COMPONENT OPERATION / Others (Upperstructure) 4-SPOOL SOLENOID VALVE UNIT Controls the control valve and the valve in travel mo- tor by the signal from MC (main controller). (Refer to Control System / SYSTEM.) The 4-spool solenoid valve unit consists of proportional solenoid valves (SC, SF, SI and SG). SC: Control the boom overload relief control valve in control valve SF: Control the boom flow rate control valve (switch valve) in control valve SI: Control the travel motor swash angle control valve SG: Increase pressure of the main relief valve in control valve SC SF SI SG T1V1-03-07-007 T3-7-3