GENERAL PURPOSE BUCKET ASSEMBLY 6A6778 - Caterpillar

Illustration 1 g00468387
Counterweight control valve (A) Outlet port (head end) (B) Outlet port (rod end) (P) Pump pressure port (P1) Pump pressure port (P2) Cooler bypass port (T) Cooler port (1) Control handle (2) Counterweight relief valve (3) Valve spool (4) Check valveThe counterweight control valve is located under the guard on the right side of the operator's compartment. The counterweight control valve controls the extending and the retracting of the counterweight.Pump pressure enters port (P1) from the hydraulic pump. Port (P) is plugged. In the HOLD position, the oil flows through spool (3) and the oil exits port (T) . The oil then travels to the hydraulic oil cooler.When handle (1) is moved to the EXTEND position, spool (3) is shifted downward. Oil from port (P1) is blocked in the center passage by spool (3) . The oil is forced through a check valve to the spool. The pressure travels through the spool and the oil exits port (A) . This oil travels to the head end of the counterweight cylinder. As the cylinder extends, oil is forced out of the rod end of the cylinder. This oil enters the counterweight control valve through port (B) . The oil travels back through spool (3) and the oil exits through port (T) .When handle (1) is moved to the RETRACT position, a similar process occurs. The pressure oil is felt through port (B) to the rod end of the cylinder. Oil from the head end is returned through port (A) . This oil exits through port (T) .If the pressure in port (P1) becomes too high, then the excess pressure is dumped through relief valve (2) . This can be caused by the end of the cylinder travel or an obstacle could block the travel of the counterweight group. The excess pressure is routed from the relief valve to port (T) .If the pressure that exits port (T) becomes blocked, check valve (4) is forced open. The pressure exits through port (P2) and the oil travels to the distribution manifold for lubrication of other hydraulic components.