A single end face seal is composed of a pair of sealing end faces (see Figure 29.7-7a), and a double end face seal is composed of two pairs of sealing end faces (see Figure 29.7-7bc). Single end face sealing structure is simple, easy to manufacture and install, generally suitable for conditions where the medium itself has good lubricity and allows for trace leakage. It is a commonly used sealing type, and should not be used when the medium is toxic, flammable, explosive, or has strict requirements for leakage.

Double end face seals include axial double end face seals and radial double end face seals. The double end face sealing structure arranged radially is more compact than the axial double end face sealing. Double end sealing is suitable for media with poor lubricity, toxicity, flammability, explosiveness, volatility, abrasive particles, and gases.

Axial double end face seals have structures arranged face-to-face or back-to-back. During operation, it is necessary to introduce sealing fluid between the two pairs of end faces that is 0.05-0.15 MPa higher than the medium pressure to improve lubrication and cooling conditions between the end faces, and isolate the medium from the outside, which may achieve "zero leakage" of the medium.

a) Single end face type; b) Axial double end face type; c) Radial double end face seal.