ABSTRACT
This chapter discusses seal design and function in a generalized way, to illustrate how concepts apply widely to different types of seal. The terms “leaking” and “sealing” are often used in a loose colloquial way, but in serious engineering they must be defined in a way appropriate to the context. Leakage is normally considered to be fluid flowing outwards past the seal to the region surrounding the machine being sealed. In many seals there are one or more secondary leakage paths, additional to the leakage path through the primary sealing gap. To control such leakage, secondary sealing elements are incorporated. Torque is transmitted from a rotating shaft, through rotating and static components of the seal, to the stationary seal housing. Convoluted membranes or rolling diaphragms allow a limited amount of axial motion. However, hermetic sealing of a rotating element by a diaphragm requires other means for transmitting the motion, for example a swashplate mechanism or magnetic coupling.
