PLATE 6I3136 - Caterpillar

Illustration 1 g01119973
(1) Tank port
(2) Pressure port
(3) Tank port
(4) Spool
(5) Return spring
(6) Cylinder port
(7) Cylinder port
(8) Pilot port
(9) Pressure reducing valve
(10) Backup relief valve
(11) Cylinder crossover relief valve
(12) Shuttle valve
(13) Cylinder port
(14) Cylinder port
(15) Pilot oil
Illustration 2 g06063228
Schematic for the steering control valve in neutral position
(4) Pilot control valve
(8) Pilot oil line
(9) Pressure reducing valve
(10) Backup relief valve
(11) Cylinder crossover relief valve
(12) Shuttle valve
(15) Pilot oil line
(16) Load sensing signal line
(17) Return line
(18) High-pressure line
(19) Reduced pilot pressureThe flow of oil to either end of pilot valve (4) is blocked once the STIC control returns to NEUTRAL. Without pilot oil on either end of the valve spool, centering spring (5) will keep pilot valve (4) in the NEUTRAL position.When the steering control valve is in the NEUTRAL position, oil from the steering pump is blocked by valve spool (4). The pump then destrokes due to the decreased demand for flow. The pressure in the cylinders is communicated through shuttle valve (12) to the compensator valve. The pump will destroke to limit the pump flow so that the pump outlet pressure is equal to the pressure at the compensator valve. If the cylinder pressure is equal to tank pressure, then the pump will destroke to the low-pressure standby setting of 3900 kPa (565 psi).In the NEUTRAL position, the valve spool also blocks the oil in the lines to the steering cylinders. If the pressure in one cylinder line exceeds 29100 kPa 700 kPa (4220 100 psi), crossover relief valve (11) will open. This action allows the oil to flow to the opposite steering cylinder.As an example, a left turn is made and the valve spool is returned to the NEUTRAL position. A force which causes the machine to turn to the right is placed on the machine. Since the oil is trapped in the cylinder lines, this force causes the pressure in the cylinder lines to increase. When the pressure exceeds 29100 kPa (4220 psi), the crossover relief valves open. Oil is then allowed to flow from the rod end of the left steering cylinder to the rod end of the right steering cylinder. Similarly, oil that is trapped in the head end of the right steering cylinder will flow to the head end of the left steering cylinder. This action will cause the machine to steer back to the right and pressure will be reduced in the cylinder lines.RIGHT TURN Position
Illustration 3 g00631305
(4) Shifted spool for right turn
(5) Compressed centering spring
(20) Return oil to hydraulic tank
(21) Pressurized oil to steering cylinders
(22) Pressurized pilot oil (4) Shifted spool for right turn. (5) Compressed centering spring. (20) Return oil to hydraulic tank. (21) Pressurized oil to the steering cylinders. (22) Pressurized pilot oil.When the steering control is moved to the right, pilot oil is sent through a check valve (steering valve) to pilot port (8) and pilot port (15) on the steering control valve. Pressure increases in the pilot chamber and the spool shifts against the force of the spring. As