Field performance testing and maintenance instructions for regulating valves

Field performance test of regulating valve
There are many performance indicators for the regulating valve. The following items should be tested and adjusted.
1) Basic error: smoothly increase or decrease the signal of 20~100kPa into the input air chamber (or positioner), measure the stroke value corresponding to each point, and calculate the relationship between the "signal-stroke" relationship and the theoretical value. The error of each point is the basic error. The test point shall be 5 points, 25%, 50%, 75%, 100% of the signal range. The basic error of the measuring instrument shall be limited to 1/4 of the basic error limit of the tested valve.
2) Hysteresis: The experimental method is the same as above. The maximum difference between the forward and reverse strokes measured on the same input signal is the hysteresis.
3) Always point deviation: The experimental method is the same as above. The basic error at the upper limit of the signal (starting point) is the starting point deviation; the basic error at the lower limit (end point) of the signal is the end point deviation.
4) Leakage test: Generally, the test medium is normal temperature water. When the pressure difference of the valve is less than 350 kPa, the experimental pressure is made at 350 kPa. When the working pressure difference of the valve is greater than 350 kPa, the allowable pressure difference is used. The experimental medium shall flow into the inlet valve according to the regulations. The valve outlet may directly connect to the atmosphere or connect the outlet to the atmospheric low-pressure head measuring device. The leakage amount can only be measured after the confirmation valve and the downstream connecting tubes are completely filled with the medium. For the main valve, a strong pressure test is also required.
5) The valve of the matching positioner should be debugged on site before installation and commissioning.

On-site inspection and maintenance of the regulating valve
Since the regulating valve directly contacts the process medium, its performance directly affects the system quality and environmental pollution. Therefore, the regulating valve must be regularly maintained and regularly inspected, especially for the use of harsh conditions and important occasions. It focuses on checking the maintenance site:
1) For the use of regulating valves in the case of high pressure difference and corrosive media, the inner wall of the valve and the diaphragm are often subjected to the impact and corrosion of the medium. The pressure and corrosion resistance should be checked.
2) The thread for fixing the valve seat, the inner surface is susceptible to corrosion and the valve seat is loose. The part should be inspected. The valve working under the high pressure difference should also check whether the sealing surface of the valve seat is eroded or cavitation.
3) The valve core is most seriously washed and corroded by the medium. During the inspection, it is necessary to carefully check whether it is corroded or worn. Especially in the case of high pressure difference, the valve core is more worn due to cavitation.
4) Check for cracking or aging of the diaphragm, "O" ring and other gaskets.
5) It should be noted that the PTFE filler, sealing grease is aging, the mating surface is damaged, and should be replaced if necessary.