Control valve on-site performance testing and maintenance
Control valve on-site performance testing: a lot of performance control valve, the following items should be focused on testing and calibration. 1) The basic error: the 20 ~ 100kPa signal steadily increase or decrease the input chamber (or locator), measuring the stroke value corresponding to each point to calculate the "signal - stroke" relationship between the theoretical value The error of each point, the maximum value is the basic error. The test point should be 5% of the signal range of 0%, 25%, 50%, 75%, 100%, the basic error of the measuring instrument should be limited to the test valve basic error limit of 1/4. 2) back to the difference: the experimental method Ibid. In the same input signal measured on the positive and negative strokes of the maximum difference that backlash. 3) always point deviation: The experimental method is the same as above. The basic error at the upper limit (starting point) of the signal is the starting point deviation. The basic error at the lower limit (end point) of the signal is the ending point deviation. 4) Leakage test: The test medium is usually water at room temperature. When the pressure difference of the valve is less than 350kPa, the test pressure is to be made at 350kPa. When the working pressure difference of the valve is more than 350kPa, the allowable pressure difference shall be used. The test medium should flow into the valve as required and the outlet of the valve can be directly connected to the atmosphere or the low-pressure head measuring device connected to the outlet through the atmosphere. After confirming that the valve and the downstream connecting pipe are completely filled with the medium, the leakage can be measured. On the main valve, but also to do strong pressure test. 5) The valve supporting the positioner, before installation, put into operation, should be on-site commissioning. Control valve on-site inspection and maintenance As the direct contact with the process medium, its performance directly affects the system quality and environmental pollution, so the valve must be regularly maintained and regularly overhaul, especially for harsh conditions and important occasions should pay attention to maintenance jobs. The focus of inspection and maintenance of parts: 1) For the use of high pressure and corrosive media in the case of regulating valve, the valve body wall, the diaphragm is often subject to media impact and corrosion, stress inspection should focus on corrosion resistance. 2) For fixing the thread used for the valve seat, the inner surface is easily corroded and the valve seat is loosened. This part should be checked emphatically. For the valve working under high pressure difference, check the valve seat sealing surface for erosion and cavitation. 3) The valve core is washed by the medium and the corrosion is the most serious. During maintenance, it is necessary to carefully check if it is corroded or worn out. Especially when the valve core is worn by cavitation more seriously under high pressure drop. 4) Check diaphragm, "O" ring and other gaskets for cracking or aging. 5) should pay attention to PTFE packing, sealing grease is aging, with the surface is damaged, if necessary, should be replaced.
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