Komatsu Utility SK714-5, Shop Manual

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10-72 SK714-5 SK815-5 SK815-5 turbo
FUNCTION
1. NEUTRAL
Ports P1 and P2 of the PPC valve are connected to
drain chamber D through fine control hole f in spool
(1). (Fig. 1)
.
2. During fine control (NEUTRAL
→
fine control)
• When piston (4) starts to be pushed by disc (5), re-
tainer (9) is pushed; spool (1) is also pushed by me-
tering spring (2), and moves down.
When this happens, fine control hole
f is shut off
from drain chamber D , and at almost the same time,
it is connected to pump pressure chamber PP , so pi-
lot pressure oil from the control pump passes throu-
gh fine control hole
f and goes from port P1 .
When the pressure at port P1 becomes higher, spo-
ol (1) is pushed back and fine control hole f is shut off
from pump pressure chamber PP .
At almost the same time, it is connected to drain
chamber
D to release the pressure at port P1 .
When this happens, spool (1) moves up or down so
that the force of metering spring (2) is balanced with
the pressure at port
P1 . The relationship in the po-
sition of spool (1) and body (10) (fine control hole f is
at a point midway between drain hole D and pump
pressure chamber PP ) does not change even if the
pressure at port P1 becomaes max.
Therefore, metering spring (2) is compressed pro-
portionally to the amount of movement of the control
lever, so the pressure at port
P1 also rises in pro-
portion to the travel of the control lever. (Fig. 2)
RKS00820
1
T
P
f
D
P2 P1
Fig. 1
RKS00830
1
T
P
f
D
P
2
P
1
4
5
3
2
10
PP
9
Fig. 2
STRUCTURE AND FUNCTION
L.H. PPC VALVE - PATTERN CHANGE (OPTIONAL)