GLOSSARY

ABDC: Abbreviation for after bottom dead center.

ABSOLUTE PRESSURE: Gauge pressure plus atmospheric pressure.

ABSOLUTE TEMPERATURE: The tem-perature measured when absolute zero is used as a reference. Absolute zero is - 273.16C or .469.69F, and is the lowest measured temperature known.

ABT: Abbreviation for automatic bus transfer; an automatic electric device that supplies power to vital equipment. This device will shift from the normal power supply to an alternate power supply any time the normal supply is interrupted.

ACCELERATION: The rate of increase of velocity per time unit (for example, seconds, minutes, or hours).

ACCESSORY DRIVE: A drive consisting of gears, chains, or belts of secondary importance, not essential in itself but essential for the operation of engine accessories (fuel pump, water pump, and so forth).

ACCUMULATOR: A device used for storing liquid under pressure; sometimes used to smooth out pressure surges in a hydraulic system.

ACTUATOR: A device that uses fluid power to produce mechanical force and motion.

ADDITIVE: A material that is added to improve fuel or oil.

ADVANCE: To set the timing of the injection pump or injectors for an earlier injection.

AFTERCOOLER: A device used on turbo-charged engines to cool air that has undergone compression.

AIR BIND: The presence of air in a pump or pipes, which prevents the delivery of liquid.

AIR BLEEDER: A device that removes air from a hydraulic system. Types include a needle valve, capillary tubing to the reservoir, and a bleed plug l

AIR CLEANER: A device (filter) for removing unwanted solid impurities from the air before the air enters the intake manifold.

AIR COMPRESSOR: A device used to increase air pressure.

AIR EJECTOR: A jet pump that removes air and noncondensable gases.

AIR-FUEL RATIO: The ratio (by weight or by volume) between air and fuel.

AIR GAP: The distance between two components.

AIR-STARTING VALVE: A valve that admits compressed air to the air starter for starting purposes.

ALIGN: To bring two or more components of a unit into the correct positions with respect to one another.

ALLOY: A mixture of two or more different metals, usually to produce improved charac-teristics.

ALLOWANCE: The difference between the minimum and the maximum dimensions of proper functioning.

ALTERNATING CURRENT (a.c.): Current that is constantly changing in value and direction at regularly recurring intervals.

AMBIENT TEMPERATURE: The tem-perature of the surrounding environment.

AMMETER: An instrument for measuring the rate of flow of electrical current in amperes.

AMPERE: The basic unit of electrical current.

ANNEAL: To heat a metal and to cool it in such a manner as to toughen and soften it. Brass or copper is annealed by heating it to a cherry red color and dipping it suddenly into water while hot. Iron or steel is slowly cooled from the heated condition to anneal.

ANNUNCIATOR: A device, usually electro-mechanical, used to indicate or transmit informa-tion. See ENGINE ORDER TELEGRAPH.

ANTIFRICTION BEARING: A bearing containing rollers or balls plus an inner and outer race. The bearing is designed to roll, thus minimiz-ing friction.

API: Abbreviation for American Petroleum Institute.

API GRAVITY: Gravity expressed in units of standard API (hydrometer).

ARC: Portion of a curved line or of the circumference of a circle.

ARCING: Electrons leaping the gap between the negative and the positive poles.

ARMATURE: The movable part of a relay, regulator, or horn, or the rotating part of a generator or starter.

ATDC: Abbreviation for after top dead center.

ATMOSPHERE: The mass or blanket of gases surrounding the earth.

ATMOSPHERIC PRESSURE (BAROMETRIC PRESSURE): The pressure exerted by the atmosphere, averaging 14.7 psi at sea level with a decrease of approximately 1/2 pound per 1000 feet of altitude gained.

ATOMIZATION: The spraying of a liquid through a nozzle so the liquid is broken into tiny droplets or particles.

AUTOMATIC CONTROLLER: An instrument or device that operates automatically to regulate a controlled variable in response to a set point and/or input signal.

AUTOMATIC CONTROL SYSTEM: A system of instruments or devices arranged systematically to control a process or operation at a set point without assistance from operating personnel.

AUTOMATIC OPERATION: Operation of a control system and the process under control without assistance from the operator.

AUXILIARY MACHINERY: Any system or unit of machinery that supports the main propulsion units or helps support the ship and the crew. Examples of auxiliary machinery are pumps, evaporators, steering engines, air-conditioning and refrigeration equipment, laundry and galley equipment, deck winches, and so forth.

AXIAL: In a direction parallel to the axis. Axial movement is movement parallel to the axis.

AXIS: The centerline running lengthwise.