The safety valves produced by Hebei Zhenchen Machinery Equipment Group Co., Ltd. are widely used as overpressure relief devices on boiler pressure vessels. Whether their performance can meet the requirements is crucial to the safe operation of boiler pressure vessels. According to relevant regulations, safety valves should be inspected regularly, at least once a year. Article 145 of the “Steam Boiler Safety Technical Supervision Regulations” stipulates that for safety valves of newly installed boilers and safety valves after maintenance, their opening pressure (set pressure) and sealing pressure must also be inspected. Our country stipulates that the sealing test pressure of safety valves for steam boilers shall be the smaller of 90% of the opening pressure and the return pressure. The sealing test pressure of safety valves for air or other gases and water or other liquids, when the opening pressure is less than 0.30 MPa, is 0.030 MPa lower than the opening pressure, and when the opening pressure is greater than or equal to 0.30 MPa, it is 90% of the opening pressure.
When conducting the sealing test of the safety valve, visual or auditory methods can generally be used. Qualification is usually judged based on the pressure drop of the calibration bench. When the calibration bench pressure rises to the set pressure and opens, all valves are closed. At this time, the value of the calibration bench pressure gauge should remain unchanged within 2 minutes or the pressure drop should be less than 0.01 MPa. That is considered qualified. For safety valves with stricter use, the bubble method can be used to check whether the sealing pressure is normal. The simple method is to prepare a 5 mm thick rubber plate at the outlet of the safety valve and block the lower half of the valve outlet. After filling it with water, make the lower valve seat and valve disc surface immersed in water and maintain the test pressure for 2 minutes. If the number of observed bubbles is less than 30, it is considered qualified.
In recent years, some valve manufacturers have focused on economic benefits while ignoring product quality, resulting in a certain number of safety valves with poor manufacturing quality, large geometric size and machining accuracy errors, and unsatisfactory technical performance. The manufacturing quality of safety valves has caused many problems. Complaints about using the unit. In addition, it is worth noting that in order to improve the sealing performance of the safety valves manufactured by some valve manufacturers, they use the method of reducing the width of the sealing surface to make the valve disc surface very narrow. In this way, when discharging, the sealing surface will be damaged due to the erosion of high-speed fluid and the impact of seat return, and annular scars will appear on the valve seat surface, especially for safety valves whose equipment working pressure exceeds 0.8 MPa. This type of safety valve accounts for about 5% of the safety valves that need to be calibrated every year in our city. Our city has more than 2,000 large and small boilers and nearly 1,000 pressure vessels, and 3,000 safety valves need to be calibrated every year. Narrow disc safety valves bring certain difficulties to calibration and maintenance work. To ensure good sealing performance, the annular scars must be ground flat. On average, more than 20 valves of this type cannot be ground every year. For example, during the annual inspection, our city’s breweries submitted 35 safety valves for inspection. The spring pressure level was 1.0~1.3 MPa and the equipment operating pressure was 1.0 MPa. Among them, there were 5 such valves, and they were all from the same valve manufacturer. The valve seat sealing surface is 4 mm wide, and the valve disc sealing surface is only 1.5 mm wide. The valve disc is too narrow and has not attracted enough attention from relevant departments. We have learned from actual calibration work over the years that when the operating pressure of the equipment is high and the safety valve is opened too many times, the sealing surface of the valve disc is too narrow and the valve disc does not meet the relevant national standards, which causes annular scars on the safety valve. main reason. For this reason, it is recommended that manufacturers pay attention to not making the valve disc sealing surface too narrow when designing and processing safety valves.