Komatsu PC500LC-10R Shop Manual page 269

10 STRUCTURE AND FUNCTION COMPONENT PARTS OF HYDRAULIC SYSTEM
BOOM HYDRAULIC DRIFT PREVENTION VALVE OF CONTROL VALVE
FUNCTION OF BOOM HYDRAULIC DRIFT PREVENTION VALVE OF CONTROL
VALVE
AEP21629
When the boom is not operated with the R.H. work equipment control lever, this function is used to prevent the
pressurized oil in the boom cylinder bottom from leaking through spool (1) and causing boom hydraulic drift.
PC500LC-10R 10-175