What is the minimum flow velocity for a check valve?

There is no fixed value for the minimum flow rate of a check valve; it depends on the type, size, and design of the check valve. Generally, a check valve does not require a specific minimum flow rate to open fully, as it is usually pushed open by the fluid pressure. However, too low a flow rate may cause the valve to fail to remain fully open stably. Regarding the parameters you mentioned, with a flow velocity of 20 m/s and a medium density of 0.45 kg/m^3, this flow velocity is theoretically quite high, and it is usually sufficient to ensure that the vast majority of check valves open. However, whether a check valve can open fully also depends on the characteristics of the valve itself, including the spring load (if any), the weight of the valve disc, and the dynamic effects of the fluid. To ensure that the check valve remains fully open at low flow rates, you should select a check valve suitable for the operating conditions of your system and consult the manufacturer’s technical data. If there are strict requirements regarding pressure drop in the piping, you may need to consider check valves with low pressure drop, such as swing or wafer type check valves, and verify with the manufacturer whether these valves meet the requirements of your application. .