SANY LATIN AMERICA
4-111
SY195/205/215/225C9 Crawler Hydraulic Excavator
Structure and Function
Shop Manual - June 2013
Operation
1. When in neutral
●
Ports (A) and (B) of the control valve and
ports (P1) and (P2) of the pilot valve are
connected to drain chamber (D) via ori
fi
ce
(f) in plunger (1).
2. Fine control (Neutral to fi ne control)
●
When piston (4) is pushed by disc (5),
retainer (9) is pushed, plunger (1) is also
pushed by metering spring (2), and moves
down.
●
When ori
fi
ce (f) is shut off from drain cham-
ber (D), it is almost simultaneously inter-
connected to pump pressure chamber (PP).
Pilot pressurized oil of the control pump is
led to port (A) from port (P1) via ori
fi
ce (f).
When the pressure at port (P1) becomes
higher, plunger (1) is pushed back and
orifice (f) is shut off from pump pressure
chamber (PP). At almost the same time, it
is connected to drain chamber (D) to re-
lease the pressure at port (P1). As a result,
plunger (1) moves up and down until the
force of metering spring (2) is balanced
with the pressure at port (P1).
●
The relationship of the position of plunger
(1) and body (10) [ori
fi
ce (f) is in the middle
between drain chamber (D) and pump
pressure chamber (PP)] does not change
until retainer (9) contacts plunger (1). Me-
tering spring (2) contracts in proportion to
the stroke of the control lever. Pressure
at port (P1) also rises in proportion to the
stroke of the control lever. In this way, the
control valve spool moves to a position
where the pressure of chamber (A) (same
as pressure at port (P1)) and the force of
the return spring of the control valve spool
are balanced.
ZX215-1002115
A
M
M
B
P1
P
P2
f
1
T
D
Control valve
Pilot
pump
ZX215-1002116
A
M
M
B
P1
P
P2
f
1
T
D
Control valve
Pilot
pump
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