, Properties and Uses: A hydraulic pressure control valve. Overflow role and the security role of the constant pressure from the main hydraulic equipment. Constant pressure overflow effects: the quantitative pump throttle adjusting system, a metering pump provided a constant flow. When the system pressure increases, will make traffic demand decreases. The relief valve to open, so that the excess traffic overflow back to the tank to ensure that the relief valve inlet pressure pump outlet pressure constant (valve port often with pressure fluctuations on). Security role: the system work properly, the valve is closed. Only the load exceeds a predetermined limit (the system pressure exceeds the set pressure) to open the overflow, overload protection, so that the system pressure is no longer increased (usually so that the relief valve set pressure higher than the maximum working pressure of the system 10% to 20% ). Practical applications in general: for the unloading valve for remote relief valve, high and low voltage level control valve for the sequence valve, used to generate backpressure (string back to the oil on the road). Relief valves generally have two structures: a direct-acting relief valve. 2, the main requirements of the pilot operated relief valve: voltage range, voltage regulator deviation, runout small pressure sensitive action, overloading capacity, noise.