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| Illustration 1 | g03366232 |
location of the lift circuit relief valve behind the guard | |
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| Illustration 2 | g03051057 |
Lift circuit relief valve | |
The 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 lift valve spool is in HOLD position, the lift circuit relief valve for head end of lift cylinders limits maximum pressure in lift circuit.
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| Illustration 3 | g02998117 |
Lift circuit relief valve (1) Spring (2) Passage (3) Plate (4) Valve (5) Passage (6) Orifice (7) Inlet | |
Any 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 lift cylinders retract too fast, the lift circuit cannot supply enough oil to the rod end of 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.