STUD-WHEEL 2997607 - Caterpillar

General Information
Illustration 1 g00854788
The steering control valve is the first control valve in the valve stack. The steering control valve 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 oil flow to the steering control valve is limited to 155 L/min (41 US gpm) by the flow control valve (19). The control valve has control valve spool (1), makeup valves (5) and (9), resolver (11), priority flow control valve (19), and load check valve (22) .The steering valve is spring centered. Control valve spool (1) is a closed center spool and a manually operated spool with three positions: STEER RIGHT, HOLD and STEER LEFT.Spring (2) 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 valve spool (1) by a linkage.Resolver (11) is a two-way check valve. Resolver (11) 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. Priority flow control valve (19) 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 (5) and (9) and for load check valve (22) are in separate sections.Load Check Valve
Load check valve (22) will not open until pump oil pressure in chamber (20) becomes greater than the force of the spring for the load check valve and the steering oil pressure in passage (21) .Makeup Valves
Makeup valve (5) or (9) opens when steering oil pressure in passage (6) or (8) drops 14 kPa (2 psi) below the return oil pressure in outlet passage (7). Makeup valves (5) and (9) add return oil in outlet passage (7) to steering oil passages (6) and (8). The additional oil keeps the lines for the steering motor full and the additional oil prevents cavitation (vacuum) and aeration in the steering motor.Basic Valve Operation
Illustration 2 g00854788
When the control valve spool and all implement valve spools are in the HOLD position, pump oil from the inlet manifold flows to inlet passage (18). Then, oil flows through metering holes in priority flow control valve (19). The oil moves priority flow control valve (19) against spring (16). Then, pump oil flows out of outlet passage (17) to the next control valve. Because all implement control valves are in the HOLD position, pump oil fills the parallel oil passages at approximately 3000 kPa (435 psi). Passage (3),