What to do if the pneumatic control valve is not closed tightly
Pneumatic control valve is composed of pneumatic actuator and control valve. Firstly, the pneumatic actuator transmits signals through the control system, and drives the control valve spool to adjust the flow, pressure, and temperature of the process device, so sometimes it is inevitable. In use, it will be closed and not tightly closed.
1. When the output force of the pneumatic actuator is insufficient, the pneumatic actuator is the power part that drives the action of the regulating valve spool. Its output force is greater than the force required when the valve is closed, otherwise it will not be tightly closed, so why does it appear? In this situation, the valve core is pushed open by the pressure of the medium, and the pneumatic control valve will cause internal leakage. How can we avoid this accidental situation? Therefore, users must pay attention to it and verify when selecting the model. The pressure difference value of the process pipeline, while ensuring that the pneumatic actuator has a satisfactory output force to close the valve.
2. The incorrect selection of the control valve will also cause the problem of lax closing. Each standard control valve has a different standard pressure difference. The sleeve control valve and the double-seat control valve allow a larger pressure difference than the single-seat control valve. , The angular travel V-shaped regulating ball valve and the eccentric rotary valve allow a larger pressure difference. Under the condition of relatively large pressure difference, then for the reasonable selection of pneumatic regulating valves, electric regulating valves are extremely important.
In the process of automatic control, if the quality of the pneumatic control valve is not closed, the automatic control process will lose its high-quality adjustment. Poor flow characteristics will affect the quality of the adjustment. Large leakage and unreliable action will make the adjustment ineffective, which will affect the production process. The formation of a very large loss of labor, increasing labor intensity, so the selection and use of pneumatic control valves have attracted more and more attention.
The accuracy of the control of the pneumatic control valve can be expressed by the change of the energy and flow of the flow. The control energy of the control valve can be judged by the adjustable ratio. The adjustable ratio refers to the difference between the two sides of the control valve when the control valve pressure is a fixed value. The ratio of the large flow and the small flow that the regulating valve can control. When the regulating valve is used in series pipelines, the adjustable ratio is proportional to the square root of the pressure drop ratio. When used in parallel pipelines, the larger the bypass flow, the adjustable ratio Decrease, the smaller the control ability, when there are 2 or more control valves in parallel and working at the same time, you need to pay attention to the degree of bypass, in actual production, in addition to the control valve, there are other pipelines, so the pressure before and after the control valve The difference will change, which is called the working flow characteristic. Specifically, there are linear valves, equal percentage valves and parabolic valves. Among them, equal percentage valves are widely used and have strong adaptability.
