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Dictionary of Lubricant Terms


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PALE OIL - straight naphthenic mineral oil, MVI to HVI, straw or pale yellow in color, used as a once-through lubricant and in the formulation of process oils.

PARAFFIN (Paraffinic) - hydrocarbon identified by saturated straight (normal or branched {iso}) carbon chains. The generalized paraffinic molecule can be symbolized by the formula CH+. Paraffins are relatively non-reactive and have excellent oxidation stability. In contrast to naphthenic oils, paraffinic lube oils have relatively high wax content and pour point, and generally have a high viscosity index (VI). Paraffinic solvents are generally lower in solvency than naphthenic or aromatic solvents. See hydrocarbon, normal paraffin, and saturated hydrocarbon.

PARTICULATES - atmospheric particles made up of a wide range of natural materials (e.g., pollen, dust, resins), combined with manmade pollutants (e.g., smoke particles, metallic ash); in sufficient concentrations, particulates can be a respiratory irritant. Primary sources of manmade particulate emissions are industrial process losses (e.g. from cement plants) and stationary combustion sources. Motor vehicles contribute a relatively minor amount of particulates. PCB - polychlorinated biphenyl, a class of synthetic chemicals consisting of an homologous series of compounds beginning with monochlorobiphenyl and ending with decachlorobiphenyl. PCB’s do not occur naturally in petroleum, but have been found as contaminants in used oil. PCB’s have been legally designated as a health hazard, and any oil so contaminated must be handled in strict accordance with state and federal regulations. PCV - see positive crankcase ventilation.

PENSKY-MARTENS CLOSED TESTER - apparatus used in determining the flash point of fuel oils and cutback asphalt, under conditions prescribed by test method ASTM D 93. The test sample is slowly heated in a closed cup, at a specified constant rate, with continual stirring. A small flame is introduced into the cup at specified interval through shuttered openings. The lowest temperature at which the vapors above the sample briefly ignite is the flash point. See Tag closed tester.

PERMANENT VISCOSITY LOSS (PVL) - measure of difference between viscosities of fresh oil and same oil after engine operation or special test conditions of polymer degradation. May be determined under conditions of low or high shear.

PETROCHEMICAL - any chemical derived from crude oil, crude products, or natural gas. A petrochemical is basically a compound of carbon and hydrogen, but may incorporate many other elements. Petrochemical are used in the manufacture of numerous products such as synthetic rubber, synthetic fibers (such as nylon and polyester), plastics, fertilizers, paints, detergents, and pesticides. pH - measure of acidity or alkalinity of an aqueous solution. The pH scale ranges from 0 (very acidic) to 14 (very alkaline), with a pH of 17 indicating a neutral solution equivalent to the pH of distilled water. See neutralization number.

PHENOL - white, crystalline compound (C6H5OH) derived from benzene; used in the manufacture of phenolic resins, weed killers, plastics, disinfectants; also used in solvent extraction, a petroleum refining process. Phenol is a toxic material; skin contact must be avoided.

PHOSPHATE ESTER - any of a group of synthetic lubricants having superior fire resistance. A phosphate ester generally has poor hydrolytic stability, poor compatibility with mineral oil, and a relatively low viscosity index (VI). It is used as a fire-resistant hydraulic fluid in high-temperature applications.

PIPE STILL - see distillation.

POISE - see viscosity.

POLAR COMPOUND - a chemical compound whose molecules exhibit electrically positive characteristics at one extremity and negative characteristics at the other. Polar compounds are used as additives in many petroleum products. Polarity gives certain molecules a strong affinity for solid surfaces; as lubricant additives (oiliness agents), such molecules plate out to form a tenacious, friction-reducing film. Some polar molecules are oil-soluble at one end and water-soluble at the other end; in lubricants, they act as emulsifiers, helping to form stable oil-water emulsions. Such lubricants are said to have good metal-wetting properties. Polar compounds with a strong attraction for solid contaminants act as detergents in engine oils by keeping contaminants finely dispersed.

POLYETHYLENE (PE) - polymerized (see polymer) ethylene, ranging from a colorless liquid to a white solid; used in the manufacture of plastic films and sheets, and a wide variety of containers, kitchenware, tubing, etc.

POLYGLYCOLS - polymers of ethylene or propylene oxides used as a synthetic lubricant base. Properties include very good hydrolytic stability, high viscosity index (VI), and low volatility. Used particularly in water emulsion fluids.

POLYISOPRENE RUBBER (IR) - one of the stereo rubbers, a term designating a high uniformity of composition. Sometimes called “synthetic natural rubber” because of its similar chemical composition, high tack, resiliency, and heat resistance. It can replace natural rubber in many applications.

POLYMER - substance formed by the linkage (polymerization) of two or more simple, unsaturated molecules ({see unsaturated hydrocarbon}, called monomers), to form a single heavier molecule having the same elements in the same proportions as the original monomers; i.e. each monomer retains its structural identity. A polymer may be liquid or solid; solid polymers may consist of millions of repeated linked units. A polymer made from two or more dissimilar monomers is called a copolymer; a copolymer composed of three different types of monomers is a terpolymer. Natural rubber and synthetic rubbers are polymers.

POLYMERIZATION - in petroleum refining, polymerization refers to the combination of light, gaseous hydrocarbons, usually olefins, into high-molecular-weight hydrocarbons that are used in manufacturing motor gasoline and aviation fuel. The product formed by combining two identical olefin molecules is called a dimer, and by three such molecules, a trimer. See polymer.

POLYOLEFIN - polymer derived by polymerization of relatively simple olefins. Polyethylene and polyisoprene are important polyolefins.

POLYOL ESTER - synthetic lubricant base, formed by reacting fatty acids with a polyol (such as a glycol) derived from petroleum. Properties include good oxidation stability at high temperatures and low volatility. Used in formulating lubricants for turbines, compressors, jet engines, and automotive engines.

POLYSTYRENE - hard, clear thermoplastic polymer of styrene, easily colored and molded for a variety of applications, including structural materials. It is a good thermal and electrical insulator and, in the form of expanded foam, extremely buoyant.

POSITIVE CRANKCASE VENTILATION (PCV) - system for removing blow-by gases from the crankcase and returning them, through the carburetor intake manifold, to the combustion chamber, where the recirculated hydrocarbons are burned, thus reducing hydrocarbon emissions to the atmosphere. A PCV valve, operated by engine vacuum, controls the flow of gases from the crankcase. PCV systems have been standard equipment in all U.S. cars since 1963, replacing the simpler vent, or breather, that allowed crankcase vapors to be emitted to the atmosphere.

POUR POINT - using ASTM D 97, the lowest temperature at which the oil can be poured. Also, using FTM 203, the stable pour point is the lowest temperature at which an oil will remain fluid after being subjected to a cyclic temperature variation for six days.

POUR POINT DEPRESSANT - additive used to lower the pour point of a petroleum product. POWER - rate at which energy is used, or at which work is done. Power is commonly measured in terms of the watt (one joule per second) or horsepower (33,000 foot-pounds per minute, or 745.7 watts). PPB - parts per billion. PPM - parts per million.

PRE-IGNITION - ignition of a fuel-air mixture in an internal combustion engine (gasoline) before the spark plug fires. It can be caused by a hot spot in the combustion chamber or a very high compression ratio. Pre-ignition reduces power and can damage the engine.

PRESSURE - force per unit area, measured in kilopascals (kPa) or pounds per square inch (psi). Standard atmospheric pressure at sea level is 101.3 kPa (14.7 psi), or one atmosphere. Gauge pressure, as indicated by a conventional pressure gauge, is the pressure in excess of atmospheric pressure. Absolute pressure is the sum of atmospheric and gauge pressures. Pressure is also expressed in terms of the height of a column of mercury that would exert the same pressure. One atmosphere is equal to 760 mm (29.9 in) of mercury.

PROCESS OIL - oil that serves as a temporary or permanent component of a manufactured product. Aromatic process oils have good solvency characteristics; their applications include proprietary chemical formulations, ink oils, and extenders in synthetic rubbers. Naphthenic process oils are characterized by low pour points and good solvency properties; their applications include rubber compounding, printing inks, textile conditioning, leather tanning, shoe polish, rustproofing compounds, and dust suppressants. Paraffinic process oils are characterized by low aromatic content and light color; their applications include furniture polishes, ink oils, and proprietary chemical formulations.

PROUDNESS - ring protrusions caused by the buildup of carbon or lacquer deposits behind the ring or on the sides of the ring or groove. PSI - pounds per square inch. PSIA - pounds per square inch absolute, equivalent to the gauge pressure plus atmospheric pressure.

PUMPABILITY - the low temperature, low shear, stress-shear rate viscosity characteristics of an oil that permit satisfactory flow to and from the engine oil pump and subsequent lubrication of moving components. Measured in the mini-rotary viscometer, ASTM D 3829, and referred to as the borderline pumping temperature.