Multiple Lip Seals

Multiple Lip Seals FSA Knowledge Series

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Abstract This Fluid Sealing Association Knowledge Series training presentation introduces the design and application of multiple lip seals. A description is provided on:

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Types and design

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Seal Configurations

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Design Variations

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Advantages and disadvantages

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Typical Applications

Lip Seal Design ▪

Utilize sealing elements in contact with a rotating sleeve that is engaged with the rotating shaft circumferentially

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Sealing elements are typically facing into the fluid being pumped. Hydraulic pressure in the seal chamber acts as the closing force on the sealing elements.

Stationary Housing Sealed Fluid Atmospheric Side Hard Coated Rotating Sleeve Sealing Elements

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Lip Seal Design

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Sealing elements are typically PTFE based material running against chrome oxide or other suitable hard coating material on the sleeve.

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PTFE is often blended with other materials (e.g. polyimide or carbon graphite) to enhance its properties for specific applications.

Lip Seal Configurations ▪

Multiple lip seal designs can be used in equipment handling fluids with high concentrations of solids.

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Can be arranged in a dual seal configuration with lips opposed to each other facing the pressurized side.

Pressurized External Fluid

Sealed Fluid

Dual Seal Configuration

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Lip Seal Configurations ▪

External flush (API Plan 32) can be used to keep the environment around the seal clean.

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Can be injected between the lips to minimize flow of flush liquid.

External Flush Fluid (API Plan 32)

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External Flush Fluid Injected Between Lips

Design Variations ▪

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Multiple Lip Seals can be a combination of discrete lip elements or a unitized construction

Design Variations ▪

Example of a unitized lip seal design featuring a compact arrangement of multiple lips with a quench or flush cavity

Quench Cavity

Sealed Fluid

Atmospheric Side

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Design Variations ▪

Example of cartridge mounted multiple lip seal design

Quench Connection

Sealed Fluid Side

Atmospheric Side

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Benefits Advantages of Multiple Lip Seals

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No springs or other mechanical components to be fouled or clogged by sealed fluid

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Compared to packing, there is less leakage and no requirement for periodic adjustments

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They are not sensitive to relative axial shaft motion

Disadvantages Disadvantages of Multiple Lip Seals

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Limited to relatively low speeds and pressure (P·V) applications, and thus tend to be used on smaller size equipment

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Temperature limitations due to the temperature limit of the PTFE sealing element material

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They are sensitive to radial shaft motion (runout) and shaft to housing eccentricity

Typical Installations Multiple lip seals are ideal for dense and viscous fluids such as: * Adhesives * Paper coatings * Emulsions * Starch * Fats and Oils * Syrups * Food services * Tallow * Ink * Tar * Paint Multiple lip seals can be applied to a variety of equipment including: ▪ Positive displacement pumps ▪ Mixers ▪ Agitators 13

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