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This Fluid Sealing Association Knowledge Series training presentation introduces the design and application of multiple lip seals. A description is provided on:
▪ Types and design
▪ Seal Configurations
▪ Design Variations
▪ Advantages and disadvantages
▪ Typical Applications
Lip Seal Design
▪ Utilize sealing elements in contact with a rotating sleeve that is engaged with the rotating shaft circumferentially
▪ 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
Hard Coated Rotating Sleeve
Atmospheric Side Sealing Elements
Lip Seal Design
▪ Sealing elements are typically PTFE based material running against chrome oxide or other suitable hard coating material on the sleeve.
▪ 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.
▪ Can be arranged in a dual seal configuration with lips opposed to each other facing the pressurized side.
Sealed Fluid
Pressurized External Fluid
Dual Seal Configuration
Lip Seal Configurations
▪ External flush (API Plan 32) can be used to keep the environment around the seal clean.
▪ Can be injected between the lips to minimize flow of flush liquid.
External Flush Fluid (API Plan 32)
External Flush Fluid Injected Between Lips
Design Variations
▪ 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
Sealed Fluid
Atmospheric Side
Quench Cavity
Design Variations
▪ Example of cartridge mounted multiple lip seal design
Sealed Fluid Side
Atmospheric Side
Quench Connection
Benefits
Advantages of Multiple Lip Seals
▪ No springs or other mechanical components to be fouled or clogged by sealed fluid
▪ Compared to packing, there is less leakage and no requirement for periodic adjustments
▪ They are not sensitive to relative axial shaft motion
Disadvantages
Disadvantages of Multiple Lip Seals
▪ Limited to relatively low speeds and pressure (P·V) applications, and thus tend to be used on smaller size equipment
▪ Temperature limitations due to the temperature limit of the PTFE sealing element material
▪ 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
* Emulsions
* Fats and Oils
* Food services
* Ink
* Paint
* Paper coatings
* Starch
* Syrups
* Tallow
* Tar
Multiple lip seals can be applied to a variety of equipment including:
