The regulating valve is directly installed on the process pipeline, the use of poor conditions, such as high temperature and pressure, deep freezing, extremely toxic, flammable, explosive, easy to penetrate, easy to crystallize, strong corrosion and high viscosity, its quality directly affects the quality of the system. Thus affect the quality of the final product and the efficiency of the system operation. Problems can occur if not properly selected or maintained. For example, some regulating circuits are not stable: they oscillate all the time, and if the selection is improved, the quality of regulation is greatly improved after changing the linear characteristic spool to the logarithmic characteristic spool or changing the flow direction. For example, some continuous oscillations occur in the adjustment process, not because the proportion of the regulator is too large or too small, but because the dry friction of the valve stuffing box is too large, and the action is not flexible. For example, the leakage of the regulating valve will cause factory pollution and even cause accidents. Therefore, attention should be paid to the role of the regulating valve, and maintenance and maintenance should be strengthened. What are the problems with manual control?
Above is a schematic diagram of a manually controlled level. The liquid continuously flows through the inlet valve 2 into the storage tank 1, and continuously flows out through the outlet valve 4. We can see that the liquid level in the tank will fluctuate with the inflow or outflow. When the fluctuation is serious, the liquid in the tank may overflow or be evacuated. To solve this problem and keep the level within a certain range, the simplest way is to install a glass tube level gauge 3. With the upper and lower limits of the level gauge as the standard, when the liquid level rises to close to the upper limit scale, you can open the export valve, or close the inlet valve opening; When the liquid level drops to the lower limit scale, you can close the outlet valve or open the opening of the inlet valve, so as to avoid the tank overflow due to excessive liquid level, or because of the liquid level down and the evacuation of the accident occurred, so that the liquid level remains within a certain range. This process is directly controlled by people, so it is called manual control. It can be seen that manual control has at least the following problems and thus cannot meet the requirements of modern industry for process control. 1. Poor control accuracy. When the liquid level requirements are more accurate, that is, the upper and lower limits of the liquid level change range requirements are small, because of human reflection to manual operation there is a process, resulting in excessive liquid level control. 2. Slow response time. 3. Fatigue failure.
The pneumatic regulating valve is to use compressed gas as the power source, the cylinder as the actuator, and drive the valve with the help of valve positioner, converter, solenoid valve, position valve, gas storage tank, gas filter and other accessories to realize the switching quantity or proportional adjustment, and receive the control signal of the industrial automation control system to complete the regulating pipeline. Medium: flow, pressure, temperature, liquid level and other process parameters. The characteristics of pneumatic regulating valves are simple control, fast response, and intrinsically safe, and there is no need to take additional explosion-proof measures.
The International Electrotechnical Commission IEC defines the control valve (known as Control Valve in foreign countries) as: "The terminal component formed by a power-operated device in the industrial process control system, which includes a valve body component. There is a component inside that changes the flow rate of the process, and the valve body component It is also connected with one or more executive agencies. The actuator is used to respond to the signals sent by the control. It can be seen that the regulating valve is composed of two parts: the actuator and the valve body parts, namely:
Regulating valve = actuator + valve body parts + accessories
Among them, the actuator is the propulsion device of the regulating valve, which generates a corresponding thrust according to the size of the signal pressure, so that the putter produces a corresponding displacement, thus driving the core action of the regulating valve; the valve body component is the regulating part of the regulating valve, which is directly in contact with the medium and changes the joints of the regulating valve through the displacement of the putter rod of the actuator. Flow area, to achieve the purpose of adjustment.