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| Illustration 1 | g00557421 |
(1) Work port. (2) Valve. (3) Spring chamber. (4) Poppet valve. (5) Locknut. (6) Adjusting screw. (7) Drain for the work port. (8) Drain for the poppet valve. (9) Spring. (10) Spring. | |
The main relief valve is ahead of all other valves in the implement hydraulic system. The main relief valve is a pilot-operated cartridge type valve. The pressure setting of the main relief valve is approximately 24100 kPa (3500 psi).
Implement system oil flows into work port (1), through the orifice in the center of valve (2), and into spring chamber (3). The oil in spring chamber (3) contacts pilot valve (4) .
Closed Operation
Implement system oil flows from work port (1), through the passage in valve (2), and into spring chamber (3). This pressure combines with spring (9) in order to hold valve (2) closed. The pressure of the oil also acts against pilot valve (4). This valve is held closed by spring (10) when the pressure in port (1) is below the relief valve setting.
Relief Operation
When the oil pressure in spring chamber (3) overcomes the force of spring (10), pilot valve (4) moves to the right. The oil in spring chamber (3) flows past the open pilot valve (4) through port (8). The oil flows through port (8) at a faster rate than the oil that flows through the passage in valve (2) .
When the oil pressure in spring chamber (3) overcomes the force of spring (10), pilot valve (4) moves to the right. The oil in spring chamber (3) flows past the open pilot valve (4) through port (8). The oil flows through port (8) at a faster rate than the oil that flows through the passage in valve (2) .
The pressure from the oil in work port (1) acts against valve (2). Because the oil is relieved from the spring chamber (3), the only force that is resisting the pressure from work port (1) is spring (9). Oil pressure from work port (1) causes valve (2) to move to the right. This relieves some of the pressure in work port (1) and the excess oil pressure flows back to the hydraulic tank through port (7) .
Since part of the oil is routed back to the hydraulic tank, oil pressure in work port (1) decreases. The relief valve protects the implement pump and the lines from high pressures. During short pressure spikes, only pilot valve (4) opens to the tank.
Screw (6) is used to adjust the relief valve setting, if adjustment is required. Locknut (5) is used to keep screw (6) from turning after the adjustment is made.