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| Illustration 1 | g00872549 |
Schematic for the Implement Hydraulic System (1) Check valve (2) Lift cylinder (3) Pilot controlled check valve (4) Tilt cylinder (5) Main relief valve (6) Main control valve (7) Lift spool (8) Tilt spool (9) Filter screen (10) Primary reducing valve (11) On/Off valve (12) Solenoid control valve (lower) (13) Solenoid control valve (tilt right) (14) Pilot valve (oil manifold) (15) Secondary reducing valve (16) Shuttle valve (17) Solenoid control valve (raise) (18) Solenoid control valve (tilt left) (19) Electronic control module (ECM) (20) Pilot/brake pump (21) Implement pump (22) Joystick control (23) Hydraulic tank (24) Filter assembly (AA) Pilot system (steering) (BB) Brake system | |
The 825H Soil Compactor hydraulic system is made up of four basic systems. The four basic systems are the implement electronic control system, the pilot hydraulic system, the main hydraulic system and the hydraulic fan system.
Note: For information about the operation of the hydraulic fan system, refer to the Service Manual module Systems Operation, "Hydraulic Fan System" for the machine that is being serviced.
The main components of the electronic control system are the implement electronic control module (ECM) (19) and joystick control (22) .
The main components of the high pressure circuit are implement pump (21), main relief valve (5), main control valve (6), and hydraulic tank (23) .
The pilot oil circuit includes pilot/brake pump (20), hydraulic tank (23), and pilot control valve (14) .
Pilot System
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| Illustration 2 | g00872550 |
Pilot System (1) Check valve (2) Lift cylinder (9) Filter screen (10) Primary reducing valve (11) On/off solenoid valve (12) Solenoid control valve (lower) (13) Solenoid control valve (tilt right) (14) Pilot valve (oil manifold) (15) Secondary reducing valve (16) Shuttle valve (17) Solenoid control valve (raise) (18) Solenoid control valve (tilt left) (19) Electronic control module (ECM) (20) Pilot/brake pump (22) Joystick control (23) Hydraulic tank (A) End cap (lower) (B) End cap (raise) (C) End cap (tilt right) (D) End cap (tilt left) (CC) Pilot system (steering) (DD) Brake system | |
Pilot/brake pump (20) draws oil from hydraulic oil tank (23). The pilot/brake pump provides oil to the brake system and the pilot system.
The pilot oil flows through filter screen (9) to the primary reducing valve (10). The pressure setting for the primary reducing valve is set above the pressure setting for the secondary reducing valve (15). The higher pressure in the primary reducing valve will force the spool in shuttle valve (16) to shift. When the spool is shifted, the oil flow from the secondary reducing valve is blocked and the pilot oil will flow to on/off solenoid valve (11). The pressure at the primary reducing valve must be higher than the pressure in the secondary reducing valve in order to keep the spool shifted.
The shuttle valve will direct pilot supply oil to on/off solenoid valve (11). When the engine is activated and joystick control (22) is moved from the CENTER position, pilot oil can flow to the proportional valves.
On/off solenoid valve (11) will be open until the joystick control returns to the CENTER position.
If the engine is disabled, the hydraulic system will allow the operator to lower the blade. If the blade is in the RAISE position, lift cylinder (2) has pressure in the rod end of the cylinder. The pressure flows back to the pilot valve through secondary reducing valve (15). Shuttle valve (16) will shift because the pressure will be higher in the secondary reducing valve. Oil from the rod end will flow to on/off solenoid valve (11) .
If the key start switch is placed in the ON position, on/off solenoid valve (11) will be energized. Pressurized oil can flow to the proportional valves. If the joystick control is moved in the forward direction, there will be enough pilot pressure in order to lower the blade.
Raise
When the operator moves the joystick control in the forward direction, a signal from the lift position sensor will be sent to the implement electronic control module (ECM). The ECM will send a current to proportional solenoid valve (17). The amount of current will depend on the movement of the joystick control. The proportional solenoid valve will shift and pilot oil will flow to end cap assembly (B) for the blade raise function.
Lower
When the operator moves the joystick control in the rearward direction, a signal from the lift position sensor will be sent to the implement electronic control module (ECM). The ECM will send a current to proportional solenoid valve (12). The amount of current will depend on the movement of the joystick control. The proportional solenoid valve will shift and pilot oil will flow to end cap assembly (A) for the blade lower function.
Tilt Right
When the operator moves the joystick control to the right, a signal from the tilt position sensor will be sent to the implement electronic control module (ECM). The ECM will send a current to proportional solenoid valve (13). The amount of current will depend on the movement of the joystick control. The proportional solenoid valve will shift and pilot oil will flow to end cap assembly (C) for the blade tilt right.
Tilt Left
When the operator moves the joystick control to the left, a signal from the tilt position sensor will be sent to the implement electronic control module (ECM). The ECM will send a current to proportional solenoid valve (18). The amount of current will depend on the movement of the joystick control. The proportional solenoid valve will shift and pilot oil will flow to end cap assembly (D) for the blade tilt left.
Main Hydraulic System
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| Illustration 3 | g00872551 |
Main Hydraulic System (1) Check valve (2) Lift cylinder (3) Pilot controlled check valve (4) Tilt cylinder (5) Main relief valve (6) Main control valve (7) Lift spool (8) Tilt spool (21) Implement pump (23) Hydraulic tank (24) Filter group (A) End cap (lower) (B) End cap (raise) (C) End cap (tilt right) (D) End cap (tilt left) (EE) Pilot line for dead engine lower | |
In the main hydraulic system, there are four main components. The components are the implement pump, the main relief valve, the main control valve, and the implement cylinders.
Implement pump (21) supplies high pressure oil that operates the implement cylinders. The implement pump draws oil from the hydraulic tank. The implement pump sends pressurized oil to main relief valve (5). The main relief valve regulates the pressure that flows into the main control valve. The main relief valve opens when the oil pressure in the hydraulic system rises above the relief valve setting. The relief valve setting is 24125 ± 350 kPa (3500 ± 50 psi).
Reference: For more information about the main relief valve, refer to the Service Manual module Systems Operation, "Main Relief Valve" for the machine that is being serviced.
Main control valve (6) is a bank valve with two sections. The two sections control the lift function, and the tilt function of the blade. The main control valve has an open center. When the engine is running and the joystick control is in the CENTER position, the oil that is flowing into the main control valve flows through the valve and back to the hydraulic tank. The return oil will pass through filter group (24) that is within the hydraulic tank.
When pilot oil is sent to the end caps of the main control valve the spools are shifted and the pressurized oil is directed to the implement cylinder.
Reference: For more information about the main control valve, refer to the Service Manual module Systems Operation, "Main Control Valve" for the machine that is being serviced.
Lift Function
The lift functions of the blade are controlled by the spool (7) in the main control valve. When the joystick control sends a signal to lift the blade, pilot oil is directed to end cap (B). The spool shifts and the open center is blocked. The high pressure oil opens the makeup check valve, and flows through the main control valve to the rod end of the lift cylinder.
The hydraulic oil that is in the head end of the lift cylinder will flow through pilot controlled check valve (3), through main control valve (6), and back to hydraulic tank (24). The blade will raise.
When joystick control sends a signal to lower the blade, pilot oil is directed to end cap (A). The spool will shift and the open center is blocked. The high pressure oil opens the makeup check valve, and flows through the main control valve to the head end of the lift cylinder.
The oil that is in the rod end of the lift cylinder will flow through the main control valve and back to the hydraulic tank. The blade will lower.
When joystick control is moved to the FULL LOWER position, pilot oil is directed to end cap (A) and the spool is shifted to the FLOAT position. When the lift spool is in the FLOAT position, the high pressure oil will flow to the hydraulic tank. The oil that is in the rod end and the head end of the cylinder is allowed to flow back to the hydraulic tank. The weight of the blade and lift arms control the movement of the blade. The blade will follow the contour of the ground.
Tilt Function
The tilt functions of the blade is controlled by spool (8) in the main control valve. When joystick control sends a signal to tilt the blade to the right, pilot oil is directed to end cap (C). The spool shifts and the open center is blocked. The high pressure oil opens the makeup check valve, and flows through the main control valve by way of the tilt spool. The oil will force open pilot controlled check valve (3) and flow to the rod end of tilt cylinder (4).
The high pressure oil also sends pilot oil to pilot controlled check valve (3). The check valve opens and oil in the head end of the tilt cylinder will be allowed to flow through the main control valve and back to the hydraulic tank. The blade will tilt to the right.
When joystick control sends a signal to tilt the blade to the left, pilot oil is directed to end cap assembly (D). Spool (8) shifts and the open center is blocked. The high pressure oil opens the makeup check valve, and flows through main control valve (6) by way of the tilt spool. The oil will force open pilot controlled check valve (3) and flow to the head end of tilt cylinder (4) .
The high pressure oil also sends pilot oil to pilot controlled check valve (3). The check valve opens and oil in the head end of the tilt cylinder will be allowed to flow through the main control valve and back to the hydraulic tank. The blade will tilt to the left.