Compression fittings used with copper or plastic tubing seal by means of what?

Compression fittings are designed to create a tight and secure seal between copper or plastic tubing and the fitting itself. The sealing mechanism involves compressing a beveled gasket or seal against the surface of the pipe or tubing.

When the compression nut is tightened, it pushes the compression ring or sleeve onto the pipe or tubing. This action compresses the beveled gasket, creating an effective watertight seal. The beveled edge helps ensure that the connection is not only secure but also resistant to leaks under pressure.

In contrast, other sealing methods like a screw cap involve threading and do not provide the same level of direct compression on the pipe surface, while welded joints rely on melting the materials together, and plastic sleeves do not effectively create the same type of sealing action as a compressed gasket in a compression fitting. Thus, the correct choice highlights the specific mechanism of action that makes compression fittings effective in sealing applications.