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Hyundai Excavator R210LC-7. Service and repair manual - page 5

2-30

Negative control(With fine metering)

(2)

XAb1

XBb1

Ab1

Bb1

LCb1

Ab1R

Bb1R

379

370

303 511

In the case, for example, when the pilot control lever for main boom is slightly operated, the pilot
pressure XAb1 shifts the main boom spool(303) partially in the left direction. So the path(19) is
partially opened and the center bypass(18) is shut slightly. The hydraulic fluid thereby separates.
One part flows via the orifice(7) through the path(18) and the other portion flows into the parallel
path(6), the path(19) and the port Ab1. The flow from the path(18) through the orifice(7) decreases
slightly and the pressure Fr in the path(10) thereby also slightly decreases. As the pressure Fr
becomes lower, the discharge of the pump P2(27) increases. With the pilot control lever shifted
even more the path(18) is shut off by the shifting of the spool(303) and then the flow through the
bypass becomes zero. The pressure in the path(10) becomes zero and the discharge of the pump
P2(27) becomes maximum.(Qmax)
Because the discharge of the pump is adjusted by operating the pilot control lever slightly, the
precise moving of the actuator is realized.
For the pump P1(28) the same negative control principle of operation occurs utilizing the orifice(9).

2-31

EACH SPOOL OPERATION

Boom control

Boom up operation

(1)

511

303

372

374

307

XAb1

XAb2

(PSP)

XBb1

Ab1

Bb1

379

370

LCb1

Ab1R

CSP

376 370

CCb

511

516

Bb1R

The main boom up operation becomes fast because the hydraulic fluid from the pump P2 that is
directed to the port P2 is combined in the casing that of the pump P1 which enters port P1. The
confluence flow is supplied to the head side of the boom cylinder. In low speed operation, only the
boom1 spool(303) operates and is supplied with hydraulic fluid from the pump P2.

The hydraulic fluid from the pump P2 flows into the boom1 spool(303) through port P2 and parallel
path(6). The hydraulic fluid from the pump P1 flows to the boom2 spool(307) through pump port
P1 and the parallel path(22).
During the boom up operation, the pilot pressure from the pilot control valve is supplied into the port
XAb1 and shifts the boom1 spool(303) in the left direction against the springs(370) and (370). the
hydraulic fluid from the pump P2 enters the parallel path(6) and then passes through the load check
valve LCb1(511) and boom1 spool(303) and check valve HV(516) then flows into the port Ab1.
Following this it flows into the head side of the boom cylinder.

At the same time, the pilot pressure through the port XAb2 shifts the boom2 spool(307) in the left
direction against the springs(374) and (372). The hydraulic fluid from the pump P1 enters via the
parallel path(22) and center bypass(21), then passes through the load check valve CSP(511),
boom2 spool(307) and the load check valve CCb(511). Then flows combine in path(8) and are
directed to port Ab1 and the head side of the boom cylinder.
The flow from the rod side of the boom cylinder returns to the boom1 spool(303) through the port
Bb1. Thereafter it is directed to the return port R2 through path(13).

2-32

Boom down operation

511

303

372

374

307

XAb1

XAb2

(PSP)

XBb1

Ab1

Bb1

379

370

LCb1

Ab1R

CSP

376 370

CCb

511

516

Bb1R

During the boom lowering operation, the pilot pressure from the pilot control valve is supplied to port
XBb1 and PbL and shifts the boom1 spool(303) in the right direction against the springs(370) and
(379).
The hydraulic fluid from the pump P2 enters the parallel path(6) and is directed to the port Bb1
through the load check valve LCb1(511). Following this is flows into the rod side of the boom
cylinder.
The return flow from the head side of the boom cylinder returns to the boom1 spool(303) through
the port Ab1. Thereafter it is directed to the return port R2 through path(4).
Additionally, the return flow is restricted in path(45), which lowers the boom cylinder at a suitable
speed.

2-33

Arm control

Arm roll out operation

(2)

379

511

302

XAa1

Aa1

Aa1R

LCa1

516

Ba1R

XBa1

370

306

372

374

XBa2

LCa2

XAa2

Ba1

During the arm roll out operation, the pilot pressure from the pilot control valve is supplied to the
pilot ports(XBa1& XBa2) and shifts the arm1 spool(302) in the left direction against the springs
(370) and (379) and shifts the arm2 spool(306) in the left direction against the springs(374) and
(372). The hydraulic fluid from the pump P1 flows through the load check valve LCa1(511), lock
valve HV(516), and then through parallel path(22). It is then directed to the rod side of the arm
cylinder through the port Ba1.

At the same time, the pilot pressure through the port XBa2 shifts the arm2 spool(306) in the left
direction against the springs (374) and (372). The hydraulic fluid from the pump P2 enters via the
parallel path(22) and center bypass(21), then passes through the check valve of the boom priority
valve(104), arm2 spool(306). The flows are combined and directed to port Ba1 and the rod side of
the arm cylinder.
The flow from the head side of the arm cylinder returns to the arm1 spool(302) through the port
Aa1. Thereafter it is directed to the return port R2 through path(13).

2-34

379

511

302

XAa1

Aa1

Aa1R

LCa1

516

Ba1R

XBa1

370

306

372

374

XBa2

LCa2

XAa2

Ba1

(c)

(a)

Arm roll in operation

During light load only

2-35

379

511

302

XAa1

Aa1

Aa1r

LCa1

516

Ba1R

XBa1

370

306

372

374

XBa2

LCa2

XAa2

Ba1

(d)

(e)

(f)

(a)

(b)

The pressure in the arm cylinder head side increases

2-36

During the arm roll in operation, the pilot pressure from the pilot control valve is supplied to the
ports XAa1, XAa2 and PaL and shifts the arm1 spool(302) in the right direction against the
springs (370) and (379) and shifts the arm2 spool(306) in the right direction against the springs
(384) and (372).
During the arm roll in operation, the hydraulic fluid from the pump P1 flows into the arm1
spool(302) through the parallel path(22). Then it enters into the head side of the arm cylinder
through the load check valve LCa1(511), check valve HV(516) and port Aa1.
At the same time, the hydraulic fluid from the pump P2 flows into the arm2 spool(306) through
the parallel path(22). Then it enters into the head side of the arm cylinder through the check
valve of boom priority valve(104) and port Aa1.

The return flow from the rod side of the arm cylinder is pressurized by self-weight of arms and so
on, and returns to port Ba1. The pressurized oil returning to port Ba1 enters into the arm1 spool
through the outside of the arm1 spool. During a light load only, it pushes open the sleeve check
valve, flows the parallel path reversely from spool hole(c), and joints into port Aa1. This is called
the arm regeneration function.
When the pressure in the arm cylinder head side increases, the piston(d) and sub spool(e) are
transferred in the right direction, and at the same time the sleeve check valve(f) is from the arm
cylinder rod side enters flow port Ba1 through the periphery hole(a) of the arm1 spool into the
spool, flows out through the periphery hole(b) of the spool, and returns through the tank port R2
to the hydraulic oil tank.

2-37

Bucket control

Bucket roll in operation

(3)

304

511

XBk

XAk

Bk1

Ak1

BkR

AkR

LCk

379 370

During the bucket roll in operation, the pilot pressure from the pilot control valve is supplied to port
XBk and shifts the bucket spool(304) in the left direction against the springs(370) and (379).
The hydraulic fluid from the pump P2 enters the parallel path(6) and is directed to the port Bk1
through the load check valve LCk(511). Following this it flows into the head side of the bucket
cylinder.
The retutn flow from the rod side of the bucket cylinder returns to the bucket spool(304) through the
port Ak1. Thereafter it is directed to the return port R2 through path(13).

2-38

Bucket out operation

304

511

XBk

XAk

Bk1

Ak1

BkR

AkR

LCk

379 370

During the bucket roll out operation, the pilot pressure from the pilot control valve is supplied to port
XAk and shifts the bucket spool(304) in the right directed agains the springs (370) and (370).
The hydraulic fluid from the pump P2 enters the parallel path(6) and is directed to the port AK1
through the load check valve LCk(511). Following this it flows into the rod side of the bucket
cylinder.
The return flow from the head side of the bucket cylinder returns to the bucket spool(304) through
the port Bk1. Thereafter it is directed to the return port R2 through path(4).

2-39

Swing control

(4)

370

251

305

XAs

XBs

Pns

379

254

During the swing right or left operation, only the hydraulic fluid of the pump P1 is supplied to the
swing motor.
The pilot pressure from the pilot control valve is supplied to the port XAs and shifts the swing spool
(305) in the left direction against springs (370) and (379). Hydraulic fluid from the pump P1 flows
into the swing spool(305) through the parallel path(22). Then it is directed to the swing motor
through the check valve LCs(254) and the port As. As a result, the swing motor turns and the
return flow from the swing motor enters port Bs. The flow from the motor returns to the tank port
R2 through the swing spool(305) and path(13). In the case of the opposite operation, the operation
is similar.

2-40

Travel control

(5)

329

328

310

XAtl

XBtl

Atl

Btl

328 329

301

XAtr

XBtr

Btr

Atr

During the travel operation, the hydraulic fluid of the pump P1 is supplied to the travel motor and the
hydraulic fluid of the pump P2 is supplied to the other travel motor.
The pilot pressure from the pilot control valve is supplied to the port XAtr and XAtl.
And it shifts the travel right spool(301) and travel left spool(310) in the left direction against springs
(328) and (329). Hydraulic fluid from the pump P1 flows into the travel left spool(310) through the
parallel path and hydraulic fluid from the pump P2 flows into the travel right spool(301). Then they
are directed to the each travel motor through port Atl and Atr. As a result, the travel motors turn
and the return flow from the travel motors enter port Btl and port Btr. The flow from the motors
returns to the tank port R2 through the travel spools(310 and 301).
In the case of the opposite operation, the operation is similar.

2-41

CIRCUIT PRESSURE PROTENCTION

The control valve has two kinds of relief valve to limit the pressure in a circuit.

Main relief valve

Limits the pressure of the main hydraulic system.

(1)

CMR1

CMR2

324

325

391

601

338

The hydraulic fluid from the pump P1 and the pump P2 enters the control valve through ports P1
and P2, respectively. From here the flow is directed to the main relief valve(601) through the check
valve CMR1 or CMR2(511) and path(11). The pressure in path(11) is limited by the main relief
valve(601) to its set pressure.

2-42

Main relief operation while working

While the pressure in path(11) is lower than the set pressure of main relief valve(601), the poppet
(24) is seated and the hydraulic fluid in path(11) can not escape to the return(14). When the
pressure in path(11) approaches the pressure setting, poppet(24) opens against the spring(39). As
the flow in chamber(33) escapes into the return(14) through path(32), its pressure decreases. At
the same time, hydraulic fluid in path(11) flows into path(30) with a pressure drop across orifice(31).
Then pressure in spring chamber(35) becomes lower because it bleeds off through path(30). The
pressure from path(11) pushes the plunger(38) in the left direction against the spring(34). Then
plunger(38) opens and hydraulic fluid in path(11) escapes into the return(14) and maintains the
pressure setting. The pressure setting is adjusted with adjustment screw(25).

2-43

Port relief valve

Limits the service pressure in a cylinder circuit.

(2)

Port relief valves and make up valves are fitted between the cylinders of the working devices(Boom,
arm, bucket) and their spools. In the case of an external force acting on the cylinder rod with its
spool in neutral, the pressure in the cylinder could become excessive. The port relief valve(602)
restricts this pressure to the set pressure of the valve.
Port relief valve(602) have also the additional function of a make up valve. It is possible, under the
influence of an external force acting on a cylinder that a condition can occur where insufficient flow
is available to match cylinder velocity. If this occurs then a vacuum and thereby cavitation could
exist. To eliminate such an occurrence, a make up valve operates to break this vacuum by
supplying the return flow into the cylinder.
The hydraulic fluid between the cylinder and its spool flows into the path(6) to pressurize the port
relief valve(602). The hydraulic fluid in the path(6) flows into the spring chamber(3) through the
path(4) in the piston(10). If the pressure is lower than the pressure setting, the poppet(2) is shut off
because the force of the spring(1) overcomes the pressure. So the path(6) and the spring
chamber(3) have the same pressure. Because the spring chamber(3) side pressured area of the
seat(8) and the plunger(9) is larger than that of the path(6) side, seat(8) and the plunger(9) are
pushed in the right direction to be seated securely and then the hydraulic fluid in the path(6) doesn't
escape into the return path(5).

2-44

Port relief function

When the pressure in the path(6) is pressurized to the pressure setting, the poppet(2) is pushed
open against the spring(1). The hydraulic fluid in the chamber(11) flows into the return path(5)
through the path(13) with reducing its pressure. The piston(10) is shifted in the left direction by the
pressure in the path(6) and stops on the end of the plug(7).
The hydraulic fluid in the path(6) flows into the chamber(11) through the path(4) in the piston(10)
and the spring chamber(3). Because the differential pressure occurs between the pass(6) and the
pass(4) by the orifice between the outernal diameter of the end of the piston(10) and the internal
diameter of the plunger(9), the pressure in the spring chamber(3) becomes low and therefore the
plunger(9) is pushed in the left direction with the path(12) opened so that the hydraulic fluid in the
path(6) flows into the return path(5).

2-45

Make up function

Following this then the case of a port relief valve operating as a make up valve is now explained.
In the case that the hydraulic fluid in the cylinder rod(Head) side escapes from the port relief valve
(602), then hydraulic fluid needs to be supplied because vacuum occurs in the head(Rod) side.
When cacuum occurs in the side of the path(6), it also occurs in the spring chamber(3) through the
path(4). The pressure in the side of the return path(5) acts on the seat(8). The seat(8) is shifted in
the left direction by the return pressure because the spring chamber(3) sides of the seat(8) and the
plunger(9) are under a vacuum. The hydraulic fluid in the return path(5) flows into the path(6) so as
to break the vacuum in the path(6) side.

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