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The main performance and test of the regulating valve
1.1 The main performance and test of pneumatic control valve
Pneumatic control valve performance indicators are: basic error, hysteresis, dead, always point difference, rated stroke deviation, leakage, sealing, pressure strength, appearance, rated flow coefficient, inherent flow characteristics, vibration resistance, operating life There are 13 items and the first 9 are factory inspection items. Due to factors such as the transportation of regulating valves and the adjustment of the working spring range, it is often necessary to adjust and test the following properties before installation:
1) The basic error will input the specified input signal steadily in the direction of increase and decrease into the actuator air chamber "or positioner", measure the corresponding stroke value of each point, calculate the actual "signal - stroke"; relationship and theoretical relationship The difference between the points. The maximum value is the basic error. Experimental points should include at least 5, 25%, 50%, 75%, 100% of these signal points. The basic error limit of the measuring instrument should be less than 1/4 of the basic error limit of the test valve.
2) The hysteresis test procedure is the same as described in point 1 above. The difference between the positive and negative strokes measured on the same input signal is the hysteresis.
3) Always point deviation method with the first point. The basic error at the upper limit of the signal (starting point) is the starting point deviation; the basic error at the lower limit of the signal (end point) is the end point deviation.
4) Rated stroke deviation Add the rated input signal to the pneumatic actuator's air chamber (or positioner) so that the valve rod is fully traveled. The ratio of the difference between the actual stroke and the rated stroke and the rated stroke is the rated stroke deviation. The actual trip must be greater than the rated trip.
5) Leakage test medium is clean gas (air and nitrogen) or liquid (water or kerosene) at 10~50°C; the test pressure A program is: when the allowable pressure difference of the valve is greater than 350KPa, the test pressure is made at 350KPa. When less than 350KPa, press the allowable pressure difference; B test procedure is done according to the maximum working pressure difference of the valve. The test signal pressure should ensure that the valve is closed. In the A test procedure, the signal pressure of the air-opening valve actuator is zero; the signal pressure of the air-closing valve actuator is the upper limit value of the input signal plus 20 KPa; the signal pressure of the actuator of the two-way valve should be the design specification value. In the B test procedure, the signal pressure of the actuator should be the design specification. The test medium should flow into the valve according to the regulations. The outlet of the valve can be directly connected to the atmosphere or connected to the low-pressure head loss measuring device at the outlet. After confirming that the valve and the downstream connecting pipes are completely filled with medium, leakage can be measured.
1.2 The main performance and test of electric control valve
The main performance indicators of electric control valve are: basic error, hysteresis, dead zone, rated stroke deviation, leakage, sealing, pressure strength, appearance, rated flow coefficient, inherent flow characteristics, resistance to vibration, temperature, long-term operating reliability , Explosion-proof, damping characteristics, power supply voltage variation, ambient temperature change, insulation resistance, dielectric strength, etc. The requirements and test methods of the first 10 indicators are the same or similar to those of the pneumatic valve. Among them, the basic error hysteresis, dead weight, leakage, sealing, appearance, damping characteristics, influence of power supply voltage change, and insulation resistance are the factory test items. The requirements and test methods for the performance indicators are:
1) Damping Characteristics The damping characteristics of the electric control valve are specified in the two directions of positive and negative strokes so that the valve stem does not exceed three "half-cycle" oscillations. The test method is to add 20%, 50%, and 80% of the input signal range value at the input end, and observe the “half-cycle” swing times of the valve stem at the corresponding positions of the positive and negative strokes.
2) When the supply voltage changes affect the power supply voltage of the electric control valve to change within the range of 220+20-30V, the change value of the displacement of the valve stem should not exceed 1.5% of the full stroke. Test method When the power supply voltage is 220V, add 20% of the signal range value at the input to measure the corresponding valve stem stroke value, then adjust the supply voltage to 190V and 240V and measure the corresponding stem stroke variation. Then add signals of 50% and 80% of the signal range values in order, and measure the valve stem stroke variation.
3〕 Insulation resistance When the ambient temperature is 10~35°C and the relative humidity does not exceed 85%, the insulation resistance of the electric control valve shall meet the following requirements: Each input terminal is not less than 20MΩ to the chassis; each input terminal is not less than the power supply terminal 50MΩ; power supply terminal to chassis is not less than 50MΩ. The test method is a 500 megohmmeter test.