EDGE-CUTTING 6Y0480 - Caterpillar

Limitation Of Pressure In Circuit
Two types of relief valves are installed on the main control valves to limit the pressure in the hydraulic circuit.
The main relief valve limits the pressure in the main hydraulic system.
The line relief valve limits the pressure which is built into the cylinder circuits.Main Relief Valve
Illustration 1 g06203225
Main relief valve (sectional view)
(1) Main control valve
(2) Line
(3) Heavy lift solenoid valve
(4) Straight travel control valve
(5) Check valve
(6) Check valve
(7) Passage
(8) Main relief valve
(9) Line
(10) Passage
(11) Solenoid manifold
(12) Pump 1
(13) Pump 2
(14) LineOil from pump 1 (12) and pump 2 (13) enters main control valve (1) through lines (9) and (14). Pump oil goes through check valves (5) and (6) to passage (7). The higher oil pressure from pump 1 (12) or pump 2 (13) goes through passage (7) to main relief valve (8).CLOSED Position (Heavy Lift OFF)
Illustration 2 g06203307
Main relief valve (CLOSED)
(7) Passage
(15) Valve
(16) Spring chamber
(17) Spring
(18) Poppet
(19) Spring
(20) Passage
(21) Orifice
(22) Return passageWhen main pump oil pressure in passage (7) is less than the main relief pressure setting, valve (15) and poppet (18) are closed by the force of spring (17) and spring (19). The oil in passage (7) goes through orifice (21). Oil enters spring chamber (16). The pressure in passage (7) and the pressure in spring chamber (16) are equal. Valve (15) shifts down by the force of spring (17). Valve (15) closes passage (20). There is no oil flow from passage (7) to return passage (22).OPEN Position (Heavy Lift OFF)
Illustration 3 g06203309
Main relief valve (OPEN)
(7) Passage
(15) Valve
(16) Spring chamber
(17) Spring
(18) Poppet
(19) Spring
(20) Passage
(21) Orifice
(22) Return passage
(23) Passage
(24) ChamberOil pressure in passage (7) nears the relief pressure setting. Oil pressure in passage (7) overcomes the force of spring (19). The oil pressure opens poppet (18). The oil in valve chamber (24) goes through passage (23) to return passage (22). The oil is called low-pressure oil. The oil pressure from passage (7) decreases at orifice (21). The oil then goes through spring chamber (16) to valve chamber (24). Because of the decreased oil pressure in spring chamber (17), the oil pressure from passage (7) pushes valve (15) up against the force of spring (17). Passage (20) now opens allowing the high-pressure oil flow from passage (7) to return passage (22).Heavy Lift Operation
Illustration 4 g06203372
(7) Passage
(15) Valve
(16) Spring chamber
(17) Spring
(18) Poppet
(19) Spring
(20) Passage
(21) Orifice
(22) Return passage
(23) Passage
(24) Chamber
(25) Piston
(26) Passage
(27) PortWhen heavy lift is activated from the monitor, heavy lift solenoid (3) shifts. Pilot oil now flows from solenoid manifold (11) through solenoid (3), line (10), and port (27). Pilot oil enters passage (26) which forces piston (25) to shift down which causes a higher force on valve (18). A higher pressure is now needed to open main relief valve (8). The larger pressure results in a greater overall system pressure. The greater system pressure allows more pressure in the boom and stick cylinders which increases the lifting capacity.