Vapor degreasing: cleaning procedure to remove oil, grease and lightly attached solids from metals. An appropriate solvent, e.g., hexane or cleaners solvent, is boiled; as the vapors condense on the metal surfaces, contaminants fall into the reservoir.

Vapor phase corrosion inhibitors: fine, volatile powders made from stable nitrites of organic amines that prevent rusting; after vaporizing, they are adsorbed by metal surfaces. They are also marketed as treated papers; see VCI paper.

Vapor pressure: measure of the volatility of a liquid at specified temperatures and pressures (or vacuum).

Variable displacement pumps: pumps that can be adjusted to deliver a variable volume while the speed remains constant.

Varnish: in lubrication, a deposit resulting from oxidation and polymerization of fuels and lubricants; like lacquer, but softer.

Volatile corrosion-inhibiting (VCI) paper: corrosion-inhibiting papers and films impregnated with vapor phase corrosion inhibitors to prevent corrosion of ferrous and non-ferrous metals; may be used to wrap new parts to prevent corrosion during storage or shipping (see vapor phase corrosion inhibitors).

Vegetable oils: oily fluids with varying percentages of fatty acids, obtained from vegetable sources; examples are coconut oil, rapeseed oil, sunflower oil, crambe oil, etc.

Vent valve (lube systems): device for relieving supply line pressure.

Venturi: tube, constricted at the middle and flared at both ends, in the pathway of a fluid, to reduce fluid pressure in the constricted area.

Venturi meter: a form of flow measuring device containing no moving parts that operates on the principle of velocity to pressure conversion with values taken on each side of the venturi tube.

VI: see viscosity index.

Vibrational analysis: analytical method used to monitor bearing conditions during operations.

Virgin oil: a fresh oil product not recycled or reclaimed.

Viscometer/viscosimeter: an apparatus for determining the viscosity of a fluid.

Viscosity: the property of a fluid, semi-fluid or semi-solid substance that causes it to resist flow. Its numerical value is based on the ratio of shear stress to the rate of shear during flow. The standard unit of absolute viscosity in the English system is the reyn, expressed as lb-s/in.2. The standard unit of viscosity in the cgs and ISO system is the poise, expressed as dyne-s/cm2. Conversion from one system to the other is as follows:

reyn = poise X 1.45 X 10-5
poise = reyn X 6.895 X 104
centipoise = poise X 10-2
microreyn = reyn X 10-6
For Saybolt seconds, convert to centistokes, then to centipoise before converting
to reyns. Specific calculations are: cp = cSt X specific gravity
SUS – 180
cSt = 0.22 X
(see absolute viscosity, kinematic viscosity).
Viscosity Index/VI: common measure of changes in viscosity with temperature; the higher the viscosity index, the smaller the relative change in viscosity with temperature.

Volatile organic/VOC: as potential hazard or pollutant, applies to any carbon compound that can be evaporated using standard test methods, except for carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates and ammonium carbonate. Because of the complexities involved in measuring VOC, no universal definition has been formulated. VOC control is often enforced by local government agencies.

Volatility – the tendency of a fluid to evaporate. High evaporation rate means high volatility.

Vapor phase inhibitor/VPI: corrosion inhibitor in the form of vapor, also referred to as a vapor corrosion inhibitor (see VCI).