CARRIER NO. 1 0946436 - Caterpillar

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
Illustration 1 g00705101
Straight travel control valve and main relief valve (sectional view) (1) Straight travel control valve (2) Main control valve (3) Right travel control valve (4) Check valve (5) Upper pump (6) Check valve (7) Passage (8) Pilot pump (9) Main relief valve (10) Lower pump (11) Line (12) Line (13) LineOil from upper pump (5) and lower pump (10) enters main control valve (2) through lines (12) and (11). Upper pump oil and lower pump oil goes through check valves (6) and (4) to passage (7). The higher oil pressure from the upper pump or the lower pump goes through passage (7) to main relief valve (9). The main relief pressure is 34300 kPa (4975 psi). CLOSED Position
Illustration 2 g00705109
Main relief valve (CLOSED) (7) Passage (14) Valve (15) Spring chamber (16) Spring (17) Valve (18) Spring (19) Passage (20) Orifice (21) Return passageWhen main pump oil pressure in passage (7) is less than the main relief pressure setting, valve (17) is closed by the force of spring (18). The oil in passage (7) goes through orifice (20). Oil enters spring chamber (15). The pressure in passage (7) and the pressure in spring chamber (15) are equal. Valve (14) shifts left by the force of spring (16). Valve (14) closes passage (19). There is no oil flow from passage (7) to return passage (21). Operation
Illustration 3 g00705112
Main relief valve (OPEN) (7) Passage (14) Valve (15) Spring chamber (16) Spring (17) Valve (18) Spring (19) Passage (20) Orifice (21) Return passage (22) Adjuster (23) Passage (24) Valve chamberOil pressure in passage (7) nears the relief pressure setting. Oil pressure in passage (7) overcomes the force of spring (18). The oil pressure opens valve (17). The oil in valve chamber (24) goes through passage (23) to return passage (21). The oil is called low pressure oil. The oil pressure from passage (7) decreases at orifice (20). The oil then goes through spring chamber (15) to valve chamber (24). Because of the decreased oil pressure in spring chamber (15), the oil pressure from passage (7) pushes valve (14) to the right against the force of spring (16). Passage (19) now opens allowing the high pressure oil flow from passage (7) to return passage (21). Pressure adjustments can be made with adjuster (22) .