COVER 5S7884 - Caterpillar

Illustration 1 g00624465
Location of Line Relief ValvesThe boom function, stick function, bucket function and bucket bottom dump functions have line relief valves that limit maximum pressure due to external loads on the cylinders. Only the bucket bottom dump line relief and makeup valve has an internal makeup function.The pressure setting for the line relief valves is 33500 350 kPa (4860 50 psi).Operation of the Stick, Boom, Crossover and Bucket Line Relief Valves
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Line Relief ValveImplement circuit pressure enters the left end of the line relief valve. Implement circuit pressure then passes through the center of the valve spool to the small spring chamber in the center of the line relief valve. When the pressure exceeds 33500 350 kPa (4860 50 psi), the poppet is pushed off the poppet's seat. The pressure in the small spring chamber drains past the poppet to the hydraulic tank. The implement circuit pressure pushes the relief valve spool off the relief valve seat. Lifting the relief valve spool off the relief valve seat opens the passage that connects the implement circuit pressure to the tank return line.As the implement circuit pressure decreases, the spring force moves the poppet. This closes the passage between the small spring chamber and the tank return line. The Implement circuit pressure increases in the small spring chamber and the pressure increase closes the relief valve spool.Operation of the Bucket Bottom Dump Line Relief and Makeup Valve
Illustration 3 g00576107
Line Relief Valve with Internal Makeup ValveThe relief valve function of the bucket bottom dump line relief and makeup valve operates in the same manner as the stick, the boom, and the bucket line relief valves.The makeup function of the valve operates in the following manner. When the bucket bottom dump is operated, the load on the bucket clam can cause the implement to move too quickly and the supply circuit can not supply the cylinders with oil. This can cause the pressure in the return circuit to be greater than the implement circuit pressure. If this occurs, the return circuit pressure works against the shoulder of the relief valve sleeve. The relief valve sleeve will move to the right and off the relief valve seat. This opens the passage between the tank return line and the implement supply circuit. The tank return line then supplies makeup oil to the implement supply circuit.