Glossary of Compressed Air Terms :: I :: 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 IBV Inlet butterfly valve. These are fitted on the inlet of most types of compressor and the valve opens and closes to throttle the air flow. However, the term IBV is usually associated with turbo compressors. ICFM CFM flowing through the compressor inlet filter or inlet valve under rated conditions I.D. A measurement. Inside diameter. Ideal gas Is a gas that follows the perfect gas laws without deviation. There is no such thing, however it is the basis from which calculations are made and corrections applied. Ideal multi stage compression The condition when a perfect gas is isentropically compressed, and the gas inlet temperature and also the amount of work spent is the same for each stage. IGV Inlet guide-vane valve. Valve assembly at the air inlet of a "blower" (single stage, low pressure, centrifugal air compressor). Usually advised to be mounted in very close proximity to the "blower" impeller. Provides "pre-swirl" of air flow in same rotational direction as "blower" impeller. Proven to improve efficiency (reduced bhp) during throttled-down modulation of "blowers". Effectiveness, when used with multi-stage centrifugal air compressors, degrades rapidly. Immiscible Incapable of being mixed without separation phases. Water and petroleum oil are immiscible under most conditions, although they can be made miscible with the addition of an emulsifier. Impeller The part of the rotating element of a dynamic compressor that imparts energy to the flowing medium by means of centrifugal force. It consists of a number of blades mounted so as to rotate with the shaft. Inches of water A measurement of vacuum or pressure that is used to measure the airflow restriction. Indicated power Power as calculated from compressor-indicator diagrams. Indicator card A pressure-volume diagram for a compressor or engine cylinder produced by direct measurement made by the use of a device called an indicator. Indicator pressure An indicator that signals pressure conditions. Induced draft An air flow caused by a fan that draws air through the heat exchanger core in a uniform pattern to dissipate the sensible heat. Inducer A curved inlet section on an impeller. Inert gas Is one that does not enter into known chemical combination, either with itself or another element. There are four known gases of this type: helium; neon; argon and krypton. or a gas that does not supply any of the needs of combustion. Inertia base A concrete foundation with lateral supports which rests upon a number of steel springs. Designed to deal with disturbing frequencies in vibration isolation Inertia forces When reciprocating compressors run, the moving parts such as pistons, rods, crossheads, connecting rods are repeatedly accelerated and retarded. These velocity changes set up pulsating inertia forces. The forces are of the first and second order. The first order forces have the same frequency as the compressor shaft speed and the second order forces have a frequency twice the shaft speed. Influent The fluid entering a component. Ingested contaminants Environmental contaminant that ingresses due to the action of the system or machine. Inlet pressure Is the total pressure (static plus velocity) at the inlet flange of the compressor. Inlet temperature Is the temperature at the inlet flange of the compressor. Inlet throttle A compressor control mechanism designed to control performance output of the compressor to the demands of the plant process. Inline filter A filter assembly in which the inlet, outlet and filter element axes are in a straight line. Insolubles Insoluble material suspended in the lubricating oil. This material may come from contamination or oil degradation. Instrument air A quality of compressed air for use with pneumatic instruments and controls. (usually dry and free from contaminants) Intake filter A device for separating solids or suspended particles in the air before they enter the air intake of the compressor. Intake filter silencer A device for separating solids or suspended particles in the air before they enter the air intake of the compressor and reduce intake noise as on reciprocating compressors through a silencing chamber in the filter housing. Intank check valve A valve designed to prevent air volume and pressure from escaping the compressor tank back into compressor heads while compressor is not operating. Intercooler Heat exchangers for removing the heat of compression between stages of a compressor. Intercooling The removal of heat from the air or gas between stages. Internal energy Energy which a substance possesses because of the motion and configuration of its atoms, molecules, and subatomic particles. International Organization for Standardization ISO. Irreversible process is one in which a portion of the original system energy is dissipated and cannot be returned to the system through its own operation. The system and/or surroundings cannot be returned to their original state. Isentrop Is a process taking place without any heat exchange with the surroundings. Isentropic compression An adiabatic compression with no increase in entropy; a reversible-adiabatic compression. Isentropic efficiency The ratio of the real gas isentropic power consumption to shaft input. Isentropic power consumption The power which is theoretically required to compress a gas under constant entropy from a given inlet pressure to a given discharge pressure. (calculated assuming ideal conditions). ISO International Organization for Standardization. Isobar Is a process taking place under constant pressure. To change the volume from state 1 to state 2, heat must be removed. The temperature change is proportional to the change in specific volume. Isochor Is a process taking place under constant volume. To raise the pressure from state 1 to state 2, heat must be added. The pressure change is proportional to the change in temperature. Isotherm Is a process taking place under constant temperature. To compress the gas from state 1 to state 2, heat must be removed to keep the temperature constant. The pressure change is reciprocal to the change in specific volume. Isothermal compression Is a compression in which the temperature of a gas remains constant. Isothermal efficiency The ratio of the isothermal power consumption to shaft input. Isothermal power consumption The power which is theoretically required to compress a gas under constant temperature, in a compressor free from losses, from a given inlet pressure to a given discharge pressure. 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