3-8
3. BOOM PRIORITY SYSTEM
PS
(P4)
(P3)
N2
Pca
Dr3
P2c2
Ba
Aa
PAa
PBa
Bo
Ao
PAo
PBo
(Ck2)
Drb
PBb2
PSp
Dra
Bs
As
PAs
PBs
Dr4
Pns
Br
Ar
PAr
PBr
R3
TRAVEL(RH)
SWING
BOOM 2
T1
Pa
P2
P1 P1g
P2g
R4
(PTb)
PS
PL1
Py
PBL
PAL
Px
P
PBb
PAb
Ab
Bb
P2c1
Dr3'
PBc
PAc
PAcs
Bc
Ac
PBa2
PAa2
Pcb
N1
OPTION
ARM 1
ARM 2
BUCKET
BOOM 1
TRAVEL(LH)
PS
PS
PS
PS
PS
A
B
C
TRAVEL
P
T
RCV PEDAL
(2)
PBr
(1)
PAr
(4)
PBL
(3)
PAL
BOOM
P
T
BUCKET
ARM
P
T
SWING
c
e2
d1
h1
h2
P2c1
PAb
(4)
PBc
Pca
PAc
PAcs
PBb2
PBb
PAa2
P2c2
PAa
PBa2
PBa
PBs
PAs
PSp
Dr#,dr#
T
LINE FILTER
P3
P2
P1
P4
Pns
(MCV)
PL1
(MCV)
P
(T/Joint)
A1
A2
A4
A5
SH
(2)
(1)
(3)
(4)
(2)
(3)
(1)
HYDRAULIC TANK
BOOM PRIORITY
EPPR VALVE
Swing
reducing
spool
TRAVEL MOTOR
SWING MOTOR
ARM
CYLINDER
BUCKET
CYLINDER
BOOM
CYLINDER
PILOT
PUMP
BL
AL
PG(S/Motor)
Pa(MCV)
Psv1(M/PUMP)
P(MCV)
Boom speed
B
a
b
d
e
f
g
h
j
PUMP
A1
PUMP
A2
A
D
E
F
G
H
J
380L3HC04
When carrying out the combined operation of swing and boom up, the boom up operating speed is
lowered then normal operation.
To increase working efficiency, swing speed reducing system is used.
The pilot oil from pilot pump flow into Pns port in main control valve through boom EPPR valve. Pns
oil pressure moves swing reducing spool to upper position and oil flow rate to the swing motor
decreased.
Then, the boom up speed is increased. This is called the boom priority system.
The boom up speed can be adjusted by the cluster. Refer to page 3-20 of the operator's manual.