Limitation Of Pressure In Circuit
Two types of relief valves are installed on the main control valves in order 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
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| Illustration 1 | g02707256 |
Straight travel control valve and main relief valve (sectional view) (1) Main control valve (2) Right travel control valve (3) Straight travel control valve (4) Check valve (5) Check valve (6) Passage (7) Pilot pump (8) Drive pump (9) Heavy lift solenoid valve (10) Main relief valve (11) Passage (12) Line (13) Idler pump (14) Line (15) Line (16) Pilot manifold (17) Line | |
Oil from drive pump (8) and idler pump (13) enters main control valve (1) through lines (15) and (14). Drive pump oil and idler pump oil goes through check valves (5) and (4) to passage (6). The higher oil pressure from the drive pump or the idler pump goes through passage (6) to main relief valve (10).
CLOSED Position (Heavy Lift OFF)
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| Illustration 2 | g02130315 |
Main relief valve (CLOSED) (6) Passage (18) Valve (19) Spring chamber (20) Spring (21) Valve (22) Spring (23) Passage (24) Orifice (25) Return passage | |
When main pump oil pressure in passage (6) is less than the main relief pressure setting, valve (21) is closed by the force of spring (22). The oil in passage (6) goes through orifice (24). Oil enters spring chamber (19). The pressure in passage (6) and the pressure in spring chamber (19) are equal. Valve (18) shifts left by the force of spring (20). Valve (18) closes passage (23). There is no oil flow from passage (6) to return passage (25).
OPEN Position (Heavy Lift OFF)
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| Illustration 3 | g02130418 |
Main relief valve (OPEN) (6) Passage (18) Valve (19) Spring chamber (20) Spring (21) Valve (22) Spring (23) Passage (24) Orifice (25) Return passage (26) Passage (27) Chamber | |
Oil pressure in passage (6) nears the relief pressure setting. Oil pressure in passage (6) overcomes the force of spring (22). The oil pressure opens valve (21). The oil in valve chamber (27) goes through passage (26) to return passage (25). The oil is called low-pressure oil. The oil pressure from passage (6) decreases at orifice (24). The oil then goes through spring chamber (19) to valve chamber (27). Because of the decreased oil pressure in spring chamber (19), the oil pressure from passage (6) pushes valve (18) to the right against the force of spring (20). Passage (23) now opens allowing the high-pressure oil flow from passage (6) to return passage (25) .
Heavy Lift Operation
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| Illustration 4 | g02130822 |
(6) Passage (18) Valve (19) Spring chamber (20) Spring (21) Valve (22) Spring (23) Passage (24) Orifice (25) Return passage (26) Passage (27) Chamber (28) Passage (29) Chamber (30) Passage (31) Chamber (32) Piston | |
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| Illustration 5 | g02638138 |
Soft Switch Panel (right console) (33) Heavy lift switch | |
When the heavy lift switch (33) is placed in the ON position, heavy lift solenoid (9) shifts. Pilot oil now flows from pilot manifold (16) through solenoid (9) to passage (30). Pilot oil enters chamber (31) and flows to passage (28). Pilot oil enters chamber (29) which forces piston (32) to shift to the left which causes a higher force on valve (21). A higher pressure is now needed to open main relief valve (10). 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.