SANY LATIN AMERICA
4-115
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 lever (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
chamber (D), it is almost simultaneously
interconnected 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).
●
Metering spring (2) contracts in proportion
to the stroke of the control lever.
●
Pressure at port (P1) also rises in propor-
tion to the stroke of the control lever.
●
In this way, the control valve spool moves
to a position where the pressure of cham-
ber (A) (same as pressure at port (P1)) and
the force of the return spring of the control
valve spool are balanced.
ZX215-1002121
P1
P2
B
A
1
P
f
D
T
Pilot pump
Control valve
ZX215-1002122
10
P1
P2
B
A
1
P
f
D
T
PP
5
4
9
2
Pilot pump
Control valve
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