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| Illustration 1 | g03788720 |
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(1) Stick cylinders
(2) Stick lowering control valves | |
The stick lowering control valves are located on the head end of the stick cylinders.
The stick lowering control valves have the following two functions:
- The stick lowering control valve prevents the stick from falling if a hydraulic supply line fails. The stick lowering control valve prevents the stick from failing if a supply tube fails.
- The stick lowering control valve allows the operator to lower the stick manually when the engine is shut down.
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| Illustration 2 | g03788762 |
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Stick raise hydraulic schematic (1) Stick cylinder (2) Stick lowering control valve (3) Spool (4) Relief valve (5) Pilot valve (6) Main control valve (7) Joystick control valve | |
When the operator moves the joystick to the STICK RAISE position, pilot oil flows from joystick control valve (7) to main control valve (6). This pilot oil will shift the stick control valve spool upward.
During a STICK RAISE operation, oil from main control valve (6) flows to both stick lowering control valves (2). Oil flows through the check valve within pilot valve (5) and flows to keep spool (3) shifted upward. Oil also flows through the check valve of spool (3) to the head end of stick cylinders (1). The rods extend and the stick raises.
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| Illustration 3 | g03789037 |
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Stick lower hydraulic schematic (1) Stick cylinder (2) Stick lowering control valve (3) Spool (4) Relief valve (5) Pilot valve (6) Main control valve (7) Joystick control valve | |
When the operator moves the joystick to the STICK LOWER position, pilot oil flows from joystick control valve (7) to main control valve (6). This pilot oil will shift the stick control valve spool downward.
As the joystick is moved to the STICK LOWER position, pilot oil will shift pilot valves (5) upward. As oil from the head end of cylinders (1) exit the cylinder, the oil pressure will overcome the oil and spring force of spool (3). Spool (3) shifts downward to allow oil from the head end of the stick cylinders to flow through to the main control valve. The stick cylinder rods retract and the stick lowers.
Stick lowering control valve (2) includes relief valve (4) which senses pressure at port "B" and opens under overload or shock conditions. In turn opening the valve will allow cylinder pressure to be relieved downstream through the main hose at port "A". The pressure will also be relieved through the main control valve.