Suppose here we want to calibrate an Air to Close control valve. In other words, just set its bench set. Note that the bench set is set without a positioner and the positioner should be calibrated before setting the bench set. Use a calibration standard to see how much pressure is applied to the actuator.
The calibration steps are as follows:
The first step in setting up is to start moving the stem:
If the start of movement of the stem does not occur at a pressure lower or higher than the desired pressure, you must adjust the spring by turning the adjusting screw. By turning the Spring adjustor counterclockwise, the actuator spring compression will be reduced. In fact, it causes motion to occur even at a lower load pressure. By turning the Spring adjustor clockwise, the actuator spring compression will increase. For an actuator with a diaphragm pressure range of 1-2 kg / cm 2, the valve must be ready to move at a pressure of 0.2 kg / cm 2 and start moving at 0.22 kg / cm 2 .
At this point we want to adjust the high value of the actuator range:
To do this, first loosen the stems behind the stem and loosen the screws on the stem connector. Then increase the pressure applied to the diaphragm chamber and reach a high value of the actuator range. At the same time, watch the movement of the valve. Make sure that the valve plate is sitting on the seat ring. If the stem movement is not enough and the plug is not on the seat, we should screw the valve plug stem into the stem connector. To rotate the stem, a French wrench can be placed on the nuts behind the stem and rotated. Note that when the plug is placed on the seat, you should not rotate the stem in any way. Because by doing so, you will damage the plug or the seat. When the stem movement is well adjusted, lock the stem connector, tighten the cap screws and close the nuts on the back of the stem.
- If our valve control is Air to Close, when the maximum stroke pressure is applied to the actuator, the travel indicator and scale indicator should indicate the valve is closed, and when no pressure is applied to the diaphragm, the Travel indicator and scale indicator should indicate the valve is open. If the Travel indicator and scale indicator do not show these conditions correctly, you must loosen the screws and the scale indicator and move it so that the open and closed position of the valve can be shown accurately.
- It should be checked again after the control valve is installed and connected to the controller. You should check for things like correct movement, no friction, no leakage, proper performance, and compliance with the controller.
The steps mentioned above are a general method for calibrating the control valve. But it can be done in a simpler and more practical way. In the following, the practical calibration method for controlling ATO valves, ATC is briefly described.
Practical steps to calibrate the Air To Open lull control:
Follow the steps below to calibrate an Air To Open valve control. Here we assume that our actuator range is 0.2-1 kg / cm 2 . In fact, with a pressure of 0.2 kg / cm 2, the valve is completely closed and ready to move. And with the application of 2 kg / cm, the valve opens completely.
- Connect the calibration equipment to each other with suitable tubes and fittings as shown below. As you can see, in this arrangement, a suitable pressure regulator has been used to adjust the desired pressure. The pressure gauge is also responsible for displaying the pressure applied to the actuator.
- First open the nuts on the back of the stem and then open the cap screws to open the stem connector. This separates the actuator stem from the plug stem.
- Spring adjustor t Akchvytvr set to shoot in kg / cm 2 2 ready to move in and kg / cm 2 0.22 began to move. This is usually an iterative process and should be Spring adjustor several times to loosen and tighten up the Achieve the desired result.
- Put the plug on the seat, but due to the compression of the stem by packing, this is usually difficult work and requires a lot of force. You can first apply a pressure of 1 1 kg / cm to the actuator and place a piece of wood and copper metal between the two actuator shafts and the plug stem and then remove the pressure from the actuator. Due to the actuator spring force, the actuator stem pushes the plug stem down with high force and places the plug on the seat well. Then a pressure kg / cm 2 1 Akchvytvr imposed on a piece of wood or metal and copper checkbox.
- Air pressure kg / cm 2 22 to Akchvytvr apply. Close the stem connector and tighten the cap screws. This connects the plug stem to the actuator stem. Finally, tighten the back nut nuts under the stem connector. Applying air pressure of 0.22 kg / cm 2 instead of 0.2 kg / cm 2 is due to the fact that even when closed, it can operate as a Tihgt shutoff.
- Set the Travel indicator and scaleindicator to show the open and closed status of the valve correctly.
- Check the valve movement with a pressure of 2 kg / cm 2 to 2 kg / cm 2 and test the points 0%, 25%, 50%, 75%, 100%.
Practical steps of calibrating an Air to Close valve control:
Follow the steps below to calibrate an Air to Close valve control. Here we assume that our actuator range is 0.2-1 Kg / cm 2 . In fact, with a pressure of 0.2 Kg / cm 2, the valve is completely open and ready to move. And by applying 1 Kg / cm, 2 valves are completely closed.
- Connect the calibration equipment to each other with suitable tubes and fittings.
- First open the nuts on the back of the stem and then open the cap screws. To open the stem connector. This will separate the actuator stem from the plug stem (although it is better to apply a pressure of 5 Kg / cm 2 to the actuator before opening the cap screws, because this will remove the spring pressure from the stem and the stem connector and the cap screws will open more easily. .)
- Batnzym Spring adjustor something that stalk Akchvytvr in Kg / cm 2 2 and ready to move in Kg / cm 2 0.22 began to move. This is usually a repetitive process and you have to loosen and tighten the Spring adjustor several times to achieve the desired result.
- Place the plug on the Seat. Of course, due to the compression of the stem by packing, this is usually a difficult task and requires a lot of force. You can place a piece of wood or a piece of copper metal between the two stems of the actuator and the stalk of the plug and apply a pressure of 1 Kg / cm 2 to the actuator so that the plug fits snugly on the seat. Then remove the pressure from the actuator and remove the piece of wood or copper metal.
- Apply air pressure of 98 kg / cm 2 to the actuator. By doing this, the actuator stem moves and approaches the end of its range of motion. Now close the Stem connector and tighten the cap screws. This connects the plug stem to the actuator stem. Finally, tighten the back nut nuts under the stem connector. Applying an air pressure of 0.98 Kg / cm 2 instead of 1 Kg / cm 2 is due to the fact that even when closed, it can act as a tight shot.
- By setting the Travel indicator and scale indicator, make sure that the open and closed status are displayed correctly.
- Check the movement of the valve with a pressure of 2 Kg / cm 2 to 1 Kg / cm 2 and test at points of 100%, 75%, 50%, 25%, 0%.
Valve Position Calibration:
Positioner is a device that is installed on the valve control and puts the valve in the desired position. A positioner is usually installed on the valve controls because by installing it on the valve control, the response is faster. Also, when the process pressure changes, the positioner helps the movement length of the valve to be proportional to the controller signal, and eventually the valve to reach the desired position. Therefore, if the valve control is equipped with a positioner, after calibrating the valve control itself and in fact bench setting it, the positioner should be installed on the actuator and calibrated.
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