THEORY OF OPERATION - CONTINUED
STEERING SYSTEM - CONTINUED
a. Pilot circuit consists of a metering pump, neutralizer valve for a left turn, neutralizer valve for a right turn, selector
spool, directional spool, steering pump, flow control orifice, and hydraulic oil tank.
b. Pilot system controls spool movement in steering control valve. Steering pump draws oil from hydraulic oil tank.
Pressure oil from steering pump flows to steering control valve, then through flow control orifice. Flow control
orifice reduces amount of oil flow to metering pump.
c. Metering pump is a small hydraulic pump used as a metering valve and directional control valve. When an opera-
tor turns steering wheel, a spool and sleeve rotates inside metering pump, allowing oil to flow to either right-turn
or left-turn neutralizer valve. Turning steering wheel faster causes more oil to flow to neutralizer valve.
d. Oil then flows to steering control valve. Oil pressure causes selector spool to move either right or left. This causes
directional spool to move in same direction as selector spool. Directional spool allows high-pressure oil to flow to
High Pressure Circuit.
a. High pressure circuit consists of a steering control valve, crossover relief valve for steering cylinders, left steering
cylinder, right steering cylinder, steering pump, backup relief valve, and hydraulic oil tank.
b. High pressure circuit provides high-pressure oil for steering cylinders. Oil is drawn from hydraulic oil tank by
steering pump. Steering pump is a variable piston pump. A pressure and flow compensator valve is attached to
steering pump to help control pump output.
c. A backup relief valve in steering control valve prevents excessive pressure in high pressure circuit if there is a mal-
function in pressure and flow compensator valve.
d. When pilot oil moves directional spool, pressure oil is directed to steering cylinders. When a right turn is made,
pressure oil flows to head end of left-hand steering cylinder and rod end of right-hand steering cylinder. This
causes machine to turn right. When a left turn is made, pressure oil flows to head end of right-hand steering cylin-
der and rod end of left-hand steering cylinder. This causes machine to turn left.
e. Crossover relief valve prevents excessive pressure spikes in steering cylinders. Pressure spikes could develop if a
front tire hits an object.