What Is a Double Check Valve?
A check valve is a valve whose opening and closing member is a circular disc and acts on its own weight and medium pressure to block the backflow of the medium. It is an automatic valve, also known as a check valve, check valve, return valve or isolation valve. The movement of the valve disc is divided into lifting type and swinging type. The lift check valve is similar in structure to the shut-off valve, except for the valve stem that drives the valve disc. The medium flows in from the inlet (lower side) and flows out from the outlet (upper side). When the inlet pressure is greater than the sum of the flap weight and its flow resistance, the valve is opened. Conversely, the valve is closed when the medium flows backward. The swing check valve has an oblique valve disc that can be rotated around the shaft. The working principle is similar to that of a lift check valve. Check valve is often used as the bottom valve of the pumping device to prevent the backflow of water. The combination of check valve and shut-off valve can play a role of safety isolation. The disadvantage is that the resistance is large and the sealing is poor when closed. [1]
- Non-return valve can also be used to increase the pressure in the system
- The opening and closing parts rely on the force of the medium to open or close by themselves, and the valve to prevent the medium from flowing backward is called a check valve. Check valve belongs to
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- 1) Product standards
- "General Valve Iron Swing Check Valve" GB / T 13932-92
- "Universal Valve Steel Swing Check Valve" GB 12236 -2008
- General Valve Iron
- (1) Quality control of the body blank All parts of the valve are forgings. Forging is strictly performed in accordance with the forging process regulations and process cards. The forging temperature, the forging temperature, the degree of deformation and the deformation speed are strictly controlled. The cooling method performs cooling. The chemical composition analysis, mechanical property test, intergranular corrosion test, and metallographic structure analysis of the forged product are in accordance with the corresponding standards after analysis, test and determination.
The quality of forgings is ensured by ultrasonic inspection and liquid penetration inspection. According to the requirements of RCC-M, 100% ultrasonic flaw detection and evaluation are performed on the forgings, and liquid penetration inspection and evaluation are performed on all surfaces of the forgings.
(2) Welding In order to improve the quality of surfacing, plasma argon arc welding is used for surfacing of the sealing surfaces of valve discs and valve seats. At the same time, in order to ensure the welding quality, the welding process used in production was re-evaluated.
(3) Assembly test High-quality products not only require high-precision parts, but also the key is how to assemble these high-precision parts into high-performance products. China Nuclear Su Valve has organized an experienced and highly skilled assembly and commissioning team composed of multiple technicians and senior technicians. It is responsible for valve assembly, commissioning, and testing. It has formulated the cleaning process and assembly process of parts and components. Strict control during commissioning, and strive for excellence, to ensure the successful assembly and commissioning of the valve, and various performance tests have been performed, and all indicators meet the requirements of the design task.
(4) Process inspection has prepared a quality plan for the valve to ensure that the valve is quality controlled and audited from raw materials, blank input, machining, welding, heat treatment, non-destructive testing, cleaning, assembly, factory test and various type tests. Industry Second Research and Design Institute recognized and witnessed on-site.
- Butterfly type double flap check valve is suitable for high-rise building water supply pipe network, pipe network with certain chemically corrosive medium, pipe network with limited installation space, and also suitable for sewage pipe network.
- The lift type mute check valve is suitable for the pipe network with high quality requirements for water supply and drainage projects; the pipe network with relatively high pressure requirements (PN2.5Mpa); it can be installed at the exit of the pump and is an economical and practical waterproof hammer check valve.
- Lifting muffler check valve is suitable for water supply and drainage systems, high-rise building pipe network, can be installed at the pump outlet, the structure is slightly modified, it can be used as a water suction bottom valve, but it is not suitable for sewage pipe network.
- The selection criteria of check valve are as follows:
- China's valve industry chain is numerous, but not a valve powerhouse. On the whole, China has entered the ranks of the world's valve powers, but from the perspective of product quality, there is still a long gap between China and the valve powers. The industry's low concentration of production, low R & D capabilities of valves supporting high-end products, and low manufacturing technology in the valve industry still exist, and the import and export trade deficit continues to expand.
- The next few years will be a period of high-speed shocks in the valve industry. The direct consequence of such high-speed shocks is the expansion of the polarization trend in the valve cabinet brand camp. There are definitely not so many valve companies that can really survive the market in the next few years. However, this high-speed shock of the valve industry will bring huge opportunities, and the results of the shock will make the market operation more rational.
- The localization of high-end valves is unusually bumpy. Basic parts have become a short board that restricts the development of high-end manufacturing in China. During the 12th Five-Year Plan period, the government will continue to increase the localization of high-end equipment components. Here we select several representative valves in key development industries mentioned in the "Implementation Plan" for feasibility analysis of import substitution. From the analysis, we can see that the feasibility of import substitution of valves in various sub-sectors is very different. High-end valves need more policy guidance and scientific research support.
- The valve industry plays a very important role in the development of the national economy as an important link in preparing the manufacturing industry. As China's domestic valve manufacturing industry still has a certain gap compared with the international advanced level, many key valves with high parameters, high temperature, high pressure and high pounds have always depended on imports. After the "Several Opinions of the Equipment Manufacturing Industry", the relevant state departments have made a series of major deployments in accordance with the national requirements for major equipment localization, and are led by the National Development and Reform Commission. Deployed and formulated valve localization plans for major equipment in related fields, and coordinated with relevant departments many times. Nowadays, valve localization has reached a consensus in the domestic valve industry.
- Actively adopt international standards for product design; absorb excellent design structures from abroad; product tests and performance inspections are carried out in strict accordance with international standards; absorb foreign production process experience and attach importance to the research and promotion of new materials; clarify the technology of imported high parameter valve products Parameters and working conditions are the way to speed up the localization process, promote the continuous updating of valve products, and fully realize the localization of valves.
- With the acceleration of the restructuring of the valve industry, the future industry will be competition between valve product quality and safety and product brands. The products will develop in the direction of high technology, high parameters, strong corrosion resistance, and long life. Only through continuous technological innovation and development New products and technical transformation can gradually improve the technical level of the product, meet the domestic equipment supporting, and fully realize the localization of the valve. China's valve manufacturing industry will present a better development prospect under the huge demand environment.