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| Illustration 1 | g00543765 |
Pilot control valves | |
Pilot Control Valve (Boom and Bucket)
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| Illustration 2 | g00543766 |
(1) Port (Boom Raise) (2) Port (Bucket Close) (3) Port (Boom Down) (4) Port (Bucket Open) (P) Inlet port (T) Return port | |
Each pilot control valve has four valves that control two operations. For example, the left pilot control valve has two valves for the stick and two valves for the swing.
When the joystick is moved to the left, the plate tilts to the left. The plate pushes down on the rod. The seat pushes the metering spring and the centering spring. The force of the metering spring moves the spool downward and the passage is opened. The oil can go through the passages and out of the port through the line to the main control valve. The oil pressure that is generated at the pilot control valve moves the main control valve spools. This permits oil flow to the implements.
Pilot Control Valve (Stick and Swing)
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| Illustration 3 | g00543767 |
(1) Port (Stick In) (2) Port (Swing Left) (3) Port (Stick Out) (4) Port (Swing Right) (P) Port (Inlet) (T) Port (Return) | |
The oil at the opposite end of the main control valve stem flows through the port return passage and to the return chamber to the hydraulic tank.
The centering spring in the pilot control valve provides the necessary force in order to allow the joysticks to return to the NEUTRAL position when the joysticks are released.
When the joystick is actuated, the metering springs are compressed. This causes the metering spool to move downward. The metering spool controls the pilot oil pressure to the main control valve. The pilot pressure that is delivered to the main control valve is proportional to the travel distance of the joystick. Movement of the main control valve stems causes a change in the flow rate of oil to the implements and/or the motors proportionally to the change in pilot pressure.