The cross-sectional shape of a seal dramatically affects how it functions, especially at low pressure. The greatest trade-off in dynamic sealing is low friction performance vs. low pressure sealability. At low pressure, friction, wear and sealing ability are affected by whether or not the seal is a lip or squeeze profile (see Figure 2-3). With this in mind, seals are often categorized as either “lip seals” or “squeeze seals,” and many fall somewhere in between. Lip seals are characterized by low friction and low wear; however, they also generate poor low pressure sealability.

Squeeze seals are characterized by just the opposite: high friction and high wear, but better low pressure sealability. As described above, a squeeze type seal will generate much more sealing force than a lip type seal. The assumption here is that both seals are under zero or low pressure. However, as fluid pressure increases, the differences between seal types become insignificant due to the force from the fluid pressure overcoming the designed squeeze. Pressure generally improves leakage control, but increases friction and its associated heat, wear and potential for
extrusion.