COLLAR ASSEM. 1P5018 - Caterpillar

Secondary Gear Pump
Illustration 1 g03670736
(1) Secondary steering pump
(2) Diverter valve
(3) Relief valve
(4) Steering system pressure system The secondary steering pump (1) on the 824K Wheel Dozer supplies oil for steering if the engine shuts down or the primary steering system pump fails. The pump is driven by the drive line and is only suppling oil flow when the machine is moving. The secondary steering pump will supply oil both in forward and reverse directions.The diverter valve (2) is attached to the pump housing. The diverter valve directs oil to the hydraulic tank when the oil flow is not required for the steering system or the steering control valve if the primary steering system loses hydraulic oil flow. The diverter valve contains a relief valve ( 3). The relief valve limits the steering system pressure when the secondary steering pump is providing the steering system oil flow.The pilot system accumulator supplies oil flow for the STIC steering control valve to shift the steering control valve directional spool. The secondary steering system is only designed to bring the machine to a safe stop.If steering system pressure is too low, the steering system pressure sensor sends a signal to the Implement ECM. This action alerts the monitoring system to illuminate an indicator lamp. This action may also be an indication that the secondary steering pump is providing the steering system oil flow. A pressure reducing valve, inside the diverter valve, protects the steering system pressure sensor by reducing steering system pressure.Hydraulic Schematic for the Secondary Steering System
Illustration 2 g03670802
(1) Secondary steering pump
(2) Diverter valve
(3) Relief valve
(4) Steering system pressure system If the steering pump fails or the engine stops while the machine is moving, the secondary steering pump (1) (824K only) supplies oil to the steering system. The secondary steering pump is ground driven and turns when the machine is moving.When the engine is running and the steering system is in the NO TURN position, pilot pump oil is blocked at the STIC pilot control valve. Oil from the main steering pump flows to the steering control valve. The control valve spool blocks oil flow to the steering cylinders and no signal pressure is generated. With no signal pressure, the pump is in "LOW PRESSURE STANDBY" as previously described. The pump produces enough flow to compensate for system leakage and sufficient pressure to provide for instantaneous response when the steering control valve is moved.