Hydraulic Schematic of Main Control Valve
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| Illustration 1 | g02450576 |
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Main control valve (1) Return port (2) Relief valve (Outer pump) (3) Supply port (Outer pump) (4) Swing control valve (5) Stick control valve (6) Left travel control valve (7) Blade control valve / Variable gauge cylinder control valve (Track) (8) Attachment control valve (9) Parallel feeder passage (10) Center bypass passage (11) Right travel control valve (12) Control valve for the swing boom (13) Bucket control valve (14) Boom control valve (15) Supply port (Inner pump) (16) Load check valve (17) Relief valve (Inner pump) | |
The main control valve is located in the hydraulic system between the main pump and the actuators (cylinders and motors). According to the machine operation, components in the main control valve control the flow of pump oil. The components also control the maximum pressures in the circuits for the tandem gear pumps. In this way, the operating speed and directions of the cylinders and motors are changed, and the maximum pressure of the pump oil is controlled.
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| Illustration 2 | g02450537 |
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Main control valve main hydraulic oil ports (A1) Swing control valve (swing RIGHT) (A2) Stick control valve (stick IN) (A3) Left travel control valve (FORWARD travel) (A4) Blade control valve (blade UP) / Variable gauge cylinder control valve (track IN) (A5) Auxiliary hydraulic circuit (A6) Right travel control valve (FORWARD travel) (A7) Swing boom control valve (swing RIGHT) (A8) Bucket control valve (bucket CLOSE) (A9) Boom control valve (boom RAISE) (B1) Swing boom control valve (swing LEFT) (B2) Stick control valve (stick OUT) (B3) Left travel control valve (REVERSE travel) (B4) Blade control valve (blade DOWN) / Variable gauge cylinder control valve (track OUT) (B5) Auxiliary hydraulic circuit (B6) Right travel control valve (REVERSE travel) (B7) Swing boom control valve (swing LEFT) (B8) Bucket control valve (bucket OPEN) (B9) Boom control valve (boom DOWN) (P1) Supply port (Outer pump) (P2) Supply port (Inner pump) (T1) Return port | |
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| Illustration 3 | g02451116 |
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Main control valve (1) Swing control valve (2) Right travel control valve (3) Control valve for the swing boom (4) Bucket control valve (5) Boom control valve (6) Relief valve (Outer pump) (7) Stick control valve (8) Left travel control valve (9) Blade control valve / Variable gauge cylinder control valve (Track) (10) Attachment control valve (11) Relief valve (Inner pump) | |
Oil from the outer gear pump enters the main control valve through inlet port (P1). Next, oil flows to the swing control valve (1), stick control valve (7), left travel control valve (8), and blade/track control valve (9).
Oil from the inner gear pump enters through inlet port (P2). Next, the oil flows to the boom control valve (5), bucket control valve (4), swing boom control valve (3), and right travel control valve (2).
The major valves in the main control valve have the following functions:
Control in the NEUTRAL position - When the joysticks are in the NEUTRAL position, oil passes through the center bypass passage in the main control valve. The oil is exits the system through return port (1).
Operation of individual valves - Individual valves are used in extending the cylinder rods and retracting the cylinder rods. These valves are also used to actuate the hydraulic motors. Pump oil is supplied to the valves through the center bypass passage and the parallel feeder passages.
Prevention of leakage and drift in cylinders and motors - This function is performed through the use of load check valves.
Limitation of circuit pressure - This function is performed through the use of relief valves.
Note: The bucket control valve is used in order to describe the operation of the individual control valves.
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| Illustration 4 | g02453018 |
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Bucket control valve (bucket CLOSE) (1) Cylinder port A (2) Cylinder port B (3) Return passage (4) Spool (5) Center bypass passage (6) Parallel feeder passage | |
Spool (4) has a mechanical linkage which actuates the valve. When the linkage is pulled, spool (4) shifts upward. The pump oil then flows to cylinder port A (1). The oil flows through lines to the head end of the bucket cylinder in order to extend the cylinder rod. Return oil in cylinder port B (2) flows through the spool to return passage (3). The oil then returns to the tank.