INJECTOR GP-FUEL 7E8836 - Caterpillar

Standard Pilot System
Illustration 1 g03563479
Steering hydraulic schematic with standard steering
(P1) To steering control valve (Redundant Supply)
(P2) Pilot supply to steering control valve
(SP) From steering pump supply
(T) Tank
(S1) From (P2) on brake valve
(S2) From (P1) on brake valve
(D) Drain
(1) Brake/Fan/Pilot pump
(2) Brake control valve
(3) Brake system relief valve
(4) Reducing valve
(5) Shuttle valve
(6) Reducing valve
(7L) Left secondary (Redundant) steering solenoid
(7R) Right secondary (Redundant) steering solenoid
(8) Resolver
(9L) Left primary steering solenoid
(9R) Right primary steering solenoid
(10) Steering pilot enable solenoid
(11) Pilot accumulator
(12) Steering pump
(13) Steering valve
(15) Line from steering pump to the shuttle valve in brake control valve Under normal conditions, pilot oil flows from (P2) in the brake valve to (S1) on the steering valve. This reduced oil flows through valve (11) for primary steering valves (9L) an (9R). Oil also flows from (P1) to secondary steering valves (7L) an (7R). Part of the oil from steering pump (12) is routed back to the brake valve through line (15). Under normal conditions, oil in line (15) is blocked at valve (5) because pressure keeps valve (5) shifted to the right.Primary Pilot Oil Fails
If the pilot oil from (P2) fails, the ECMs communicate with secondary valves (7L) an (7R). These valves control the pilot oil from reducing valve (6). If pumps (1) and (12) are working, brake oil pressure keeps valve (5) shifted to the right. Brake pump oil flows through (P1) to secondary valves (7L) an (7R).Brake Pump Pressure Fails
If supply pressure from the brake system fails, valve (5 ) will shift back to the left under spring pressure. Oil in line (15) will flow through reducing valve (6) to supply pilot oil to secondary valves (7L) an (7R).Pilot with Electric Secondary Steering Pump
Illustration 2 g03563480
Steering hydraulic schematic with electric secondary steering attachment
(P1) To steering control valve (Redundant Supply)
(P2) Pilot supply to steering control valve
(SP) From steering pump supply
(T) Tank
(S1) From (P2) on brake valve
(S2) From (P1) on brake valve
(D) Drain
(1) Brake/Fan/Pilot pump
(2) Brake control valve
(3) Brake system relief valve
(4) Reducing valve
(5) Shuttle valve
(6) Reducing valve
(7L) Left secondary (Redundant) steering solenoid
(7R) Right secondary (Redundant) steering solenoid
(8) Resolver
(9L) Left primary steering solenoid
(9R) Right primary steering solenoid
(10) Steering pilot enable solenoid
(11) Pilot accumulator
(12) Steering pump
(13) Steering valve
(14) Secondary steering diverter valve
(14a) Check valve preventing back flow to steering pump
(14b) Check valve to prevent pump (12) flow back through secondary pump
(15) Line from steering pump to the shuttle valve in brake control valve
(16) Secondary steering pump Some machines may be equipped with a secondary (electric) steering pump and motor. This pump provides temporary steering to move the machine safely to an area for safe shutdown.For further information concerning the steering operation, refer to System Operation, "Steering Control (System Operation)" in this manual.If steering pump (12) fails or the engine fails, the secondary steering pump (16) will operate.Oil flow from pump (16) creates oil flow through valve (14). Oil flow through (14a) flows to the control steering control valve. Check valve (14b) prevents oil from flowing back into steering pump (12). Part of the oil flows through