One of the most effective ways of sealing rotating shafts is by mechanical seals.
These consist of two plane faces arranged perpendicular to the axis of the rotating shaft (which gives rise to the alternative name, "radial face seal"). One face is fixed to the equipment casing or vessel, while the other is fixed to the shaft and so rotates with it. Frictional heat generation and wear are controlled by maintaining a film of lubricant between the seal faces. As such, mechanical seals resemble thrust bearings.
Mechanical seals have replaced packings as the seal of choice in many applications, primarily because mechanical seals offer:
reduced wear (from lower friction)
reduced heat generation (from lower friction)
lower energy consumption (from lower friction)
reduced maintenance requirement (from reduced wear)
tighter control of shaft leakage (from extremely low or zero fluid emissions)
Mechanical seals are precision devices, requiring in general more careful installation and higher initial investment than those of soft packings.