The air-controlled hydraulic directional valve plays a crucial role in a dump truck’s hydraulic system. Its performance directly impacts the lifting efficiency of the truck bed. While the hydraulic system of a dump truck is relatively simple compared to other specialized vehicles, its unique working conditions and harsh operating environments make it prone to malfunctions.
Four Key Operating States of the Air-Controlled Hydraulic Directional Valve
1. Lifting State
When raising the dump truck bed, the air control valve is shifted left into the lifting position, allowing system air pressure to flow into the lifting valve through the lift port. This air pressure acts on the cylinder piston, moving it leftward and pushing the valve spool in the same direction. This action connects the oil pump port with the hydraulic cylinder port, allowing high-pressure oil to enter the cylinder and raise the dump body.
If the lifting pressure exceeds safe levels, the bypass relief valve activates to prevent excessive pressure buildup that could damage the gear pump and pipelines.
2. Lowering State
To lower the truck bed, the air control valve is moved right into the lowering position. This directs system air pressure into the lifting valve’s lowering channel, pushing the piston rightward and moving the spool in the same direction. This connects the hydraulic cylinder port with the return oil port, allowing the high-pressure oil inside the cylinder to flow back into the oil tank through the return filter.
3. Neutral Hold (Mid-Stop) State
Regardless of whether the truck bed is rising or lowering, it can be stopped at any time by shifting the air control valve to the neutral position. When in this state, the compressed air in the lifting valve is released through the valve’s exhaust port, and the spring force returns the valve spool to the center position. This disconnects all ports, stopping the oil flow and keeping the hydraulic cylinder stationary.
4. Limit Stop State
When the dump cylinder reaches the preset lifting height, it activates the limit valve, moving the valve spool leftward and cutting off the air supply between the system and the lifting valve. The compressed air acting on the piston is then exhausted through the limit valve’s exhaust port. As a result, the spring force returns the valve spool to the center position, stopping the oil flow and preventing further lifting.
To ensure optimal performance, regular cleaning and maintenance of the hydraulic air control valve is essential. If you’re experiencing issues with your dump truck’s lifting mechanism, understanding how the directional valve works can help diagnose and resolve problems more effectively.
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