LINES G-FUEL 8N8168 - Caterpillar

Make-up Valves
Make-up valves are held closed by a spring and pressure of the oil in their respective cylinders. If the pressure of the oil in any of the hydraulic circuits becomes less than the pressure in the tank, the make-up valve will open and oil will go from the tank to the cylinder.The make-up valve opens to add oil to pump flow when the cylinders are returning oil to the tank faster than the pump can supply it. This will prevent air from getting into the system and result in movement by the cylinders that is faster.The make-up valves in the tilt circuits will open when either of the tilt relief valves are opened and the tilt control valve is in the HOLD position.A vented make-up valve is used in the head end of the lift cylinder on the left side circuit. It lets the bucket be lowered when the engine is not running. (See topic VENT VALVE).Relief Valves for the Rod Ends of the Tilt Circuit
The relief valve for the tilt circuit gives protection to the components in the circuit when pressures caused by outside forces become too high. This valve works when the spool in the main control valve is in the HOLD position.
RELIEF VALVE (3J8878) FOR TILT CIRCUIT (Rod Ends)
1. Oil passage. 2. Dump valve. 3. Shims. 4. Piston. 5. Outlet to tank. 6. Inlet from cylinder.The dump valve (2) and spacer are held against the block by the force of springs. The pressure in the rod ends of the cylinders is felt through passage (1) in the piston chamber and on piston (4). When the pressure of the oil in the piston chamber becomes more than the force of the springs, the piston and spacer are pushed against the dump valve. This action moves the dump valve causing compression of the springs. A passage to tank from the cylinder inlet is opened by movement of the dump valve. This relieves the pressure on the rod end and lets the piston in the cylinder move without any damage. There are orifices in the dump valve that cause the pressure reduction to be gradual.Shims are put in the valve to control the force of the springs. If a shim is removed, it will increase the pressure needed to open the valve.Relief Valves for the Head Ends of the Tilt Circuit (Differential)
The relief valves on the head and rod ends of the tilt cylinders are similar. The difference is the head end relief valves have two pistons (6 and 11) where the rod end relief valves have only one.
RELIEF VALVE FOR TILT CIRCUIT (Head Ends) (Differential)
1. Shims. 2. Return springs for dump valve. 3. Dump valve. 4. Orifices. 5. Body. 6. Piston (head ends, tilt). 7. Chamber. 8. Inlet from cylinder (head end, tilt). 9. Outlet to tank. 10. Spacer. 11. Piston (head ends, lift). 12. Inlet from head end of lift cylinder.The pressure of the oil in the head end of the tilt cylinder is felt