What are the two classes of packing and gasket joints?

The correct classification of packing and gasket joints lies in the distinction between static and dynamic joints. Static joints are those that do not experience movement during operation, while dynamic joints involve parts that move relative to one another. This distinction is crucial in determining the appropriate materials and designs used for effective sealing.

In the context of static joints, packing and gaskets are designed to create a seal between stationary components, such as flanges or covers. On the other hand, dynamic joints, which are subject to movement, require packing or gaskets that can accommodate or adapt to the changes in position without compromising the seal's integrity.

Understanding this classification helps machinists and engineers select the right type of sealing materials and designs based on the operational conditions, thereby ensuring functionality and reliability in mechanical systems.