COMPONENT OPERTATION / Control Valve Releasing Operation 1. During boom lower operation (arm roll-in opera- tion in case of the arm anti-drift valve), spool (8) in boom 1 moves to the left. Pressure oil from port 4Pc3 acts on piston (2) through the inner pas- sage. 2. As piston (2) pushes switch valve (3), switch valve (3) is shifted. 3. Pressure oil in the spring (5) chamber of check valve (6) pushes to open check valve (1) through the external circumference of switch valve (3) so that pressure oil flows to the hydraulic oil tank. 4. Therefore, pressure in the spring (5) chamber decreases.
At this time, a pressure difference between port 4A3 and the spring (5) chamber arises due to orifice (7) in check valve (6). 5. When this pressure difference becomes stronger than the spring (5) force, check valve (6) opens. Consequently, return oil from the boom cylinder bottom side flows to the hydraulic oil tank. From Port 4Pc3 (Pressure Oil from Pilot Pump) From Pump 1 Boom 1 Spool Anti-Drift Valve (Switch Valve) Boom Cylinder To Boom 2 Spool (Hydraulic Oil Tank) Check Valve Anti-Drift Valve (Check Valve) T450-03-03-038 T3-3-30