HOSE AS 2Q7274 - Caterpillar

Illustration 1 g01038322
Main control valve
(A) Line relief valve
(B) Line relief valveThe line relief valves are on the main control valve. The main control valve is located in the front frame.Line relief valve (A) is for the head end of the tilt cylinder, line relief valve (B) is for the rod end of the tilt cylinder.When the tilt valve spool is in the HOLD position. The line relief valve for the head end, and the line relief valve for the rod end of the tilt cylinder limits the maximum pressure in the tilt circuit.Note: The operation of the line relief valves is similar. An explanation of a typical line relief valve is given.
Illustration 2 g06002663
Line relief valve
(1) Spring
(2) Passage
(3) Plate
(4) Valve
(5) Passage
(6) Orifice
(7) Inlet
Illustration 3 g00910952Any external force on the tilt cylinder 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 to prevent damage to the components of the tilt circuit.The tilt circuit has two makeup valves in the main control valve. When line relief valve (A) opens, the tilt cylinder retracts. The tilt cylinder retracts too fast, the tilt circuit cannot 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.