Jacobsen SLF 1880, Technical/Repair Manual

Page: 181 / 236

8L-79
SECTION 8L. HYDRAULIC CIRCUITS THEORY OF OPERATION
STEERING CIRCUIT SCHEMATIC
AND THEORY OF OPERATION
System Conditions:
• Engine running
• Steering wheel turned to the right or left (left turn
shown)
Oil Supply to Steering Unit
Hydraulic oil is drawn from the hydraulic oil tank by the
charge pump. Operating pressure oil from the charge
pump is routed to the “IN” port of the steering unit.
Steering Circuit
Operating pressure oil enters the steering unit at the
“IN” port, and is routed against the check valve and to
the steering valve.
With the steering wheel in the neutral (straight ahead)
position, the steering valve routes the operating pres-
sure oil out of the steering unit through the “OUT” port,
supplying charge pressure oil to the hydrostatic traction
pump.
With the steering wheel turned to the left, the steering
valve is moved, allowing oil to flow through the valve to
the gerotor metering section. Oil is then routed out port
“LT” of the steering unit to the steering cylinder for a left
turn.
Oil from the rod end of the cylinder is forced out of the
cylinder and routed back to port “RT” of the steering
unit, and back through the steering valve, exiting the
steering unit through the “OUT” port. Oil exiting the
steering unit is routed to the hydrostatic traction pump.
Circuit Relief
The steering circuit is protected by the 1160 psi (80
bar) relief valve located in the hydrostatic traction
pump. When the steering wheel is turned right or left
and the steering reaches the end of its stroke, the pres-
sure will increase to 1160 psi (80 bar), opening the
relief valve and allowing the oil from the charge pump
to bypass to the low-pressure charge circuit.
8L