Degradation

The progressive failure of a machine or lubricant.

Dehydrator

A separator that removes water from the system fluid.

Delaminating 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.

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.

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 re-disperse deposits already formed.

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.)

Differential pressure indicator

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

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.

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.

Duplex filter

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