COMPONENT OPERATION / Others (Upperstructure) SHOCKLESS VALVE The shockless valve is provided in the boom lower circuit and operated when the boom lower control lever is suddenly returned. Operation 1. When the boom lower control lever is returned, return oil from the spool in control valve (boom lower side) acts on port A. 2. Oil in port A flows to chamber D (1) through ori- fice (6). 3. Pressure in chamber D (1) is routed to port B through passage (2) in spool (5) and housing (4), so that pressure in chamber D (1) decreases. 4. As pressure difference between front and rear of orifice (6) occurs, spool (5) is move to the left by pressure acting on the spring (3) side.
Therefore, passage (2) in spool (5) and housing (4) is closed and pressure oil is blocked. 5. When passage (2) is closed, pressure in cham- ber D (1) increases and spool (5) moves to the right. Passage (2) is open again and pressure oil flows to port B. 6. By repeating steps 3 to 5, pressure oil returns to the port B side gradually, so that the spool in con- trol valve is slowly returned. 2 3 Port B 4 1 T1J1-03-07-012 Port A 1 - Chamber D 3 - Spring 5 - Spool 6 - Orifice 2 - Passage 4 - Housing 5 6 T3-7-8