Standards and performance of control valves

Thread Content

The new national standard for control valves: the national standard GB4213-84, \"General Technical Requirements for Pneumatic Control Valves,\" was issued on March 21, 1984, and came into effect on January 1, 1985. This standard was revised again in 1992; the revised standard was designated as GB/T4213-92 and came into effect in October 1993. This standard is primarily based on IEC international standards, and formulated in consideration of China’s specific conditions. The previously applicable departmental standards become invalid as of the date of implementation of the new national standards. When comparing the old and new standards, the main differences are as follows: (1) The new national standard adds a \"service life\" parameter, bringing the total number of performance indicators to 14: 1 basic error ； 2-cycle difference ； 3 Dead Zone ； 4 Constant point deviation ； 5 Rated stroke deviation ； 6 Leakage amount ； 7 Sealing performance of the stuffing box and other connections: 8 Sealing performance of the air chamber ； 9 Voltage withstanding strength ； 10 Rated flow coefficient ； 11 Inherent flow characteristics ； 12 Vibration resistance ； 13 Action Life Span ； 14 Appearance. (2) The new national standard classifies basic error, hysteresis, dead zone, constant position deviation, and rated stroke deviation into 8 grades: A, B, …… H, so as to select the grade with the best performance-cost ratio based on the different functional requirements of various valves. The old standard assigned a unique indicator for each type of valve, lacking flexibility. (3) The new national standard classifies leakage amounts into A, B… F – these 6 grades, with grade F being the highest, measured in bubbles per minute. The old standard had only one grade, and requiring a leakage rate of 0 for high-pressure valves was not practical. (4) Flow characteristic error testing method: The new national standard adds a method for testing using the slope approach. (5) The new national standard replaces the term \"circulation capacity\" in the old standard with \"flow coefficient\". The values were previously standardized under old regulations, while the new national standards allow manufacturers to determine them on their own, which facilitates the design and finalization of new products. (6) The number of test points for basic error and hysteresis has been changed from 10 according to the old standard to 5. (7) Requirements of the new national standard for the air supply and ambient temperature of control valves. The air source should be clean and dry, free of significant corrosive gases, solvents, or other liquids. For control valves equipped with positioners, the air supply should contain less than 0.1 g/m of solid particles, the diameter of these particles should be greater than 3 μm, and the oil content should be less than 1 ppm. The ambient temperature for the control valve is -25 to +55°C or -40 to +70°C. The control valve must meet the above requirements when in operation. An unclean air supply for the locator is the main cause of abnormal operation of the locator, accounting for over 2/3 of all failures; special attention should be paid to this issue.