Surface speed below 25 m/ s High vacuum

Mechanical seal:

Low leak, long life potential

Lip seal:

Elastomer or plastic depending on liquid. Finite life, some leak through plastic seal, suitable elastomer for vacuum required

Low vacuum

Lip seal:

Elastomer or plastic, as above

Mechanical seal:

Optimum for long life and low leak

Compression packing:

Some leakage

Segmented rings:

Some leakage

Splash sealing, zero/ very low pressure differential

Lip seal:

Elastomer or plastic, finite life, selection depends on liquid, temperature, environment

Labyrinth:

No wear out but vapour leakage, high speed

Labyrinth+vapour barrier seal:

No wear out

Mechanical seal:

Compact design, e. g. magnetic or wavy spring

Piston rings:

Potentially some leak

Viscoseal:

Very high speed, but gas ingestion

Segmented rings:

High speed, but some leak

Low pressure <5 bar

Lip seal:

Specially designed elastomer seal, limited life/ speed. Provides a compact design

Lubricating liquid below vapour pressure

Plastic designs:

Potentially small leak, but compact design

Compression packing:

If some leakage acceptable

Mechanical seal:

Compact or elastomer bellows design depending on application, space/cost constraints

Low pressure <5 bar

Lip seal:

Plastic, provided some leak permissible

Non-lubricating liquid or close to vapour pressure

Elastomer:

Specific designs for application, limited speed or design for leakage may be constraints

Mechanical seal:

Selection of seal and system to suit liquid

Compression packing:

If some leakage permissible

Segmented rings:

Some leakage will occur, useful...