Which type of fittings shall not be used unless for introducing lines at the top of the tank?

Compression fittings should be used with care in fuel oil systems due to their design and function. They are typically utilized to create a tight seal without the need for soldering or welding. However, when it comes to oil fuel systems, compression fittings can introduce potential leak points and are generally not recommended for most applications. Their use is limited to specific situations, such as when introducing lines at the top of a tank, where the risk of leaks can be more easily managed.

In proper installations, it is crucial to select fittings that provide a secure, leak-free connection for safety and efficiency. Other types of fittings, such as welded or flare fittings, are typically designed to handle fluid systems more effectively and provide a stronger, more reliable connection in fuel lines. Therefore, it is important to adhere to the guidelines that limit the use of compression fittings to ensure optimal safety and compliance with regulations in fuel oil installations.