How to set the delayed opening time of the air valve?

Hello Jing,

Which product are you using? HAMMER?

You can set the delay in air valve opening or closure by defining air flow curves. You can  use the custom air flow curve option to introduce this by setting the air flow rate to zero for negative pressures. See the below article for more details;

Modeling Reference - Air Valves

In the above article, refer the section titled Using a Custom Air Flow Curve

Hope this helps.

thank you !