SEAL 0643882 - Caterpillar

Illustration 1 g00897401
Main control valve (A) Line relief valve for the rod end of the tilt cylinder (B) Line relief valve for the head end of the tilt cylinder (C) Line relief valve for the rod end of the auxiliary cylinders (D) Line relief valve for the head end of the auxiliary cylindersThe line relief valves are located on the main control valve. The main control valve is located on the front frame.There is a line relief valve for the the rod end of the tilt cylinder (A) and a line relief valve for the head end of the tilt cylinder (B). The auxiliary control valve has a line relief valve for the rod end of the auxiliary cylinders (C) and a line relief valve for the head end of the auxiliary cylinders (D) .When the tilt valve spool is in the HOLD position, the line relief valves for the head end of the tilt cylinder and the line relief valve for the rod end of the tilt cylinder limit the maximum pressure in the tilt circuit.When the auxiliary valve spool is in the HOLD position, the line relief valve for the head end of the auxiliary cylinders and the line relief valve for the rod end of the auxiliary cylinders limit the maximum pressure in the auxiliary circuit.Note: The operation of all the line relief valves is similar. An explanation of a typical line relief valve is given.
Illustration 2 g00910952
Line relief valve (1) Spring (2) Passage (3) Plate (4) Valve (5) Passage (6) Orifice (7) InletAny external force on the tilt cylinder or the auxiliary cylinders will increase the oil pressure in inlet (7). If the oil pressure against valve (4) exceeds the force of spring (1), valve (4) will open.Oil then flows through passage (5) to the hydraulic tank. The pressure in inlet (7) is reduced in order to prevent damage to the components of the tilt circuit and the auxiliary circuit.The tilt circuit has a makeup valve in the main control valve. When line relief valve (B) opens, the tilt cylinder retracts. If the tilt cylinder retracts too fast, the tilt circuit can not supply enough oil to the rod end of the tilt cylinder creating a pressure decrease. The pressure decrease causes the makeup valve to open allowing makeup oil to flow to the rod end of the tilt cylinder.