THEORY OF OPERATION - CONTINUED
STEERING SYSTEM - CONTINUED
Secondary steering valve is located on upper left inside frame above secondary steering pump.
Secondary valve contains two check valves which act as a selector valve. Primary steering check valve
monitors primary steering oil pressure. Secondary steering check valve monitors secondary steering oil
During normal operating conditions, oil pressure from primary steering pump keeps primary steering
check valve unseated while keeping secondary steering check valve seated. This allows pressure oil to
flow from primary steering pump, through secondary steering valve, and to steering control valve through
outlet. With secondary steering check valve seated, no pressure oil flows to secondary steering pump.
If primary steering pump fails, flow of pressure oil from primary steering pump stops. After a brief pause,
electric motor attached to secondary steering pump starts, causing secondary steering pump to pump oil.
Pressure oil from secondary steering pump flows to secondary steering valve, causing secondary steering
check valve to unseat. With no oil pressure from primary steering pump, pressure from secondary steering
pump causes primary steering check valve to seat.
Oil then flows to steering control valve through outlet. With primary steering check valve seated, no oil is
allowed to flow to primary steering pump.
Secondary steering valve also contains two pressure switches. Primary oil pressure switch senses pressure
in primary steering circuit. If primary oil pressure switch detects a loss of oil pressure from primary steer-
ing pump, pressure switch sends a signal to monitoring system and illuminates primary steering alert indi-
cator to alert operator of a loss of primary steering pressure.
Secondary oil pressure switch senses pressure in secondary steering circuit. When secondary oil pressure
switch detects oil pressure from secondary steering pump, pressure switch sends a signal to monitoring
system and illuminates secondary steering warning indicator to alert operator that secondary steering sys-
tem is in operation.