WIRE GP 3096078 - Caterpillar

This schematic shows the auxiliary hydraulic system in the following conditions:
Tow points (DECREASE)
Truck hitch (CLOSE)
Screed extensions (RETRACT)
Screed (FLOAT)
Auger (LOWER)
Hopper (LOWER)
Speed range (TRAVEL)
Apron fold (LOWER)
Parking brake (RELEASED)Note: During normal operation, these conditions would not simultaneously occur. The circuit is shown under these conditions for illustration purposes only.When an active left tow point switch is in the DECREASE position, the left tow point lower solenoid is energized. The left tow point control valve directs oil to the counterbalance valve. The counterbalance valve consists of two check valves and two spools. Oil flows through the check valve of the counterbalance valve and flows into the rod end of the left tow point cylinder. The cylinder begins to retract. This retraction displaces oil from the head end of the cylinder. Displaced oil from the head end of the cylinder flows to the return side of the counterbalance valve. Initially, the counterbalance valve blocks the return oil. As the pressure in the line to the rod end of the tow point cylinder increases, the spool in the line to the head end of the cylinder shifts. This shift opens a passage which allows return oil from the head end of the cylinder to flow to the return filter in the hydraulic tank.Note: The right tow point system follows the same principles of operation as the left.At the truck hitch manifold, pump supply oil flows through a pressure reducing valve. This valve limits the downstream pressure to 6900 170 kPa (1000 25 psi). When the active truck hitch switch is in the CLOSE position, the truck hitch close solenoid is energized. The truck hitch control valve opens a passage which allows the reduced supply oil to act against the pilot opened check valve. The check valve opens, and supply oil flows to the rod ends of the truck hitch cylinders. Return oil from the head ends of the cylinders flows in the following places: through the pilot opened check valve, across the truck hitch control valve and to the return filter in the hydraulic tank.When an active left screed extension switch is in the RETRACT position, the left screed retract solenoid is energized. The screed extend control valve opens a passage which allows the pump supply oil to act against the pilot opened check valve. The check valve opens, and supply oil flows to the rod end of the left screed extend cylinder. Return oil from the head end of the cylinder flows in the following places: through the pilot opened check valve, across the screed extend control valve and to the return line in the auxiliary manifold.Note: The right screed extension system follows the same principles of operation as the left.When all the screed lift switches are in the FLOAT position, and the screed counterbalance switch is in the OFF position, the screed lower solenoid is energized. Under these conditions, the rod ends of the screed hoist cylinders are open to the return line in the auxiliary manifold.Gravity causes the