Relief valves play a crucial role in hydraulic systems, primarily functioning to provide constant pressure relief, pressure stabilization, system unloading, and safety protection. Their working principle can be summarized as follows:
1. Constant Pressure Relief: In a fixed-displacement pump throttling system, the pump provides a fixed flow rate. When system pressure rises, causing a decrease in flow demand, the relief valve opens, returning excess flow to the tank, thus maintaining a constant pump outlet pressure (i.e., system inlet pressure). During this process, the relief valve often opens with pressure fluctuations to ensure pressure stability.
2. Pressure Stabilization: The relief valve is connected in series in the return oil circuit, providing stable back pressure to moving parts, thereby increasing system stability.
3. System Unloading: By connecting a small-flow solenoid valve in series with the relief valve's remote control port, when the solenoid is energized, the relief valve's remote control port connects to the tank, unloading the hydraulic pump. In this case, the relief valve functions as an unloading valve.
4. Safety Protection: During normal system operation, the relief valve is in the closed state. However, when the load exceeds the predetermined limit (system pressure exceeds the set pressure), the relief valve opens to implement overload protection and prevent the system pressure from continuing to rise. Typically, the set pressure of the relief valve is set to 10% to 20% higher than the system's maximum operating pressure.