HOUSING AS-TANDEM DRIVE 1901691 - Caterpillar

CLOSED Condition
Illustration 1 g03877543
Line relief valve (CLOSED position)
(1) Passage
(2) Piston
(3) Makeup spool
(4) Valve
(5) Spring chamber
(6) Valve
(7) Spring
(8) Passage
(9) Spring chamber
(10) Spring
(11) Return passage
(12) Passage The high pressure between the cylinder and the control valve is transmitted to passage (1). This oil pressurizes the line relief valve. The pressure oil flows from passage (1) to piston (2). When the oil pressure is lower than the line relief valve pressure setting, valve (6) remains in the CLOSED position by the force of spring (7). Spring (10) forces piston (2), and valve (4) to the left. The high-pressure oil is not able to flow from passage (1) to return passage (11). The high pressure between the cylinder and the control valve is maintained.
Illustration 2 g03877545
Line relief valve (beginning to open)
(1) Passage
(2) Piston
(3) Makeup spool
(4) Valve
(5) Spring chamber
(6) Valve
(7) Spring
(8) Passage
(9) Spring chamber
(10) Spring
(11) Return passage
(12) Passage As the pressure begins to rise, the oil that is flowing into passage (1) will shift piston (2) to the right. High-pressure oil flows past valve (2) into spring chamber (5). The oil pressure in spring chamber (5) works against the area of valve (6). Once the force that is developed on the area around the end of valve (6) overrides the force of spring (7), valve (6) will shift to the rightOPEN Condition
Illustration 3 g03877664
Line relief valve (OPEN position)
(1) Passage
(2) Piston
(3) Makeup spool
(4) Valve
(5) Spring chamber
(6) Valve
(7) Spring
(8) Passage
(9) Spring chamber
(10) Spring
(11) Return passage
(12) Passage As pressure spikes occur in the line between the cylinder and the control valve, the oil pressure is momentarily higher in passage (1) than spring chamber (5). Piston (2) and valve (4) are forced to the right against spring (7) and spring (10). High-pressure oil is able to flow from passage (1) to passage (12), and to return passage (11) which relieves the pressure spike.Makeup Condition
Illustration 4 g03877546
Line relief valve (makeup operation)
(1) Passage
(2) Piston
(3) Makeup spool
(4) Valve
(5) Spring chamber
(6) Valve
(7) Spring
(8) Passage
(9) Spring chamber
(10) Spring
(11) Return passage
(12) Passage The oil from the hydraulic oil tank through return passage (11) flows against makeup spool (3). When the pressure of the tank oil is greater than the force that is holding makeup spool to the left, makeup spool moves off the seat. The tank oil will flow around makeup spool (3) to inlet passage (1). Then, the flow of oil will fill the void in the actuator.