Hyundai Excavator R210LC-7. Service and repair manual - page 9

2-73

OPERATION

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

1

Pilot valve

2

Pilot pump

3

Main pump

4

Main control valve

5

Hydraulic motor

6

Hydraulic cylinder

1

1

P

T

3

2

3

4

5

6

3)

2-74

The force of the spring(7) that determines the output pressure of the pilot valve is not applied to
the spool(5).   Therefore, the spool is pushed up by the spring(10) to the position of port(1, 3) 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.

Case where handle is in neutral position

7

1

3

10

5

P

T

(1)

2-75

When the push rod(14) is stroked, the spool(5) 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 the inside bottom of the push rod and the output pressure is left to be
connected with port P.

Case where handle is tilted

14

1

3

5

P

T

(2)

2-76

1.  STRUCTURE

The casing(Spacer) has the oil inlet port P(Primary pressure), and the oil outlet port T(Tank).   In
addition the secondary pressure is taken out through ports 1,2, 3 and 4 provided at the bottom face.

GROUP  6  RCV PEDAL

12.4

1

3

1

2  3

4

T

P

T

P

Hydraulic circuit

2

4

12.4

Port

P

T

1

2

3

4

Port size

PF 1/4

Port

Pilot oil inlet port

Pilot oil return port

Travel(LH, Forward)

Travel(LH, Backward)

Travel(RH, Forward)

Travel(RH, Backward)

14072SF73

2-77

CROSS SECTION

The construction of the RCV pedal is shown in the below drawing.   The casing has vertical holes in
which reducing valves are assembled.
The pressure reducing section is composed of the spool(8), spring(6) for setting secondary pressure,
return spring(10), stopper(9), and spring seat(7).   The spring for setting the secondary pressure has
been generally so preset that the secondary pressure is 5 to 19kgf/cm

2

(depending on the type).   The

spool is pushed against the push rod(14) by the return spring.
When the push rod is pushed down by tilting pedal, the spring seat comes down simultaneously and
changes setting of the secondary pressure spring.

1

Body(1)

2

Body(2)

3

Plug

4

Plug

5

Spring seat

6

Spring

7

Spring seat

8

Spool

9

Stopper

10

Spring

11

Rod guide

12

O-ring

13

Snap ring

14

Push rod

15

Spring pin

16

Seal

17

Steel ball

18

Spring

19

Plate

20

Snap ring

21

Plug

22

O-ring

23

Rod seal

24

Dust seal

25

Cover

26

Socket bolt

27

Cam

28

Bushing

29

Cam shaft

30

Set screw

31

Set screw

32

Nut

33

Bellows

34

Space

35

O-ring

36

O-ring

37

Socket bolt

32

24

23
22

16
21
13
12

11

9

5

4

3

25,26

3

36

14 15

17
18

19
20

6

7

10

8

37    1  35    34        2

27       31      30    29    28      33

14072SF70

2-78

2.  FUNCTION

FUNDAMENTAL FUNCTIONS

The pilot valve is a valve controls the spool stroke, direction, etc of a main control valve.   This
function is carried out by providing the spring at one end of the main control valve spool and
applying the output pressure(Secondary pressure) of the pilot valve to the other end.
For this function to be carried out satisfactorily, the pilot valve is composed of the following
elements.

Inlet port(P) where oil is supplied from hydraulic pump.

Output port(1, 2, 3 & 4) to apply pressure supplied from inlet port to ends of control valve spools.

Tank port(T) necessary to control the above output pressure.

Spool to connect output port to inlet port tank port.

Mechanical means to control output pressure, including springs that work on the above spools.

FUNCTIONS OF MAJOR SECTIONS

The functions of the spool(8) are to receive the supply oil pressure from the hydraulic pump at its
port P, and to change over oil paths to determine whether the pressure oil of port P is led to output
ports 1, 2, 3 & 4 or the output spool to determine the output pressure.
The spring(6) works on this spool to determine the output pressure.
The change the deflection of this spring, the push rod(14) is inserted and can slide in the plug(21).
For the purpose of changing th displacement of the push rod through the cam(27) and adjusting
nut(32) are provided the pedal that can be tilted in any direction around the fulcrum of the cam(27)
center.
The spring(10) works on the casing(1) and spring seat(7) and tries to return the push rod(14) to the
zero-displacement position irrespective of the output pressure, securing its resetting to the center
position.
This also has the effect of a reaction spring to give appropriate control feeling to the operator.

1)

2)

(1)

(2)

(3)

(4)

(5)

2-79

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.

3)

1

Pilot valve

2

Pilot pump

3

Main pump

4

Main control valve

5

Hydraulic motor

6

Hydraulic cylinder

3

5

6

4

2

2

1

1

36072SF01

2-80

Case where pedal is in neutral position

(1)

The force of the spring(6) 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(10) 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.

6

8

10

1

2

T

P

14072SF74

2-81

When the push rod(14) 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)

14

8

T

P

1                               2

14072SF75

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 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

(210-7)  3-03

3-3

All oil returned 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

2

(21psi) and 3.0kgf/cm

2

(43psi).   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.   When the oil pressure exceeds 3.0kgf/cm

2

(43psi), 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 returned from right and left side of control valve is combined and filtered by the full-flow 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

2

(21psi) differential pressure.

2. RETURN CIRCUIT

Main control valve

Actuators

Full flow filter

Check valve(1)
3.0kgf/cm

Check valve(2)
1.5kgf/cm

2

Bypass relief valve
1.5kgf/cm

Oil cooler

2

2

21073CI01

3 - 4

3. DRAIN CIRCUIT

Besides internal leaks from the motors and main pump, the oil for lubrication circulates.   These oil have
to be fed to the hydraulic tank passing through spin filter.
When the drain oil pressure exceed 1.5kgf/cm

2

(21psi), the oil returns to the hydraulic tank directly.

TRAVEL MOTOR DRAIN CIRCUIT

Oil leaked from the right and left travel motors comes out of the drain ports provided in the
respective motor casing and join with each other.   These oils pass through the turning joint and
return to the hydraulic tank after being filtered by spin filter.

SWING MOTOR DRAIN CIRCUIT

Oil leaked from the swing motor returns to the hydraulic tank passing through a spin filter with oil
drained from the travel circuit .

MAIN PUMP DRAIN CIRCUIT

Oil leaked from main pump returns to the hydraulic tank passing through spin filter.

1)

2)

3)

Travel motor

Swing motor

Main pump

Turning joint

Spin filter

Hydraulic
oil tank

Bypass valve
1.5kgf/cm

2

(210-7)  3-04

3 - 5

The pilot circuit consists of suction circuit, delivery circuit and return circuit.
The pilot pump is provided with relief valve, receives the oil from the hydraulic tank through the
suction filter.
The discharged oil from the pilot pump flows to the remote control valve through line filter, EPPR
valve, solenoid valve assemblies, swing parking brake, main control valve and safety lock solenoid
valve.

GROUP  3  PILOT CIRCUIT

Control valve

Remote control valve

(LH lever)

RCV pedal

Remote control valve

(RH lever)

Safety lock 

solenoid valve

Swing parking brake

Main pump

Line filter

Relief valve
35kgf/cm

2

Travel speed solenoid valve

Pilot pump

Suction filter

Power boost solenoid valve

Boom priority valve

Max flow cut off solenoid valve

(210-7)  3-05

3 - 6

The pilot pump receive oil from the hydraulic tank.   The discharged oil from the pilot pump flows to
the safety solenoid valve through the line filter.   The oil is filtered by the line filter.   The pilot relief
valve is provided in the pilot pump for limiting the pilot circuit pressure.
The oil filtered by line filter flows remote control valve through safety solenoid valve.
The return oil flow into the hydraulic tank.

1. SUCTION, DELIVERY AND RETURN CIRCUIT

XAtr

XA0

Atr

XB0

XBtr

Ab1

Bb1

XAb

XBb

Dr4

PbL

XAb2

XBa2

XAa2

(XBp2)

Py

PG

XAtl

XBs

XAs

Pns

Dr6

XAb2

XBa2

Fl

Fr

PBP

PaL

Dr3

Dr2

XAk

Ak1

Bk1

XBk

Px

R1

Pz

P1

PH

R2

P2

Dr1

XAa1

XAa2

XBa1

XBtl

Btr

(XBp1)

SWING MOTOR

TRAVEL MOTOR

ARM

CYLINDER

BUCKET

CYLINDER

BOOM

CYLINDER

HYDRAULIC TANK

FRONT

PUMP

REAR
PUMP

PILOT
PUMP

SW AM

BK BM

XBa1

XBk

XAb1 XBb1

XAk

XAtr

XBtr

 Pz

 Pk

 dr2

Pm1

Pm2

TR

XBtl

XAtl

XBs

XAs

XAa1

A1

A2

A3

A4

Pns

A5

PG(S/Motor)

PG(MCV)

P1

P2

P3

P4

LINE FILTER

SAFETY

SOLENOID

VALVE

TRAVEL(LH)

SWING

BOOM 2

ARM 1

ARM 2

BUCKET

BOOM 1

OPTION

TRAVEL(RH)

3 - 7

When the lever of the safety solenoid valve is moved downward, oil flows into the remote control
valve through solenoid valve and line filter.
When the lever of the safety solenoid valve is moved upward, oil does not flow into the remote
control valve, because of the blocked port.

PILOT
PUMP

XAtr

XA0

Atr

XB0

XBtr

Ab1

Bb1

XAb

XBb

Dr4

PbL

XAb2

XBa2

XAa2

(XBp2)

Py

PG

Fl

Fr

PBP

PaL

Dr3

Dr2

XAk

Ak1

Bk1

XBk

Pz

P1

XAa2

Btr

(XBp1)

SWING MOTOR

TRAVEL MOTOR

HYDRAULIC TANK

FRONT

PUMP

REAR
PUMP

SW AM

BK BM

XBa1

XBk

XAb1 XBb1

XAk

XAtr

XBtr

 Pz

 Pk

 dr2

Pm1

Pm2

TR

XBtl

XAtl

XBs

XAs

XAa1

A1

A2

A3

A4

Pns

A5

SOLENOID VALVE

LEVER
DOWN

LEVER

UP

SAFETY
SOLENOID VALVE

PG(S/Motor)
PG(MCV)

P1

P2

P3

P4

ARM

CYLINDER

BUCKET

CYLINDER

BOOM

CYLINDER

R2

P2

TRAVEL(LH)

SWING

BOOM 2

ARM 1

ARM 2

BUCKET

BOOM 1

OPTION

TRAVEL(RH)

XAtl

XBs

XAs

Pns

Dr6

XAb2

XBa2

Px

R1

PH

Dr1

XAa1

XBa1

XBtl

2. SAFETY VALVE

(SAFETY LEVER)