Komatsu PC600LC-7 Manual page 155

STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
3. At boom LOWER
Operation
• When the boom is lowered, the pilot pressure
flows to port PI from the PPC valve pushes pilot
spool (3) and the pressurized oil in chamber b in-
side the poppet is drained.
When the pressure at port CY rises because of
the pressurized oil from the bottom end of the
boom cylinder, the pressure of the pressurized
oil in chamber b is lowered by orifice a.
If the pressure in chamber b drops below the
pressure at port CY, poppet (5) opens, the pres-
surized oil flows from port CY to port V, and then
flows to the control valve.
If any abnormal pressure is generated in the cir-
cuit at the bottom end of the boom cylinder,
safety valve (1) is actuated and drain oil from
port CY to port T.
PC600, 600LC-7
BOOM HOLDING VALVE
10-123