Hyundai Excavator R450LC-7. Service and repair manual - page 6

2-28

Swing spool
When the swing spool is pushed to the right by the pilot pressure of port Pb2, the neutral
passage(L1) is closed, the oil discharged from pump P1 pushes up the load check valve(S2-1),
passage(S2-2) via parallel passage(L3) and then flows into port B2.
The oil from port A2 return to the tank via the tank passage(Ta).

(2)

45071MC05

2-29

BOOM SPOOL

Neutral
This valve is providing the anti-drift valve on the cylinder bottom side of boom 1 section.  In
neutral, the poppet(AD1) is seated by the pressure of spring chamber(AD5) because the oil from
the port A7 is connection with spring chamber(AD5) via passage(AD2), spool(AD3) and
passage(AD4).

3)

(1)

45071MC06

2-30

Boom up (flow summation)
When the boom 1 spool is pushed to the left by the pilot pressure of port Pa7, the neutral
passage(R1) is closed, the oil discharged from pump P2 flows into the port A7 via parallel
passage(R3), the load check valve(S7-1).  At the same time, the boom 2 spool is pushed to the
left by the pilot pressure of port Pa3, the neutral passage(L1) is closed, the oil discharged from
pump P1 flows into the port A7 via parallel passage(L3), the load check valve(S3-1) and then joins
to the passage(

⑥

).  

The return oil from port B7 flows into the tank via the tank passage(Ta).

(

(

2)

45071MC07

2-35

Arm recycling (arm in)
When the arm is at in position, the spool(S5-6) stroke against the passage(S5-2) pressure guided
from the passage(S5-5) is changed according to the opening angle of arm recycling orifice(Lc8).
When the pressure of the passage(S5-2) is high and this stroke is increased, the opening angle of
orifice(Lc8) become large.  On the contrary, when the pressure of passage(S5-2) is low, this
stroke is decreased, the opening angle of orifice(Lc8) become small.
Therefore, the flow rate for arm recycling is changed by the pressure in bottom side of arm
cylinder.

(3)

45071MC11