SANY LATIN AMERICA
4-54
SY195/205/215/225C9 Crawler Hydraulic Excavator
Structure and Function
Shop Manual - June 2013
4.5.2.4 Boom
[Pilot circuit]
●
When the boom 1 spool (303) is switched,
the side path is closed and pressure at port
Px (work equipment signal port) rises.
[Main circuit]
●
When boom UP is operated, pilot pressure
oil is supplied into port XAb1 and boom 1
spool (303) moves to the left. Working oil
from port P1 is introduced into neutral by-
pass (2) via main passage (1). Neutral by-
pass is cut off by switching boom 1 spool
(303). Therefore, working oil in the parallel
passage pushes open the cone valve (511)
of the check valve, and
fl
ows into the boom
1 spool (303) via the U passage. Then, it
flows into the periphery of boom 1 spool
(303) and is supplied into the boom cylin-
der head end (H) via port Ab.
●
At the same time, pilot pressure oil is also
supplied to port XAb2 and boom 2 spool
(307) moves to the right. Working oil from
port P2 is introduced into neutral bypass.
Neutral bypass is cut off by switching the
boom 2 spool (307). Therefore, working
oil in the parallel passage
fl
ows into boom
2 spool (307) via the U passage. Then, it
pushes open the cone valve (511) of the
check valve and merges with port Ab and
is supplied into the boom cylinder head
end (H). This is called the boom conflu-
ence function.
●
On the other hand, return oil from the
boom cylinder rod end (H) via port Bb
fl
ows
into the periphery of boom 1 spool (303)
and returns to the working oil tank via tank
port (R1).
(1) Boom UP
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