Hyundai HL955 Manual page 493

(3) Boom lower position
A2 B2
T
P
a2
b2
6
a2
a1
B2
P A1 A2
B1
LS
Boom
Bucket
Pst
T
6
b1 b2
Hydraulic circuit
75796WE53
When the pilot pressure is led to the port a2, the boom spool moved to lower position.
Oil from the pump flows to the cylinder port A2, through the load holding valve and oil from the
cylinder flows into the tank passage through the cylinder port B2.
When the lowering speed of boom is faster, the return oil from the large chamber of boom
cylinder combines with the oil from the pump through regeneration check valve (6), and flows into
the small chamber of the cylinder. This prevents cylinder cavitation by the negative pressure when
the pump flow cannot match the boom down speed.
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