Abstract: safety valve sealing surface is too narrow and inappropriate choice of valve materials is the main reason of safety valve annular scars.
Keywords: safety valve; valve flap; opening pressure (set pressure); sealing pressure
Safety valve is widely used in boiler and pressure vessel overpressure relief device on, the performance can meet the requirements of the safe operation of boilers and pressure vessels is essential. According to the order requirements, the safety valve should be inspected regularly, at least once a year. “The steam boiler safety technology supervision order” under Article 145, for the newly installed boiler safety valve and safety valve after repair, but also to test its opening pressure (set pressure) and the sealing pressure.
China provides: steam boiler safety valve sealing test pressure to take 90% of opening pressure and reseating pressure of the lesser value. Air or other gases and water or other liquid with a safety valve sealing test pressure, when the open when the pressure is less than 0.30MPa, lower than the opening pressure 0.030MPa, when the opening pressure of 0.30 MPa greater than or equal to 90% when the opening pressure.
When conducting a safety valve sealing test, visual, or ears to the general method can be used to carry out. Check stations are usually based on pressure drop to determine eligibility, the pressure to rise when the check station set pressure is on, close all valves, pressure gauge value at this time check station at 2 minutes should be maintained or pressure drop is less than 0.01 MPa is considered qualified.
For more stringent safety valve, bubble method can be used to test the sealing pressure is normal. Easy way is the safety valve outlet, for a 5mm thick rubber sheet, under the outlet block valve half filled with water after the surface under the valve seat and valve are immersed in water, to maintain test pressure for 2 minutes, observed number of bubbles less than 30 that qualified.
In recent years, some manufacturers emphasis on economic efficiency, to the neglect of the product quality, leading to a safety valve for a certain number of poor manufacturing quality, geometry, precision error is larger, mainly the technical performance, manufacturing quality safety valve has caused a lot of use units of complaints. In addition, it is noteworthy that the current manufacture of some of the safety valve valve manufacturer in order to improve sealing performance and protect sealed off by reducing the width of the sealing surface of the ways in which the disc surface becomes very narrow. Such as emissions, due to high velocity impact erosion and the reasons for the back seat, causing damage to the sealing surface, seat surface ring injuries occur, especially in equipment over the working pressure safety valve more than 0.8MPa. Annual accounts for the city of such safety valve check valve should be about 5%, the city has a size of more than 2000 boilers, pressure vessels, nearly a thousand units each year check valve 3000. Narrow valve safety valve to check the maintenance work to bring a certain degree of difficulty, to make good sealing performance, you have to grind flat circular scars, these valves have an average of 20 just can not grinding. For example, in the annual inspection in the city 35 breweries relief valve, spring pressure rating is 1.0 ~ 1.3MPa, equipment operating working pressure 1.0MPa, of which there are five such valves, and all from the same valve manufacturers. Seating wide 4mm, valve sealing wide only 1.5mm, narrow valve did not cause enough attention to the relevant departments.
We verify these in real understanding of the work, high work pressure in the equipment operation, safety valve opens too many times the case, the valve sealing surface is too narrow and the valve does not meet state standards, is caused by valve ring injuries the main reason. To this end, the proposed safety valve manufacturers in the design, processing time, we should focus on considering valve sealing surface is not too narrow.
Also available in: Chinese.