349F and 352F Excavators Machine System Caterpillar


Control Valve (Stick Lowering)

Usage:

352F-VG A9J
The stick lowering control valve is located on the rod end of the stick cylinder.

The stick lowering control valve has two functions:

  • The stick lowering control valve prevents the stick from falling if a hydraulic supply line fails or if a supply tube to the stick cylinder fails.

  • The stick lowering control valve allows the operator to manually lower the stick when the engine is shut down.


Illustration 1g03408886
Partial schematic (STICK IN)
(1) Stick cylinder
(2) Stick lowering control valve
(3) Main control valve
(4) Pilot control valve (stick and swing)

STICK OUT Operation



Illustration 2g03408900
(5) Spring
(6) Valve
(7) Spool
(8) Seat
(9) Throttling slot
(10) Passage
(11) Passage
(12) Port
(13) Port
(14) Spool
(15) Port
(16) Passage
(17) Check valve
(18) Spring
(19) Passage
(20) Passage
(21) Line relief valve
(22) Passage
(23) Manual lowering valve

When the operator moves the joystick to the STICK OUT position, the pump oil flows from the main control valve through a line to port (12) of the stick lowering control valve. The pump oil flows into passage (11) and the pressure of the pump oil causes check valve (17) to shift downward against spring (18). The pump oil flows through passage (19) to passage (16). Then, the pump oil flows from passage (16) to port (15) at the rod end of the stick cylinder. The rod of the stick cylinder will retract in order to move the stick to the STICK OUT position.

When the joystick is returned to the NEUTRAL position, the stick cylinder is held in the STICK OUT position. Check valve (17) and valve (6) prevent the oil in the rod end of the stick cylinder from flowing out of the stick cylinder.

STICK IN Operation



Illustration 3g03408907
(5) Spring
(6) Valve
(7) Spool
(8) Seat
(9) Throttling slot
(10) Passage
(11) Passage
(12) Port
(13) Port
(14) Spool
(15) Port
(16) Passage
(17) Check valve
(18) Spring
(19) Passage
(20) Passage
(21) Line relief valve
(22) Passage
(23) Manual lowering valve

When the operator moves the joystick to the STICK IN position, pump oil flows from the main control valve through a line that is ported to the head end of the stick cylinder.

Simultaneously, pilot oil flow is provided to port (13) of the stick lowering control valve. The pilot oil at port (13) will cause spool (14) to shift to the left. Spool (14) will force spool (7) to move to the left against spring (5).

The oil in the rod end of the stick cylinder begins to flow to port (15) of the stick lowering control valve. As oil flows into passage (16), check valve (17) will remain closed. As pressure begins to rise in passage (16), spool (6) will begin to move to the left and oil will flow to passage (10). The oil then flows from passage (10) to port (12). From port (12), the oil will flow through a line to the main control valve and back to the hydraulic tank.

When the joystick is returned to the NEUTRAL position, the loss of pilot oil pressure will allow spring (5) to force spool (7) and spool (6) to close. Oil in the rod end of the stick cylinder is trapped and the stick cylinder is held in position.

Manual Stick Lowering



Illustration 4g02173856
(20) Port
(22) Port
(23) Manual lowering valve
(24) Seat
(25) Locknut
(26) Ball

As seat (24) is turned counterclockwise, ball (26) will shift. As ball (26) is shifted, oil is allowed to flow through port (20) and manual lowering valve (23) to port (22). Oil from the rod end of the stick cylinder flows through port (22) to the hydraulic tank. This action allows the stick to lower.

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