A mechanical seal is a device used to seal fluids on a rotating shaft. It consists of two flat faces, one rotating and one that is stationary and mounted perpendicular to the shaft. Rotation of the rotary seal ring against the stationary seat ring causes a rapid pressure drop across the primary seal interface caused by friction on the liquid molecules between the seal faces. Liquid molecules also act as small ball bearings to lubricate and reduce friction which reduces heat and wear.
The factors that affect seal reliability and must be considered when selecting a seal are: