FUEL RATIO CONTROL GROUP 4N4900 - Caterpillar

Illustration 1 g06091838
Schematic shows pilot oil flow for the implement control valve.
(1) From implement pump
(2) 3PC Implement valve
(3) To auxiliary valve supply
(4) Margin relief valve
(5) Tilt spool
(6) Lift spool
(7) Ride control manifold
(8) From brake/fan combination valve
(9) Check valve
(10) Hydraulic lockout valve
(11) Tilt back pilot solenoid valve
(12) Raise pilot solenoid valve
(13) Ride control solenoid
(14) Lower pilot solenoid valve
(15) Dump pilot solenoid valve
(16) Auxiliary pilot solenoid valves
(17) Check valve
(18) Implement pump compensator valve
(19) Load sense relief/bleed valve
(20) To Auxiliary pump compensator valve
(21) Tilt pressure compensator valve
(22) Lift pressure compensator valve
(23) Manual lower valve
(24) Lift cylinders
(25) Hydraulic tank
(26) Pilot accumulator
(27) Backpressure valve
(28) Return oil filter
(29) Pump and motor case drain
(30) Case drain return screen
(31) Tilt cylindersPilot oil for the implement control valve is supplied from the brake/fan combination valve (8). A pressure reducing valve in the brake/fan combination valve regulates the pilot oil supplied to the implement control valve. The pilot oil flows to the pilot circuit in the implement valve and to the load sensing circuit.In the pilot circuit, pilot oil flows through a check valve (9) to the pilot accumulator (26) and to pilot hydraulic lockout valve (10).The pilot hydraulic lockout valve (10) is controlled by the implement lockout switch through the Implement ECM. When the implement lockout switch is in the OFF position, the Implement ECM de-energizes the implement lockout solenoid valve. Pilot oil is then blocked at the implement lockout solenoid valve. When the implement lockout switch is in the ON position, the implement ECM energizes the implement lockout solenoid valve. Pilot oil flows past the implement lockout solenoid valve to the following locations:
Tilt back pilot solenoid valve (11).
Tilt spool (5).
Raise pilot solenoid valve (12).
Lift spool (6).
Ride control solenoid (13).
Lower pilot solenoid valve (14).
Dump pilot solenoid valve (15).
Auxiliary pilot solenoid valves (16).In the load signal circuit, the pilot oil from the brake control valve flows through a check valve (17) to the following locations:
Implement pump compensator valve (18).
Load sense relief/bleed valve (19).
Auxiliary pressure compensator valve (20).
Margin relief valve (4).
Tilt pressure compensator valve (21).
Lift pressure compensator valve (22).The margin relief valve maintains a difference between the load sensing signal and the pump supply of 3,450 250 kPa (500 36 psi). The margin relief valve maintains the minimum pressure for low-pressure standby.The load sense relief/bleed valve performs the following two functions:
Limits the maximum load signal pressure sent to the implement pump
Allows a constant purge in the load signal circuit.