Overview of boiler safety valve safety valve is an important safety accessories pressure vessels and other equipment under pressure. Reliability and performance of its action is directly related to the equipment and personal safety, and is closely related to energy conservation and environmental protection. However, some users and design departments in the selection, always choose the wrong model. This paper analyzed the safety valve of choice for this purpose. Definition of safety valve: valve (Safety Valve, also known as pressure relief valve Relief Valve) is based on the work of the pressure system automatically open and close, usually installed in equipment pipeline protection system security or closed system. When the equipment or pipeline pressure exceeds the set pressure relief valve, pressure relief automatically open, to ensure that equipment and media pressure in the pipe under the set pressure, protective equipment and pipe work, to prevent accidents and reduce losses. Safety valve: valve play a security role in the system. When the system pressure exceeds a predetermined value, the safety valve opens, the system part of the gas / fluid is discharged into the atmosphere / outside the pipeline, so that the system pressure does not exceed the allowable value, in order to ensure that the system pressure is too high and not because of the accident. Safety valve Category: valve structure are two major categories: spring and leveraged. Spring means sealing valve and valve seat by spring force. Leveraged rely on leverage and weight force. With the large capacity needs, but also a pulsed valve, also known as pilot safety valve from the main valve and auxiliary valve. When the pipeline medium pressure exceeds the pressure value, the first auxiliary valve open, the media along the catheter into the main valve and the main valve is opened to reduce the media pressure increased. Emissions valve depends on the caliber of the seat and the valve opening height, can also be divided into two types: Weiqi open seat height is the inside diameter (1/15) - (1/20), the entire Kai is (1/3) - (1/4). In addition, with different requirements, there are enclosed and not enclosed. Closed discharge medium that is not compromised, all discharged along export regulations generally for toxic and corrosive media. Enclosed are not generally used for non-toxic or non-corrosive media. A. According to their different loading mechanism and its overall structure and the overall structure of the different loading mechanism can be leveraged into a heavy hammer, spring and pulsed three. 1. hammer lever safety valve safety valve lever hammer hammer and using leverage to balance the force on the valve. According to the principle of leverage, it can use a smaller mass of the weight is increased by the leverage effect of a larger force, and by moving the position of the hammer (or hammer mass conversion) to adjust the opening pressure of the safety valve. Simple hammer lever safety valve structure, adjust easily and more accurately, the applied load will not increase the valve rather have a larger increase, suitable for high temperature applications, used in the past was more common, especially is used in the higher temperature of the boiler and the pressure vessel. But hammer lever safety valve structure is relatively bulky, easy loading mechanism vibration, and often due to vibration leakage; its low pressure back seat, easy to close after opening and keep tight. 2. Spring inching valve spring inching valve is the use of a compression spring force to balance the role of the force on the valve. Ring-shaped helical spring compression can be adjusted by turning the nut on top of it is adjusted, such a structure can be corrected in accordance with safety valve opening (tuning) pressure. Spring inching valve structure is compact, lightweight, high sensitivity, the installation location is not restricted, but also because of the sensitivity of the vibration is small, it can be used on mobile pressure vessel. The disadvantage of this safety valve is applied with a load opening of the valve will vary, i.e., with increasing valve flap, increasing the amount of spring compression, acting on the valve will also increase the force. This rapid opening of the safety valve is unfavorable. In addition, the valve spring will be affected as a result of long-term high temperature leaving the stretch reduced. When used in a high temperature container, often considered spring insulation or thermal issues, so that the structure becomes complicated. 3. pulse valve pulse valve from the main valve and auxiliary valves and valve action led by the main and auxiliary valves pulses, its complex structure, usually apply only to safety discharge large boilers and pressure vessels. The three forms of safety valve, used more commonly, spring safety valve. II. According to different media according to different media emission mode discharge mode, the valve can be divided into fully enclosed, semi-enclosed and open, three. 1. closed fully enclosed valve exhaust valve, the gas all through the tailpipe emissions, the media can not leak outside the room, mainly used for toxic media. 2. The semi-enclosed portion of the gas valve semi-closed valve discharged through the exhaust pipe, also part of the leak from the gap between the bonnet and the valve stem, the medium is used for the container will not pollute the environment gas. 3. Open valve open valve bonnet is open, the spring chamber and the atmosphere, which will help to reduce the temperature of the spring, mainly applied to the medium is steam, and atmospheric pollution does not produce high-temperature gas container. III. According to the maximum height of the valve open in accordance with the size of the flow channel diameter valve open and flow channel diameter divided by the ratio of the safety valve, the valve can be divided into spring Enlight closed high-pressure safety valve and spring full-Kai safety valve two kinds. 1. Closed spring inching inching valve high pressure valve opening height is less than 1/4 the diameter of the flow channel, usually a runner diameter of 1/40 1/20. Action process inching valve is proportional action type, mainly for liquid applications, sometimes for a small gas emissions occasions. 2. The spring safety valve safety valve opening height is greater than or equal to 1/4 of the flow channel diameter. The discharge area is the safety valve seat throat smallest cross-sectional area. Its action is part of two-acting process, by means of a lift mechanism must be in order to achieve wide open, safety valve is mainly used for gaseous media applications. 3. open the safety valve between Weiqi between height and the entire Kai. That action can be made into two sections, the ratio can also be made into acting. 4. Press the action principle classified according to the role of the principle of classification, can be divided into direct-acting valve and non-direct-acting valve. 1. direct acting valve direct-acting valve is opened under the direct action of the working medium, that rely on the role of the working medium pressure against the biasing mechanism is applied to the valve flap mechanical load, the valve open. This valve has a simple structure and prompt action, good reliability advantages. But because relying on structural load, its load size is limited and can not be used for high-pressure, large diameter occasions. 2. Non-valve direct-acting valve can be divided into such pilot safety valve, safety valve driving force auxiliary device. Pilot valve is to rely on the media discharged from the pilot valve to drive or control. The pilot valve itself is a direct-acting valve, sometimes with other forms of valves. Pilot valve suitable for high pressure, large diameter occasions. The main valve pilot valve can also be designed to rely on the work of the media to seal the form, or can be applied much larger than the direct-acting valve mechanical load on the valve, which has a good sealing performance. At the same time, it moves very little affected by backpressure. The disadvantage is that it is reliable safety valve with the main valve and pilot valve related action as a direct-acting valve as quickly, reliably, and more complex structure. Relief valve driving force auxiliary device by means of a power assist device, in the case where the opening pressure of the safety valve opens below the normal forced. This safety valve for opening pressure is very close to the working pressure of the occasion, or the need to regularly open the safety valve for inspection or blowing adhesion, where the frozen medium. It also provides a means to force open the safety valve in case of emergency. 5. Press the pressure is classified according to whether the pressure can be adjusted to regulate classification, can be divided into fixed and adjustable relief valve and adjustable valve 1. Fixed non-adjustable pressure relief valve is factory set up, you can not change the use of commonly used in central air conditioning, boiler boiler, solar energy systems, such as S10 Series valve. 2. adjustable pressure relief valve off can vary in a range of needs of users can be set, commonly used in applications often need to change the system to protect pressure, such as S10 series of safety valve, but the price is generally higher.