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Pneumatic control valve debugging

 Pneumatic control valve debugging by valve supplier.

Pneumatic Drive Type Butterfly Valve before use, focus on the spring preload, neutral point, E/P converter, locator, etc., to meet the valve stroke, valve displacement linear, switching time, leakage and other performance indicators. Before commissioning, (1) the process pipeline must be purged strictly; (2) the handwheel mechanism should be in the "release" position; (3) check whether the pressure of reducing valve air supply meets the gas supply requirements.

1. BenchSet adjustment method

To prevent the valve from closing or opening, the actuator must be adjusted before it is installed into the valve body.

According to the upper and lower limits of pre-tightening force required by the valve nameplate, a simple special adjustment tool is used to adjust the initial spring force.

Open and close the valve several times by inflating the exhaust to ensure smooth movement of the pneumatic head.

Press the pneumatic head, record the pressure just moved by the pneumatic head connecting rod and compare it with the lower limit of pre-tightening force on the valve nameplate, adjust the spring pre-tightening force adjusting nut until the pressure reading when the pneumatic head connecting rod just moved is the lower limit.

Continue to increase the pressure to the upper limit and mark the stem as the pneumatic head link moves to the end of the body.

Slowly pneumatic air pressure drop back to the lower limit value, record the valve stem tags, the distance to the pneumatic head end of the connecting rod with the valve nameplate schedule is consistent, if consistent, adjusting spring pre-tightening force and prove that the valve closed or open enough force in natural state, or need to replace the spring, reinstall and according to the above steps to carry on the adjustment of the pre-tightening force.

2. Setting of NEUTRALPOINIT

The neutral point is that the handwheel is adjusted to the position that does not affect the automatic adjustment. It may be a point or an area. Too high a neutral point will cause internal leakage, and too low a setting will easily lead to insufficient flow. Usually valve isolation or automatic failure, often by destroying the neutral point of pneumatic control valve to achieve the valve fully open, fully closed or maintain a certain degree of opening. Usually have only need to handle the neutral point of roller skating piece of the neutral point of a pointer on the scale on the neutral line, also can be adjusted by hand ", loss of air pressure to open the pneumatic valve "neutral point set, should make the pneumatic valve in a loss of air pressure, full open position the handwheel clockwise in the direction of the clearance of rotating until feel resistance under the instructions manual lever to guide bush check, and then counter-clockwise 1/2 circle rotate in the direction of the open"; Set the neutral point of the pneumatic valve in the direction of deaeration and turn the handwheel counterclockwise to the open direction until the resistance is felt, indicating that the manual rod reaches the stop position of the guide sleeve, and then rotate 1/2 turn clockwise to the direction of the close. Adjust to the neutral point position with the hand wheel lever lock lock.

3. Check electrical converter (E/P)

The current source is used to provide 4mA ~ 20mA dc current signal, and the SAR provides compressed air.

Take the positive action pneumatic control valve as an example to carry on the following adjustment, its output pressure must meet the precision requirements.

Zero adjustment, input 4mA current signal, turn the zero adjustment screw to read the pressure gauge data until the output pressure is 20kPa.

Adjust range, input 20mA current signal, adjust range adjustment screw until output pressure 100kPa.

Linear check, input 8, 12, 16mA, output pressure is 40, 60, 80kPa.

Repeat until the precision requirement is met.

4. Check valve positioner

Take the pressure signal of 20kPa ~ 100kPa from E/P converter as the input signal of the locator. First open the air source of the locator to check the smooth operation of the locator.

Adjust the input signal to half of the range, open the air source, then the locator rotating arm should be in the horizontal position, the valve should be 50% open, otherwise check whether there is a leak or whether the locator CAM installation is proper.

Adjust zero so that the positioner is entered at zero, loosen the nozzle lock screw, and adjust the nozzle until the valve corresponds to the fully closed (or fully open) position.

Adjust the range so that the positioner input is full, adjust the position of nozzle baffle, so that the valve corresponds to the full open (or closed) position.

Check whether the valve meets the requirements of 0%, 25%, 50%, 75% and 100% opening at the input pressure of 20, 40, 60, 80 and 100kPa respectively, or make repeated adjustment.

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