The regulating valve is used to regulate the flow, pressure and liquid level of the medium.According to the signal of the adjustment part, the opening of the valve is automatically controlled to achieve the adjustment of the medium flow, pressure and liquid level.
Control valveElectric control valves such as electric control valves, pneumatic control valves and hydraulic control valves are important executive unit instruments in industrial automation process control.With the increasing degree of automation in the industrial field, it is being used more and more in various industrial production fields.Compared with the traditional pneumatic control valve, it has obvious advantages: energy saving (consumption of electricity only when working), environmental protection (no carbon emissions), quick and convenient installation (no need for complicated pneumatic pipelines and air pump workstations).Pneumatic control valve uses compressed air as power source, cylinder as actuator, and uses electrical valve positioners, converters, solenoid valves, retaining valves and other accessories to drive the valve to achieve on-off or proportional adjustments and receive industrial The control signal of the automation control system completes the adjustment of various process parameters such as the flow rate, pressure and temperature of the pipeline medium.Pneumatic control valve is characterized by simple control, fast response, and intrinsically safe. It does not require additional explosion-proof measures. The history of automatic control valve can be traced back to self-operated pressure regulating valve, which includes a spherical valve with a heavy rod. The object is used to balance the force of the spool, thereby obtaining a certain degree of adjustment. Another early form of self-operated pressure regulating valve is a pressure balanced pressure regulating valve.The pressure of the process is connected to the diaphragm air chamber of the spring diaphragm pressure regulating valve by pipeline.Regardless of whether it is a pressure reducing valve, a post-valve pressure regulator or a differential pressure regulator, it can be manufactured from the change of this basic valve. Flow capacity Cv is one of the main parameters for selecting a regulating valve.
Control valveThe flow capacity is defined as: when the regulating valve is fully opened, the pressure difference between the two ends of the valve is 0.1MPa, and the fluid density is 1g/cm3, the flow rate of the flow diameter regulating valve per hour is called the flow capacity, also called the flow coefficient. , Expressed in Cv, the unit is t/h, and the Cv value of the liquid is calculated by the following formula.Check the table according to the flow capacity Cv value, you can determine the nominal diameter DN of the regulating valve. The flow characteristic of the regulating valve is that the relative flow of the medium flowing through the regulating valve and its opening under the condition that the pressure difference between the two ends of the valve remains constant. The relationship between degrees.
Control valveThere are three types of flow characteristics: linear characteristics, equal percentage characteristics and parabolic characteristics.The meanings of the three fluence characteristics are as follows: (1) The parabolic characteristic flow changes in proportion to the two sides of the stroke, and generally has the intermediate characteristics of linear and equal percentage characteristics. (2) Linear characteristic (linear) The relative stroke and relative flow of the linear characteristic have a linear relationship.The flow change caused by the change of unit stroke is constant.When the flow is large, the relative value of the flow changes little, and when the flow is small, the relative value of the flow changes greatly. (3) Equal percentage characteristic (logarithm) The relative stroke and relative flow of equal percentage characteristic are not in a straight line. The change of flow caused by the change of unit stroke at each point of the stroke is proportional to the flow at this point, and the percentage of flow change Are equal.So its advantage is that when the flow is small, the flow change is small, and when the flow is large, the flow change is large, that is, it has the same adjustment accuracy at different opening degrees.From the analysis of the above three characteristics, it can be seen that in terms of its adjustment performance, the equal percentage characteristic is the best, its adjustment is stable and the adjustment performance is good.The parabolic characteristic is better than the linear characteristic. Any one of the flow characteristics can be selected according to the requirements of the use occasion.
