Glossary of Compressed Air Terms :: V :: Glossary Index 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 Vacuum pumps Compressors that operate with an intake pressure below atmospheric and discharge pressure usually atmospheric or slightly higher. Valves Devices with passages for directing flow into alternate paths. Vane compressor Is a single shaft, positive displacement rotary compressor. Vane material Most common material is phenolic resin-impregnated laminated fabrics, such as asbestos or cotton cloth. For oil free service, bronze and carbon/graphite vanes are used. Vapor Fine separated particles floating in the air and clouding it. A substance in the gaseous state. Vapor pressure Is the pressure exerted by a vapor confined within a given space. The vapor may be the sole occupant of the space, or may be associated with other gases. Varnish The oxidation of conventional hydrocarbon lubricants when they reach the end of their useful life and begin to breakdown. Can cause operating temperature increase, increase brake horsepower and plugs separator, can destroy air end. V belt drive A drive arrangement for power transmission to compressors. Venturi A tube with a narrow throat (a constriction) that increases the velocity and lowers the pressure of the liquid passing through it, creating a partial vacuum immediately after the constriction in the tube. The vacuum created has a sucking effect, and a venturi is commonly used to introduce a liquid (such as a regenerant) or gas (such as air) into a flowing water stream. Viscosity Is a measure of resistance to deformation, or reluctance to be squeezed out a bearing. Indicates the internal friction of a fluid. Viscosity in normal lubricants is reduced as temperature increases Viscosity index (VI) Is a measure of the rate of change of viscosity with temperature. Oils with high VI have low viscosity changes. Volumetric efficiency The ratio and percent of the actual delivered capacity (measured at inlet temperature, pressure and gas composition) to the piston displacement. Volute A stationary, spirally shaped passage that converts velocity head to pressure. Voting alarm (Compressors/Gas Turbines) Is an alarm system that has maybe 3 sensors connected to it and it will require minimum of 2 of the 3 to alarm before the alarm will act. There is a controller connected that does the logic decision based on set parameters. Glossary Index 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