SCREW-CAP 2057737 - Caterpillar

Illustration 1 g00534634
Section View of the Pilot Control Valve (1) Output to control valve (left) (2) Output to control valve (right) (3) Input from lift cylinder (4) Secondary pressure reducing valve (5) Primary pressure reducing valve (6) Passage (7) Shuttle valve (8) Primary pilot pressure cavity (9) Tip backward port (10) Input from pilot/brake pump (11) Resolved pressure port (12) Secondary pilot pressure cavity (13) Passage (14) Lower pilot pressure cavity (15) Tip forward port (16) Passage from shuttle valve (17) Plug (18) Output to control valve (raise) (19) Return port to the hydraulic oil tank (20) Output to control valve (left) (21) On/off solenoid valve (A) Solenoid valve (B) Solenoid valve (C) Solenoid valve (D) Solenoid valve (E) Solenoid valve (F) Solenoid valve
Illustration 2 g00658900
Note: The pilot valve for the 824G Wheel Tractor is shown in illustration 1. The following procedure describes the operation for the 824G Wheel Tractor pilot valve. The pilot valves for the 825G Soil Compactor and the 826G Landfill Compactor are similar. However, the valves may not have all three functions.The pilot valve is located in the front end frame. The pilot valve (oil manifold) controls the flow of pilot oil to the main control valve.Oil enters the pilot valve (oil manifold) at port (10) from the pilot/brake pump. Primary pressure reducing valve (5) reduces the pressure of the pilot oil to 3450 200 kPa (500 30 psi). The oil then flows through passage (8) to shuttle valve (7). Pilot pressure oil for the steering system flows through passage (6) to port (21) .Pilot on/off solenoid valve (19) controls the flow of pilot oil to the proportional solenoid valves. When the implement lockout switch is in the UNLOCKED position, a control lever must also be moved in order to open the pilot on/off solenoid valve. When all control levers are in the HOLD position, the pilot on/off solenoid valve is closed. No oil will flow to the proportional solenoid valves. The implement cylinders will not operate.The flow of oil through proportional solenoid valves (A), (B), (C), (D), (E), and (F) is controlled electronically by the electronic control module. The flow of oil increases with an increase in movement of the control lever from the HOLD position. The oil then flows to a valve spool in the main control valve in order to allow high pressure oil to flow to the implement cylinders.Lower the Blade when the Engine is Off
Secondary pressure reducing valve (4) supplies pilot oil when the engine is stopped. The secondary pilot oil allows an operator to lower the lift arms when the engine is stopped. In order to lower the lift arms with the lift control lever, the engine start switch key must be in the ON position.The blade can be lowered when the engine is off. The oil supply flows from the lift cylinder through check valves in the lines of the lift cylinder. This oil enters through port (3). The pressure of the oil is reduced to