing valve causes the delivery of oil from the fan pump to vary. The rotational speed of the fan motor varies accordingly.