416D, 420D, 424D, 428D, 430D, 432D, 438D and 442D Backhoe Loaders Hydraulic and Steering System Control Valve (Swing) (Mechanically Operated) Caterpillar


Control Valve (Swing) (Mechanically Operated)
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1.1. HOLD Position
2.1. SWING LEFT Position
3.1. SWING RIGHT Position

HOLD Position




Illustration 1g00796417

HOLD Position for the Swing Valve

(1) line relief valve for swing right, (2) Spool, (3) Metering slots, (4) Passage to tank, (5) Signal passage, (6) Cavity, (7) Flow control valve, (8) Pump passage, (9) Passage, (10) Passage, (11) Spring, (12) Signal passage, (13) Signal passage, (14) Passage to tank, (15) Metering slots, (16) Spring, (17) Line to the next valve, (18) Secondary resolver, (19) Line from previous valve, (20) Primary resolver, (21) Line relief valve for swing left, (22) Check ball, (23) Port to swing left, (24) Advance signal passage, (25) Advance signal passage, (26) Port to swing right, (27) Check ball, (A) Pump oil, (B) Return oil and (C) Blocked oil

The swing control valve is located between the boom control valve and the bucket control valve.

Supply oil from the pump flows in the valve through passage (8). Passage (8) is common in all sections of the valves and the passage has no outlet. Oil flows through passage (9) in flow control valve (7) and into chamber (8) .

Pressure in chamber (8) rises and the pressure acts against flow control valve (7). When the pressure overcomes the force of spring (11) and the pressure in chamber (12), the pressure causes flow control valve (7) to move down. As the flow control valve (7) moves down, oil flows from passage (8) into passage (10). The oil in passage (10) is blocked by spool (2) until the operator moves the control lever.

As the flow control valve (7) moves downward, the metering slots begin to close. The oil that flows from passage (8) into passage (10) is restricted. Oil is now metered through the slots in order to maintain oil pressure in chamber (6) and passage (10) .

In the HOLD position, work ports (23) and (26) are open. In the HOLD position, the signal passages are closed.

The oil in passage (10) flows into the passage in spool (2) and the oil pushes down against check ball (22) .

The oil also pushes up against the check ball (27).

The oil pressure overcomes the force of the springs that are behind the check balls and the oil pressure causes the check balls to partially move off the seats.

The oil flows from past check ball (22) into port (23) and the oil flows past check ball (27) into port (26) .

The oil that flows past the check balls and into the cylinder ports keeps the cylinder lines full of oil at all times. This keeps both sides of the cylinder pistons pressurized.

Pressure to both ports puts the swing circuit into a hydraulic lock. The boom will not move while the control lever is in the HOLD position.

SWING LEFT Position




Illustration 2g00797152

Swing Left Position for the Swing Valve

(1) line relief valve for swing right, (2) Spool, (3) Metering slots, (4) Passage to tank, (5) Signal passage, (6) Cavity, (7) Flow control valve, (8) Pump passage, (9) Passage, (10) Passage, (11) Spring, (12) Chamber, (13) Signal passage, (14) Passage to tank, (15) Metering slots, (16) Spring, (17) Line to the next valve, (18) Secondary resolver, (19) Line from previous valve, (20) Primary resolver, (21) Line relief valve for swing left, (22) Check ball, (23) Port to swing left, (24) Advance signal passage, (25) Advance signal passage, (26) Port to swing right, (27) Check ball, (A) Pump oil, (B) Return oil and (C) Blocked oil

Face the rear of the machine as you sit in the seat in order to determine the left and the right controls for the operation of the swing control valves.

When the operator places the joystick into the SWING LEFT position, spool (2) moves upward.

For a given amount of lever movement, spool (2) will move a proportional distance.

As the spool begins to move up, oil flows through advance signal passage (24) and into signal passage (13). The oil then flows back to the pump controller through the signal resolver network. The advance signal passage allows signal pressure to be sent back to the pump in order to upstroke the pump. This will provide a better response to the demand of the swing circuit.

The metering slot (15) meters the flow from the signal passages to the tank passages in order to dampen the pressure spike when the spool is returned to the HOLD position.

As the spool continues to move up, the pump oil in passage (10) flows around spool (2) into port (23). Oil in signal passage (13) is blocked from entering tank passage (14). Signal passage (13) senses the pressure in port (23). The oil in signal passage (13) flows to the primary resolver (20) and into chamber (12) .

The oil in the primary resolver (20) flows to the secondary resolver (18) and to the pump. This causes the pump to increase flow.

Flow control valve (7) compares the oil in chamber (6) to the signal pressure in chamber (12) and spring (11). Flow control valve (7) moves in order to provide the required oil flow to passage (10). Spool (2) controls the amount of flow that is desired.

As pump flow increases, more oil flows through spool (2) to the port to swing left (23).

There are two cylinder-to-cylinder crossover lines. One line connects the rod end of left swing cylinder to the head end of the right swing cylinder. The other line connects the rod end of right cylinder to the head end of the left cylinder.

The oil in port (23) flows into the rod end of the left swing cylinder. The oil also flows through the crossover line into the head end of the right swing cylinder. Oil from the head end of the left cylinder is forced outward. The oil flows through the crossover line and combines with the rod end oil from the right cylinder. This combined oil flows into port (26) .

This causes the left cylinder rod to retract and this causes the right cylinder rod to extend. This swings the backhoe to the left in a pressurized swing.

As the backhoe swings, the oil flows from port (26) into the passage in spool (2). The oil causes check ball (27) to move up. When the check ball moves up, return oil can flow through the signal passage (5) to tank passage (4). The check valve provides a smoother swing movement by maintaining pressure in both sides of the swing cylinders.

When the swing control lever is released, spring (16) returns the spool to the HOLD position.

Refer to Systems Operation, "Makeup and Relief Valve" for the operation of valve (21) .

SWING RIGHT Position




Illustration 3g00797782

Swing Right Position for the Swing Valve

(1) line relief valve for swing right, (2) Spool, (3) Metering slots, (4) Passage to tank, (5) Signal passage, (6) Cavity, (7) Flow control valve, (8) Pump passage, (9) Passage, (10) Passage, (11) Spring, (12) Signal passage, (13) Signal passage, (14) Passage to tank, (15) Metering slots, (16) Spring, (17) Line to the next valve, (18) Secondary resolver, (19) Line from previous valve, (20) Primary resolver, (21) Line relief valve for swing left, (22) Check ball, (23) Port to swing left, (24) Signal passage for the spool, (25) Signal passage for the spool, (26) Port to swing right, (27) Check ball, (A) Pump oil, (B) Return oil and (C) Blocked oil

Face the rear of the machine as you sit in the seat in order to determine the left and the right controls for the operation of the swing control valves.

When the operator places the joystick into the SWING RIGHT position, spool (2) moves downward.

For a given amount of lever movement, spool (2) will move a proportional distance.

As the spool begins to move down, oil flows through advance signal passage (25) and into signal passage (5). The oil then flows back to the pump controller through the signal resolver network. The advance signal passage allows signal pressure to be sent back to the pump in order to upstroke the pump. This will provide a better response to the demand of the swing circuit.

The metering slot (3) meters the flow from the signal passages to the tank passages in order to dampen the pressure spike when the spool is returned to the HOLD position.

As the spool continues to move down, the pump oil in passage (10) flows around spool (2) into port (26). Oil in signal passage (5) is blocked from entering tank passage (4). Signal passage (5) senses the pressure in port (26). The oil in signal passage (5) flows to the primary resolver (20) and into chamber (12) .

The oil in the primary resolver (20) flows to the secondary resolver (18) and to the pump. This causes the pump to increase flow.

Flow control valve (7) compares the oil in chamber (6) to the signal pressure in chamber (12) and spring (11). Flow control valve (7) moves in order to provide the required oil flow to passage (10). Spool (2) controls the amount of flow that is desired.

As pump flow increases, more oil flows through spool (2) to the port to swing right (26).

There are two cylinder-to-cylinder crossover lines. One line connects the rod end of left swing cylinder to the head end of the right swing cylinder. The other line connects the rod end of right cylinder to the head end of the left cylinder.

The oil in port (26) flows into the head end of the left swing cylinder. The oil also flows through the crossover line into the rod end of the right swing cylinder. Oil from the rod end of the left cylinder is forced outward. The oil flows through the crossover line and combines with the head end oil from the right cylinder. This combined oil flows into port (23) .

This causes the left cylinder rod to extend and this causes the right cylinder rod to retract. This swings the backhoe to the right in a pressurized swing.

As the backhoe swings, oil flows from port (23) into the passage in spool (2). The oil causes check ball (22) to move down. When the check ball moves down, return oil can flow through the signal passage (15) to tank passage (14). The check valve provides a smoother swing movement by maintaining pressure in both sides of the swing cylinders.

When the swing control lever is released, spring (16) returns the spool to the HOLD position.

Refer to Systems Operation, "Makeup and Relief Valve" for the operation of valve (1) .

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