ANGLE 8T4268 - Caterpillar

Head End and Rod End Relief Valve for Tilt
RELIEF VALVE FOR TILT CIRCUIT
1. Inlet for pressure oil. 2. Chamber. 3. Chamber. 4. Passage to tank. 5. Pilot valve. 6. Spring for pilot valve. 7. Outlet to tank. 8. Dump valve. 9. Spring for dump valve. 10. Shims.The relief valves for the tilt circuit give protection to the components in the circuit when pressures, caused by outside forces, become too high. These valves work when the spool in the main control valve is in the HOLD position. The valves in the head ends are the same as the valves in the rod ends. The only difference in the valves is their pressure setting. The pressure setting for the head end relief valves is 2100 50 psi (14 500 345 kPa) and the setting for rod end relief valves is 2650 50 psi (18 030 345 kPa).Since the pressure setting of the head end relief valve is lower than the main pressure relief valve, it can be opened by system pressure when the main control valve for tilt is in the DUMP position.When pilot valve (5) is closed against its seat, the pressure in chambers (2) and (3) is the same. Dump valve (8) is held closed by the force of spring (9). The opening pressure of dump valve (8) is controlled by the force of springs (6) and (9). Shims (10) are used for the adjustment of spring (6). One shim will change the opening pressure of the valve 86 psi (590 kPa). When the pressure in the cylinder goes up to the setting of the relief valve, pilot valve (5) begins to move against the force of spring (6). This will cause the orifice at the seat of the pilot valve to open a small amount and allow oil from chamber (3) to return to tank through passage (4). The orifice in the seat of pilot valve (5) is larger than the orifice in dump valve (8). As pilot valve (5) moves against the force of spring (6), the opening in the seat of the valve becomes larger. When the opening in the seat of pilot valve (5) has opened enough, the pressure in chamber (3) becomes lower than the pressure in chamber (2). Dump valve (8) will open when the difference between the two pressures becomes larger than the force of spring (9). Oil flow goes from chamber (2), out through outlet (7), to tank. The pressure in the cylinders does not increase any more.Check Valves
The check valves for the lift and tilt circuits prevent the flow of oil in the reverse direction. This will not let the cylinders drift when the main control valves are moved from one direction to another. The valves are closed until the pressure of the pump flow gets high enough to push against the force of the spring and open the valve.Make-Up Valves
The make-up valves open to add oil to pump flow when the cylinders return oil