ALTERNATOR GP-CHARGING 4777987 - Caterpillar

Illustration 1 g00638691
(1) Diverter Valve (2) Check Valve (3) Secondary Steering Relief Valve (4) Pressure Reducing Valve (5) High Pressure Screen (6) Secondary Steering Pump (7) Selector and Pressure Control Valve (8) Bypass Switch (If Equipped) (9) Filter for Case Drain Oil (10) Hydraulic TankThe secondary steering system supplies steering and pilot oil if the engine fails or if the primary steering pump fails. The secondary steering pump (6) is a ground driven gear pump. The secondary oil pump is located on the front of the transmission. The machine can only be steered by using secondary steering if the machine is moving.During normal operation, diverter valve (1) is forced downward due to oil pressure in the line from the primary steering pump. Oil from the secondary oil pump is then diverted back to the hydraulic tank.A warning switch is located in selector and pressure control valve (7). When steering oil pressure drops, the warning switch is activated. An indicator light in the cab informs the operator that a loss of steering oil pressure has occurred and secondary steering is active.If the primary steering pump fails to pump oil, diverter valve (1) will be shifted upward due to the pressure from the spring. Oil from secondary steering pump (6) travels through high pressure screen (5) to diverter valve (1). High pressure screen (5) is used on later models (ADZ, A4W, AZX and AMP) only. The oil travels through the diverter valve. Check valve (2) prevents oil from the secondary steering pump from flowing back to the primary steering pump. The oil from the secondary pump then travels to the steering control valve in order to operate the steering cylinders.The secondary steering pump can also provide pilot oil if the pilot oil pump fails. Pressure reducing valve (4) reduces oil from the secondary oil pump to pilot oil pressure. Reduced pilot oil then flows from the pressure reducing valve to the pilot valve (STIC steering).Case drain oil from the secondary oil pump flows through filter (9). Machines that are equipped with VIMS have a bypass switch (8). This switch alerts the operator that the filter has been bypassed.