Which type of seal is designed to prevent leakage in only one direction?

A lip seal is designed to prevent leakage in only one direction, typically used in rotating shafts where the seal faces the fluid or gas that requires containment. The design of a lip seal features a flexible lip that presses against the shaft surface, creating a tight closure that allows for minimal leakage while permitting motion.

This makes lip seals particularly useful in applications where the pressure of the contained fluid is significantly higher than the external environment and where one-way sealing is essential, such as in hydraulic systems or certain turbo machinery. The lip's ability to adapt to the shaft's movement and maintain contact helps maintain the integrity of the seal over time.

In contrast, O-ring seals can also be effective in one-directional applications but are commonly used in static and dynamic applications where the pressure from either side may be similar. Mechanical seals are typically used in more complex situations where both sides require containment, and flange seals are used for connecting two flanges and often require sealing in both directions.