**Abstract:** This paper compares various automatic reversing control methods used in the hydraulic pump system of concrete pumps, aiming to explain the advantages, characteristics, and challenges associated with each method. 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 continuous and efficient pumping, especially when the material is too thin, the two hydraulic cylinders must alternate their operation automatically. This allows the concrete cylinder to alternately suction and discharge material. In this study, several typical automatic reversing control circuits are analyzed and compared to highlight their respective features.
**Mechanical-Hydraulic Synergistic Control Method**
Figure 1 illustrates the mechanical-hydraulic control circuit. When the main cylinder T2 reaches the end of its stroke, the tapered surface of the piston strikes the ejector rod of the two-way valve, initiating a directional change. This action reduces the hydraulic pressure through damping, allowing the four-way valve 6 to shift to the upper position. The mechanical system then locks the spool in place. Pressure oil flows into the distribution cylinder F2, pushing the distribution valve and activating the four-way valve 3 via valve 7. This process continues until the master cylinder T1 completes its stroke, triggering a similar sequence for the next cycle. This method minimizes shock due to the use of check valves and orifices, ensuring smooth operation. However, the control circuit is relatively complex, making maintenance more challenging.
**Hydraulic Control Mode**
This method involves either manual or electric control for reversing operations. Figure 2 shows the manual reverse control circuit. When T1 reaches the end of its stroke, high-pressure oil from T1 is directed to T2, creating a pressure difference that opens valve 2.1, activating the four-way valve 5. This leads to the movement of the distribution cylinder F2, which in turn activates the four-way valve 4 to supply oil to T2. The system ensures minimal impact by prioritizing the distribution cylinder’s movement before the main cylinder, reducing backflow and shock. An accumulator helps absorb peak pressures, while a relief valve manages continuous impacts. Despite its reliability, the control circuit is intricate.
**Electronic Control Mode**
Figure 3 presents an electronic version of the hydraulic control system, where manual valves are replaced with electronic controls. This setup improves reliability and automation. Although the commutation impact is slightly higher than in previous methods, the throttle valve and accumulator effectively manage the pressure fluctuations. This method offers better precision and stability, making it suitable for advanced pumping systems.
**Electro-Hydraulic Coordinated Control**
Electro-hydraulic control combines electronic signals with hydraulic components for precise and reliable operation. Two common approaches include using cartridge valves and electro-hydraulic directional valves. Figure 4 shows a system where solenoid valves control the flow of oil, ensuring synchronized movement between the main and distribution cylinders. Similarly, Figure 5 demonstrates an electro-hydraulic directional valve system that uses programmable logic controllers (PLCs) to manage the switching process. These systems reduce environmental interference and enhance performance, making them ideal for modern concrete pumping equipment.
**Conclusion**
The paper has examined several automatic reversing control methods for concrete pumps, including mechanical-hydraulic, hydraulic, electronic, and electro-hydraulic systems. Each method has its own advantages and limitations. While mechanical systems offer simplicity, they can be less precise. Hydraulic and electronic systems provide better control and reliability, but at the cost of increased complexity. Electro-hydraulic systems, particularly those using PLCs, represent the future of concrete pump technology, offering enhanced efficiency and reduced operational impact. As the industry evolves, these advanced control systems will play a key role in improving performance and safety in construction applications.
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