Hydraulic Schematic of Main Control Valve
 | |
| Illustration 1 | g01624330 |
Main control valve (1) Bucket control valve (2) Boom I control valve (3) Left travel control valve (4) Right travel control valve (5) Stick control valve (6) Attachment control valve (7) Flow divider and combiner valve (8) Swing control valve (9) Blade control valve (10) Control valve (swing boom) (11) Boom II control valve (12) Inlet port (swing boom pump) (13) Return port (14) Inlet port (right pump) (15) Inlet port (left pump) (16) Return port (17) Right pump (18) Left pump (19) Pilot pump (20) Swing boom 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 pressures in the circuits for the following pumps: right pump (17) , left pump (18) , swing boom pump (20) and pilot pump (19) . In this way, the operating speed and directions of the cylinders and motors are changed, and the pressure of the pump oil is controlled.
Operation and Functions
 | |
| Illustration 2 | g00833730 |
Main control valve (1) Return port (2) Boom II control valve (3) Blade control valve (4) Flow divider and combiner valve (5) Stick control valve (6) Inlet port (right pump) (7) Left travel control valve (8) Return port (9) Bucket control valve (10) Inlet port (swing boom pump) (11) Control valve (swing boom) (12) Swing control valve (13) Attachment control valve (14) Right travel control valve (15) Inlet port (left pump) (16) Boom I control valve | |
There are 11 major valves in the main control valve. Oil is directed from the pumps to these valves in the following manner:
Oil from the right pump (17) enters the main control valve through inlet port (6) and the oil flows to the bucket control valve (9) , boom I control valve (16) , and left travel control valve (7) .
Oil from the left pump (18) enters through inlet port (15) and the oil flows to the right travel control valve (14) , stick control valve (5) , and the attachment control valve.
Oil from the swing boom pump (20) enters through inlet port (10) . The oil flows to boom II control valve (2) . Swing boom control valve (11) , blade control valve (3) , and swing control valve (12) .
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 (1) and (8) .
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 by using load check valves.
Release of the swing brake - Oil under pressure is required to release the swing brake.
Limitation of circuit pressure - This function is performed by using relief valves.
Changeover from single flow to combined flow - The oil supply to the PTO (power take-off) can be changed to single flow or combined flow. Oil for one-way flow is provided by the swing boom pump. Oil for combined flow is provided by the left pump and the swing boom pump.
Straight travel - The straight travel control enables the machine to continue straight travel even though an implement or the attachment control valve is used.
Individual Valve Operation
 | |
| Illustration 3 | g00833933 |
Bucket control valve (NEUTRAL position) (1) Cylinder port A (2) Load check valve (3) Cylinder port B (4) Pa port (5) Neutral passage (6) Tank passage (7) Pb port | |
When the joysticks are in the NEUTRAL position, pump oil returns to the hydraulic tank through neutral passage (5) . Cylinder port A (1) and cylinder port B (3) are closed to pump oil.
 | |
| Illustration 4 | g00833960 |
Bucket control valve in activated mode (1) Cylinder port A (2) Load check valve (3) Cylinder port B (4) Pa port (5) Neutral passage (6) Tank passage (7) Pb port | |
When pilot oil enters Pa port (4) , the spool shifts and pump oil in neutral passage (5) pushes up load check valve (2) . 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 (3) flows through the spool to return passage (6) . The oil then returns to the tank.
Pilot oil that enters Pb port (7) operates in a similar manner.
Interconnecting Valve
The interconnecting valve is used in order to change the flow of hydraulic oil from an operation of single flow to an operation of combined flow. The interconnecting valve is also used in straight travel operations.
 | |
| Illustration 5 | g00834400 |
Interconnecting valve (single flow) (1) Load check valve (2) Pi2 port (3) Neutral passage (4) Tank passage (5) Pi3 port | |
Oil in the neutral passage (3) of the swing boom pump is connected to the low-pressure passage. Therefore, the oil of the swing boom pump will not combine with the oil in the PTO system. The signal pressure that is supplied through Pi3 port (5) passes through the signal passage and the oil is connected to the low-pressure passage.
 | |
| Illustration 6 | g00834434 |
Interconnecting valve (combined flow) (1) Passage C (2) Load check valve (3) Pi2 port (4) Neutral passage (5) Tank passage (6) Pi3 port | |
When pressure oil enters Pi2 port (3) , the spool is pushed by the piston, and the spool moves to the left side. Oil from the swing boom pump then pushes up load check valve (2) . In passage C (1) , the oil then combines with the oil that is in the PTO system.
Note: When the operator operates the straight travel function and the combined flow at the same time, only the straight travel function is operable.
 | |
| Illustration 7 | g00834449 |
Interconnecting valve (straight travel) (1) Load check valve (2) Passage A (3) Pi2 port (4) Neutral passage (5) Tank passage (6) Pi3 port | |
When implements or the attachment control valve is not operated, right travel uses only the right pump and left travel uses only the left pump. However, when the machine travels left and the implements or the attachment control valve is operated, signal pressure to the interconnecting valve is cut off. Pressure increases at the cap of the Pi port in order to move the spool to the left side. Oil from the swing boom pump flows to passage A (2) to parallel passage B of the bucket and boom sections. The spool moves and neutral passage (4) opens. The neutral passage connects with parallel passage B, and the oil flows to the stick and the attachment. Therefore, the implements can be operated during travel, and the machine will travel straight ahead.