CONTROLLER 3661751 - Caterpillar

Illustration 1 g00557421
(1) Work port. (2) Valve. (3) Spring chamber. (4) Poppet valve. (5) Locknut. (6) Adjustment 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 29000 kPa (4200 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), poppet valve (4) moves to the right. The oil in spring chamber (3) flows past the open poppet valve (4) through port (8). The oil that flows past poppet valve (4) causes oil to flow through the center passage of valve (2) to replenish the oil in chamber (3). As the oil flows through the center passage of valve (2) there is a pressure drop. This pressure drop results in a reduced pressure in spring chamber (3), when the pressure is compared to the pressure at work port (1). As this pressure difference increases, the force of spring (9) is overcome and valve (2) shifts to the right. This relieves some of the pressure in work port (1) and the excess oil 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. 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.