John Deere 318 - Manual (Page 385)

STEERING VALVE/SYSTEM
OPERATION—FOUR-PORT VALVE
Function:
Supply pressurized oil to the proper side of the steering
cylinder to turn the wheels, when the engine is running.
Theory of Operation:
NOTE: Right-hand turn shown.
The “four-port” design steering valve is an open center
type valve, consisting of a self-centering fluid control
valve section (E) and a fluid metering section (H). These
are hydraulically and mechanically interconnected inside
the valve (C).
All external oil flow from the transmission is routed
through the hydraulic control valve. Pressure oil is
supplied to the steering valve after the auxiliary hydraulic
system needs have been satisfied. This will reduce
steering response when auxiliary hydraulic systems are
active.
NEUTRAL:
A—Steering Cylinder Whenever the steering wheel (G) is released, the
B—Drive Link Assembly
centering springs (D) return the control valve section to
C—Steering Valve
the center (neutral) position. In this position, pressure oil
D—Centering Springs
entering the steering valve through the “IN” port is
E—Control Valve Section
allowed to flow through the control valve section and out F—Check Valve
G—Steering Wheel
through the “OUT” port. When in neutral position, the
H—Fluid Metering Section
control valve section prevents pressure oil from entering
the fluid metering section (H).
For Power Turn, Manual Turn and Steering Cylinder
Operation, see STEERING VALVE/SYSTEM
OPERATION—FIVE-PORT VALVE in this group.
M78854
-UN
-03APR95
MX,159026010,1 -19-24APR95
Group 10
Theory of Operation
TM1590 (17MAY95)
260-10-1
316, 318 & 420 Lawn and Garden Tractors
020895
260
10
1