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Pressure-limiting valves are essential safety control components in hydraulic systems. Their function is to limit system pressure within a set range to prevent damage to hydraulic components and system failure. Based on their structure and operating principle, pressure-limiting valves are primarily categorized as direct-acting and pilot-operated. These two types exhibit significant differences in dynamic performance, directly impacting the stability, response speed, and energy efficiency of the hydraulic system.

Direct-acting pressure-limiting valves have a simple structure, consisting of a valve core, spring, and valve seat. System pressure acts directly on the valve core. When pressure exceeds the set value, the valve core overcomes the spring force to open, achieving relief and pressure limiting. Their advantages include fast response and low manufacturing cost, making them suitable for applications with low flow rates and frequent actuation. However, because pressure directly pushes on the valve core, the opening pressure of direct-acting valves is significantly affected by spring characteristics, making them susceptible to pressure fluctuations and oscillations. Furthermore, under high-pressure, high-flow conditions, the valve core is subjected to significant forces, which can easily cause wear or instability, limiting their application.

Pilot-operated pressure-limiting valves, on the other hand, consist of a main valve and a pilot valve. System pressure first acts on the pilot valve, which indirect control is achieved by regulating the force on the main valve spool by controlling the opening and closing of the pilot oil port. Because the main valve spool is not directly subjected to full pressure, the opening process is smoother and the pressure regulation range is wider, making it suitable for high-pressure, high-flow systems. However, its disadvantages include a complex structure, slightly slower response speed than direct-acting valves, and higher requirements for oil cleanliness.

In terms of dynamic performance comparison, direct-acting valves are characterized by fast response but poor stability, making them prone to pressure pulsation. Pilot-operated valves, on the other hand, exhibit good stability but slightly slower response, maintaining low pressure fluctuations even under high-pressure conditions. Experimental studies have shown that direct-acting pressure-limiting valves provide faster overpressure protection under low-pressure, low-flow conditions. In high-pressure, high-flow scenarios, pilot-operated pressure-limiting valves effectively suppress pressure oscillations, ensuring safe system operation.

In terms of design optimization, direct-acting pressure-limiting valves can reduce pressure fluctuations by improving the valve port structure and spring parameters. Pilot-operated pressure-limiting valves can improve response speed and contamination resistance by optimizing the pilot oil circuit and damping orifice design. With the development of electro-hydraulic proportional control and intelligent technologies, pilot-operated pressure-limiting valves are gradually evolving towards controllability and digitalization, while direct-acting pressure-limiting valves still have broad application in micro-hydraulic systems and fast-response devices.

In summary, direct-acting and pilot-operated pressure-limiting valves each have their own advantages in terms of dynamic performance, and the choice depends on the system pressure level, flow rate, and stability requirements. Future research can focus on combining the advantages of both, such as developing composite pressure-limiting valves with fast response and high stability to meet the higher safety and efficiency requirements of the next generation of hydraulic equipment.