The standard main control valve is equipped with three line relief valves: the relief valve for the head end of the tilt cylinder, the relief valve for the rod end of the tilt cylinder, and the relief valve for the ride control valve.
The line relief valve is installed to regulate pressure spikes from either the implement pump or any unusual outside forces acting on the work tool. When the pressure is higher than the setting of the line relief valve, the relief valve opens. This process allows high pressure to return to the hydraulic tank. The line relief valves prevent high pressure from damaging any components in the hydraulic system.
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| Illustration 1 | g06112420 |
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Top right view of main control valve (1) Line Relief Valve (Head End) (Tilt) (2) Line Relief Valve (Rod End) (Tilt) (3) Line Relief Valve (Ride Control) | |
Auxiliary Third Function Control Valve
When an auxiliary control valve is added, a head end and a rod end line relief valve are added for the auxiliary cylinders.
The line relief valve is installed to regulate pressure spikes from either the implement pump or any unusual outside forces acting on the work tool. When the pressure is higher than the setting of the line relief valve, the relief valve opens. This process allows high pressure to return to the hydraulic tank. The line relief valves prevent high pressure from damaging any components in the hydraulic system.
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| Illustration 2 | g06112512 |
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Top view of auxiliary control valve (3) Line Relief Valve (Head End) (Auxiliary) (5) Line Relief Valve (Rod End) (Auxiliary) | |
Direct Operated Line Relief Valve
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| Illustration 3 | g06113487 |
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(AA) Supply oil
(BB) Tank oil (CC) Active components (DD) Surface area (6) Locknut (7) Valve body (8) Passage to the hydraulic tank (9) Poppet (10) Adjustment screw (11) Spring (12) Passage to work port | |
Work port oil flows into passage (12). Spring (11) holds poppet (9) in the closed position. Poppet (9) will open when oil pressure in passage (12) is greater than the force of spring (11). The oil will flow past the poppet into passage (8). The oil returns to the tank.
The relief valve pressure can be adjusted. Turn adjustment screw (10) clockwise in order to increase relief pressure. Turn adjustment screw (10) counterclockwise in order to decrease relief pressure.
Reference: For additional information about line relief valves, refer to the Service Manual module for Testing and Adjusting, "Relief Valve (Line) - Test and Adjust".