Victaulic plain end couplings should not be used with which types of pipes?

Victaulic plain end couplings are specifically designed to connect pipes that have plain ends. These couplings work by utilizing a groove on the pipe ends to create a mechanical joint, which is particularly suited for grooved pipes, allowing for easier installation and flexibility in the piping system.

When considering the types of pipes that should not be used with Victaulic plain end couplings, we find that threaded pipes are not compatible. Threaded pipes use threads on their ends to create seals and connections, which differ significantly from the plain ends that these couplings are designed for. The absence of grooves means that you cannot effectively employ a Victaulic coupling, as it relies on those grooves to maintain the connection between pipes.

Additionally, coupling connections for threaded pipes typically utilize different methods, such as threaded fittings, which create a mechanical seal based on the threads rather than the grooved mechanism of the Victaulic coupling. Therefore, it's essential to match the type of connection to the appropriate fitting to ensure a secure and leak-free joint. This is why the choice involving threaded pipes is correct for not being suitable with Victaulic plain end couplings.