What is the purpose of using an inert-gas purge during brazing or welding of B28 systems?

• A. To reduce energy consumption.
• B. To prevent ignition by displacing air and flammable vapors from the joint area.
• C. To introduce moisture into the joint.
• D. To cool the joint during welding.

Answer: (B)

The main idea is preventing ignition in a joint being brazed or welded on a flammable-refrigerant system. When you heat a joint that may be holding or exposed to flammable refrigerant vapors, there’s a real risk that any sparks or hot metal could ignite those vapors. Purging with an inert gas sweeps air and any flammable vapors out of the joint area and replaces it with a nonreactive atmosphere. By displacing oxygen and fuel vapors, the environment around the weld becomes effectively inert, so even if a torch or spark is present, there isn’t enough oxidizer or fuel vapor to support combustion. This purge is kept active during the heat process to maintain that safe atmosphere, and it’s not about cooling the joint, reducing energy use, or introducing moisture.