Piercing-type valves should only be used on which tubing materials?

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Piercing-type valves are designed to pierce the refrigerant tubing and create a access point for charging or testing. The tubing material needs to be soft and ductile enough to allow a clean hole to form without cracking or deforming around the piercing point. Copper and aluminum meet that requirement, making it possible to pierce reliably and seal effectively. Steel tubing, being much harder and more rigid, is prone to cracking, galling, or failing to pierce cleanly, which can lead to leaks or damage. For this reason, piercing-type valves should only be used on copper and aluminum tubing.