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| Illustration 1 | g01042405 |
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(1) Inlet passage
(2) Valve (3) Passage to tank (4) Spring (5) Locknut (6) Adjusting screw (7) Port (8) Passage to tank (9) Valve | |
The line relief valves are in the tilt control valve, lift control valve, and the auxiliary control valves (If Equipped). Refer to Specifications, "Relief Valve (Line)" for the pressure settings of the line relief valve.
The relief valve is a direct acting valve. Pressure oil flows into passage (1). The oil acts against the left side of valve (2) which is held closed by the force of spring (4).
When an outside force causes pressure in any of the cylinders to rise, that increase in pressure is also felt in passage (1). As the pressure rises above the valve setting, the oil overcomes the force of spring (4) and the oil causes valve (2) to move to the left. Oil flows through port (7) through passage (8) to the tank. The oil flow through port (7) causes a pressure drop to the left of valve (2). This pressure drop causes valve (9) to shift to the left because system pressure is acting against valve (9).
Oil in the hydraulic line flows past valve (9) and through passages (3) to the hydraulic tank.
Since the relief valve is allowing oil to travel to the tank, the oil pressure in the cylinders cannot increase. When the oil pressure goes below the setting of the relief valve, spring (4) moves valve (2) back to the left onto the valve seat. Valve (9) shifts to the right.
Line relief valve pressure settings are factory set and cannot be adjusted. Line relief valves can only be replaced.