PUMP GP-UNIT INJECTOR HYD 2014202 - Caterpillar

The steering pump (1) provides flow to the steering control valve (2). Supply oil will enter the steering control valve and flow to the steering control spool (15).Pump supply oil is blocked when the control spool is in the HOLD position. Oil in the load sense circuit is blocked by the steering cylinders (8L) and (8R), and the pump control valve. Pump supply oil is also sent to the brake/fan combination valve (4) to provide a secondary source of pilot oil in the event of a brake/fan pump failure.The steering control valve contains a back-up relief valve (3) and a back pressure valve (5). The back-up relief valve limits the maximum pressure in the steering control valve if the pressure compensator spool of the steering pump fails. The back pressure valve restricts the return oil flow to the hydraulic tank. The purpose of the back pressure valve is to maintain enough pressurized oil in an internal passage to prevent steering cylinder voiding.The brake/fan combination valve contains two pressure reducing valves that supply pilot oil to the steering control valve. The pilot oil (12) is supplied to the pilot accumulator (11), steering pilot solenoid (13), and primary steering solenoids (9L) and (9R). Secondary steering solenoids (14L) and (14R) receive a redundant pilot oil supply (10) from the brake/fan combination valve. For additional information about the pilot oil, refer to System Operation, "Steering Pilot System".The primary steering solenoids meter the amount of pilot oil that is sent to the control spool in the steering control valve. The amount of oil that is sent to the steering control valve is based on the amount of current sent to the primary steering solenoid. The primary steering solenoids are an output of the Implement ECM.The secondary steering solenoids are used as a back-up in case the primary steering solenoids fail. The secondary steering solenoids meter the amount of pilot oil that is sent to the control spool in the steering control valve. The amount of oil that is sent to the steering control valve is based on the amount of current sent to the secondary steering solenoid. The secondary steering solenoids are an output of the Power Train ECM.The relief and makeup valves (6) and (7) protect the steering cylinders for sudden pressure spikes. The crossover relief and makeup valves will dump oil from one side of the cylinder to the other if the pressure in the steering cylinders raises above the setting of the relief valves.
Illustration 10 g03562424
Steering Hydraulic System - Primary Steering (RIGHT TURN)
(1) Steering Pump
(4) To brake/fan combination valve
(8L) Left side steering cylinder
(8R) Right side steering cylinder
(10) Pilot oil from brake/fan combination valve (redundant)
(12) Pilot oil supply from brake/fan combination valve
(13) Steering pilot solenoid
(14R) Right primary steering solenoid
(15) Steering control spool
(16) Resolver valve
(17) Resolver valve
(18) Steering control spool position sensorThe Implement ECM receives a request from the left-hand steering control to steer the machine to the right.The Implement ECM sends a current, based on the request, to the primary right steering