SPACER 4K8859 - Caterpillar

Illustration 1 g01012254
Lift circuit relief valveThe main control valve is located on the front frame. The lift circuit relief valve is located in the manifold mounted on the main control valve.When the lift valve spool is in the HOLD position, the lift circuit relief valve for the head end of the lift cylinders limits the maximum pressure in the lift circuit.
Illustration 2 g00910952
Lift circuit relief valve (1) Spring (2) Passage (3) Plate (4) Valve (5) Passage (6) Orifice (7) InletAny external force on the lift 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 lift cylinder circuit.The lift circuit has a makeup valve in the main control valve. When the lift circuit relief valve opens, the lift cylinders retract. If the lift cylinders retract too fast, the lift circuit can not supply enough oil to the rod end of the lift cylinders creating a pressure decrease. The pressure decrease causes the makeup valve to open allowing makeup oil to flow to the rod end of the lift cylinders.