lip vs face
In recent
years there has been a move towards lip type seals amongst some navies on their water lubricated systems. The
decision is not straight forward as each type of seal has specific advantages.
The table sets out the advantages and disadvantages of a typical
arrangement of each type.
|
|
Lip Type |
Face Type |
|
Seal Reliability / Security |
2 sealing areas |
1 sealing area |
|
Cooling |
By fresh water via a circulation tank |
By seawater flushing or by anular space |
|
Axial Movement |
Very tolerant due to seal's ability to move along its liner |
Poor tolerance due to removal of compression of face seal |
|
Radial Movement |
Not so tolerant as seals can lift off the liner |
More tolerant due to width of the seal face |
|
Sensitivity to Vibration |
Reasonably tolerant because of sealing ring flexibility |
Less tolerant due to dampaning of the frequency leading to possible opening of the seal faces |
|
Water Leakage |
Very small indeed |
Appreciable quantities on daily basis |
|
Service |
All wear items can be easily exchanged whilst afloat |
The seal is more complex and difficult to maintain |
|
Spares Logistics |
The seals are designed on a modular basis. All parts are available ex stock with short
delivery times |
Some parts are often tailor-made for each seal. Delivery of spares is much more likely to
be delayed |
|
Initial Cost |
The cost of the seal is more than a normal lip seal due to the
materials required but it is still cheaper than most larger equivalent face-type seals |
Complex face seals are very expensive, but for smaller seal sizes,
below approx 350 mm diameter, cheaper , simpler seals are available |
|
Through-life cost |
Much cheaper than the larger complex face seals |
The smaller, simpler face seals provide an economic solution for
sizes below approx 350 mm |
