PULLEY GP-FAN DRIVE 7W8143 - Caterpillar

Steering Hydraulic System
STEERING SYSTEM SCHEMATIC (STEERING CIRCUIT IN NEUTRAL AND ACCUMULATOR CHARGED)
1-Sector gear. 2-Steering shaft. 3-Nut gear. 4-Follow-up link. 5-Shims (unloading). 6-Unloading valve. 7-Orifice. 8-Pilot valve. 9-Pilot relief valve. 10-Shims (pilot relief valve). 11-Dump valve (large pump). 12-Dump valve (small pump). 13-Orifice. 14-Ball check. 15-Spool. 16-Orifice. 17-Orifice. 18-Check valve.The steering hydraulic system of all tractor-scrapers that use a mechanical follow-up mechanism includes: a two-section vane-type oil pumpa steering control valvesteering cylindersa steering column and steering geara follow-up mechanisman oil filteran oil supply.A diverter valve and an oil cooler are part of the 633C hydraulic steering system. The diverter valve is located in the oil line between the oil pump large section and the steering control valve. Oil flow through the diverter valve is unrestricted when the diverter valve is OFF (control handle vertical). When the diverter valve is ON (control handle moved from vertical), the pump large section oil flow is routed to the elevator hydraulic motor. Small section oil flow only is available for steering.Oil flows directly from the pump small section to the steering control valve on all models.The steering control valve controls the oil flow and oil pressure to the steering cylinders. The steering control valve spool is moved by steering gear reaction to steering wheel rotation or to follow-up mechanism force. Steering gear reaction to steering wheel rotation moves the control valve spool from its centered position (NEUTRAL) and directs oil to the steering cylinders to turn the machine. When the machine turns, the follow-up linkage returns the steering gear and the control valve spool to their centered position (NEUTRAL). The machine's turning radius is maintained until the steering wheel is rotated.In NEUTRAL position oil pressure is applied equally to both steering cylinder lines, and oil is dumped through spool valve throttling slots to the tank.Steering Gear
The steering gear and follow-up mechanism controls the steering gear control valve spool. Turning of the steering wheel opens the valve and turning of the machine closes the valve. Following is a description of the steering gear in a left turn:As the steering wheel is turned counterclockwise, the steering shaft worm gear screws downward in nut gear (3). The nut gear (in this instance) is held stationary by sector gear (1) which is connected to the follow-up link (4). Linkage connected to the upper end of the steering shaft (2) pulls the steering control valve spool outward. With the spool outward pressure oil is directed to the head end of the right steering cylinder and the rod end of the left steering cylinder to turn the machine to the left.Steering Control Valve
The steering control valve consists basically of a control valve spool (15); a large section pump flow control valve which also operates as a pilot-operated unloading valve for the large section of the pump; and a pilot-operated relief valve for the small section pump.In a SLOW RIGHT TURN, only the oil flow from the small section of the steering pump is necessary to turn the machine. (This