On site commissioning method of control valve

On site commissioning method of control valve

After the installation of the control valve, the on-site commissioning of the control valve shall be carried out before the start-up of the production process. The control valve can be put into use only after the commissioning is normal. At the same time, the existing problems are found so as to solve them as soon as possible. Of course, pipeline cleaning before commissioning is also essential. The on-site commissioning of control valve is divided into line commissioning and system commissioning.

1、 Line commissioning

Line commissioning is used to check whether the signal line, air supply pipeline or hydraulic pipeline connecting the control valve are correctly connected.

1.1 Connection of control valve input signal. Normally, check with the valve positioner. The input signal of the control valve comes from the controller. Therefore, a starting point signal is output from the controller to check whether the control valve is at the starting point position; Output an end signal and check whether the control valve is at the end position. Therefore, for pneumatic control valve, check whether the air supply pressure is normal; Whether the filter pressure reducer works normally; The hydraulic control valve shall check whether the oil pressure supplied by the hydraulic system is normal; Check whether the power supply of the electric control valve is normal; Whether the output signal is correct, etc., and take at least 5 points within the measurement range to check whether the required relationship between the input signal and the valve position is met. Check whether the action mode of gas on and gas off is correct and meets the safety production requirements of the process production process.

1.2 Connection of control valve output signal. The output signal of control valve is valve position signal, which can be analog signal or digital signal. Check whether the valve position signal is correct while checking the input signal of the control valve. When Hart or intelligent electric valve positioner is used, check whether the valve position status information can be transmitted correctly. During the full stroke operation of the control valve, the valve core and valve seat of the control valve shall be monitored for mechanical vibration and abnormal noise.

1.3 Commissioning of hand wheel mechanism. Check whether the hand wheel mechanism can rotate and act correctly, and whether the limit and locking device is easy to use.

1.4  When the deviation exceeds the allowable deviation limit, corresponding commissioning shall be carried out. For example, change the position of the valve position switch, check whether there is leakage in the wiring or pipeline, and adjust the dead zone of the controller.

2、 System debugging

The control valve is the final component of the control system. Therefore, the system commissioning shall be carried out before the operation of the control valve. System commissioning shall be carried out in cooperation with process operation. 

2.1 Negative feedback commissioning. The control system shall meet the negative feedback requirements. Therefore, the controller, detection transmitter and control valve (including valve positioner) shall be considered together with the controlled object, and the positive and negative reactions of the controller shall be set. The negative feedback criterion is that the total open-loop gain of the control system is positive. After setting the positive and reaction modes of the controller, the input signal can be simulated at the measuring 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 action direction of the control valve is correct and whether the controlled variable can change in the decreasing direction. 

2.2 Pressure drop inspection of control valve. The pressure drop inspection of control valve shall be carried out during clean water simulation commissioning. During the full stroke operation of the control valve, check whether the pressure drop at both ends of the control valve changes, whether there is noise caused by cavitation or flash, how the flow changes, and whether it conforms to the designed flow characteristics.

2.3 Response time check. When some control systems have requirements for the response time of the control valve, the response time of the control valve shall be checked. Start timing when the output signal of the controller changes, and the time required to reach 63% of the final steady-state position of the control valve is the response time, which shall meet the operation requirements of the process production process.