CONTROL ASSEM. 6S8155 - Caterpillar

HMU Steering Pilot System
Illustration 1 g03720923Standard Pilot System For Electrohydraulic Steering (optional)
Pilot oil for the steering system is supplied by the brake/fan/pilot pump (1) mounted on the front gear train of the engine. The brake/fan/pilot pump supplies oil to the brake/fan combination valve (2). Relief valve (3) limits the system pressure for the braking system if the control valve on the pump fails.Pressure reducing valve (4) reduces the pressure for primary solenoids (9). Reducing valve (6) reduces pressure for the secondary (Redundant) solenoids (7).Pump pressure in brake valve (2) will keep shuttle valve (5) shifted to the right. Shuttle valve (5) directs brake pump oil through valve (6) for pilot oil to the secondary (redundant) solenoid valves.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. The pilot system for this pump is explained later in this document.For further information concerning the steering operation, refer to System Operation, "Steering Control (System Operation)" in this manual.
Illustration 2 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