PLATE-SIDE-RH. 4B4483 - Caterpillar

Main Relief Valve
The main relief valve is located on the inlet section in the main control valve. The main relief valve limits the pressure from the implement pump to the main hydraulic system. Access to the main control valve is at the articulation hitch.When the pressure between the discharge of the implement pump and the inlet to the main control valve exceeds the adjusted setting, the main relief valve opens. Then, oil flows from the relief valve through the main control valve to the hydraulic tank.Reference: For information on the pressure settings for the main relief valve, refer to the Service Manual module Testing and Adjusting, UENR0331, "Relief Valve (Main) - Test and Adjust" for the machine that is being serviced.
Illustration 1 g02025152
Main relief valve
(1) Inlet
(2) Tank passage
(3) Spring
(4) Cavity
(5) Valve
(6) Locking nut
(7) Valve
(8) Tank passage
(9) Seat
(10) Cavity
(11) Spring
(12) Adjustment screw
(AA) Supply oil
(BB) Tank oil
(CC) Active components
(DD) Surface area Supply oil in the hydraulic system flows into the relief valve through inlet (1), through the orifice in the center of valve (7), and into cavity (4) for spring (3). The oil in the cavity (4) contacts valve (5). When the oil pressure in the hydraulic system is less than the relief valve setting, the force of spring (11) on valve (5) keeps valve (5) in contact with seat (9). Valve (5) blocks any supply oil from flowing through the main relief valve to the hydraulic tank.Illustration 1 shows the valve with the oil pressure below the adjusted pressure.
Illustration 2 g02025179
Main relief valve
(1) Inlet
(2) Tank passage
(3) Spring
(4) Cavity
(5) Valve
(6) Locking nut
(7) Valve
(8) Tank passage
(9) Seat
(10) Cavity
(11) Spring
(12) Adjustment screw
(AA) Supply oil
(BB) Tank oil
(CC) Active components
(DD) Surface area If the supply oil in inlet (1) exceeds the relief valve setting, the oil pressure overcomes the force of spring (11). When the pressure of the supply oil at inlet (1) exceeds the adjusted pressure, the force that is built up by the pressure in cavity (4) is greater than the force of spring (11). Valve (5) moves away from seat (9). Oil flows into cavity (10) and back to the hydraulic tank through tank passage (8).The flow of oil is shown in Illustration 2. This illustration shows the hydraulic oil pressure higher than the adjusted pressure. At this point, the main relief valve will not drain an adequate amount of oil to the hydraulic tank in order to lower the pressure.
Illustration 3 g02025182
Main relief valve
(1) Inlet
(2) Tank passage
(3) Spring
(4) Cavity
(5) Valve
(6) Locking nut
(7) Valve
(8) Tank passage
(9) Seat
(10) Cavity
(11) Spring
(12) Adjustment screw
(AA) Supply oil
(BB) Tank oil
(CC) Active components
(DD) Surface area
(EE) Reduced supply pressure When the pressure of the supply oil exceeds the adjusted pressure of the main relief valve, the force that is built up by the pressure in cavity (4) is greater than the force of spring (11). Valve (5) moves away from seat (9). When valve (5) shifts to the right, the pressure of