At the production site, the main items of the pneumatic regulating valve adjustment are basic error, hysteresis, constant deviation, rated stroke deviation, and leakage.
The equipment required for adjustment is a filter pressure reducing valve, a common pressure gauge, a calibrator, a standard pressure gauge, a dial gauge, and the like.
How to verify the basic error, hysteresis and constant point deviation of the pneumatic regulating valve?
1. Basic error Input the specified input signal smoothly into the actuator (or positioner) in the direction of increasing or decreasing, measure the stroke value corresponding to each point, and calculate the actual "signal-stroke" relationship between the theoretical relationship The error of each point, the large value of zui is the basic error. The checkpoint shall include at least five points of the signal range of 0%, 25%, 50%, 75%, and 100%. The basic error of the measuring instrument should be less than 1/4 of the basic error limit of the valve being calibrated.
2. The hysteresis method is the same as the difference in the zui difference between the forward and reverse strokes measured on the same input signal.
3. The deviation method is always the same as 1, the basic error at the lower line of the signal is the starting point deviation, and the basic error at the upper line of the signal is the end point deviation.
How to decompress the rated stroke deviation of the pneumatic control valve?
The 120% signal is added to the actuator chamber, and the ratio of the stroke to the rated stroke from the 100%-120% signal stem is the nominal stroke deviation (the purpose is to ensure that the gas shutoff valve can be closed).
How to verify the leakage of the pneumatic control valve?
The test medium is a cleaning gas (air or nitrogen) or a liquid (water or kerosene) at 10 to 50 °C.
The test pressure A program is: when the allowable pressure difference of the valve is ≥350KPa, the test pressure is made at 350KPa, and the allowable pressure difference is allowed when the pressure difference is <350KPa. The B program is made according to the large working pressure difference of the regulating valve. The test signal pressure should ensure that the valve is closed.
In the A procedure, the signal pressure of the gas-opening valve actuator is zero; the signal pressure of the gas-closing valve actuator is the upper limit of the input signal plus 20KPa, and the signal pressure of the two-position valve actuator should be the design specified value. In the B program, the actuator signal pressure is the design specified value.
The test medium shall flow as specified in the valve, and the valve outlet may directly pass through the atmosphere or link the outlet to the atmospheric low-pressure head loss measuring device. When it is confirmed that the valve and the downstream link pipes are completely filled with the medium, the leakage amount can be measured.
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