What is valve control?
Control valves are devices that regulate fluid flow.
Control valves receive command signals from PID controllers in a PLC or DCS system.
Itopy valve positioners adjust the air flow of the tool based on the signal received from the PLC or DCS systems to the valve actuator.
This allows control of fluid flow through the valve and thus control of process variables such as pressure, temperature and level.
In simpler words, control valves are the main elements of the final control.
Read more: valve control, pneumatic valve control
List of tools required for valve control calibration
4-20mA calibrator or feeder source
Regulator to supply 3-15 PSI signal
Regulator to supply 20 psi
Pressure gauge (range 3-15 PSI)
HART Communicator
Valve control calibration method
A control valve must be calibrated in three steps:
Valve calibration is without accessories (i-ball positioner or pressure regulator).
The second method of valve control calibration is installed with a pneumatic positioner.
And the last step is the calibration of a control valve with Smart Valve Positioner.
All the methods mentioned above are slightly different from different brands based on specific needs.
Today, the method of calibrating a valve control with an intelligent positioner is a common method used in industries.
Before commencing work, obtain the appropriate work permits and notify the process engineers and disconnect the valve if necessary.
Put the PID controller in manual mode in PLC or DCS systems.
1-valve control calibration without accessories
To begin calibrating a control valve, it is important to determine its operating range, i.e., whether it is 3-15 PSI or a split range (3-9 PSI, or 9-15 PSI), as well as knowing the type of operation (using air pressed to close or open the valve)
After determining the operating range and type of operation of the valve, pressure simulation will be applied to calibrate it. This is nothing more than a stroke test to determine the full opening and closing of a control valve
- Now let’s calibrate a valve with 3-15 PSI, if the action is reverse (open air), the valve closes, slowly starts simulating the pressure and should start to open almost. 3 psi. The valve movement indicator should be at 0%.
- When we apply with 3 PSI, the valve will be at 0%. Next, we continue to apply 15 PSI, then the valve should open 100% and the stroke indicator will show full scale.
If there is a problem with the 0% and 100% calibration, then adjust the spring tension nut on the control valve until the desired value is reached.
The 0% and 100% checks are repeated as many times as necessary until the valve is properly calibrated.
Note: The above steps are done with the reverse valve (without closing the air).
The calibration of a direct valve (no venting) is done in reverse, ie at 15 PSI the valve should be closed while at 3 PSI it is fully open. The open and closed percentages also change inversely.
2-Pneumatic valve control calibration with i-topy positioner
- After calibrating the control valve without installing accessories, do it with one of them (Positioner).
To calibrate an automatic valve with a pneumatic positioner, an air regulator is mounted to the valve body or connected directly to the positioner and a 20 PSI air supply. Apply 3-15 PSI from a good regulator and it will send an opening signal to the valve.
With a 3 PSI signal the valve should be at 0%. If this is not the case with the zero screw, adjust the position of the valve so that it closes. - When the positioner sends an output of 15 PSI to the valve actuator, the valve sets its position to 100%. If not, adjust the opening screw to give the specified amount of opening.
As many times as necessary, these steps are repeated until the valve shows the correct reading, i.e. open and closed parameters. - After setting the percentages of 0% and 100%, intermediate values will be checked.
3-Valve control with intelligent positioner itopi calibration method
The method of controlling the valve with the calibration method of the smart positioner i-topi can also be called the electro-pneumatic positioner i-topi with a control valve.
- In the pneumatic positioner calibration method, this work is done mechanically and with control air.
As for the electro-pneumatic positioner, it works with a 4-20mA current signal and controls air through a valve actuator.
To check whether the valve is 0% open, 4 mA is simulated to the electronic positioner and this indicates the valve’s 0% position.
If this percentage of opening is not obtained, then connect the HART communicator to the valve positioner and begin calibration.
- To check 100% opening, 20mA is simulated and this indicates 100% valve status. If there is a problem, connect the HART communicator to the valve positioner and then start the calibration.
In some control valves, a display and control buttons are provided to you.
You can use these to check the status of the positioner iTopy and you can also start calibration. (no need for HART communicator)
Once the 0% and 100% percentages are calibrated, intermediate values will also be validated, such as 8 mA -> 25%, 12 mA -> 50% and 16 mA -> 75%.
Valve control percentage opening table
Air to open: The pneumatic valve control is held close by spring force, and a pneumatic signal causes it to open. Also called reverse action.
Air to close: The air to close control valve requires a pneumatic signal to move to the closed position. Also called direct action.
AFR: AFR stands for Air Filter Adjuster. AFR is used to adjust the air requirement of the instrument to the control valve.
Summary
There is no doubt that having a well calibrated valve control is very important for any industrial process.
Without proper calibration, you may end up with costly mistakes and lower performance. Valve control calibration is an important process in the industry.
Calibrating a control valve ensures that the valve is operating at maximum efficiency.
This in turn leads to better overall performance in the industry process. Having a properly calibrated control valve can save time and money by optimizing the process.
Kiasanat is a supplier of all types of valve controls, Samson valve controls, Fisher valve controls, Samson three-way valve controls, Masonilan valve controls, Honeywell valve controls, Yoshitaki valve controls, etc.
Masoneilan Positioner Model 8012
