Pore leaks
Channels or hairline cracks, especially in polycristalline materials. Formed during mechanical processing/stressing (e.g. bending) or thermal treatment.

Example: cast iron body.

Leaks in detachable / non-detachable joints and flanges.
Leaks that occur when flange connections are improperly made.

Example: damaged sealing elements, improper use of grease, welding or soldering defects.

Thermal leaks
Open and close due to temperature fluctuations

Permeation leaks
Gas transport through materials, mainly plastics and elastomers

Virtual leaks
Hollow spaces, which are connected to the space to be evacuated by openings with small section.

Examples: Column/pipe in cast parts/evaporation of liquids