Pressurization denotes the pressure applied at the mechanical seal. It can be applied

• from the outside (external pressurization), i.e. the pressure to be sealed acts on the external sliding face diameter D
• from the inside (internal pressurization), i. e. the pressure to be sealed acts on the internal diameter of the mechanical seal.

The desirable norm is the externally pressurized mechanical seal.

The merits of this arrangement are its relatively low leakage and the greater stability of its sliding faces. Internally pressurized seals are employed in exceptional cases (in spite of their fundamental drawbacks such as close pressure and velocity limits and higher leakage), if e. g. no metal parts are allowed to make contact with the aggressive medium (seal arrangement). An alternating direction of pressure calls for special design measures to prevent the sliding faces from disengaging. Mechanical seals for alternating directions of pressure.