IMPLEMENT AND STEERING HYDRAULIC SYSTEM CONTINUED
Control Valve (Steering)
The steering control valve is the first control valve in the valve stack and has priority over the remaining control
valves. This is important so that the tractor has the ability to turn regardless of the load requirements and flow
requirements of the implement circuits that are down stream. The steering control valve controls the speed of the
steering motor and the direction of rotation for the steering motor. The pump oil flows to the steering control valve
from the inlet manifold. The control valve has a control valve spool, makeup valves #1 and #2 and resolver, priority
flow control valve, and load check valve.
The steering valve is spring centered. The control valve spool is a closed center spool and a manually operated
spool with three positions: STEER RIGHT, HOLD, and STEER LEFT.
The spring keeps the spool in the HOLD position when the steering circuit is not active. Movement of the spool is
controlled manually by the operator. The steering control lever is connected to a valve spool by a linkage.
The resolver is a two-way check valve which sends the signal oil with the highest pressure to the inlet manifold.
The inlet manifold sends the signal oil to the compensator valve on the pump. The priority flow control valve gives
flow priority to the steering control valve over all of the implement control valves. Descriptions of the resolver and of
the priority flow control valve are in this section. These descriptions are given with the steering valve spool in
different positions. Descriptions for makeup valves and for the load check valve are in separate sections.
a. Load Check Valve
The load check valve will not open until pump oil pressure in the chamber becomes greater than the force of the
spring for the load check valve and the steering oil pressure in the passage.
b. Makeup Valves
Makeup valves open when steering oil pressure in a passage drops 2 psi (14 kPa) below the return oil pressure in
outlet passage #1. Makeup valves add return oil in outlet passage #1 to steering oil passages. The additional oil
keeps the lines for the steering motor full and the additional oil prevents cavitation (vacuum) and aeration in the