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Valve Oil Part II

In the first open letter we discussed the valve oil properties that effect
initial valve Speed.  This second letter discusses why some valve oils give
a smoother action and last longer than others.
Endurance is the oil's ability to maintain the original fast and smooth
valve action over many hours despite playing conditions.  This
characteristic is very difficult to develop in an oil without compromising
speed  because endurance is the end result of a complex series of
interrelated properties and conditions: evaporation rate, film strength,
surface tension,  water solubility, and valve cleanliness.
The first property is evaporation rate.  In most student and mid-line horns,
when a valve oil evaporates so that less than 40% of the original oil
remains on the valves, they will begin to hesitate in an unpredictable
fashion.  In more expensive horns with clean and very tight valves, the
slowdown is much sooner and sudden seizing of a valve is common. In the
relative evaporation rate table below,  we have listed the percent of oil
remaining on a surface as a function of time at room temperature.   The data
does not suggest that a given valve oil will last the number of days shown,
but rather the percentage of oil remaining after a given period of time.
Compare the evaporation rates of the oils with their viscosities, and
remember that Endurance is enjoying fast consistently smooth action for a
long time - not slow action for a long time.  Some trumpet oil manufacturers
include a heavy oil in their formulation to slow down the apparent
evaporation rate, and (hopefully) to make the oil last longer.
Unfortunately, as evaporation occurs, the lighter oil content diminishes
until only the slow heavy oil remains on the valves.  Our experiments back
in 1976 proved this.
Products        Vis.(cSt)    19 hrs  48 hrs  72 hrs  96 hrs  120 hrs
WATER           1.00             0%
MINERAL SPIRITS 1.34             0%
CLARK TERRY     1.83            16%      7%      6%      0%
BENGE           1.99            35%     13%      8%      5%      4%
BLUE JUICE      1.99            44%     23%     17%     12%      8%
PLAYERS         2.15            44%     20%     13%      8%      4%
JUPITER         2.20            33%     17%     15%     13%     10%
ROCHE-THOMAS    2.31            16%     13%     13%     12%     11%
HOLTON          2.38            25%      7%      4%      0%
HYBRID 141-A7   3.02            92%     75%     64%     55%     46%
PRO-OIL RED     3.61            74%     44%     33%     21%     11%
AL CASS         3.73            75%     48%     37%     26%     16%
PRO-OIL BLUE    3.80            77%     50%     37%     25%     13%
SPACE FILLER I  5.10           100%    100%    100%    100%    100%
SLIDE (t-bones) 5.12           100%    100%    100%    100%    100%
ALISYN          7.59           100%    100%    100%    100%    100%
Endurance is very sensitive to the integrity of the oil film on the valve
surfaces.  As the piston slides down the valve casing it rubs against the
oil film.  This movement  tends to rupture the film and allow direct
metal/metal contact. In hyper-tight valve assemblies (i.e., Monette and
Schilke) oil film rupture is potentially more frequent and disastrous.  This
is a purely mechanical phenomenon which can only be prevented with an oil
having a high film strength.
Achieving a high film strength oil within the optimum viscosity range  (2.5
- 4.0 cSt) is quite difficult.  Although it is not easy to measure this film
strength directly, it is best understood through demonstration.  Firstly, a
high film strength will give a smooth, slippery feel when the oil is rubbed
rapidly between the fingers.  When shaken, an oil with a high film strength
will yield bubbles that  collapse within 1- 3 seconds.  Whereas an oil with
poor film strength will tend to entrap air for a much longer time.
Oil film rupture can also occur for a different reason: moisture.  Water
trapped in the valve chamber experiences the shear force of the piston
moving rapidly past the walls of the valve casing. This action tends to
emulsify the trapped moisture into the oil.   This micro emulsion not only
has an elevated viscosity, but also displaces the oil from the valve
surface. With the oil film thus compromised, the valve and casing easily rub
against each other to produce friction, slowed action and wear. Therefore,
in addition to the properties discussed above, for an oil to be truly
effective it must also resist emulsion formation.
How many times have you heard, "My valves were slowing down, so I reoiled
with a different oil and suddenly the valves stuck."    The tendency is to
blame the oil, and although the oil played a part, other causes are more
likely for this 'Gunking Up' phenomenon.
Every note pushed through the horn is borne in the musician's moist breath
with the valve chamber acting as a trap for not only this moisture but the
aerosols suspended in it. These aerosols contain enzymes, proteins, and
salts.  As long as the valve oil rejects this mixture, it will simply pass
through the valve chamber.   But, as the oil boundary film becomes depleted
or compromised, the moisture and its aerosols become attached to the metal.
When the musician reapplies oil to the moisture impacted valves (or to
valves that had enough time for the spit to dry onto the metal)  the oil
will actually deposit on top of this layer.   As this process is repeated a
series of sticky layers and high spots build up until the valves become
sluggish or stick completely. There is no oil that can permanently protect
against this "spit sandwich"  but you can prevent it through effective
cleaning and proper oiling.
A lesser know consideration in selecting a valve oil is corrosion. It is
absolutely necessary to liberally coat the valve and casing surfaces so that
excess oil will transfer to the internal solder joints. In doing so it will
protect them against dezincification (red discoloration) and corrosion
(blue-green discoloration) which are caused by exposing the naked metal to
moisture.  Monel valves will similarly be protected against spotting.  An
oil with low surface tension and a low viscosity will spread quickly and
evenly, thereby coating these surfaces without fear of over oiling.  It is
very difficult to properly coat a valve, the casing and the solder joints
with a high viscosity oil. The topic of corrosion will be covered in depth
at a later time.  Players of rotary valved instruments will want to pay
close attention to this article.
1.  A high speed oil is a thinner oil. If you don't recall which oils are
heavy, a quick test in a store is to apply a drop or two of each valve oil
onto smooth surface (ie. a clean mirror, a sheet of glass or a sheet of
metal). Tilt the surface and see how fast the oils run down the sheet; heavy
oils move slower and can be eliminated from the selection.
2.  The oil should have a slow evaporation rate and be remain slippery.  A
good evaporation test is to place some of the oil in the palm of your hand
and feel how long it feels slippery relative to a different oil.  Kerosene
based oils are not desirable because they evaporate quickly.  The presence
of kerosene is apparent from its characteristic odor which will become
evident in this test.
3.  The film strength is crucial.  Hold a group of well capped bottles of
high speed oils in your hand, turn them upside down and shake them as a
group for 5 seconds.  Note how fast the foam breaks; the faster the better.
Weed out the ones that have a slow foam break.
4.  Water rejection is important.  This is a test of how fast the water and
oil separate but since it requires sacrificing some oil, a store owner might
not want to do it.  The test is to add equal amounts of water and the valve
oil to a small container (a test tube or even an old bottle), and shake
vigorously for 10 seconds.  Observe how long it takes for the oil and water
to separate almost completely.
Speed and Endurance in an oil are two different properties; experience will
show that the best oil will not sacrifice one for the other. To quote a long
time friend of ours (Art Farmer),  "I play very fast, and I have to
concentrate on the music.  I can't afford to even think about my valves
during a performance."
To develop an oil for horns built on better technology, one must employ
better lubrication technology. Until now, no one has tried to enlighten
either the musicians or store owners that there is a science to improving
valve oil, and only a few valve oils take advantage of the science.
Hopefully the results of our research brought out in this article will
dispel the mystique of valve oils, and make oil selection almost bulletproof.
David Holloway <musichem@cts.com>

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