Main Relief Valve
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| Illustration 1 | g00822927 |
Main Control Valve (Three Valve) | |
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| Illustration 2 | g00822928 |
Main Control Valve (Two Valve) | |
The main relief valve is located on the inlet section to the main control valve. The main control valve is located in the front loader frame. The main relief valve limits the pressure from the implement pump to the main hydraulic system. Access to the main control valve can be gained by removing the loader tower access panel.
When the pressure at the inlet to the main control valve exceeds the pressure setting of the main relief valve, the main relief valve opens. The hydraulic oil then flows through the main relief valve to the hydraulic oil tank.
Reference: For information on the pressure settings for the main relief valve, refer to the Service Manual module Specifications, "Hydraulic System, Relief Valve (Main)" for the machine that is being serviced.
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| Illustration 3 | g00888630 |
Relief Valve (1) Inlet. (2) Valve. (3) Passage. (4) Passage. (5) Spring. (6) Seat. (7) Valve. (8) Spring. (9) Locking nut. (10) Adjuster. | |
High pressure oil flows into the relief valve through inlet (1), through the orifice in the center of valve (2), and into the chamber for spring (5). The oil in the spring chamber contacts valve (7). Seat (6) can not move. Seat (6) is pressed into the valve body.
When the pressure of the oil in the circuit is less than the relief valve setting, the force of spring (8) on valve (7) keeps the main relief valve from allowing oil to flow to the hydraulic tank. The flow of oil is shown in Illustration 3. The illustration shows the valve with the oil pressure below the adjusted pressure.
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| Illustration 4 | g00888584 |
Main Relief Valve (1) Inlet. (2) Valve. (3) Passage. (4) Passage. (5) Spring. (6) Seat. (7) Valve. (8) Spring. (9) Locking nut. (10) Adjustment screw. | |
If the high pressure oil in inlet (1) exceeds the relief valve setting, the oil pressure overcomes the force of spring (8). This causes valve (7) to move off seat (6). The oil in the chamber for spring (5) flows through the hole in seat (6). The oil then flows through passage (4) to the hydraulic tank. The flow of oil is shown in Illustration 4. This illustration shows the hydraulic oil pressure higher than the adjusted pressure. At this point, the relief valve can not drain enough oil to the hydraulic tank in order to lower the pressure.
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| Illustration 5 | g00888585 |
Main Relief Valve (1) Inlet. (2) Valve. (3) Passage. (4) Passage. (5) Spring. (6) Seat. (7) Valve. (8) Spring. (9) Locking nut. (10) Adjustment screw. | |
When valve (7) opens, the pressure of the oil in the chamber for spring (5) decreases. The force of spring (5) and the force of the oil in the chamber of spring (5) is less than the force of the inlet oil. The pressure of the oil at inlet (1) pushes valve (2) in order to allow the high pressure oil to flow out of the relief valve through passage (3). Oil can then flow through passage (3), and back to the hydraulic tank. The oil flow is shown in Illustration 5. Oil is flowing back to the hydraulic tank.
Valve (2) remains in this position until the pressure at the inlet is below the adjusted pressure. At this time, the force of spring (8) moves valve (7) until the valve is in contact with seat (6). The oil flow through passage (4) is blocked. The combination of the pressure in the chamber for spring (5) and the force of spring (5) will move valve (7). The movement of valve (7) will be over the hole to passage (3). Valve (7) will block the flow of oil to passage (3). Spring (8) will hold valve (7) in this position until the pressure in inlet (1) rises above the adjusted pressure.
The adjusted pressure can be changed by turning adjustment screw (10). Rotating adjustment screw (10) in the clockwise direction will increase the pressure setting. Rotating adjustment screw (10) in the counterclockwise direction will decrease the pressure setting. In order to adjust the main relief valve, locking nut (9) must be loose.
Reference: For more information on testing and adjusting the pressure setting of the main relief valve, refer to the Service Manual module for Testing and Adjusting, "Hydraulic System, Main Relief Valve - Test and Adjust".
Line Relief Valve
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| Illustration 6 | g00905943 |
Main Control Valve (Three Valve) (1) Line relief valve (Auxiliary head end). (2) Line Relief valve (auxiliary rod end). (3) Dump line relief valve. (4) Tilt back line relief valve. | |
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| Illustration 7 | g00905944 |
Main Control Valve (Two Valve) (3) Dump line relief valve. (4) Tilt back line relief valve. | |
The line relief valves are located on the main control valve. The main control valve is mounted on the front frame. There is a line relief valve for both the head end of the tilt cylinder, and for the rod end of the tilt cylinder. Access to the main control valve can be gained by removing the loader tower access panel.
Note: For machines with auxiliary functions, the head end of the auxiliary cylinders and the rod end of the auxiliary cylinders also have a line relief valve.
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| Illustration 8 | g00905947 |
Line Relief Valve (15) Inlet. (16) Passage to the hydraulic tank. (17) Poppet. (18) Washer. (19) Spring. (20) Locking nut. (21) Adjustment screw. | |
When the pressure of the oil in the circuit is less than the relief valve setting, the force of spring (19) on poppet (17) keeps the main relief valve from allowing oil to flow to the hydraulic tank. Illustration 8 shows the line relief valve with the oil pressure below the adjusted pressure.
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| Illustration 9 | g00905989 |
Line Relief Valve (15) Inlet. (16) Passage to the hydraulic tank. (17) Poppet. (18) Washer. (19) Spring. (20) Locking nut. (21) Adjustment screw. | |
If there is any outside force on the work tool the oil pressure at inlet (15) will increase. If the high pressure oil in inlet (15) exceeds the relief valve setting, the oil pressure overcomes the force of spring (19). This causes poppet (17) to move off the seat. The oil then flows through passage (16) to the hydraulic tank. Illustration 9 shows the line relief valve with the hydraulic oil pressure higher than the adjusted pressure.
Adjustment of the line relief valve is made by loosening locking nut (20). In order to raise the pressure adjustment, turn adjustment screw (21) clockwise. In order to lower the pressure adjustment, turn adjustment screw (21) counterclockwise.
Reference: For information about testing and adjusting the line relief valves, refer to the Service Manual module for Testing and Adjusting, "Relief Valve (Line) - Test and Adjust".