Hoist Control Valve
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| Illustration 1 | g01004288 |
(1) Hoist control valve (2) Tank port (3) Lower port (4) Raise port (5) Spring (6) Pilot control actuator (7) Lowering control valve (stopped engine) (8) Pump port (9) Relief valve (10) Stem (11) Spring (12) Pilot control actuator | |
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| Illustration 2 | g00754555 |
Typical Example (1) Hoist control valve (3) Lower port (4) Raise port (6) Pilot control actuator (7) Lowering control valve (stopped engine) (9) Relief valve | |
The position of stem (10) is determined by the magnitude of the pilot pressure within pilot control actuators (6) and (12). This pilot pressure, which acts on the stem, is controlled by the solenoids which are part of the pilot control actuators. The solenoids are connected to the hoist control, which is in the cab, via the ECM. The stem has four positions.
HOLD Position
When the engine is shut off, the magnitude of the pilot pressure within pilot control actuators (6) and (12) is zero. The stem is centered to the HOLD position by springs (5) and (11).
When the hoist control is moved to the HOLD position and the engine is running, equal pilot pressure within the pilot control actuators moves the stem to the HOLD position. Oil flows from pump port (8) to tank port (2). All other ports are blocked by the stem.
RAISE Position
When the hoist control is moved to the RAISE, the ECM sends a current to pilot control actuator (12), which is proportional to the displacement of the hoist control in the cab. Pilot control actuator (12) is energized. The pilot pressure within pilot control actuator (12) is relieved and the stem is moved to the RAISE position by the pilot pressure within pilot control actuator (6). The stem is moved fully to the left. Oil flows from pump port (8) to the piston sides of the hoist cylinders from raise port (4). Oil flows from the rod sides of the hoist cylinders to lower port (3). This oil flows from lower port (3) to tank port (2). The hoist cylinders extend and the body is raised.
LOWER position
When the hoist control is moved to the LOWER, the ECM sends a current to pilot control actuator (6), which is proportional to the displacement of the hoist control in the cab. Pilot control actuator (6) is energized. The pilot pressure within pilot control actuator (6) is relieved and the stem is moved to the LOWER position by the pilot pressure within pilot control actuator (12). The stem is moved fully to the right. Oil flows from pump port (8) to the rod sides of the hoist cylinders from lower port (3). Oil flows from the piston sides of the hoist cylinders to raise port (4). This oil flows from raise port (4) to tank port (2). The hoist cylinders retract and the body is lowered.
FLOAT position
When the hoist control is moved to the FLOAT position, Pilot control actuator (6) is partially energized. The pilot pressure within pilot control actuator (6) is partially relieved and the stem is moved to the FLOAT position by the pilot pressure within pilot control actuator (12). The stem is moved partially to the right. Oil flows from pump port (8) to tank port (2). Raise port (3) and lower port (4) are also connected to tank port (2) .
Relief Valve
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| Illustration 3 | g00754489 |
(9) Relief valve (9a) Piston (9b) Spring (9c) Port | |
Relief valve (9) is a two-stage relief valve with two relief settings.
When the body is being lowered, the relief setting on the relief valve is determined by spring (9b) .
When the body is being raised, pressure is transmitted to port (9c). This moves piston (9a) against spring (9b) which increases the relief setting of the relief valve.
Lowering Control Valve (Stopped Engine)
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| Illustration 4 | g00754491 |
(7) Lowering control valve (stopped engine) (7a) Plunger (7b) Piston (7c) Hole (7d) Port | |
Lowering control valve (7) can be used to connect raise port (4) to tank port (2). This is required in order to lower the body when the engine is deactivated.
Plunger (7a) is unscrewed from the lowering control valve. Pressure at port (7d) moves piston (7b) to the right. This connects port (7d), which is connected to raise port (4), to hole (7c) which is connected to the tank.