{"data":{"id":"us/10-cfr-431.342","jurisdiction":"us","citation":"10 CFR 431.342","heading":"Definitions concerning compressors.","body":"The following definitions are applicable to this subpart, including appendix A. In cases where there is a conflict, the language of the definitions adopted in this section take precedence over any descriptions or definitions found in any other source, including in ISO Standard 1217:2009(E), “Displacement compressors—Acceptance tests,” as amended through Amendment 1:2016(E), “Calculation of isentropic efficiency and relationship with specific energy” (incorporated by reference, see § 431.343). In cases where definitions reference design intent, DOE will consider all relevant information, including marketing materials, labels and certifications, and equipment design, to determine design intent.\nActual volume flow rate means the volume flow rate of air, compressed and delivered at the standard discharge point, referred to conditions of total temperature, total pressure and composition prevailing at the standard inlet point, and as determined in accordance with the test procedures prescribed in § 431.344.\nAir compressor means a compressor designed to compress air that has an inlet open to the atmosphere or other source of air, and is made up of one or more compression elements (bare compressors), driver(s), mechanical equipment to drive the compression elements, and any ancillary equipment.\nAir-cooled compressor means a compressor that utilizes air to cool both the compressed air and, if present, any auxiliary substance used to facilitate compression, and that is not a liquid-cooled compressor.\nAncillary equipment means any equipment distributed in commerce with an air compressor but that is not a bare compressor, driver, or mechanical equipment. Ancillary equipment is considered to be part of a given air compressor, regardless of whether the ancillary equipment is physically attached to the bare compressor, driver, or mechanical equipment at the time when the air compressor is distributed in commerce.\nAuxiliary substance means any substance deliberately introduced into a compression process to aid in compression of a gas by any of the following: Lubricating, sealing mechanical clearances, or absorbing heat.\nBare compressor means the compression element and auxiliary devices (e.g., inlet and outlet valves, seals, lubrication system, and gas flow paths) required for performing the gas compression process, but does not include any of the following:\n(1) The driver;\n(2) Speed-adjusting gear(s);\n(3) Gas processing apparatuses and piping; and\n(4) Compressor equipment packaging and mounting facilities and enclosures.\nBasic model means all units of a class of compressors manufactured by one manufacturer, having the same primary energy source, the same compressor motor nominal horsepower, and essentially identical electrical, physical, and functional (or pneumatic) characteristics that affect energy consumption and energy efficiency.\nBrushless electric motor means a machine that converts electrical power into rotational mechanical power without use of sliding electrical contacts.\nCompressor means a machine or apparatus that converts different types of energy into the potential energy of gas pressure for displacement and compression of gaseous media to any higher pressure values above atmospheric pressure and has a pressure ratio at full-load operating pressure greater than 1.3.\nCompressor motor nominal horsepower means the motor horsepower of the electric motor, as determined in accordance with the applicable procedures in subparts B and X of this part, with which the rated air compressor is distributed in commerce.\nDriver means the machine providing mechanical input to drive a bare compressor directly or through the use of mechanical equipment.\nFixed-speed compressor means an air compressor that is not capable of adjusting the speed of the driver continuously over the driver operating speed range in response to incremental changes in the required compressor flow rate.\nFull-load actual volume flow rate means the actual volume flow rate of the compressor at the full-load operating pressure.\nLiquid-cooled compressor means a compressor that utilizes liquid coolant provided by an external system to cool both the compressed air and, if present, any auxiliary substance used to facilitate compression.\nLubricant-free compressor means a compressor that does not introduce any auxiliary substance into the compression chamber at any time during operation.\nLubricated compressor means a compressor that introduces an auxiliary substance into the compression chamber during compression.\nMaximum full-flow operating pressure means the maximum discharge pressure at which the compressor is capable of operating, as determined in accordance with the test procedure prescribed in § 431.344.\nMechanical equipment means any component of an air compressor that transfers energy from the driver to the bare compressor.\nPackage isentropic efficiency means the ratio of power required for an ideal isentropic compression process to the actual packaged compressor power input used at a given load point, as determined in accordance with the test procedures prescribed in § 431.344.\nPackage specific power means the compressor power input at a given load point, divided by the actual volume flow rate at the same load point, as determined in accordance with the test procedures prescribed in § 431.344.\nPositive displacement compressor means a compressor in which the admission and diminution of successive volumes of the gaseous medium are performed periodically by forced expansion and diminution of a closed space(s) in a working chamber(s) by means of displacement of a moving member(s) or by displacement and forced discharge of the gaseous medium into the high-pressure area.\nPressure ratio at full-load operating pressure means the ratio of discharge pressure to inlet pressure, determined at full-load operating pressure in accordance with the test procedures prescribed in § 431.344.\nReciprocating compressor means a positive displacement compressor in which gas admission and diminution of its successive volumes are performed cyclically by straight-line alternating movements of a moving member(s) in a compression chamber(s).\nRotary compressor means a positive displacement compressor in which gas admission and diminution of its successive volumes or its forced discharge are performed cyclically by rotation of one or several rotors in a compressor casing.\nRotor means a compression element that rotates continually in a single direction about a single shaft or axis.\nVariable-speed compressor means an air compressor that is capable of adjusting the speed of the driver continuously over the driver operating speed range in response to incremental changes in the required compressor actual volume flow rate.\nWater-injected lubricated compressor means a lubricated compressor that uses injected water as an auxiliary substance.","path":["Title 10—Energy","CHAPTER II—DEPARTMENT OF ENERGY","SUBCHAPTER D—ENERGY CONSERVATION","PART 431—ENERGY EFFICIENCY PROGRAM FOR CERTAIN COMMERCIAL AND INDUSTRIAL EQUIPMENT","Subpart T—Compressors"],"source_url":"https://www.ecfr.gov/api/versioner/v1/full/2026-08-25/title-10.xml","current_through":"2026-08-25","vintage":"","retrieved_at":"2026-08-27T02:24:09Z","sha256":"515af7842cf5f945ccaba61528cd8f0df16c8f01fa7a7e4defbc01790ffbb4fe","source_id":"us-cfr","stale":true,"prev":"us/10-cfr-431.341","next":"us/10-cfr-431.343"},"notice":"GroundRules: Original legal text. Not legal advice."}