TUBE AS 1538593 - Caterpillar

Illustration 1 g06266969
(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 g06266775
Steering hydraulic system - no turn
(4) Directional Spool
(9) Pressure Reducing Valve
(10) Backup Relief Valve
(11) Cylinder Crossover Relief Valve
(12) Shuttle Valve
(16) STIC Steering Pilot Valve
(17) Steering Control Valve
(18) Shuttle Valve
(19) Load Sensing Signal Line
(20) Return Line
(21) High-Pressure Line
(22) Reduced Pilot Pressure
(23) Steering Pump
(24) Steering CylinderOil flow is blocked from either side when STIC steering pilot valve (16) returns to the NEUTRAL position. Without pilot oil on either end of the valve spool, return spring (5) will keep pilot valve (4) in the NEUTRAL position.When STIC steering pilot valve (16) is in the NEUTRAL position, oil from the steering pump is blocked by directional 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. Steering pump (23) with destroke to limit 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, direction spool (4) also blocks the oil in the lines to steering cylinders (24). 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.RIGHT TURN Position
Illustration 3 g06267045
(4) Directional spool
(20) Return oil to hydraulic tank
(22) Pressurized pilot oil
(25) Pressurized oil to steering cylinders
(26) Centering SpringWhen the STIC steering control valve is moved to the right position, 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 directional spool (4) shifts against the force of centering spring (26). As the spool shifts, pump inlet (2) is opened to the cylinder port, to the rod end of the right steering cylinder, and to the head end of the left steering cylinder.During a turn, the pressure inside the steering cylinders is sensed at the compensator for the steering pump. This system is called a load sensing system. The pump compensator adjusts the outlet flow of the pump so that the pressure at the pump outlet is higher than the pressure in the steering cylinders by 2400 kPa (350 psi). This extra pressure of 2400 kPa (350 psi) allows pressure drops throughout the system from the pump to the cylinders. As an example, if the cylinder pressure that is required to turn the machine is 10000 kPa (1450 psi), the pressure at the pump will be 12400 kPa (1800 psi). The pressure increases in the cylinder until the machine begins to turn to the right.The oil from the head end of the right