SANY LATIN AMERICA
4-56
SY195/205/215/225C9 Crawler Hydraulic Excavator
Structure and Function
Shop Manual - June 2013
[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.
At the same time, pressure oil is supplied
to port PbL and the release signal of lock
valve option set (252) is sent out.
[Main circuit]
●
When boom DOWN is operated, pilot pres-
sure oil is supplied to port XBb1. Boom 1
spool (303) moves to the right. As a result,
working oil from P1 is introduced into the
neutral bypass (2) via main passage (1).
Neutral bypass is cut off by switching boom
1 spool (303). Therefore, working oil
fl
own
into 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 cylinder rod end (R) via port Bb.
●
On the other hand, return oil from the
boom cylinder head end (H) passes the
hole (a) and the periphery of boom 1 spool
(303).
●
Return oil pressure rises due to the self
weight of the boom. Cone valve (303-317)
in the spool is pushed to the right. Return
oil
fl
ows to the outside of spool. The pres-
sure oil is supplied into the boom cylinder
rod end (R) as the working oil for boom
DOWN operation. This is called the boom
regeneration function. Part of the oil that
fl
ows into the inside passage of the spool
via hole (a) returns to the working oil tank
via hole (b).
(2) Boom DOWN
H
Ab
511
R
Bb
XBb1
(a)
(b)
(303-317)
ZX225-1102017
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