Hydraulic Schematic of Main Control Valve
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| Illustration 1 | g01279795 |
Main control valve (1) Bucket control valve (2) Boom control valve (3) Right travel control valve (4) Straight travel control valve (5) Left travel control valve (6) Stick control valve (7) Attachment control valve (8) Combiner valve for the PTO and Boom (9) Control valve (boom swing) (10) Blade control valve (11) Swing control valve (12) Inlet port (Left pump) (13) Inlet port (Right pump) (14) Return port (15) Inlet port (swing boom pump) (16) Return port (17) Right pump (18) Left pump (19) Swing boom pump (20) Pilot pump (21) Hydraulic tank | |
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 right pump (18) , left pump (17) , swing pump (19) , and pilot pump (20) . 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.
Operation and Functions
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| Illustration 2 | g01179546 |
Main control valve (1) Bucket control valve (2) Boom control valve (3) Right travel control valve (4) Straight travel control valve (5) Left travel control valve (6) Stick control valve (7) Attachment control valve (8) Combiner valve for the PTO and Boom (9) Control valve (boom swing) (10) Blade control valve (11) Swing control valve (12) Inlet port (Left pump) (13) Inlet port (Right pump) (14) Return port (15) Inlet port (swing pump) (16) Return port | |
There are eleven major valves in the main control valve. Oil is directed from the pumps to these valves in the following manner:
Oil from the left pump (18) enters the main control valve through inlet port (12) and the oil flows to the stick control valve (6) , attachment control valve (7) , and left travel control valve (5) .
Oil from the right pump (17) enters through inlet port (13) and the oil flows to the bucket control valve (1) , boom control valve (2) , and right travel control valve (3) .
Oil from the swing pump (19) enters through inlet port (15) . The oil is directed from the swing pump through the control valve for boom swing (9) , blade control valve (10) , and swing control valve (11) .
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 exhausted through return ports (14) and (16) .
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.
Release of the swing brake - Pilot oil under pressure is used to release the swing brake.
Limitation of circuit pressure - This function is performed through the use of relief valves.
Straight travel - The straight travel control enables the machine to continue a straight travel during the activation of an implement or the attachment. This valve works in either forward or reverse.
Individual Valve Operation
Note: The bucket control valve is used in order to describe the operation of the individual control valves.
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| Illustration 3 | g01281261 |
Bucket control valve (CLOSE position) (1) Cylinder port A (2) Bridge passage (3) Parallel passage (4) Cylinder port B (5) Pilot port A1 (6) Spool (7) Bypass passage (8) Return passage (9) Pilot port B1 | |
When pilot oil enters A1 port (5) spool (6) shifts. 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 (4) flows through the spool to return passage (8) . The oil then returns to the tank.
Pilot oil that enters B1 port (9) operates in a similar manner.
Straight Travel Valve
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| Illustration 4 | g01281265 |
Straight travel control valve (1) Inlet port (Right pump) (2) Parallel passage (3) Inlet port (Left pump) (4) Straight travel spool (5) Bypass passage (6) Bypass passage (7) Pilot port PP1 | |
When pilot oil enters PP1, the spool is shifted. The spool comes in contact with the cover against the force of the spring. The cover stops the spool in the proper location. After the changeover of the spool, the pressure oils from the right pump and left pump combines at the inner passage with the spool. The oil is supplied to both the right travel motor and the left travel motor through bypass passage (5) and bypass passage (6) . The oil is also supplied to each parallel passage (2) through check valves in the inlet port (1) and inlet port (3) . As a result, the pressure oil is divided into the control valves for the front equipment. According to this function, operation of the front equipment is possible during the travel operation.
Attachment control valve
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| Illustration 5 | g01281270 |
Bucket control valve (CLOSE position) (1) Cylinder port A (2) Bridge passage (3) Parallel passage (4) Cylinder port B (5) Spool (6) Bypass passage (7) Return passage | |
Spool (5) has a mechanical linkage which actuates the valve. When the linkage is pulled, spool (5 ) shifts. The pump oil then flows to cylinder port A (1) . The oil flows through lines to the attachment. Return oil in cylinder port B (4) flows through the spool to return passage (7) . The oil then returns to the tank.
When spool (5) is pushed, the valve operates in a similar manner.