6-8
WHEN THE RCV LEVER IS IN THE DUMP POSITION
If the RCV lever (4, bucket) is pushed right, the bucket spool is moved to dump position by pilot oil
pressure from EH control block (6).
The oil from main pump (1) flows into main control valve (3) and then goes to the small chamber of
bucket cylinder (14) by pushing the load check valve of the bucket spool.
The oil at the large chamber of bucket cylinder (14) returns to hydraulic tank (22).
When this happens, the bucket is dumped.
When the dumping speed of bucket is faster, the oil returned from the large chamber of bucket
cylinder combines with the oil from the pump, and flows into the small chamber of the cylinder.
This prevents cylinder cavitation by the negative pressure when the pump flow cannot match the
bucket dump speed.
·
·
·
·
·
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
Dump
Roll back
Up
Down
Floating
Bucket
Boom
Aux
Regeneration
check valve
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)
4)
757F6WE06
Summary of Contents for HL955
Page 557: ...7 6 MEMORANDUM MEMORANDUM ...
