SHIM 1258650 - Caterpillar

Illustration 1 g06024031
Hydraulic Schematic STRAIGHT TRAVEL
(1) Steering cylinder
(2) Steering control unit
(3) Control spool
(4) Metering pump
(5) Relief valve
(6) To return manifold
(7) Steering pump
(8) Hydraulic tank
(9) Suction strainerWhen the engine is operating, steering pump (7) draws oil through suction strainer (9) inside hydraulic tank (8). The steering pump sends flow to port "P" of steering control unit (2). The steering control unit consists of control spool (3), metering pump (4), and relief valve (5).When the machine is traveling in a straight line, the center envelope of the steering control spool is active. This condition prevents oil from flowing to the metering pump and to steering cylinder (1). Pump supply oil flows across the center envelope of control spool (3) and flows out port "T" to return manifold (6).
Illustration 2 g06024032
Hydraulic Schematic LEFT TURN
(1) Steering cylinder
(2) Steering control unit
(3) Control spool
(4) Metering pump
(5) Relief valve
(6) To return manifold
(7) Steering pump
(8) Hydraulic tank
(9) Suction strainerWhen the operator turns the steering wheel to the left, pump supply oil flows across control spool (3) to metering pump (4). The metering pump rotates with the rotation of the steering wheel. The metering pump directs flow through the control spool and into the rod end of steering cylinder (1). Oil flowing into the rod end of the steering cylinder causes the rod to retract. Rod retraction causes the machine to turn left. Oil in the head end of the steering cylinder flows to return manifold (6) through the control spool.As the operator turns the steering wheel faster, metering pump (4) increases the flow to the rod end of steering cylinder (1). Therefore, the machine turns faster. The metering pump continues to direct flow to the rod end until the operator stops turning the steering wheel. When rotation of the steering wheel is stopped, the centering springs in control spool (3) return the spool to the center position. Oil is blocked at the steering cylinder. The machine continues to turn at the same radius until the operator moves the steering wheel again.If steering cylinder (1) reaches the end of the cylinder stroke but the operator continues to turn the steering wheel, pressure in the system increases. When pressure in the system reaches 17200 1400 kPa (2500 200 psi), steering relief valve (5) opens. The relief valve directs a portion of flow from steering pump (7) to the return manifold.Note: Operation of the steering system follows a similar logic when the machine is turned to the right. During a right turn, oil is directed into the head end of the steering cylinder.If the engine stops while the machine is traveling, the operator can manually operate the steering control unit. When the operator turns the steering wheel, metering pump (4) of the control unit acts as a pump. The suction from the metering section opens the check valve in steering control unit (2). Under these conditions, oil flows from one end of steering cylinder (1) to the other.