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Safety valve is one of the important safety accessories of the boiler. It is an important guarantee for safe and trouble-free operation of the boiler. Its accuracy and reliability will directly affect the safe and economical operation of the boiler. At present, the inspection of safety valves in our country has formed a system, but there is no uniform requirement on test methods and means. Thus in the safety valve inspection will inevitably be some problems. This article explores these issues, with a view to get together to improve. This article collected by the Shanghai Five Valve Manufacturing Co., Ltd. finishing, Shanghai Wu Yue specializing in the production of various types of spring-type safety valve to provide relevant technical exchanges and sharing.
First, the basic characteristics of safety valves and requirements
1. Pressure relief valves to the maximum allowable pressure: When the medium through the relief valve discharge, the maximum pressure allowed to be protected within the container. Operating pressure: the container often withstand the gauge pressure at work. Computation of the container Working pressure: The pressure at which the container wall thickness is calculated. Full pressure: the safety valve in the full opening stroke of the valve pressure, it is also called discharge pressure. Set pressure: Adjust the inlet pressure to open the safety valve. Closure pressure: also known as the seat back pressure, is the safety valve is opened, when the container pressure drops to the pressure relief valve closed. Back to the difference: refers to the working pressure of the container with the safety valve closing pressure difference. Back pressure: refers to the safety valve discharge side to establish the pressure. The back pressure may be fixed or variable, affecting the safety device's work, back to the atmosphere when the back pressure is zero.
2. Safety valve work requirements
(1) When the maximum allowable pressure is reached, the safety valve shall be opened as far as it will reach and a specified amount of medium shall be discharged.
(2) to open pressure, to quickly open.
(3) The relief valve should be stable and free from shock when it is discharged.
(4) When the pressure is reduced to the back seat pressure, it should be able to shut down in time.
(5) the safety valve is closed, should maintain a good sealing performance.
3. The safety valve discharge capacity refers to the flow of medium through the safety valve per unit time. Safety valve discharge capacity to ensure that the system can let go of the maximum amount of excess medium, to give system equipment effective protection.
Second, the use of boiler safety valve problems
1. The parameters are not properly selected. Due to the boiler with the factory distribution of the safety valve, almost all matching the rated parameters, and in the actual use of the boiler buck operation is very common phenomenon. Some man-made step-down to ensure operational safety, and some are the pressure of the process, but the pressure relief valve is limited, the commonly used spring-type safety valve, the safety valve spring used due to manufacturing materials, physical properties , Chemical properties, manufacturing processes and other differences, each spring can only work in a limited pressure range (the amount of deformation of the spring is equal to 20% to 80% of the maximum deformation of the spring, the maximum shear stress of the spring design is not greater than the allowable Cutting stress of 80%), in order to ensure its action performance to meet the requirements. In actual work because I do not know the safety valve of the limited pressure range, so that the opening of the repeatability and sealing performance significantly reduced. The correct approach is to adjust or replace the rated parameters meet the operating pressure requirements of the safety valve.
2. Operating poor working conditions, the boiler operating safety valve in high temperature and high pressure, some boiler room operation in the larger dust, improper operation of the boiler and so on, easy to make the spool jam, rust died, to the critical moment can not take off and Lost its due role.
3. Operating pressure range is too large, safety valve frequent take-off. Because the safety valve opening pressure is determined according to the high value of the boiler operating pressure, and the pressure difference between the two smaller, if the boiler management, improper operation can easily lead to frequent relief valve safety, which not only damage the sealing surface, but also Easy to plug the spool, resulting in failure of safety valve.
4. In the process of inspection of the boiler, attention should be paid to the installation position of the safety valve. For safety valves requiring some discharge media, the exhaust pipe should be installed in accordance with the relevant regulations of the state, and the exhaust gas should be unobstructed to minimize the resistance Reduce the back pressure in order to avoid back pressure on the safety valve opening pressure caused by the adverse effects of safety valve to ensure safe and reliable operation.
In addition, the safety valve manufacturer of domestic safety valve because of technology, material and other different, poor interchangeability, so maintenance, the valve, the spring should not be easily replaced, so as not to affect the valve action performance.
Third, the safety valve test methods and reliability
Safety valve inspection, in addition to the strength of the manufacturing unit testing, performance testing, as well as post-operation inspection and periodic inspection. Operational inspection, the main test valve in the boiler on the opening pressure, back pressure and sealing performance, the work can be carried out by the inspector or experienced operator. Periodic inspection is the operation of a certain period of time (usually at least once a year), by a full-time inspection of the inspection unit to ensure safety valve opening pressure and tightness, to prevent the safety valve rust, do not open and other issues to ensure that the boiler safe operation. Safety valve cold constant pressure adjustment, the test process generally use compressed air or nitrogen, mainly to confirm the opening pressure and tightness.
Safety valve open, in theory, only the pressure at the entrance to the valve size, and has nothing to do with its media. The main factor is the temperature, with the increase of the temperature, the strength of the material is reduced and the part is expanded. Thus the spring-loaded safety valve, its opening pressure slightly lower, but the lever safety valve has no effect.
In safety valve use and calibration process, should avoid the frequency hopping (safety valve flap abnormal rapid back and forth movement, the movement of valve contact valve seat) phenomenon, to prevent frequent contact with the valve seat and the valve damage the sealing surface , Leading to a reduction of the airtightness of the safety valve.
Due to the impact of the working environment of the safety valve, there are some differences between the opening pressure of the safety valve in the actual work and the cracking pressure determined in the cold constant pressure calibration of the safety valve. If it is found during the actual operation, the cracking pressure during actual use And the cold constant pressure difference between the larger adjustment, the operator or the unit should not be unauthorized use of equipment to change the pressure relief valve opening pressure should be sent to a full-time inspection unit to re-determine the opening pressure to prevent accidents. This article collected by the Shanghai Five Valve Manufacturing Co., Ltd. finishing, Shanghai Wu Yue specializing in the production of various types of spring-type safety valve to provide relevant technical exchanges and sharing.
Fourth, a few suggestions
1. The inspection and correct use of safety valve is an important guarantee to ensure the normal and safe operation of the boiler. The inspection department and the operating unit should attach great importance to this and establish the corresponding rules and regulations and technical files.
2. Safety valve operation inspection and periodic inspection should be carried out over the same period. On the basis of regular inspection, run the test to ensure the integrity and reliability of the safety valve inspection.
3. The supervision department should strictly monitor the customs and resolutely refrain from allowing boilers running without safety valves tested by full-time inspection agencies to prevent accidents. (Finish)
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