THEORY OF OPERATION - CONTINUED
STEERING SYSTEM - CONTINUED
Pilot oil then flows through an orifice, causing selector spool to move leftward, allowing oil to flow
through a passage to fill hydraulic oil tank drain passage cavity.
Oil pressure in hydraulic oil tank drain passage cavity causes directional spool to move left, compressing
spring. Movement of directional spool causes metering orifices to open into a passage. Right turn pilot
load check valve is located inside passage. This causes pilot oil pressure to unseat right turn pilot load
Oil displaced from chamber by movement of directional spool flows back to hydraulic oil tank.
As directional spool moves left, pressure oil from steering pump flows through steering pump inlet pas-
sage. Oil then fills right turn steering cylinder passage.
Pressure oil then flows out of right turn steering cylinder port to rod end of right-side steering cylinder.
Pressure oil also flows to head end of left-side steering cylinder.
Simultaneously, return oil from rod end of left-side steering cylinder flows through left turn steering cylin-
der port. Return oil from head end of right-side steering cylinder flows through left turn steering cylinder
port, causing machine to articulate right.
Oil then flows into left turn steering cylinder passage. From passage, oil flows through a passage to
hydraulic oil tank port.
Steering metering pump supply port is connected to control section of steering pump. Control section con-
sists of a pressure and flow compensator valve which regulates steering pump output.
Movement of directional spool and turning speed of machine depend on two factors: steering wheel turn-
ing speed and engine speed.
Flow control orifice regulates oil supply to steering metering pump, therefore, it also regulates maximum
steering wheel turning speed.
As maximum speed is reached, pilot oil pressure between steering metering pump and directional spool
decreases. Pump output decreases slightly as sensing line signal pressure decreases. This causes greater
effort to be required to turn steering wheel, resulting in slower steering wheel rotation.
When operator stops turning steering wheel, pilot oil flow to steering control valve is cut off. Oil flow
stops because spool in steering metering pump is spring-centered. Also, if left- or right-turn steering neu-
tralizer valve is actuated, flow of steering pilot oil to either end of selector spool stops.
Steering cylinder pressure closes right turn pilot load check valve, causing spring to move directional
spool to NEUTRAL position. Pilot oil in hydraulic oil tank drain passage is displaced through metering
When wheels contact a stationary object, steering cylinders may experience a sudden shock load. Any
pressure generated in steering cylinders from a shock load is sensed in right and left turn steering cylinder
passages. Steering cylinder crossover relief valve senses oil pressure in those passages.
If pressure exceeds steering cylinder crossover relief valve settings, valve opens. This causes oil to flow to
passage with lower pressure.
Makeup check valves connect with right and left turn steering cylinder passages, allowing oil to be drawn
through hydraulic oil tank port. This prevents voiding in steering cylinder that causes steering cylinder
crossover relief valve to open. Makeup check valves are normally seated by spring force.