6-6
WHEN THE RCV LEVER IS IN THE LOWER POSITION
When the RCV lever (4, boom) is pushed forward, the boom spool is moved to lower position by
pilot pressure from EH contril block (6).
The oil from main pump (1) flows into main control valve (3) and then goes to small chamber of
boom cylinder (13) by pushing the load check valve of the boom spool.
The oil returned from large chamber of boom cylinder (13) returns to hydraulic tank (22) through
the boom spool at the same time.
When the lowering speed of boom is faster, the return oil from the large chamber of boom cylinder
combines with the oil from the pump through the regeneration check valve, and flows into the small
chamber of the cylinder.
This prevents cylinder cavitation by the negative pressure when the pump flow cannot match the
boom down speed.
·
·
·
·
Dump
Roll back
Up
Floating
Bucket
Boom
Aux
Down
Regeneration
check valve
1
T
A1
P1
X1
X2
X3
S1
B2
L3
L4
B1
L1
L2
S1
S2
X1
X2
PS
Aux
Bucket
Boom
Joystick
4
1
EH20
EH19
EH22
EH21
P
T
6(4)
3(2)
5(3)
2(1)
( ) : 2 Spool
EH18
EH17
To MCV
a3 b3 a1 b1
a2
b2
Return line
Fan & brake pump
Steering system
Return line
Steering valve
(EHPS) EF port
Steering valve
(EHPS) LS port
3
LH
B1
A1
B2
A2
LS
a2
b2
b1
a1
Pst
B3
A3
b3
a3
T
P
PS
PS
RH
23
22
25
24
12
11
26
28
28
29
6
5
4
4'
40
14
13
29
29
Control unit
(Electro-Hydraulic & Joysick steering)
2)
757F6WE04
Summary of Contents for HL955
Page 557: ...7 6 MEMORANDUM MEMORANDUM ...
