The class B autoclave has vacuum system, it is the highest class of autoclave,which is conforming to the most strict requirement and therefore can be unrestrictedly used for the steriliazation of all possible loads for all kinds ot sterilization packaging(solid, hollow instruments with wrapped and unwrapped).
A "class B " autoclave must pass every Helix test as EN867-5:2001 by the test system of EN 13060 in any cases. According to experts opinions, which can only be achieved by the fractionating per vacuum procedure. Post vacuum drying provides completed drying of porous loads and hollow instruments at the end of the sterilization process.
The class N autoclave dose not have vacuum system, you only need an autoclave capable of running class N system.