GAUGE GLASS: A device for indicating the liquid level in a tank.

GAUGE PRESSURE: Pressure above atmospheric pressure.

GALVANIZING: The process of coating one metal with another, ordinarily applied to the coating of iron or steel with zinc. The chief purpose of galvanizing is to prevent corrosion.

GAS: The form of matter that has neither a definite shape nor a definite volume.

GAS FREE: A term used to describe a space that has been tested and its atmosphere found safe for human occupation and for hot work (welding and cutting).

GASKET(S): (1) A class of material that provides a seal between two stationary parts. (2) Packing materials by which air, water, oil, or steam tightness is secured in such places as on doors, hatches, cylinders, manhole covers, or in valves, between the flanges of pipes, and so forth. Such materials as rubber, canvas, asbestos, paper, sheet lead and copper, soft iron, and commercial products are extensively used.

GEARING: A term applied to wheels which have teeth that mesh, engage, or gear with similar teeth or other wheels in such manner that motion given one wheel will be imparted to the other.

GENERATOR: A machine that converts mechanical energy into electrical energy.

GLAND SEALING: Water piped to a pump casing stuffing box to maintain a seal against air entering the pump casing.

GOVERNOR: A speed-sensitive device designed to control or limit the speed of the engine.

GRAPHITE: A crystalline form of carbon having a slippery feel and black color with metallic luster. Used for a lubricant.

GRAVITY HEAD: A supply of fluid above the suction level of a pump; also called statichead.

GROUND PLUG: A three-pronged electricalplug used to ground portable tools to the shipsstructure. It is a safety device which always must be checked prior to your using portable tools.

HALIDE LEAK DETECTOR: A device that is used to locate leaks in refrigeration systems.

HANDHOLE: An opening large enough for the hand and arm to enter areas, such as the engine, for making slight repairs and for inspection purposes.

HARDENING: The treatment or heating and cooling (quenching) of metal to harden the surface.

HARDNESS: A quality exhibited by water containing various dissolved salts, principally calcium and magnesium. Hard water can deposit a heat transfer resistant scale on the heat exchanger surface.

HEAD: (1) A separate unit from the engine cylinder block designed to seal the cylinder at the combustion end. (2) The pressure or energy content of a hydraulic system, expressed in the height of a column of water in feet.

HEAT: A thermal form of energy.

HEAT EXCHANGER: Any device that is designed to allow the transfer of heat from one fluid (liquid or gas) to another.

HEATING SURFACE: The exposed surface of a heating unit in a heat exchanger which is directly exposed to the heat of the flue gases.

HEATING SYSTEM: A system for adding heat to maintain the desired air temperature, as distinguished from heat added incidentally or unavoidably.

HELICAL: A spiraling shape such as that made by a coil spring.

HELIX: The curve formed on any cylinder by a straight line in a plane that is wrapped around the cylinder with a forward progression.

HELM: (1) The term applied to the tiller, wheel, or steering gear, and also the rudder. (2) A mechanical device used to turn the rudder; usually a wheel aboardship, or a lever (tiller) in boats.

HERTZ: The measurement of frequencies in cycles per second, 1 hertz being equal to 1 cycle per second.

HORSEPOWER (hp): A unit for measuring the power of motors or engines, equal to a rate of 33,000 foot-pounds per minute. The force required to raise 33,000 pounds at the rate of 1 foot per minute.

HOT WELL: A reservoir attached to the bottom of a condenser for collecting condensate.

HUMIDITY: The vapor content of the atmosphere. Humidity can vary depending on air temperature; the higher the temperature, the more vapor the air can hold.

HUNTING: A rhythmic variation of speed that can be eliminated by blocking the fuel supply manually or with load limit. The speed variation will reappear when the engine is returned to governor control.

HYDRAULICS: That branch of mechanics or engineering that deals with the action or use of liquids forced through tubes and orifices under pressure to operate various mechanisms.

HYDROCARBON: Chemical compound of hydrogen and carbon. All petroleum fuels are composed of hydrocarbons.

HYDROGEN: A highly explosive, light, invisible, nonpoisonous gas. It is produced in small quantities when batteries are charged.

HYDROMETER: An instrument used to determine the specific gravities of liquids.

HYDROSTATIC: Static (nonmoving) pres-sure generated by pressurizing liquid.

HYDROSTATIC TEST: A test using pressurized water to detect leaks in a closed system.