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Method of on-site debugging of control valves
After the installation of the control valve, on-site debugging of the control valve should be carried out before the production process is started. Only after the debugging is normal and then it can be put into use, and at the same time, the existing problems are found to solve as soon as possible. Of course, the cleaning of the pipeline before commissioning is also essential. The on-site debugging of the control valve is divided into line debugging and system debugging.
1. Line debugging
Line commissioning is used to check whether the signal line, air supply line or hydraulic line connected to the control valve are correctly connected.
1) Connection of the input signal of the control valve. Usually, check with the valve positioner. The input signal of the control valve comes from the controller. Therefore, a starting signal is output from the controller to check whether the control valve is at the starting position; an ending signal is output to check whether the control valve is at the ending position. For this reason, the pneumatic operated control valve should check whether the pressure of the air supply source is normal; whether the air set works normally; the hydraulic operated control valve should check whether the oil pressure supplied by the hydraulic system is normal; the electric operated control valve should check whether the power supply is normal; Whether the signal is correct, etc., and take at least 5 points within the measurement range to check whether the input signal and the valve position meet the required relationship. It should be checked whether the mode of action (Air to open or Air to Close)are correct and whether they meet the requirements of safe production in the process of production.
2) Connect the output signal of the control valve. The output signal of the control valve is the valve position signal, which can be an analog signal or a digital signal. While checking the input signal of the control valve, check whether the valve position signal is correct. When using HART or intelligent type valve positioners, check whether the valve position status information can be transmitted correctly. During the full-stroke operation of the control valve, listen for mechanical vibration and abnormal noise in the valve plug and seat of the control valve.
3) Commissioning of handwheel mechanism. Check whether the handwheel mechanism can rotate and move correctly and whether the limit and locking devices are easy to use.
4) When the deviation exceeds the allowable deviation limit, the corresponding debugging should be carried out. For example, change the position of the valve position switch, check the wiring or pipeline for leaks, and adjust the dead zone of the controller.
2. System Debugging
The control valve is the final element of the control system, therefore, the system needs to be debugged before the control valve runs. System debugging shall be carried out in coordination with technological operations.
1) Negative feedback debugging. The control system should meet negative feedback requirements. Therefore, the controller, detection transmitter, and control valve (including valve positioner) and the controlled object should be considered together, and the direct-acting and reaction of the controller should be set. The negative feedback criterion is that the total open-loop gain of the control system is positive. After setting direct-acting and reaction modes of the controller, you can simulate the input signal at the measurement end of the controller to increase or decrease it, observe whether the output change of the controller meets the requirements of the action mode, and check whether the movement direction of the control valve is correct and whether Can make the controlled variable change to decrease direction.
2) Check the pressure drop of the control valve. The pressure drop check of the regulating valve is carried out during the commissioning of clean water simulation. During the full-stroke operation of the control valve, check whether the pressure drop across the control valve changes, whether there is the noise caused by cavitation or flash evaporation, how the flow changes, and whether it meets the designed flow characteristics.
3) Check the response time. When some control systems have requirements on the response time of the control valve, the response time of the control valve should be checked. The timing starts when the output signal of the controller changes. The time required for the valve position of the regulating valve to reach 63% of the final steady state position is the response time, and the time should meet the operation requirements of the process production process.
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