The valve is a tool used in the transmission and control of gas and liquid with at least a thousand years of history.
At present, in the fluid pipeline system, the regulating valve is the control element, and its main function is to isolate the equipment and the pipeline system, regulate the flow, prevent backflow, regulate and discharge the pressure. Since it is very important to choose the most suitable regulating valve for the pipeline system, it is also very important to understand the characteristics of the valve and the steps and basis for selecting the valve.
Nominal pressure of valve
The nominal pressure of the valve refers to the design given pressure related to the mechanical strength of the piping components, that is to say, it is the allowable working pressure of the valve at the specified temperature, which is related to the material of the valve. The working pressure is not the same, therefore, the nominal pressure is a parameter that depends on the material of the valve and is related to the allowable working temperature and working pressure of the material.
A valve is a facility in a medium circulation system or a pressure system, which is used to adjust the flow or pressure of the medium. Other functions include shutting off or switching on media, controlling flow, changing media flow direction, preventing media backflow, and controlling or venting pressure.
These functions are achieved by adjusting the position of the valve closure. This adjustment can be done manually or automatically. Manual operation also includes the operation of manually controlling the drive. Manually operated valves are called manual valves. The valve that prevents backflow is called a check valve; the one that controls the relief pressure is called a safety valve or a safety relief valve.
So far, the valve industry has been able to produce a full range of gate valves, globe valves, throttle valves, plug valves, ball valves, electric valves, diaphragm control valves, check valves, safety valves, pressure reducing valves, steam traps and emergency shut-off valves. Valve products of 12 categories, more than 3000 models, and more than 4000 specifications; the maximum working pressure is 600MPa, the maximum nominal diameter is 5350mm, the maximum working temperature is 1200℃, the minimum working temperature is -196℃, and the applicable medium is Water, steam, oil, natural gas, strong corrosive media (such as concentrated nitric acid, medium concentration sulfuric acid, etc.).
Pay attention to valve selection:
1. In order to reduce the soil covering depth of the pipeline, the butterfly valve is generally selected for the larger diameter pipeline; the main disadvantage of the butterfly valve is that the butterfly plate occupies a certain cross section of the water, which increases a certain head loss;
2. Conventional valves include butterfly valves, gate valves, ball valves and plug valves, etc. The range of valves used in the water supply network should be considered in the selection.
3. The casting and processing of ball valves and plug valves are difficult and expensive, and are generally suitable for small and medium-diameter pipes. Ball valve and plug valve maintain the advantages of single gate valve, small water flow resistance, reliable sealing, flexible action, convenient operation and maintenance. The plug valve also has similar advantages, but the water-passing section is not a perfect circle.
4. If it has little effect on the depth of the cover soil, try to choose a gate valve; the height of the electric gate valve large-diameter vertical gate valve affects the soil-covering depth of the pipeline, and the length of the large-diameter horizontal gate valve increases the horizontal area occupied by the pipeline and affects the arrangement of other pipelines ;
5. In recent years, due to the improvement of casting technology, the use of resin sand casting can avoid or reduce mechanical processing, thereby reducing costs, so the feasibility of ball valves used in large-diameter pipelines is worth exploring. As for the demarcation line of caliber size, it should be considered and divided according to the specific situation.
original source: https://www.tws-valve.com/news/valve-as-a-tool-has-been-born-for-thousands-of-years/
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