What is the relationship between a valve’s flow rate and velocity?

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The flow rate and velocity of a valve depend primarily on its diameter, as well as on the resistance exerted by the valve’s structure on the medium. They are also closely related to factors such as the valve’s pressure, temperature, and the concentration of the medium. What is the relationship between the two? The flow area of a valve is directly related to the flow velocity and flow rate, and flow velocity and flow rate are two interdependent quantities. When the flow rate is constant, a higher flow velocity allows for a smaller cross-sectional area of the flow channel ； With a low flow rate, the flow channel area can be larger. Conversely, the larger the flow channel area, the lower its flow velocity ； The flow channel has a small area, resulting in a high flow velocity. When the flow rate of the medium is high, the valve diameter can be smaller, but the pressure loss is greater and the valve is prone to damage. High flow rates can generate static electricity in flammable and explosive materials, posing a danger ； The flow rate is too low, resulting in low efficiency and poor economic viability. For media with high viscosity and explosiveness, a lower flow rate should be used. For oils and liquids with high viscosity, the flow rate is selected based on their viscosity, typically ranging from 0.1 to 2 m/s. Under normal circumstances, the flow rate is known, and the flow velocity can be determined empirically. The nominal diameter of a valve can be calculated from the flow rate and volume flow. When the valve diameters are the same but their structural types differ, the flow resistance also varies. Under the same conditions, the greater the resistance coefficient of the valve, the more the flow velocity and flow rate of the fluid passing through the valve decrease ； The lower the valve resistance coefficient, the less the flow velocity and flow rate of the fluid passing through the valve decrease.