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Glossary

Definitions:

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Abbreviations       Organizations

D

Deaerator

A separator that removes air from the system fluid through the application of bubble dynamics.

Degas

Removing air from a liquid, usually by ultrasonic and/or vacuum methods.

Degradation

The progressive failure of a machine or lubricant.

Degree Day

A unit of temperature. Experience has shown that, for buildings requiring an inside temperature of approximately 70°F, the amount of fuel or heat used per day is proportional to the number of degrees the average outside temperature falls below 65°F. The degree-day is based upon this principle. The number of degree-day (65°F base) for a given period is the difference between 65°F and the United States Weather Bureau daily mean temperature, when the latter is less than 65°F, multiplied by the number of days.

Degree Engler

A measure of viscosity. The ration of the time of flow of 200 ml of the liquid tested, through the viscometer devised by Engler, to time required for the flow of the same volume of water gives the number of degrees Engler.

DEO

Diesel Engine Oil

Dehydrator

A separator that removes water from the system fluid.

Delamination wear

A complex wear process where a machine surface is peeled away or otherwise removed by forces of another surface acting on it in a sliding motion.

Demerit rating

Classification of an engine part condition on an open-ended numerical scale. The scale starts at 0 which represents a new part condition. In this system, the higher the rating number, the worse the part condition. Generally used for diesel engines.

Demulsibility

The ability of a fluid that is insoluble in water to separate from water with which it may be mixed in the form of an emulsion. Demulsibility is an important consideration in lubricant maintenance in many circulating lubrication systems.

Density

The mass of a unit volume of a substance. Its numerical value varies with the units used.

Deposits

Oil-insoluble materials that result from oxidation and decomposition of lube oil and contamination from external sources and engine blow-by. These can settle out on machine or engine parts. Examples are sludge, varnish, lacquer and carbon.

Depth filter

A filter medium that retains contaminants primarily within tortuous passages.

Desorption

Opposite of absorption or adsorption. In filtration, it relates to the downstream release of particles previously retained by the filter.

Detergent

In lubrication, either an additive or a compounded lubricant having the property of keeping insoluble matter in suspension thus preventing its deposition where it would be harmful. A detergent may also redisperse deposits already formed.

Dewaxing

Removal of paraffin wax from lubricating oils to improve low temperature properties, especially to lower the cloud and pour points.

Dielectric Strength

A measure of the ability of an insulating material to withstand electric stress (voltage) without failure. Fluids with high dielectric strength (usually expressed in volts or kilovolts) are good electrical insulators. (ASTM Designation D 877.)

Diesel Fuel

Obtained through the partial distillation of crude oil. Diesel fuel is ignited in an internal combustion engine cylinder by the heat of air under high compression--in contrast to motor gasoline, which is ignited by electrical spark. Because of the mode of ignition, a high cetane number is required in a good diesel fuel. Diesel fuel also often contains higher quantities of mineral compounds and sulfur.

Diesel Index

An expression for the ignitability of a fuel relative to its aniline point: Diesel index = aniline pint (°F) X API gravity 100

Diester Oil

A synthetic lubricating fluid made from esters; also called ester oil.

Differential pressure indicator

An indicator which signals the difference in pressure between any two points of a system or a component.

Diluent

An un-reactive substance used to increase the bulk of some other substance. Petroleum oils and solvents are commonly used as diluents in such products as paints, pesticides, and additives.

Dirt capacity (dust capacity) (contaminant capacity)

The weight of a specified artificial contaminant which must be added to the influent to produce a given differential pressure across a filter at specified conditions. Used as an indication of relative service life.

Dispersant

In lubrication, a term usually used interchangeably with detergent. An additive, usually nonmetallic ("ashless"), which keeps fine particles of insoluble materials in a homogeneous solution. Hence, particles are not permitted to settle out and accumulate.

Disposable

A filter element intended to be discarded and replaced after one service cycle.

Dissolved gases

those gases that enter into solution with a fluid and are neither free nor entrained gases.

Distillate

Wide range of products produced by distillation.

Distillation method (ASTM D-95)

A method involving distilling the fluid sample in the presence of a solvent that is miscible in the sample but immiscible in water. The water distilled from the fluid is condensed and segregated in a specially-designed receiving tube or tray graduated to directly indicate the volume of water distilled.

Drum

A container with a capacity of 55 U.S. gallons.

Dropping Point

In general, the dropping point is the temperature at which the grease passes from a semisolid to a liquid state. This change in state is typical of greases containing conventional soap thickeners. Greases containing thickeners other than conventional soaps may, without change in state, separate oil.

Dry-Film Lubricant

Solid material left between two moving surfaces to prevent metal-to-metal contact, thus reducing friction and wear. Such materials are especially useful in the region of boundary lubrication, and for lubrication under special conditions of extremely high or low temperature where usual lubricants are inadequate. They may be applied in the form of a paste or solid stick, or by spraying, dipping, or brushing in an air-drying carrier which evaporates leaving a dry film. Some examples are graphite, molybdenum disulfide, boron nitride, and certain plastics such as tetrafluorethylene resins.

Dual Fuel Engine

A diesel engine which may be operated as an oil diesel, a gas diesel, or a combination of both, as it is equipped with controls or parts to permit operating as one or the other.

Dumbbell blend

Mixture of hydrocarbons, usually two components that have different viscosities or other properties.

Duplex filter

An assembly of two filters with valving for selection of either or both filters.

Dynamometer

Device for measuring the force output of a mechanical device such as the driving torque of a rotating machine.