Valve flow rate and flow rate depends mainly on the valve diameter, but also with the valve structure of the medium resistance, at the same time with the valve pressure, temperature and the concentration of the medium and other factors have a certain intrinsic relationship. The flow channel area of the valve is directly related to the flow rate and flow rate, and the flow rate and flow rate are two of the interdependence. When the flow rate is large, the flow path area can be smaller, the flow rate is small, the channel area can be bigger. On the contrary, the flow channel area is big, its velocity is small, the flow path area is small, its flow rate is big. The medium flow rate is big, the valve diameter may be smaller, but the resistance loss is big, the valve is apt to damage. The flow rate is large, the electrostatic effect of flammable and explosive medium will be caused, the flow rate is too small, the efficiency is low, the economy is not economical. For viscous and explosive medium, a small flow rate should be taken.

Oil and viscosity of the liquid with the viscosity of the choice of flow rate, generally take 0.1~2m/s.

Generally, the flow is known and the flow rate can be determined by experience. The usual flow rate of various mediums is shown in table 2-2.

The nominal diameter of the valve can be calculated by flow rate and flow rate. Valve size is the same, the structure of different types of fluid resistance is not the same. Under the same conditions, the greater the resistance coefficient of the valve, the flow of fluid through the valve, the flow rate decreased more; the smaller the valve drag coefficient, the flow of fluid through the valve flow rate, less.