Shibaura ST330, Workshop Manual

Page: 179 / 250

169
(4) Bypass spool.
The bypass spool and spring are located in the control valve spool.
The bypass spool actions for prevent the shock to the hydraulic system when the much oil flows from the oil pump at a
time.
The bypass spool is stayed the R.H. side by spring and the cylinder passage pressure (A) higher than the oil pump
passage pressure (B).
When the control lever is moved to the raising position and the much oil f1ows from the oil pump, the cylinder passage
pressure (A) lower than the oil pump passage pressure (B), and the bypass spool is moved to the L.H. side then the
bypass circuit is opened, and remained oil flows via the bypass spool to the sump.
When the cylinder passage pressure (A) and oil pump passage pressure (B) are became equal, the bypass spool returns
to the R.H. side then close the bypass passage.
492Y
Bypass spool-oil flow
1.
Control valve spool
2. Spring
3. Bypass spool
A. Cylinder passage pressure
B. Oil pump passage pressure