Description of adjustable ratio of pneumatic control valve
In the automatic control process, 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. It causes very large losses and increases labor intensity. Therefore, people pay more and more attention to the selection and use of pneumatic control valves.
The accuracy of the control of the pneumatic control valve can be expressed through changes in the energy and flow of the material flow. The regulating control energy of the regulating valve can be judged by the adjustable ratio, which refers to the ratio of the large flow and the small flow that the regulating valve can control when the differential pressure on both sides of the regulating valve is a fixed value. 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 lower the adjustable ratio and the smaller the control ability. When the above regulating valves are operated in parallel and at the same time, the degree of bypass needs to be paid attention to. In actual production, in addition to the regulating valve, there are other pipelines, so the pressure difference before and after the regulating valve will change, which is called the operating flow characteristic. There are linear valves, equal percentage valves and parabolic valves in detail. Among them, equal percentage valves are widely used and have strong adaptability.
The selection of pneumatic control valves needs to be reasonably selected according to the characteristics of the medium, the control requirements, and the installation environment in combination with its own flow characteristics and structure. In addition to these considerations, we also need to consider the way of the valve cover and the selection of packing.
The main contents of daily maintenance of pneumatic control valve should include the following items:
1. The inner wall of the valve. Check its pressure and corrosion resistance.
2. Valve seat. Due to the infiltration of the medium, the inner surface of the thread for fixing the valve seat is susceptible to corrosion and the valve seat is loosened. Pay attention to it when inspecting. For high-pressure occasions, check whether the sealing surface of the valve seat is damaged.
3. Spool. It is necessary to carefully check whether each part of the spool is corroded and worn, especially when the spool wears more seriously under the condition of high pressure difference, you should pay attention to it. In addition, check whether the valve stem has similar phenomena, or the connection with the valve core is loose.
