What should you do when changing pneumatic tools close the air supply valve and what?

When changing pneumatic tools, always close the air supply valve to prevent accidental activation of the tools and ensure safety. After closing the valve, relieve the pressure in the system by either using the tool briefly or activating the pressure relief valve, if available. This step ensures that there is no residual pressure in the lines, reducing the risk of injury during the tool change. Finally, check the connections and fittings before re-opening the air supply valve.