Oakum: shredded rope or hemp fiber impregnated with some form of light tar
and used as a caulking or packing for joints.
Octane number: number indicating the knock rating or resistance to detonation
of motor gasoline, defined as the percent by volume of isooctane (C8H18) in a
mixture with n-heptane; this mixture has the same knock rating under standard
engine test conditions as the test fuels.
Oil: common term applied to slippery liquids consisting of various
hydrocarbons; found in nature as petroleum, animal, vegetable or marine
products, or synthesized in industry.
Oil-air lubrication: see air-oil lubrication.
Oil groove(s): frequently termed “oil ducts”; one or more grooves cut into the
surface of bearing metal, the location and design of which are important for
proper distribution of the lubricant. They prevent excessive oil loss from the
bearing, serve as reservoirs to replenish lubricant supply and distribute the oil.
Oiliness: property of a lubricant that yields low friction under conditions of
boundary lubrication, because of its affinity for metal surfaces. Polar compounds
in the lubricant enhances this property, causing a physical adherence
(absorbance) to the surfaces; the lower the friction, the greater the oiliness.
Oil mist or flog lubrication: oil atomized by compressed air, then conveyed by
the air in a low- pressure distribution system to multiple points of lubricant
application. At these points, as the mist flows through a nozzle of the proper
type and size, it may condense as small quantities of liquid oil that lubricate the machine elements. The nozzles, or reclassifiers, include fog, spray mist and
Oil pad: oil-saturated felt pad, generally used on plain bearings, that lubricates
the rubbing surfaces; oil is supplied to the pad by wick, capillary, syphon, etc.
Oil ring: a loose ring, generally of greater in diameter than the shaft, the inner
surface of which rides the shaft or journal, causing the ring to rotate; the ring
dips into a reservoir from which it carries lubricant to the top of the shaft for
distribution to a bearing.
Oil seal: one of many contact sealing devices used to reduce or eliminate oil
leakage or to exclude foreign matter from a lubrication system (see lip seal). Oil
seals are generally used on moving parts while gaskets seal non-moving parts
such as housing (see gaskets).
Oil strainer: strainer that uses a metal screen or disc as the filtering medium;
usually rated according to mesh size, not micrometer size.
Open gear lube: extremely heavy gear lubricants with viscosities in the asphaltic
Organic acid: an organic compound with acid properties, obtained from such
organic substances as animal, vegetable and mineral oils; for example, a fatty
acid. Chemically, organic acids most often contain a carboxyl group (COOH).
O-ring: an “O” –shaped automatic or squeeze-type packing manufactured from
metallic or elastomeric materials, used for static and dynamic applications. The
seal is compressed against the shaft or collar and energized by the pressure of the fluid being sealed to prevent leakage.
OSHA: Occupational Safety and Health Administration
Outboard bearing: one of two bearings supporting a shaft farthest from the
drive unit. Some extend outside the machine, e.g., a shaft extended from a
machine upon which is mounted a direct connected generator, pump, etc.
Oxidation: chemical process in which oxygen combines with another substance;
enhanced by elevated temperature and the presence of a catalyst, such as copper,
water or foreign matter. Oxidation of lubricants eventually produces acids and
polymers, resulting in metal corrosion and sludge formation. Oxidation
inhibitors function by interrupting the oxidation process at the first step, the
formation of peroxides that serve as catalysts for the entire process (see
Oxidation stability: resistance of lubricants to chemical reaction with oxygen;
several test methods are used.
Oxidation inhibitors : additives added in small quantities to petroleum and other products to retard oxidation reactions, increase shelf & service life. Also known as anti-oxidants. They function by interrupting the oxidation process at the first step, the formation of peroxides that serve as catalysts for the entire process (see inhibitors).