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2-38
Boom down operation
刯
During the boom down operation, pilot pressure enters through port P2c1 and PAb. Pilot
pressure transfers the spool (511) in lock valve assy in the right direction in figure. By the transfer
of the spool, firstly the hole (a) is blocked and pressurized oil from the boom cylinder head side
(H) does not enter to spring chamber (RH). Secondly, oil in spring chamber (RH) enters through
hole (b) and flows to port Dr3'.
Therefore, the poppet is lifted by the pressure of the boom cylinder head side (H) and the
function of the lock valve is released.
Boom cylinder
head side(H)
511
P2c1
Dr3'
(a)
(b)
LCb1
(RH)
HV
PBb
3809A2MC25
Boom up operation
到
During the boom up operation, the pilot pressure enters through port PBb. The oil flowing from
the boom 1 spool pushes open the poppet (513) and flows to Port Bb.