**Abstract:** This paper compares various automatic reversing control methods used in concrete pump hydraulic systems, highlighting their advantages, characteristics, and potential issues. Concrete pumps are widely used in modern construction projects both domestically and internationally. The most common type of domestic concrete pump is a single-acting double-row hydraulic piston system. To ensure smooth operation, especially when pumping thin concrete, the two hydraulic cylinders must alternate automatically, allowing the concrete cylinder to alternately suction and discharge material. In this study, several typical automatic reversing control circuits are analyzed and compared.
**A Mechanical-Hydraulic Synergistic Control Method**
Figure 1 shows the schematic of the hydraulic control circuit. When the main cylinder T2 reaches the end of its stroke, the conical surface of the piston hits the ejector rod of the two-way valve, causing it to switch direction. The damping mechanism reduces the hydraulic pressure, enabling the four-way valve to shift to the upper position. The mechanical system then locks the spool in place. Pressure oil flows into the distribution cylinder F2, which pushes the distribution valve. Control oil from the distribution line activates the four-way valve, directing oil to the main cylinder T1. When T1 reaches the end of its stroke, the cone on the piston triggers the second two-way valve, causing the four-way valve to move down and lock again. This process repeats, ensuring continuous pumping.
This method minimizes circuit shock, as the impact at the end of the stroke is absorbed by check valves in the main cylinder. The sequence ensures that the distribution cylinder switches quickly (0.2–0.3 seconds) to prevent backflow, while the main cylinder begins its stroke slightly earlier (0.03–0.05 seconds). The accumulator helps absorb sudden pressure spikes, making this control method highly reliable, though the circuit can be complex to maintain.
**Hydraulic Control Mode**
This control method involves either manual or electric reverse delivery. Figure 2 illustrates the manual control circuit. When T1 reaches the end of its stroke, T2 retracts fully, and high-pressure oil from T1 acts on valve 2.1, creating a pressure difference that opens the X port, activating the four-way valve to direct oil to the distribution cylinder F2. Simultaneously, the control oil drives another four-way valve to supply oil to T2. This cycle continues, ensuring smooth operation.
The circuit design reduces shock by prioritizing the distribution cylinder’s switching action, preventing backflow. The main cylinder starts its stroke before the distribution cylinder completes its movement, reducing pressure impact. An accumulator and relief valve further help manage pressure surges. While reliable, the control circuit is more complex than some alternatives.
**Electronic Control Mode**
Figure 3 shows an electronic version of the same principle. Instead of manual valves, solenoid valves are used for automated control. This method offers greater reliability and precision, with smoother transitions between strokes. Although the impact is slightly higher than in previous methods, the throttle valve and accumulator effectively manage pressure fluctuations.
**Electro-Hydraulic Coordinated Control**
Electro-hydraulic control combines electrical and hydraulic components for more precise operation. Figure 4 shows a system using cartridge valves and solenoid valves. After the main pump is activated, the system uses timing and pressure signals to control the switching of cylinders. This approach ensures accurate and consistent performance, with minimal interference from external factors.
Figure 5 illustrates a similar system using electro-hydraulic directional valves. By energizing specific solenoids, the system controls the movement of the cylinders in a cyclic manner. This method improves efficiency and reliability, especially in environments where manual control is impractical.
**Conclusion**
Various automatic reversing control methods exist, each with unique advantages. Figure 3 uses two four-way solenoid valves, while Figures 1 and 2 rely on manual two-way valves. Figures 4 and 5 employ logical control through electrical systems. Modern electro-hydraulic systems often use programmable logic controllers (PLCs) to enhance performance and reduce environmental interference. These advancements contribute to more efficient and reliable concrete pumping operations.
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