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| Illustration 1 | g02025839 |
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Line relief valve (13) Inlet (14) Tank passage (15) Cavity (16) Poppet (17) Tank passage (18) Spring (19) Makeup spool (20) Valve (21) Dump spool (22) Spring (23) Cavity (AA) Supply oil (BB) Tank oil (CC) Active components (DD) Surface area | |
Illustration 1 shows a line relief valve with the pressure at inlet (13) below the adjusted pressure of the valve.
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| Illustration 2 | g02025858 |
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Line relief valve (13) Inlet (14) Tank passage (15) Cavity (16) Poppet (17) Tank passage (18) Spring (19) Makeup spool (20) Valve (21) Dump spool (22) Spring (23) Cavity (AA) Supply oil (BB) Tank oil (CC) Active components (DD) Surface area (EE) Reduced supply pressure | |
Illustration 2 shows a line relief valve with the pressure at inlet (13) that is starting to rise above the adjusted pressure of the valve. As the pressure begins to rise, the oil that is flowing into inlet (13) will shift valve (20) to the right. High-pressure oil flows past valve (20) into cavity (15). The oil pressure in cavity (15) works against the area of poppet (16). The force that is developed on the area around the end of poppet (16) overrides the force of spring (18). Poppet (16) shifts to the right.
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| Illustration 3 | g02025875 |
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Line relief valve (13) Inlet (14) Tank passage (15) Cavity (16) Poppet (17) Tank passage (18) Spring (19) Makeup spool (20) Valve (21) Dump spool (22) Spring (23) Cavity (AA) Supply oil (BB) Tank oil (CC) Active components (DD) Surface area (EE) Reduced supply pressure | |
When poppet (16) shifts to the right, the pressure in cavity (15) will decrease. The pressure on the end of valve (20) overrides spring (22). Then, dump spool (21) moves toward the right. The flow of oil that is needed to lower the pressure at inlet (13) is allowed to flow out of tank passage (14).
When the pressure at inlet (13) is less than the adjusted pressure, the force of spring (28) moves poppet (16) to the left. Poppet (16) will seat. Then, the combination of the pressure in cavity (15) and the spring force from spring (22) moves dump spool (21) to the left against the seat. At this time, the flow of oil to tank passage (14) is blocked.
The line relief valve can be used as a makeup valve. When either the lift cylinder or the tilt cylinder is moving and the pump cannot supply the amount of oil that is needed to fill the void in the cylinder, oil through the makeup valve is available to assist in filling the void.
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| Illustration 4 | g02025960 |
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(13) Inlet
(19) Makeup spool (24) Main control valve (25) Tank port (BB) Tank oil (CC) Active components (DD) Surface area (FF) Reduced tank oil | |
When the line relief valve is installed into main control valve (24), makeup spool (19) will be seated against the main control valve. The seat separates the inlet from tank port (25).
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| Illustration 5 | g02025975 |
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(13) Inlet
(19) Makeup spool (24) Main control valve (25) Tank port (BB) Tank oil (CC) Active components (DD) Surface area (FF) Reduced tank oil | |
The oil from tank port (25) flows against makeup spool (19). When the pressure of the tank oil is greater than the force that is holding makeup spool (19) to the left, makeup spool (19) moves off the seat. The tank oil will flow around makeup spool (19) to the inlet (13). Then, the flow of oil will fill the void in the actuator.
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| Illustration 6 | g02026013 |
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(13) Inlet
(19) Makeup spool (24) Main control valve (25) Tank port (26) Disc springs (BB) Tank oil (CC) Active components (DD) Surface area (FF) Reduced tank oil | |
The line relief valve that protects the head end of the lift cylinder will not function as a makeup valve. The line relief valve has disc springs (26) that are installed between the frame of the valve and makeup spool (19). This process will prevent makeup spool (19) from moving away from the seat.