A safety valve is a valve-type overpressure relief device consisting of three main parts: seat, disc and loading mechanism. It is an automatic valve that USES the pressure of the medium itself to discharge a nominal amount of overpressure fluid through the opening of the disc to prevent the pressure in the device from exceeding a predetermined safety limit. When the pressure returns to normal, the disc will automatically close under the action of the loading mechanism to prevent the media from continuing to discharge.
The whole structure and loading mechanism can be divided into lever type and spring type. Lever type safety valves use balance weights and levers to balance the medium on the valve. The load imposed by the valve does not increase as the disc rises and the valve is cumbersome due to its simple construction so the lever relief valve is limited to low pressure conditions. Valve loading mechanisms are vibration sensitive and often leak as a result. This valve is suitable for high temperature service, but the backflow pressure is generally less than 70% of the working pressure to maintain the seal, so it is not suitable for continuous operation.
A spring-loaded safety valve USES spring force to balance the force of the medium on the disc. Adjust valve opening pressure by screw and spring compression. It has compact structure, high sensitivity and wide application range, but poor sensitivity to vibration. Installation location is not strictly restricted. It can also be used in mobile containers. The spring force varies with the opening of the disc, which is not conducive to the rapid opening of the disc. Long-term high temperature will affect the spring force. Therefore, when using a container with a higher temperature, the thermal insulation or heat dissipation of the spring must be considered, which will lead to a complex structure.
According to the ratio of valve opening and flow diameter, the safety valve can be divided into full open safety valve and micro open safety valve.
For nozzle seats, the momentum of the disc of the fully open relief valve is given as the medium flow increases. The recoil mechanism is used to change the direction of flow of the medium and the momentum changes to a tremendous lift, thereby increasing the opening height of the disc. (the opening height is greater than or equal to 1/4 of the flow diameter.) The valve is suitable for applications with large discharge and small pressure fluctuation.
The opening height to diameter ratio of the micro-opening safety valve is 1/40-1/20. Convenient for manufacturing, maintenance and adjustment, it should be used under low emission and low requirement. Its diameter is much larger than the full open type, the same emissions.
The safety valve can be divided into closed and open type according to gas discharge. The cover of the enclosed relief valve is closed so that the medium does not leak and is discharged through the drain line. It is mainly used in containers containing toxic and flammable media.
A relief valve with an open cover does not have a drain connection, so the medium is vented directly out. It is mainly used in containers with medium such as air and steam.