From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: All Bike Enthusiasts - I need your help
Date: 8 Feb 1997 23:37:57 GMT

Mygrainboy writes anonymously:

>> What are labyrinth seals? Do you mean some kind of interlocking hub
>> to seal setup that won't leak or wear out?

> Most seal designs use some form of rubber wiper or "lip" seal. These
> seal pretty well when they're new, but the contact pressure leads to
> wear at the crucial part of the seal, and then they stop sealing so
> well. A really waterproof lip seal requires a lip pressure that
> might even generate noticeable drag.

Seals cannot separate two fluids with a single seal lip because the
fluid retained is the lubricant of the seal lip.  If two fluids meet
at such a lip (like water and oil) the milky suspension intrudes into
the bearing and causes rust.  Typically the seal lip runs dry at some
point and gets burned by friction.  Then it becomes a capillary
suction device that attracts water into the bearing.  A text on seals
will clarify this but the old axiom that: "The seal that doesn't leak,
leaks." is correct.  If the seal lip doesn't weep to lubricate itself,
it fails and becomes a big leaker later on.

> A labyrinth seal takes a different approach. Instead of using contact
> pressure over a small area, it reduces the pressure and increases the
> contact.  Rather than trying to seal with a single strong barrier, a
> labyrinth seal uses a long path to accomplish the same reduction in
> flow.  Labyrinths are usually made of two hard surfaces with carefully
> matched diameters such that  they barely contact.  Not only is seal
> friction reduced, but more importantly so is seal wear.

Labyrinth seals are non contacting rotating labyrinths through which
splash water cannot enter and gravity drains them.  Sturmey Archer hubs
are classic examples of such seals.  They are more than 40 years old
and used in the rain, yet the hubs are clean and dry inside with no
wear or frictional drag.

>> Where are labyrinth seals currently used? Why

> I believe Goldtec are using them. Goldtec are a small Welsh company
> who specialise in TiN (titanium nitride) coatings on their products.
> This is a very wear-resistant gold-coloured coating for metals. It's a
> good technology to work in conjunction with the labyrinth approach.

I think you have the concept screwed up.  No wonder you post
anonymously with such conjecture.  Plain old plastic will suffice for
a labyrinth seal because there is no contact.  My Sun Tour New Winner
Pro freewheels have brass labyrinth seals that work just fine without
exotic materials for wear resistance.

> this seems like a great design, but don't you guys get sick of paying
> tons and tons of money for something that is hardly noticed, and
> only appreciated when you would normally think its time to overhaul
> your wheel bearings?

I get more tired of "tons and tons" of BS gratuitously spread right
here on the net.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: FAQ Question: Jobst on "Sealed" Bearings
Date: 31 Oct 1998 00:53:49 GMT

Andrew S Mein writes:

>> Where's all that muck coming from, and why aren't you using oil if
>> these bearings are so well protected?

> Go ride an MTB in the East or Pacific NW.  Should we ride in
> conditions that encounter as much poop as these seals warrant?
> Probably not.  Do we?  Yup.

I know, the going is always tougher in your area than anywhere else.
Besides, the water is wetter and the dirt dirtier.  If this were a
labyrinth seal, not used on a submarine adventure, then there should
be no dirt in the bearing.  The point is, this is not what he claimed.
The bearings of my 1950's three speed hub is still as clean as a
whistle useing only labyrinth seals.

> As for oil, even with a multiple seal configuration, a la Shimano,
> these puppies still get contaminated mighty quick- and oil provides
> even less of a mechanical barrier to H2O than grease.

You may not know this but grease is oil, suspended in a 'soap' matrix
that gives it body.  The lubrication is oil, however, and it is not in
the least more water resistant than oil when it comes to emulsifying
on the bearing surfaces.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: FAQ Question: Jobst on "Sealed" Bearings
Date: 30 Oct 1998 22:30:08 GMT

Matt O'Toole writes:

> I have seen the labyrinth seals on the old Suntour hubs and
> freewheels, and I don't understand why this design didn't
> become the standard.  Just one more example of where someone
> could out-do Shimano, but no one bothers to try...

I use the (New Winner Pro) freewheels and was disappointed in the
execution of the design.  The labyrinth has too little clearance
making in effect a capillary gap that occasionally sucks water in
heavy rain.  Just the same, I use them because they give me a nearly
symmetric rear wheel with their 6-speeds on my old Campagnolo hubs.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Loose Crank
Date: 23 Apr 2001 22:13:16 GMT

Johan Bornman writes:

>> sealing it from the environment.  I wish they would recognize the
>> superiority of the labyrinth seal over a contact seal.

> What is a labyrinth seal?  For that matter, even though I think I
> can picture it, what is a contact seal?

Moving seals are a more complicated science than they first appear and
are only slightly related to fixed seals such as beer caps, mason jars
gas or radiator caps.  This is best emphasized by the old saying that
"the seal that doesn't leak, leaks" that being the essence of the
problem.  If the seal doesn't leak a little, its flexible sealing lip
will burn for lack of lubrication by the fluid that it is intended to
contain.  Therefore, there must be a fluid under the seal lip.

If a seal is intended to contain oil and seal it from water, the
principal problem is one of mixing disparate fluids under the seal
lip.  Because circulation occurs under the seal lip, an emulsion will
develop and even if the volume of oil on the inside is too large to be
contaminated significantly, the shaft will rust when standing to
destroy the seal lip.  Automotive bearings are sealed to retain grease
and oil but are protected from water exposure by splash shields.

Separating two fluids requires two seal lips separated by a drained
dry space.  This is done on automatic transmission and differentials
gears that use incompatible oils, to prevent contamination by
circulation under each seal lip.  This is not possible with oil and
water on bicycles because there is no water most of the time, leaving
the water seal lip dry and unlubricated, which renders it useless when
exposed to water.

Most so called sealed bearings are not water tight mainly because they
have run dry, burning the seal lip which becomes a capillary to suck
water if it gets wet.  Phil Wood used bearings commonly used in
electric motors that use a rubber lip seal to prevent air (dust) flow
because rotating machinery always acts as an air pump, sucking at the
axle and blowing at the periphery.  These bearings were never meant to
prevent water intrusion, something they can do for a short time when
new.  This is the main reason why such "sealed" hubs were not offered
at the time he introduced them.  To make this work, one would have to
protect the seal lip from contacting anything but oil by a shield,
otherwise known as a labyrinth seal.

The most common labyrinth seals on bicycles are found on Campagnolo
Pedals, threaded head bearings, and above all on Sturmey Archer
3-Speed hubs that are rust free and working 50 years after
manufacture.  Bendix and New Departure coaster brakes are examples of
excellent water rejection unless the hub was submerged.

The nature of a labyrinth seal is that it uses gravity to purge water
from its entrance.  Typically this requires nothing more than two
nested channel cross section washers of two diameters, one rotating in
the other that is anchored in the housing.  To visualize this make a
"C" shape with both hands, interleaving the thumb and forefingers so
they move freely in a rotary motion from the elbows.  You can see that
vertically, water has no ability to enter, and tilted the pair either
way only enhances the barrier.

The last such device I am aware of was the New Winner Pro Sun Tour
freewheel, whose labyrinth was visible as a tiny brass ring on both
faces.  It's problem was that such a seal must take into account the
wetting angle of water and must have a large enough air gap to prevent
capillary attraction.  The Sun Tour execution lay at the lower limit
with its small spacing but they worked under most conditions.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Labyrinth Seals (was: Loose Crank)
Date: 4 May 2001 19:05:34 GMT

Helmut Springer writes:

>> It's problem was that such a seal must take into account the
>> wetting angle of water and must have a large enough air gap to
>> prevent capillary attraction.  The Sun Tour execution

> Any data about how large this gap should be?  I may have someone
> with a lathe making me some caps for a hub, and I could add some
> diameters to process...

I think the ideal is about the dimensions used on cones of Sturmey
Archer hubs although I suspect that one could make an improvement on
the shape by adding a re-entrant lip on the innermost edge.

Jobst Brandt      <jbrandt@hpl.hp.com>