A recent Hydrocarbon Processing (HP)
article conveyed an industry finding that dates back several
decades: Oil mist successfully lubricates operating machinery,
protects and preserves standby equipment, and provides superior
lubrication to electric motors driving process pumps. In a
follow-up communication, an HP reader had questions
regarding these findings. He believed that closed-loop oil-mist
systems would possibly: 1) require oil sampling and oil changes
at times, 2) not protect or preserve standby equipment and 3)
be of no use to drive motors. Under those conditions, he
believed his facility would continue to depend on inferior
grease lubrication. Some of this readers conclusions and
beliefs are refuted by decades of highly satisfactory
Oil sampling recommendations
In response to point No. 1, a prudent practitioner of
predictive maintenance (PdM) would occasionally
sample the oil that has passed through the equipment bearings.
We believe the coalesced bulk oil in a coalescer-collector
vessel, as shown in Fig. 1, should be sampled
twice per year. Sampling the coalesced mist drawn from the
bottom of an equipment-bearing housing is optional because the
total bearing condition is best determined by widely available
PdM devices. These devices monitor vibration amplitude and
frequency spectra. Still, with superior synthetic lubricants
made cost-effective due to very low oil consumption and cooler
running bearings, a five-year oil service life can be attained
Fig. 1. A small oil-mist
console manages 20
pumps. It is shown on the left, and the
mist coalescer-collector vessel is on the
Source: Lubrication Systems Co., a
of Colfax Industries, Houston, Texas.
Rely on pump wisdom
In response to point No. 2, protective action on standby
equipment is very important and has been fully proven since
about 1965. In over 5,000 large plant-wide oil-mist
systemsincluding hundreds of closed systems and many
open-air equipment storage yardsthe oil mist envelops the
antifriction bearings in a protective fog. Existing at a
slightly higher-than-ambient pressure in bearing housings, oil
mist keeps out ambient air typically contaminated by water
vapor and airborne dust. Properly applied oil mist travels
through the bearings and to the bearing housing drain port.
Thus, the oil mist protects non-running or standby equipment.
Without this preservation method, standby equipment is exposed
to the risk of the lubrication oil being wiped off
due to vibration transmitted from the adjacent running
In addition, without this preservation method, corrosion of
bearings in non-running equipment is a greater probability. The
rate of corrosion is a function of ingress and egress of air
(breathing action) of the affected bearing
housings. This breathing action occurs only in unprotected
bearing housings, and it is not possible in bearing housings
filled with oil mist at about 1 psi over atmospheric pressure.
Industry now has in excess of four decades of experience with
this protection method on many thousands of pumps and motors.
In 1978, a user company commissioned 132 electric motors
driving vertical pumps. We were told that none of them had ever
failed in 32 years.
Regarding No. 3, all motors with rolling-element bearings
will benefit from dry-sump oil-mist applications. Thousands of
motors have been lubricated in this manner for over 40 years.
Many books and papers have been written about this subject.
Inferior grease lubrication has been superseded by superior
dry-sump oil-mist systems for decades. A recent book on pumps
again shows how oil mist eliminates slinger rings, constant
level lubricators, dessicant breathers and bulls-eye sight
glasses.1 Oil mist safeguards against over-greased
motor bearings and greatly reduces bearing failures.
Closed-oil-mist systems are proven technology; they excel by further
reducing lubricant consumption and protecting the environment. HP
1 Bloch, H. P., Pump Wisdom: Problem
Solving for Operators and Specialists, John Wiley &
Sons, Hoboken, New Jersey, April 2011.
Heinz P. Bloch resides in
Westminster, Colorado. His professional career began
in 1962 and included long-term assignments as Exxon
Chemicals regional machinery specialist for the
US. He has authored over 520 publications, among them
18 comprehensive books on practical machinery
management, failure analysis, failure avoidance,
compressors, steam turbines, pumps, oil-mist
lubrication and practical lubrication for industry.
Mr. Bloch holds BS and MS degrees in mechanical
engineering. He is an ASME Life Fellow and maintains
registration as a Professional Engineer in the States
of New Jersey and Texas.