ENGINE AR 2W8871 - Caterpillar

References
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Illustration 1 g06341486Reference: For more information, refer to "730 and 735 Articulated Trucks Modes of Operation (Steering System)" on Caterpillar Channel1.https://channel1.mediaspace.kaltura.com/media/730+and+735+Articulated+Trucks+Modes+of+Operation+%28Steering+System%29/1_b7x2r6jy
Steering System hold Position
Illustration 2 g06284715
Steering system hold position
(1) Steering and hoist / ejector pump
(2) Pump Drive housing
(3) Cutoff spool
(4) Flow compensator spool
(5) Primary steering pressure sensor
(6) Combination valve
(7) Signal resolver
(8) Secondary steering pump
(9) Steering control valve
(10A) Right steering cylinder
(10B) Left steering cylinder
(11) Rotary spool
(12) Gerotor pump
(13) Slow return check valves
(14) Main hydraulic oil tank
(15) Diverter valve
(16) Margin spool
(17) Backflow check valve
(18) Load sense line from hoist / ejector
(19) Diverter Valve
(A) Supply to hoist / ejector valve
(B) Return oil from hoist / ejector valve
(C) Main fan drive return
(D) ATAAC fan drive return
(E) XAD valve returnThe illustration above shows the steering hydraulic system in the "HOLD" position, with no input for steering from the operator.Oil from steering and hoist pump (1) flows through backflow check valve (17) in combination valve (6), and to steering control valve (9). Load sense oil flows into the steering signal circuit, where it flows through signal resolver (7) to low compensator spool (4).When the system is in the hold position, rotary spool (11) in steering control valve (9) blocks the oil from flowing to gerotor pump (12), steering cylinder (10A), and steering cylinder (10B). The trapped oil between the steering cylinders and steering control valve (9) holds the steering cylinders in place.A passage in the rotary spool allows the oil in the signal circuit to be continually metered through steering control valve (9) to the tank in the hold position. Steering signal oil is metered to the tank to keep the pump slightly upstroked to the low-pressure standby condition. The flow compensator in the pump control valve maintains a margin pressure of approximately 2200 kPa (320 psi), which ensures a rapid response to a steering input when requested. The oil flowing through the orifice and passage in steering control valve (9) also restricts some oil flow. This action helps to warm steering control valve (9).The signal oil from steering control valve (9) flows back to main hydraulic oil tank (14) through slow return check valve (13), which maintains a slight back pressure in the signal network. Maintaining this back pressure will ensure a rapid response from steering control valve (9) to a steering request.Diverter valve (19) has an opening pressure of approximately 1000 kPa (145 psi). A light signal pressure from steering control valve (9) adds to the spring value so the diverter valve maintains a pressure in the system that provides an instant response to a steering request. If a higher signal from hoist valve (18) should be transmitted into the signal network, the steering and hoist pump will UPSTROKE to meet the demand. The diverter valve will then open, allowing the oil to flow to the hoist circuit. A steering request will increase the signal from the steering circuit,