What should be done to the torch valve before adjusting the working pressure on the regulator?

Before adjusting the working pressure on the regulator, the torch valve should be opened. This practice is essential because it allows for the safe adjustment of the pressure without any pressure build-up in the system that could lead to inaccurate settings or even accidents. When the torch valve is opened, gas can flow freely, which helps to ensure that the regulator can accurately reflect the desired pressure setting.

By opening the torch valve, the user can also effectively purge the system of any old gas and ensure that the pressure gauge is reading the actual conditions under which the system will operate. This step is critical for both safety and performance, ensuring that the welding equipment is set up correctly and ready for use.

Other actions, such as closing the valve or disconnecting the torch, would not allow for this accurate adjustment and could lead to potential safety hazards or equipment malfunctions when the torch is eventually lit. Calibrating the torch is also not required at this stage, as that process involves adjusting for accuracy, which is separate from the task of setting the working pressure.