Views: 227 Author: Site Editor Publish Time: 2021-07-01 Origin: Site
There are thirteen performances for air actuated control valve, including basic error, hysteresis, dead zone, point deviation, rated stroke deviation, leakage, tightness, compressive strength, appearance, rated flow coefficient, inherent flow characteristics, vibration resistance and operating life.
Due to factors, including the transportation of the regulating valve and the adjustment of the working spring range, it is always necessary to adjust and inspect the following performance before installation:
Firstly, we should input the specified input signal into the chamber of pneumatic gate valve actuator (or valve positioner and actuator) smoothly in increasing and decreasing directions, and then we need measure the stroke value corresponding to each point, finally calculate the basic error between the actual "signal-stroke" relationship and the theoretical relationship. The maximum value is the basic error. The test points should include 0, 25%, 50%, 75%, and 100%. The basic error limit of the measuring instrument should be less than one fourth of the basic error limit of the tested regulating valve.
The maximum difference between the positive and negative travel measured on the same input signal is the hysteresis.
The basic error at the upper limit of the signal is the start point deviation; the basic error at the lower limit of the signal is the end point deviation.
The air operated gate valve chamber (or valve positioner and actuator) will be added to make the valve stem go the whole stroke. The ratio of the difference between the actual stroke and the rated stroke to the rated stroke is the rated stroke deviation. The actual stroke must be greater than the rated stroke.
The test medium is clean gas (air and nitrogen) or liquid (water or kerosene) at 10-50°C.
Test pressure A: When the allowable pressure difference of the regulating valve is greater than 350KPa, the test pressure is set at 350KPa; when it is less than 350KPa, the test pressure is set at the allowable pressure difference. The signal pressure of the pneumatic air actuator is zero, and the signal pressure of the pneumatic control valve actuator is input and added 20KPa to the upper limit of the signal. The signal pressure of the two-position globe valve with pneumatic actuator should be the design specified value.
Test pressure B: According to the maximum working pressure difference of the regulating valve, we can test directly. The test signal pressure should ensure that the air actuated solenoid valve is closed. The signal pressure of the actuator should be the designed value.
The test medium should be added into the air actuator valve according to the specified flow direction. The outlet of the regulating valve can be directly vented to the atmosphere or connected to the low-pressure head loss measuring device of the outlet to the atmosphere. Leakage can be measured after confirming that the valve and downstream connecting pipes are completely filled with the medium.
