Working principle of impulse safety valves; there are many types of safety valves – who has a comprehensive list?

The impulse safety valve, also known as a lever-type safety valve, is primarily used in power station boilers or steam pressure pipelines. It can be used in combination with other devices or on its own. When the pressure of the medium inside the pressure vessel exceeds the allowable level, the valve disc opens to release the excess steam; when the pressure drops to a certain level, the weight on the lever causes the valve disc to close quickly, ensuring the safe operation of the equipment. An impulse safety valve is mainly composed of a valve body, valve disc, valve seat, lever, weight, etc. Working principle: A safety valve is a safety device designed to prevent pressure equipment and containers from exploding due to pressure increases or when the internal pressure exceeds acceptable limits. A safety valve is a safety device widely used in pressure systems such as pressure vessels, boilers, and pressure pipelines to ensure the safe operation of these systems. When the pressure in the container exceeds the specified value, the safety valve opens automatically to release the excess pressure inside the vessel, thereby preventing damage to the container or pipelines. When the pressure inside the container drops to the normal operating pressure, it shuts off automatically to prevent all the gas from being released due to overpressure in the container, thereby avoiding waste and production interruptions. A safety valve mainly consists of three parts: a valve seat, a valve disc (valve core), and a loading mechanism. The valve seat is either integrated with the valve body or assembled with it, and it is connected to the equipment. The valve disc is often accompanied by a valve stem, which fits tightly against the valve seat. Above the valve disc is a loading mechanism, and the magnitude of the load can be adjusted. When the pressure inside the device is within a certain operating range, the force exerted by the medium inside on the valve disc is less than the force applied to the valve by the actuating mechanism; the difference between these two forces constitutes the sealing force between the valve disc and the valve seat, which keeps the valve disc pressed tightly against the valve seat, preventing the medium in the device from escaping. When the pressure inside the device exceeds the specified operating pressure and reaches the opening pressure of the safety valve, the force exerted by the medium inside on the valve disc becomes greater than the force applied to it by the loading mechanism; as a result, the valve disc moves away from the valve seat and the safety valve opens, allowing the medium inside the device to be discharged through the valve seat. If the discharge capacity of the safety valve is greater than the device’s safe discharge rate, the pressure inside the device gradually decreases, and after a short period of discharge, the pressure returns to the normal operating level. At this point, the force exerted by the internal pressure on the valve disc is less than the force applied to it by the loading mechanism; the valve disc presses tightly against the valve seat, flow of the medium stops, and the equipment continues to operate at its normal working pressure. Therefore, a safety valve closes or opens on its own by the interaction between the force of the medium acting on the valve disc and the force exerted by the loading mechanism, thereby preventing the equipment from experiencing overpressure.

This type of safety valve is an obsolete product, but due to historical reasons and other factors, it is still used to some extent in older equipment, and is particularly common in devices such as power station boilers. This type of safety valve can be completely replaced by a spring-loaded safety valve. Regarding the issue of classification, it depends on your perspective; just don’t be fooled by all the various opinions out there. When categorizing, be sure to pay attention to the basis for classification and avoid confusion; that way it’s simple. I. Based on their overall structure and loading mechanism 　　They can be classified into three types according to their overall structure and loading mechanism: weight-lever type, spring type, and pulse type. 　　1. Weight-lever type safety valve 　　　The weight-lever type safety valve uses a weight and a lever to balance the force acting on the valve disc. Based on the principle of levers, it can use a weight with a smaller mass to generate a greater force through the amplifying effect of the lever, and adjust the opening pressure of the safety valve by changing the position of the weight (or its mass). 　　The weight-lever type safety valve has a simple structure, is easy and relatively accurate to adjust, and the load applied does not increase significantly as the valve disc rises. It is suitable for high-temperature environments and was widely used in the past, especially in boilers and pressure vessels operating at high temperatures. However, the structure of the weight-lever type safety valve is relatively bulky; the loading mechanism tends to vibrate, and leakage often occurs as a result of these vibrations ； Its seating pressure is low, making it difficult to close and maintain a tight seal once it is opened. 　　2. Spring-loaded slightly open safety valve The spring-loaded slightly open safety valve uses the force of a compressed spring to counteract the force acting on the valve disc. The compression amount of the helical coil spring can be adjusted by turning the adjustment nut on it; this mechanism allows the opening (setting) pressure of the safety valve to be corrected as needed. The spring-loaded slightly-open safety valve is lightweight and compact, has a high sensitivity, and its installation location is not restricted. Moreover, due to its low sensitivity to vibrations, it can be used in mobile pressure vessels. The disadvantage of this type of safety valve is that the applied load changes as the valve opens; that is, as the valve disc rises, the degree of compression of the spring increases, and the force acting on the valve disc also increases accordingly. This is unfavorable for the rapid opening of the safety valve. Furthermore, the spring on the valve may lose its elasticity due to prolonged exposure to high temperatures. When used on containers with high temperatures, the insulation or heat dissipation of the spring often needs to be considered, which complicates the design. 　　3. Pulsating safety valve The pulsating safety valve consists of a main valve and an auxiliary valve; the pulsing action of the auxiliary valve drives the main valve to operate. It has a complex structure and is generally suitable only for boilers and pressure vessels that require a large amount of safety discharge. 　　Among the three types of safety valves mentioned above, the spring-type safety valve is the most commonly used. II. According to the method of medium discharge 　　Based on the way in which the medium is discharged, safety valves can be classified into three types: fully enclosed, semi-enclosed, and open-type. 　　1. Fully enclosed safety valve: When a fully enclosed safety valve releases gas, all of the gas is discharged through the exhaust pipe, preventing any leakage of the medium; it is mainly used for situations where the medium is toxic. Containers for flammable gases. 　　2. Semi-enclosed safety valve: The gas discharged by a semi-enclosed safety valve passes partly through the exhaust pipe, while some of it leaks out through the gap between the valve cover and the valve stem; it is commonly used in containers containing gases that do not pollute the environment. 　　3. Open-type safety valve The valve cover of an open-type safety valve is open, allowing the spring chamber to be in contact with the atmosphere; this helps to reduce the temperature of the spring. It is mainly suitable for containers containing steam or high-temperature gases that do not cause pollution to the atmosphere. III. Classification based on the degree of valve disc opening and the flow channel diameter: Safety valves can be divided into two types according to the ratio of the maximum height of valve disc opening to the diameter of the safety valve’s flow channel – spring-actuated slightly open high-pressure safety valves and spring-actuated fully open safety valves. 　　1. Spring-loaded slightly-opened closed-type high-pressure safety valve: The opening height of a slightly-opened safety valve is less than 1/4 of the diameter of the flow channel; it is usually between 1/40 and 1/20 of the diameter of the flow channel. The operating mechanism of a slightly opening safety valve is proportional in nature; it is primarily used in liquid applications, and sometimes in gas applications where the discharge volume is very low. 　　2. Spring-loaded full-open safety valve The opening height of a full-open safety valve is greater than or equal to 1/4 of the diameter of the flow channel. The discharge area of a fully open safety valve is the minimum cross-sectional area at the valve seat throat. Its operating mechanism is of two-stage type; a lifting mechanism is required to achieve full opening. Full-opening safety valves are mainly used in applications involving gaseous media. 　　3. Semiclosed safety valve 　　　The opening height is between that of a slightly opened valve and a fully opened valve. It can operate in two-stage mode or in a proportional mode. IV. Classification by operating principle 　　Based on their operating principle, safety valves can be divided into directly-acting safety valves and indirectly-acting safety valves. 　　1. Direct-acting safety valve A direct-acting safety valve opens under the direct action of the working medium; that is, it relies on the pressure of the working medium to overcome the mechanical load applied to the valve disc by the loading mechanism, thereby causing the valve to open. This type of safety valve has advantages such as a simple structure, rapid operation, and good reliability. However, due to reliance on structural loading, its load capacity is limited, so it cannot be used in high-pressure or large-diameter applications. 　　2. Indirect-acting safety valves 　　　These types of safety valves can be divided into pilot-operated safety valves and safety valves equipped with power-assist devices. 　　A pilot-operated safety valve is driven or controlled by the medium discharged from the pilot valve. The pilot valve itself is a direct-acting safety valve; sometimes other types of valves are also used. Pilot-operated safety valves are suitable for high-pressure and large-diameter applications. The main valve of a pilot-operated safety valve can also be designed to be sealed by the working medium, or a much greater mechanical load can be applied to the valve disc than in a directly-acting safety valve, thereby achieving excellent sealing performance. At the same time, its operation is little affected by back pressure. The disadvantage of this type of safety valve is that its reliability depends on the main valve and pilot valve; it does not operate as quickly or reliably as directly-acting safety valves, and its structure is more complex. 　　A safety valve equipped with a power assist device forces the safety valve to open at a pressure lower than the normal opening pressure, by means of such a power assist device. This type of safety valve is suitable for applications where the opening pressure is very close to the operating pressure, or in situations where the safety valve needs to be opened regularly for inspection or to remove adhered or frozen media. At the same time, it also provides a means to force the safety valve to open in emergency situations. V. Classification by whether the pressure can be adjusted 　　Based on whether the pressure can be adjusted, safety valves can be divided into fixed, non-adjustable safety valves and adjustable safety valves. 　　1. Fixed, non-adjustable safety valves have their pressure values set at the factory and cannot be changed during use. They are commonly used in systems such as central air conditioning, boiler heat pumps, and solar systems; examples include the S10 series of safety valves. 　　2. The setting pressure of adjustable safety valves can be adjusted within a certain range to meet various user requirements; they are commonly used in situations where the system protection pressure needs to change frequently, such as in S10 series safety valves. However, their price is generally relatively high. 　　VI. Classified by operating temperature into normal-temperature safety valves and high-temperature safety valves. 1. Normal-temperature safety valves are generally those that can withstand temperatures of up to 110°C and are installed in heating, ventilation, air conditioning, or water systems; examples include the S10 series of safety valves. 　　2. High-temperature safety valves are safety valves designed for use in solar systems and mold temperature control systems, with a temperature resistance of up to 180°C, such as the S10 series of safety valves.

For such fundamental questions, one should read more books and look up information online; the key is to have a clear mindset and avoid confusion.

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