COMPONENT OPERATION / Others (Upperstructure) Proportional Solenoid Valve Controls by an electric current signal from MC and outputs pressure in proportional to degree of the electric current. When not energized (In neutral): 1. Spring (2) pushes spool (1) to the right and output port S is connected to tank port T. When energized: 1. Solenoid (3) pushes spool (1) to the left due to force in proportional to the electric current flowing through solenoid (3). 2. Pilot oil pressure from port P flows into output port S and pressure at output port S increases. 3. Pressure at outpur port S acts on step part a on spool (1).
Because of difference in the pressure receiving area between step part a, spool (1) is pushed to the right. 4. When pressure at port S increases and the force to push spool (1) to the right overcomes the force to push spool (1) to the left by solenoid (3), spool (1) moves back to the right side and the passage between output port S and port P is closed. As a result, pressure increase at port S stops. T107-02-07-005 1 - Spool 2 - Spring 3 - Solenoid T3-7-4 1 2 3 T S P a a