Force analysis of spring safety valve
Time: 2021-02-24 22:45:44 Source: Yonglong Valve Reading: zero second
Force analysis of spring safety valve
Spring type safety valve is one of the main safety accessories of steam boiler and storage tank equipment. As a valve with important pressure relief protection function, safety valve is widely used in various pressure vessels and piping systems of steam boiler. When the pressure vessel reaches the upper limit of the specified pressure bearing value, it can automatically open by induction, The redundant medium is discharged out of the pressure vessel and can be automatically closed after the discharge, so as to ensure that the pressure vessel can operate within the allowable range of safe and reliable pressure and avoid safety accidents due to overpressure.
Spring type Safety valve The normal operation of the safety valve is not only related to the normal and safe use of pressure vessels such as steam boilers. Therefore, the common faults of the safety valve spring must be paid great attention to and discharged in time. In the following paragraphs Safety valve The causes of spring failure are analyzed and discussed.
The spring of the safety valve of the steam boiler is subjected to 4.30MPa downward positive stress when it is assembled. When the valve is fully opened, it will be subjected to 4.80MPa pressure. The steam temperature in the pipeline changes about 200 ℃. Because the spring is closed and installed on the upper part of the valve body, its temperature is slightly lower. The factors affecting the failure of safety valve spring include relaxation failure, temperature difference failure and spring material itself. The main factors are the corrosion of safety valve spring of steam boiler, which is affected by non central load and impact load.
Stress analysis of safety valve spring of steam boiler
1. Axial or radial load
Most of the safety valve springs used on steam boilers are cylindrical. According to the calculation, when the safety valve spring is subjected to axial or radial load by the axial spring, the deformation and shear stress are inversely proportional to the diameter of the spring wire; When the spring is corroded in use, the diameter of the spring wire becomes smaller, and the spring deformation and shear stress increase, leading to the spring failure.
2. Affected by non central load
During the operation of steam boiler, the safety valve shall regularly discharge overpressure steam. After steam exhaust, the valve rod is liable to deflect, resulting in air leakage of the safety valve and eccentricity of the spring under non central load, which reduces the safety stress value of the round spring. That is, the safety stress is inversely proportional to the load eccentricity, which makes the safety valve spring invalid and shortens its service life.
3. Affected by impact load
During the operation of the steam boiler, the safety valve is in a state of frequent pulsation, which produces a large impact speed during the exhaust. At this time, the first three coils of the spring bear the impact load first, absorbing more impact energy. Because the impact load can not be transmitted to the following spring coil quickly and effectively. The first three circles are plastic deformation and then fail.
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