The flow and velocity of the electric regulating valve mainly depend on the diameter of the electric regulating valve. It is also related to the resistance of the electric regulating valve to the medium. At the same time, it has a certain connection with the pressure, temperature and concentration of the medium of the electric regulating valve. 

The flow channel area of the electric regulating valve is directly related to the flow rate and flow rate, and the flow rate and flow rate are two quantities that are mutually dependent. When the flow rate is necessary, the flow rate is large, the flow channel area can be smaller; the flow rate is small, the flow channel area can be larger. On the contrary, the flow channel area is large, its flow velocity is small; the flow channel area is small, its flow velocity is large.

The flow rate of the medium is large, the diameter of the electric regulating valve can be smaller, but the resistance loss is larger, and the electric regulating valve is easy to be damaged. If the flow velocity is large, it will have electrostatic effect on the flammable and explosive medium, posing a risk; the flow velocity is too small, the efficiency is low, and it is not economical. For the medium with high viscosity and explosive, the flow rate should be smaller. The flow rate of oil and liquid with high viscosity is selected according to the viscosity, usually 0.1~2m/s.

Under normal conditions, the flow rate is known, and the flow rate can be confirmed by experience. After the flow rate and flow rate, the nominal diameter of the electric regulating valve can be calculated.

Electric regulating valves have the same diameter, different structural styles, and different fluid resistance. Under the same conditions, the larger the resistance coefficient of the valve, the more the flow rate and flow drop of the fluid passing through the valve; the smaller the resistance coefficient of the valve, the less the flow speed and flow drop of the fluid passing the valve.

The selection of valve diameter should take into account the machining accuracy and size deviation of the valve, as well as the influence of other factors. The valve diameter should have a margin, usually 15%. In theoretical work, the valve diameter depends on the diameter of the process pipeline.