330D, 336D and 340D Excavators Hydraulic System – Relief Valve (Cushion Crossover) – Anti-Reaction Valves

At the stop of a swing operation, it is difficult to smoothly stop the upper structure and implements at the desired position. This is due to the mass (weight and size) of the upper structure. The outlet port of the swing motor is blocked. This causes an oscillation or a rocking motion in the swing motor. Anti-reaction valves (3) and (4) provide a more exact swing movement. The anti-reaction valves also prevent shock load at the stop of a swing operation. Anti-reaction valves (3) and (4) are located in block (1) . Block (1) is mounted on swing motor (2) .

During a swing operation of the upper structure, the oil delivery from the idler pump flows through passage (8) or passage (10) in block (1) to motor rotary group (5) . When the swing joystick is in the NEUTRAL position, the swing control valve is in the NEUTRAL position. The oil delivery from the idler pump is blocked at the swing control valve. No oil delivery flows to the motor rotary group. The return oil from the swing motor is also blocked at the swing control valve.

Plunger (24) in anti-reaction valve (3) shifts downward by the force of spring (25) until the plunger is stopped by piston (26) . Valve seat (23) shifts downward by the force of spring (22) until the valve seat comes in contact with plunger (24) . Plunger (16) and valve seat (14) in anti-reaction valve (4) are shifted downward in the same manner as anti-reaction valve (3) .

When the swing joystick is moved from the NEUTRAL position in order to perform a swing operation, the swing control valve shifts. The oil delivery from the idler pump flows through the swing control valve and port (11) in block (1) . The oil delivery then flows through passage (10) , passage (12) and motor rotary group (5) . Return oil from the motor rotary group flows through passage (6) , passage (8) , port (7) and the swing control valve to the hydraulic tank. The motor rotary group rotates.

A portion of the pressure oil from the idler pump at port (11) also flows to anti-reaction valves (3) and (4) .

At anti-reaction valve (3) , pressure oil from the idler pump and the force of spring (22) shifts valve seat (23) downward against plunger (24) . Plunger (24) shifts downward against piston (26) .

Pressure oil from the idler pump also flows through passage (9) . The pressure oil enters spring chamber (34) of anti-reaction valve (4) . Plunger (16) shifts upward against the force of spring (18) . Valve seat (14) is moved upward against the force of spring (13) by plunger (16) .

When the swing joystick is returned to the NEUTRAL position, the oil delivery from the idler pump to motor rotary group (5) is blocked at the swing control valve. The motor rotary group continues to rotate due to the mass (weight and size) of the upper structure. Since the return oil flow from the motor rotary group is also blocked at the swing control valve, the oil pressure in passage (8) increases. The oil pressure in passage (10) decreases. The increased oil pressure in passage (8) then enters anti-reaction valve (4) . The oil flows through passage (15) and passage (17) . The oil then enters piston chamber (19) . The oil pressure in piston chamber (19) forces plunger (16) upward against the force of spring (18) . Valve seat (14) shifts upward against the force of spring (13) .

A portion of the increased oil pressure in passage (8) flows through passage (31) and passage (20) . The oil then enters spring chamber (21) in anti-reaction valve (3) . The oil pressure in spring chamber (21) forces plunger (24) and valve seat (23) upward against the force of springs (22) and (25) .

As the motor rotary group of the swing motor continues to attempt to stop, the oil pressure in passage (8) gradually decreases. The oil pressure in piston chamber (19) decreases. The force of spring (18) causes plunger (16) to shift downward at a rapid rate. Valve seat (14) shifts downward by the force of spring (13) . Since orifice (27) restricts the flow of oil from valve chamber (28) , valve seat (14) moves in a downward direction more slowly than plunger (16) .

The contact between plunger (16) and valve seat (14) is no longer maintained. The oil pressure in passage (15) forces ball (30) against the top end of plunger (16) . The oil in passage (8) now flows through passages (29) and (9) to passage (10) .

During the separation of plunger (16) and valve seat (14) in anti-reaction valve (4) , anti-reaction valve (3) activates also. In anti-reaction valve (3) , The pressure of the oil that flows from spring chamber (21) to passage (8) decreases. The force of spring (25) causes plunger (24) to shift downward. The force of spring (22) causes valve seat (23) to shift downward. Since orifice (32) restricts the flow of oil from valve chamber (35) , valve seat (23) shifts more slowly than plunger (24) . The contact between plunger (24) and valve seat (23) is no longer maintained. The oil pressure in passage (20) forces ball (33) against the valve seat (23) . Now, the oil flow from passage (8) through passage (31) to passage (10) is blocked by ball (33) .

Since passages (8) and (10) are connected by activation of anti-reaction valve (4) , the swing movement of the upper structure stops with a minimal shock load at a desired position. A more exact swing movement is possible. A slight shock load may occur due to the gear backlash of the swing drive.

When motor rotary group (5) is slightly rotated in the reverse direction due to the gear backlash, oil pressure in passage (10) increases and oil pressure in passage (8) decreases. Anti-reaction valves (3) and (4) function in order to stop the swing movement of the upper structure with a slight reversed motion. The increased oil pressure in passage (10) causes a shock load. The absorption of the shock load is described in the following manner.

In anti-reaction valve (3) , plunger (24) and valve seat (23) separate from each other. Ball (33) is forced against plunger (24) by the pressure oil in passage (10) . Oil can now flow from passage (10) through passages (20) and (31) to passage (8) .

In anti-reaction valve (4) , plunger (16) and valve seat (14) separate from each other. Ball (30) is forced against valve seat (14) by the pressure oil in passage (29) . The flow of oil from passage (10) through passage (9) to passage (8) is blocked.

The oil pressure in passage (10) decreases and the rotation of motor rotary group (5) is prevented. The swing movement is gradually stopped.