Mechanical seals including tungsten carbide seals, silicon carbide seals being used increasingly on fluid pump to replace packed gland and lip seal. Pump with mechanical seals perform more efficiently and generally perform more reliably for extended periods of time.

Tungsten carbide seals is provided to prevent pumped fluid from leaking out along the drive shaft. The controlled leakage path is between two flat surfaces associated with the rotating shaft and the housing respectively. The leakage path gap varies as the faces are subjected to varying external load which tend to move the faces relative to each other.
 

In order for the tungsten carbide seals, silicon carbide seals to perform over an extended time period with low frictional the mechanical seals faces are generally hydrodynamically lubricated. The fluid film will need to carry substantial load. If the load becomes to high for the film surface contact will take place with consequent bearing failure. This lubricating film is generally of the order of 3 micrometres thick , or less. This thickness is critical to the required sealing function. tungsten carbide seals, silicon carbide seals often have one face of a suitable solid lubricant such that the tungsten carbide seals, silicon carbide seals can still operate for a period without the fluid film.