EXTENSION-FENDER 3478068 - Caterpillar

Illustration 1 g00641012
Main Control Valve with Auxiliary Control Valve (1) Rod end line relief valve (tilt cylinder). (2) Rod end line relief valve (auxiliary cylinder). (3) Head end line relief valve (tilt cylinder). (4) Head end line relief valve (auxiliary cylinder). (5) Main relief valve for the main control valve. (6) Main relief valve with the addition of an auxiliary control valve.When an auxiliary control valve is added, a head end line relief valve and a rod end line relief valve are added for the auxiliary cylinders.The main relief valve and the relief valve for the rod end of the tilt cylinder limit the oil pressure in the implement pump section. The relief valve for the head end of the tilt cylinder and the line relief valves for the auxiliary cylinders are not opened by implement oil pressure because the pressure setting for the main relief valve is lower than the settings for these other three relief valves.
Illustration 2 g00290729
Main Relief Valve (7) Inlet. (8) Valve. (9) Pilot valve. (10) Locknut. (11) Plunger. (12) Outlet. (13) Passage. (14) Spring. (15) Spring. (16) Spacer.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 20700 kPa (3000 psi).Implement system oil flows into inlet (7), through the orifice in the center of valve (8), and into the chamber for spring (14). The oil in the spring chamber contacts pilot valve (9) .When the pressure of the oil in the circuit is less than the relief valve setting, the force of the spring in the pilot valve keeps the pilot valve closed.If the pressure of the oil through inlet (7) and in the chamber for spring (14) reaches the relief valve setting, the oil pressure overcomes the force of spring (15) and pilot valve (9) is moved to the right.When the pilot valve opens, the oil in the spring chamber flows past the open pilot valve, through passage (13), and to the hydraulic tank.When only the pilot valve is open, the force of spring (14) is acting against valve (8). The pressure of the oil at inlet (7) moves valve (8) enough to the right so that implement oil can flow through the inlet, through outlets (12), and back to the hydraulic tank. The pressure of the oil cannot increase higher than the relief valve setting.The relief valve setting can be adjusted by changing the force of spring (15) which keeps pilot valve (9) closed. Loosen locknut (10) and turn plunger (11) clockwise in order to increase the relief valve setting. Turn plunger (11) counterclockwise in order to decrease the relief valve setting.