ENGINE AR-COMPLETE 2121860 - Caterpillar

Line Relief Valve
Illustration 2 g01305479
Line Relief Valve (2A) in the HOLD position.Line Relief Valve (2B) with the relief valve in the ACTIVE position.Line Relief Valve (2C) with the makeup valve in the ACTIVE position. (6) Passage to the tank (14) Passage to the head end of the cylinder (16) Adjustment screw (17) Nut (18) Spring (19) Plunger (20) Ball (21) Chamber (22) Spring (23) Spool (24) Valve (25) Inlet passage (26) Drain passage (27) PassageThere is a line relief valve (2) in the line of the head end of the lift cylinder. The valve has two purposes. As a relief valve, the valve limits the maximum amount of pressure in the cylinder line, when the valve spool is in HOLD position. As a makeup valve, the valve permits oil from the return line to add with implement oil.Relief Valve Operation
Cylinder oil flows into passage (25) of line relief valve (2). The oil then flows through passage (27) that is between spool (23) and valve (24). The oil then fills chamber (21) for spring (22). The pressure of the oil and the force of spring (22) keep valve (24) closed when the oil pressure is less than the setting of the relief valve.When the pressure of the oil in passage (14) that is acting on the right end of valve (24) and the right end of spool (23) is high enough to overcome the force of the oil in chamber (21), the force of spring (22), and the force of spring (18) plunger (19) will move to the left. This will allow spool (23) and valve (24) to move to the left. The valve is now open. The oil from inlet passage (25) can now flow through drain passage (26) to outlet passage (6). The pressure of the cylinder oil in passage (14) can not go higher than the setting of the relief valve.An increase or a decrease in the force of spring (18) changes the pressure setting of the relief valve. Loosen nut (17) and turn adjustment screw (16) clockwise in order to increase the pressure setting. Turn adjustment screw (16) counterclockwise in order to decrease the pressure setting of the relief valve.Makeup Valve Operation
When the pressure of the cylinder oil in chamber (21) becomes less than the pressure of the drain oil in outlet passage (26), valve (24) is held to the right by spring (22). If the oil in passage (26) becomes high enough to overcome the force of spring (22), valve (24) will open. The drain oil that is in outlet passage (6) can now flow around valve (24) into passage (14). The additional oil prevents cavitation (vacuum) in the cylinders.Basic Valve Operation
Bulldozer Raise
Illustration 3 g01306149
Bulldozer lift control valve with the control valve spool in the RAISE position (1) Valve spool in the RAISE position (2) Line relief valve (3) Port to the head end of the lift cylinder (4) Port to the rod end of the lift cylinder (5) Spring (6) Passage to the tank