J
Jobst Brandt
Guest
Terry Morse writes:
>> Maybe some day I can get someone to make labyrinth sealed hubs, seals like we find only on
>> Sturmey Archer gear hubs. You'll find that on disassembly these hubs are always clean inside even
>> though they are 50 years old.
> How much mileage do folks get out of Phil Wood hub bearings? I've never been inclined to try them,
> but I know some long distance riders who swear by them for wet conditions.
People swear by all sorts of things but a contact face lip seal is not reliable for that use.
Typically seals on automobiles are used to keep oil IN and are protected by a labyrinth from water.
There are two rules of seals that bicycle "sealed bearings" violate.
1. No two liquids can be reasonably separated by a single contact lip.
2. A contact lip seal that doesn't leak, leaks.
The second bears on the first. If the retained fluid does not seep under the lip, the seal lip will
go dry and burn away its preload for lack of lubrication, thereby becoming a capillary for external
water in the case of the bicycle. If there is water on one side and oil on the other, the two will
mix under the lip. Separating two fluids requires two lips with a vent between to make sure the
interstitial does not fill with one or the other fluid. Typically an automatic transmission oil on a
Corvair and its Hypoid oil required two seals.
Bicycle people do not come from a background of tribology and have no idea what that is all about. I
find it surprising that SA hubs were designed with labyrinth seals but then New Departure coaster
brakes also had such a seal. It seems there were still skilled engineers employed in the bicycle
business in the early 20th century.
The Phil Wood hub was a great disservice to bicycling when it introduced electric motor shaft
bearings with air flow seals posing as water seals. Unfortunately, the bicycle industry, not knowing
much about seals went head over heels to imitate this "great success."
Electric motors that are natural air pumps (that's how they cool themselves) use simple lip face
seals to prevent air being sucked through the shaft bearings, the natural low pressure zone, and gum
up the bearing grease with atmospheric dust. These seals were never intended to seal the bearing
against water although most people believe they can do that. This may be true for an occasional
splash, but hydrostatic water pressure will go into the bearing.
Jobst Brandt [email protected] Palo Alto CA
>> Maybe some day I can get someone to make labyrinth sealed hubs, seals like we find only on
>> Sturmey Archer gear hubs. You'll find that on disassembly these hubs are always clean inside even
>> though they are 50 years old.
> How much mileage do folks get out of Phil Wood hub bearings? I've never been inclined to try them,
> but I know some long distance riders who swear by them for wet conditions.
People swear by all sorts of things but a contact face lip seal is not reliable for that use.
Typically seals on automobiles are used to keep oil IN and are protected by a labyrinth from water.
There are two rules of seals that bicycle "sealed bearings" violate.
1. No two liquids can be reasonably separated by a single contact lip.
2. A contact lip seal that doesn't leak, leaks.
The second bears on the first. If the retained fluid does not seep under the lip, the seal lip will
go dry and burn away its preload for lack of lubrication, thereby becoming a capillary for external
water in the case of the bicycle. If there is water on one side and oil on the other, the two will
mix under the lip. Separating two fluids requires two lips with a vent between to make sure the
interstitial does not fill with one or the other fluid. Typically an automatic transmission oil on a
Corvair and its Hypoid oil required two seals.
Bicycle people do not come from a background of tribology and have no idea what that is all about. I
find it surprising that SA hubs were designed with labyrinth seals but then New Departure coaster
brakes also had such a seal. It seems there were still skilled engineers employed in the bicycle
business in the early 20th century.
The Phil Wood hub was a great disservice to bicycling when it introduced electric motor shaft
bearings with air flow seals posing as water seals. Unfortunately, the bicycle industry, not knowing
much about seals went head over heels to imitate this "great success."
Electric motors that are natural air pumps (that's how they cool themselves) use simple lip face
seals to prevent air being sucked through the shaft bearings, the natural low pressure zone, and gum
up the bearing grease with atmospheric dust. These seals were never intended to seal the bearing
against water although most people believe they can do that. This may be true for an occasional
splash, but hydrostatic water pressure will go into the bearing.
Jobst Brandt [email protected] Palo Alto CA