YOKE 8K6858 - Caterpillar

Illustration 1 g00357894
Location of the priority valve group
Illustration 2 g00356212
Components of the priority valve group (1) Torque converter inlet relief valve (1A) Relief valve spool (9) Passage to torque converter (10) Passage to bevel gear case (11) Relief valve spring (12) Relief valve adjustment (13) Priority valve adjustment (14) Priority valve spring (15) Priority valve (15A) Priority valve spool (16) Passage from torque converter and lubrication section of the pump (17) Slug chamber (18) Supply chamber (19) Slug
Illustration 3 g00357896
Priority valve group (1) Torque converter inlet relief valve (12) Inlet relief valve (13) Priority valve adjustment (15) Priority valve (20) Solenoid valveThe priority valve group contains priority valve (15) and torque converter inlet relief valve (1) . The priority valve is mounted on the lower left side of the bevel gear case.The priority valve makes sure that oil pressure is first available for steering, braking, and transmission control, and then for torque converter operation and lubrication of the steering clutches, brakes, and transmission.The priority valve has two modes of operation. In the normal mode, oil flow to the torque converter, the lubrication system, and the controls are separate. No priority is given to the flow to the controls.In the priority mode, oil flow to the torque converter and the lubrication system have priority in order to maintain pressure for steering, braking, and transmission control.The priority valve setting for the flow mode is determined when on/off solenoid (20) selects oil from either inlet (16) or drain (10) in order to supply chamber (18) .For the normal mode, the solenoid is ON and inlet (16) is selected.For priority mode, solenoid (20) is OFF and drain (10) is selected.The electronic control module controls the current to the solenoid.No current is sent to the priority valve under specific operating conditions in order to maintain adequate pressure to the steering and brake controls and the transmission controls. The priority valve is at high pressure in this mode. No current is applied to the priority valve during the following conditions:
Engine speed that is less than 1300 RPM
Power train oil temperature less than 40°C (104°F)
Changes in transmission speed
Directional changesIn the normal mode, inlet pressure in chamber (18) acts on more of the spool area around slug (19) . This causes spool assembly (15A) to move toward adjusting screw (13) . This allows oil from the torque converter and lubrication section of the pump to pass through the priority valve to the torque converter.In priority mode, the pressure in supply chamber (18) is drained. This release of pressure causes the inlet pressure in slug chamber (17) to move spool assembly (15A) . The inlet pressure that is required is the pressure setting for the priority valve.This setting can be adjusted by turning adjusting screw (13) and locking in place with a locknut.Oil from section (A) of the oil pump enters inlet passage (16) in the priority valve. The oil goes from inlet passage (16)