Hyundai Excavator R450LC-7. Service and repair manual - page 10

2-74

OPERATION
The operation of the pilot valve will be described on the basis of the hydraulic circuit diagram shown
below ant the attached operation explanation drawing.
The diagram shown below is the typical application example of the pilot valve.

Pilot valve

Pilot pump

Main pump

Main control valve

Hydraulic motor

Hydraulic cylinder

2-76 (210-7)

2-75

Case where pedal is in neutral position

(1)

The force of the spring(11) that determines the output pressure of the pilot valve is not applied to
the spool(8). Therefore, the spool is pushed up by the spring(18) to the position of port 2 in the
operation explanation drawing. Then, since the output port is connected to tank port T only, the
output port pressure becomes equal to tank pressure.

2-77 (210-7)

2-76

When the push rod(19) is stroked, the spool(8) moves downwards.
Then port P is connected with port 1, and the oil supplied from the pilot pump flows through port 1
to generate the pressure.
When the pressure at port 1 increases to the value corresponding to the spring force set by tilting
the handle, the hydraulic pressure force balances with the spring force. If the pressure at port 1
increases higher than the set pressure, port P is disconnected from port 1 and port T is connected
with port 1. If it decreases lower than the set pressure, port P is connected with port 1 and port T
is disconnected from port 1.
In this manner the secondary pressure is kept at the constant value.
Besides, in some type, when the handle is tilted more than a certain angle, the upper end of the
spool contacts with inside bottom of the push rod and the output pressure is left to be connected
with port P.

Case where pedal is tilted

(2)

2-78 (210-7)

SECTION 3 HYDRAULIC SYSTEM

Group 1 Hydraulic Circuit - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3-1

Group 2 Main Circuit - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3-2

Group 3 Pilot Circuit - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3-5

Group 4 Single Operation - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3-13

Group 5 Combined Operation - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3-23

3-2

The main hydraulic circuit consists of suction circuit, delivery circuit, return circuit and drain circuit.
The hydraulic system consists of one main pump, one control valve, one swing motor, four cylinders
and two travel motors.
The swash plate type variable displacement tandem axial piston pump is used as the main pump and
is driven by the engine at ratio 1.0 of engine speed.

1. SUCTION AND DELIVERY CIRCUIT

To cylinders

To motors

To hydraulic oil tank

Hydraulic oil tank

Main control valve

Main pump

GROUP 2 MAIN CIRCUIT

The pumps receive oil from the hydraulic tank through a suction filter. The discharged oil from the
pump flows into the control valve and goes out the tank ports.
The oil discharged from the main pump flows to the actuators through the control valve.
The control valve controls the hydraulic functions.
The return oil from the actuators flows to the hydraulic tank through the control valve and the oil
cooler.

To oil cooler

Suction filter

3-02 (210-7)

3-3

All oil from each actuator returns to the hydraulic tank through the control valve.
The bypass check valves are provided in the return circuit.
The setting pressure of bypass check valves are 1.5kgf/cm

(21psi) and 5.0kgf/cm

(71psi). Usually, oil

returns to the hydraulic tank from the left side of control valve through oil cooler.
When oil temperature is low, viscosity becomes higher and flow resistance increases when passing
through the oil cooler. The oil pressure exceeds 5.0kgf/cm

(71psi), the oil returns directly to the hydraulic

tank, resulting in the oil temperature being raised quickly at an appropriate level.
When the oil cooler is clogged, the oil returns directly to the hydraulic tank through bypass check
valve(1).
The full-flow filter and bypass relief valve are provided in the hydraulic tank.
The oil from right and left side of control valve is combined and filtered by the return filter. A bypass
relief valve is provided in the full-flow filter.
When the filter element is clogged, the bypass relief valve opens at 1.5kgf/cm

(21psi) differential pressure.

2. RETURN CIRCUIT

Main control valve

Actuators

Full flow filter

Oil cooler

Check valve(2)

1.5kgf/cm

Check valve(1)

5.0kgf/cm

Check valve(3)

1.5kgf/cm