SYSTEM / Hydraulic System Swing Parking Brake Release Circuit (Refer to the Swing Device group / COMPONENT OPERA- TION.) When the front attachment and/or swing function is operated, pilot pressure selected by the shuttle valves in signal control valve shifts the swing parking brake release spool. Consequently, release signal pressure is routed to the swing motor and releases the swing park- ing brake. Travel Motor Swash Angle Control Circuit (Refer to the Travel Device group / COMPONENT OP- ERATION.) Pilot pressure from solenoid valve unit (SI) regu- lates the travel motor swash angle control valve.
(Refer to the Valve Control in Control System group / SYSTEM.) Hydraulic Oil Heat Circuit (Refer to the Others (Upperstructure) group / COMPONENT OPERA- TION.) When the pilot shut-off solenoid valve is closed, pilot pressure oil is routed to the signal control valve so that hydraulic oil is warmed while pass- ing through the orifice in signal control valve. This warmed hydraulic oil flows to the signal con- trol valve and pilot valves so that the pilot system components are warmed. T2-4-10