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| Illustration 1 | g00905829 |
Cross section of earlier steering pump (1) Cavity (2) Priority valve spool (3) Pilot load sensing signal port (4) Orifice (5) Charge outlet port (6) Inlet port (flow from pump gears) (7) Outlet port to charge circuits and brake and shift valve (8) Unloading relief valve (9) Steering pump gears | |
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| Illustration 2 | g01409600 |
Cross section of later steering pump (1) Cavity (2) Priority valve spool (3) Pilot load sensing signal port (4) Orifice (5) Charge outlet port (6) Inlet port (flow from pump gears) (7) Outlet port to charge circuits and brake and shift valve (8) Unloading relief valve (9) Steering pump gears | |
The steering pump is a fixed displacement gear pump. The steering pump is driven by the tandem propel pumps.
The steering pump supplies oil for the following systems:
- steering system
- charge oil for the propel and vibratory systems
- oil for the brake and shift circuit
Priority valve spool (2) is a pressure compensated flow divider. The priority valve divides the flow between the steering circuit and the charge circuit. The steering circuit has priority oil flow through charge outlet port (5) . The return flow from the steering circuit returns into the charge circuit.
Unloading relief valve (8) dumps into inlet port (6) of the steering pump. Unloading relief valve (8) is the pressure relief for the steering cylinders.
Output oil flow from steering pump gears (9) acts against the lower end of priority valve spool (2) . Oil pressure forces priority valve spool (2) against the spring in cavity (1) . This directs oil flow in order to charge outlet port (5) .
Oil from the steering control unit enters pilot load sensing signal port (3) . This oil acts against the upper end of the priority valve spool in addition to the force of spring pressure in cavity (1) . The pilot load sensing signal also acts against unloading relief valve (8) . The unloading relief valve empties into pump inlet (6) . The pump inlet is the relief passage for the steering cylinders.
Oil flows through orifice (4) . The orifice serves as a flushing passage for priority spool (2) . This flushing oil minimizes the "bottoming out" of priority valve spool (2) against the pump housing during pressure surges in the steering circuit. During operation, the priority valve spool oscillates.