SHELL-LAMP 8T9722 - Caterpillar

Illustration 1 g00394537
Main Control Valves (1) Left main control valve. (2) Right main control valve. (3) Makeup valve. (4) Line relief/makeup valve for the rod end of the tilt cylinder. (5) Line relief/makeup valve for the head end of the lift cylinder. (6) Line relief/makeup valve for the head end of the tilt cylinder.Left main control valve (1) has line relief/makeup valves (4), (5) and (6). Right main control valve (2) has makeup valves (3) .Line Relief/Makeup Valve
Illustration 2 g00323025
View A-ALine Relief/Makeup Valve (7) Plug. (8) Spring. (9) Passage. (10) Seat. (11) Pilot valve. (12) Spring. (13) Valve assembly. (14) Passage to tank. (15) Valve. (16) Passage from cylinder. (17) Shims. (18) Passage.When the main control valve spool is in the HOLD position, the pressure in any line between the control valve and a cylinder is maintained by the line relief/makeup valve.The pressure setting of line relief/makeup valve (4) is 24100 700 kPa (3500 100 psi). The pressure setting of line relief/makeup valve (6) is 31000 700 kPa (4500 100 psi). Shims (17) are used to adjust both line relief/makeup valves.The pressure setting of line relief/makeup valve (5) is 38000 700 kPa (5500 100 psi). Shims (17) are used to adjust the line relief/makeup valve.Valve (13) and valve seat (10) are held against pilot valve (11) by spring (12). Oil from passage (16) flows through holes in valve (15). The oil then fills the area around the base of valve (13). Oil cannot flow into passage (14) while valve (13) is seated.The oil flows through passage (18). The oil fills the chamber in plug (7). When the main control valve spool is in the HOLD position, the oil that is flowing through the lines to the cylinders is blocked. If an outside force causes pressure to become too high, pilot valve (11) will open.When pilot valve (11) opens, oil flows from the chamber in plug (7) through passage (9). The oil then flows through valve (13) into passage (14). The oil then returns to the hydraulic tank.When pilot valve (11) opens, the pressure decrease in the chamber in plug (7) allows valve (13) to overcome the force of spring (8). Valve (13) moves off the seat in valve (15). Oil in the line that is under pressure flows through the small holes in valve (15). The oil then flows through passage (14) to the tank.The line relief/makeup valve functions as a makeup valve when the pressure in the cylinder is below the pressure in the tank. The makeup function of the valve is explained for the dumping of the bucket.When the operator places the control lever in the DUMP position and the bucket is loaded, the tilt cylinders move. The tilt cylinders move faster than the supply of oil from the pump. During this condition, the pressure in passage (16) is lower than the pressure in passage to the tank (14). The higher pressure in passage (14) will unseat valve (15). The oil