LEVER AS 3337386 - Caterpillar

Hydraulic Operation with Loading Valve
The following is the system operation of the pump and loading valve on the site preparation tractor. The first section is the operation when the system is NOT ARMED. The Secton section describes the system operation when the system is ARMED.Engine Operating, System NOT ARMED
Illustration 5 g03594717
Implement pump control not armed (1) Loading relief valve (2) Loading manifold (3) Loading control valve (4) Return to tank (5) From port "LS1" of implement control valve (6) Flow compensator spool (7) Implement pump solenoid (8) Brake accumulator (9) Pressure reducing valve (10) Rear differential lock (11) Rear differential lock solenoid (12) Needle valve (13) Pump unloading valve (14) To port "P" of brake manifold (15) Return from other systems (16) Attachment load sensing solenoid (17) Implement pump (18) Bias piston (19) Actuator piston (20) Pressure compensator spool (21) To port "LX" of implement control valve (22) To port "P" of implement control valve (23) Loading enable valve (24) Implement resolverBefore the engine is started, bias spring (18) forces the swashplate in implement pump (17) to the maximum angle. As the engine is started, the pump immediately generates flow. The implement pump draws oil from the hydraulic tank through port "S." The pump delivers oil to pressure compensator spool (20), flow compensator spool (6), and to the small actuator piston. Oil is then sent to port "P" of the middle manifold, to port "P" of loading manifold (2) and to port "P" of implement control valve (22) .Refer to System Operation, "Main Hydraulic System" for additional information about the implement control valve.Inside the middle manifold, supply oil from the implement pump flows through an orifice. Downstream from this orifice, oil divides into two branches. One branch flows through a check valve and into brake accumulator (8). This oil also acts on pump unloading valve (13) .The second branch of oil flows through a second orifice. Downstream from this orifice, oil flows out port "LSB" of the middle manifold. This branch of oil also acts on pump unloading valve (13), in conjunction with the pressure from the accumulator supply line.When the machine systems are not armed, implement pump solenoid (7) is not energized. In this case, oil at the spool of the solenoid is directed into the return line, and the load sensing signal from port "LS1" of implement control valve (5) for implement pump (17) is at tank pressure.At implement pump (17), system pressure acts against one side of flow compensator spool (6), and the combined force from the margin spring and the load sensing signal acts against the opposite side of the spool. Since the load sensing signal is open to the return line when the system is not armed, the margin spring provides the only force which acts in opposition to the pump supply pressure.When the pump supply pressure rises above 2100 kPa (305 psi), flow compensator spool (6) shifts, opening a passage for pump supply oil to flow into the piston chamber of large actuator