Cylinder valves on propane and oxygen cylinders should be ____________________ when in use.

Cylinder valves on propane and oxygen cylinders should be open all the way when in use to ensure a consistent and adequate flow of gas. Fully opening the valve allows for maximum gas delivery pressure, which is critical for generating the temperatures needed in thermite welding and similar applications. If a valve is only partially opened, it can restrict the flow, leading to inadequate combustion or unstable flames, which may compromise safety and the quality of the welding process. Therefore, fully opening the valves ensures that the equipment operates efficiently and safely under the intended conditions.