About safety valve Safety Valve is a one type of valve that automatically actuates when the pressure of inlet side of the valve increases to a predetermined pressure, to open the valve disc and discharge the fluid ( steam or gas ) ; and when the pressure decreases to the prescribed value, to close the valve disc again. Safety valve is so-called a final safety device which controls the pressure and discharges certain amount of fluid by itself without any electric power support. Safety Valve is mainly installed in a chemical plant, electric power boiler, gas storage tank, preventing the pressure vessels from exploding or damaging. Function of safety valve Nozzle” inside the Safety Valve starts to receive a higher pressure from the inlet side of the valve. When the pressure becomes higher than the set pressure, “Disc” starts to lift and discharge the fluid. When the pressure decreases until the predetermined pressure, the force of the spring closes “Disc”. Spring-loaded Pressure-relief Valves Generally, the safety valveｓ are referred to the Spring-loaded Pressure-relief valves, the most common type ( See the left figure ). The load of the spring is designed to press the “Disc” against the inlet pressure. Depending on the fluid type, such as steam, gas or liquid, we are offering a Bellows model to clear the back pressure effect. Pilot-operated Pressure-relief Valves Pilot-operated Pressure-relief Valves are composed of Pilot Assy and Main Valve. Although Spring-loaded Pressure-relief valves adopts the force of the spring against the inlet pressure, the reliving pressure and reseating pressure of the Pilot-operated Pressure-relief Valves is controlled by Pilot Assy, which acts nearly as same as Spring-loaded Pressure-relief valves. There is no adjusting function in the Main Valve. Pilot-operated Pressure-relief Valves have larger size variations compared to Spring-loaded type, which is applied in a severe condition such as high pressure. Dead-Weight Pressure-relief Valves In case the design pressure of the pressure vessel is set at very low pressure, Dead-weight Pressure-relief valve adjusts relieving pressure only by the disc weight. The Vacuum relief valve has been adopting this functional characteristic which absorbs the pressure when the inside of the pressure vessel falls into a negative pressure.