Power Engineering Dictionary
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LABYRINTH SEAL - A labyrinth seal consists of a number of rings 1 - 2 millimeters thick fixed to the shaft, tapered at the outer periphery to nearly knife-sharp with a clearance to the casing of a few hundreds of a millimeter. The rings are of brass or stainless steel, the sharp edge gives better sealing and rubs off easily without excessive heating in case of a slightly eccentric shaft. Some labyrinth seals are very simple, others are complicated.

LAG - A delay in the effect of a changed condition at one point in the system, on some other condition to which it is related. Also, the delay in action of the sensing element of a control, due to the time required for the sensing element to reach equilibrium with the property being controlled; i.e., temperature lag, flow lag, etc.

LAMINAR FLOW - A non-turbulent flow regime in which the stream filaments glide along the pipe axially with essentially no transverse mixing.

LANGELIER SATURATION INDEX - An index (SI) based upon the pH of saturation of calcium carbonate; used to determine the tendencies of a water supply toward corrosion or scaling. A positive index indicates scaling tendencies; a negative one means corrosion tendencies. (Langlier Index = pH - pHs, where pH = actual pH of water and pHs = pH at which water having the same alkalinity and calcium content is just saturated with calcium carbonate.

LATENT HEAT - Change of enthalpy during a change of state, usually expressed in Btu per lb. With pure substances, latent heat is absorbed or rejected at constant pressure.

LATENT HEAT - Heat energy absorbed in process of changing form of substance (melting, vaporization, fusion) without change in temperature or pressure.

LATENT HEAT OF CONDENSATION - Amount of heat released (lost) by a pound of a substance to change its state from a vapor (gas) to a liquid.

LATENT HEAT OF FUSION - The heat required to change 1.0 kg of a substance from the solid to the liquid state.

LATENT HEAT OF VAPORIZATION - The energy required to produce saturated vapor from saturated liquid at constant pressure per unit mass of fluid.

LAW OF PARTIAL PRESSURE, DALTONíS - Each constituent of a mixture of gases behaves thermodynamically as if it alone occupied the space. The sum of the individual pressures of the constituents equals the total pressure of the mixture.


LEADING EDGE - Refers to the point where the steam enters the blade of an impulse turbine.

LEAK DETECTOR - Device or instrument such as a halide torch, an electronic sniffer; or soap solution used to detect leaks.

LEAKAGE - In water treatment, it refers to the passing of impure steam or boiler water through the drum internals.

LEAKAGE - In water treatment, the phenomenon in which some of the influent ions are not adsorbed and appear in the effluent when a solution is passed through an under regenerated exchange resin bed.

LIGHT CRUDE OIL - A crude oil of relatively high API gravity (usually 40įC degrees or higher).

LIGHT EMITTING DIODE - A low current and voltage light used as an indicator on load management equipment. Abbreviated: LED.

LIME - A common water treatment chemical.

LIME-SODA SOFTENING - A process by which the calcium and magnesium salts, constituting the harness content of a water, are chemically precipitated and removed.

LINE VOLTAGE - In the control industry, the normal electric supply voltages, which are usually 120 or 240 volts.

LIQUEFACTION - The change of state from a gas to a liquid. (The term liquefaction is usually used instead of condensation when referring to substances which are in a gaseous state at ordinary pressures and temperatures.)

LIQUID - Substance whose molecules move freely among themselves, but do not tend to separate like those of gases.

LIQUID ABSORBENT - Chemical in liquid form which has the property to "take on" or absorb other fluids. Glycol is such a liquid and widely use in the petroleum chemical industry

LIQUID IMPINGEMENT - Material removal due to action of an impingement stream of a fluid.

LIQUID INDICATOR - Device located in liquid line which provides a glass window through which liquid flow may be watched.

LIQUID LINE - Tube which carries liquid refrigerant from the condenser or liquid receiver to the refrigerant control mechanism.

LIQUID LINE CHARGING VALVE - The line used for charging from the high side of the refrigeration system.

LIQUID NITROGEN - Nitrogen in liquid form which is used as a low temperature refrigerant in expendable or chemical refrigerating systems.

LIQUID PENETRANT INSPECTION - A type of nondestructive inspection that locates discontinuities that are open to the surface of a metal by first allowing a penetrating dye or fluorescent liquid to infiltrate the discontinuity, removing the excess penetrant, and then applying a developing agent that causes the penetrant to seep back out of the discontinuity and register as an indication.

LIQUID RECEIVER - Cylinder (container) connected to condenser outlet for storage of liquid refrigerant in a system.

LIQUID RECEIVER SERVICE VALVE - Two or three-way manual valve located at the outlet of the receiver and used for installation and service purposes. It is sometimes called the king valve.

LIQUID-VAPOR VALVE REFRIGERANT CYLINDER - Dual hand valve on refrigerant cylinders, which is used to release either gas or liquid refrigerant from the cylinder.

LIQUOR - Solution used in absorption refrigeration.

LITHIUM BROMIDE - A chemical used in combination with water in absorption cooling systems.

LOAD - The amount of heat per unit time imposed on a refrigeration system or the required rate of heat removal.

LOAD (AIR CONDITIONING) - The amount of heat per unit time imposed on a refrigeration system or the required rate of heat removal.

LOAD TURBINE (GAS) - Is the turbine which is directly coupled to the load, which can only be the case with a multishaft gas turbine arrangement.

LOCKED ROTOR CURRENT - See "Inrush Current".

LONGITUDINAL SEAM - A riveted or welded seam along the longitudinal axis of a boiler shell or drum.

LOW SIDE - The refrigerating system from the expansion point to the point where the refrigerant vapor is compressed; where the system is at or below evaporated pressure.

LOW TEMPERATURE CUTOUT, REFRIGERATON - A pressure or temperature actuated device with sensing element in the evaporator, which will shut the system down at its control setting to prevent freezing chilled water or to prevent coil frosting. Direct expansion equipment may not use this device.

LOW VOLTAGE - In the control industry, a power supply of 25 volts or less.


LOW-SIDE FLOAT VALVE - Refrigerant control valve operated by level of liquid refrigerant in low-pressure side of system.

LOW-SIDE PRESSURE - Pressure in cooling side of refrigerating cycle.

LOW-SIDE PRESSURE CONTROL - Device used to keep low side evaporating pressure from dropping below certain pressure.

LUBRICANT - A substance - usually petroleum based, that is used to reduce friction between two moving parts.

LUBRICANT, BONDED FILM - (see lubricant, bonded solid).

LUBRICANT, BONDED SOLID - A solid lubricant dispersed in a continuous matrix of a binder or attached to a surface by an adhesive material.

LUBRICANT, CHLORINATED - A lubricant containing a chlorine compound that reacts with a rubbing surface at elevated temperatures to protect it from sliding damage, (see extreme pressure lubricant).

LUBRICANT, SYNTHETIC - A lubricant produced by synthesis rather than by extraction or refinement.

LUBRICATION, AERODYNAMIC - (see gas lubrication).

LUBRICATION, AEROSTATICS - (see pressurized gas lubrication).

LUBRICATION, BATH - (see lubrication, flood).

LUBRICATION, BOUNDARY - A condition of lubrication in which the friction and wear between two surfaces in relative motion are determined by the properties of the surfaces and by the properties of the lubricant other than bulk viscosity.

LUBRICATION, DRIP FEED - A system of lubrication in which the lubricant is supplied to the bearing surface in the form of drops at regular intervals.

LUBRICATION, DRY FILM - Lubrication that involves the application of a thin film of solid lubricant to the surface or surfaces to be lubricated.

LUBRICATION, FLOOD - A system of lubrication in which the lubricant is supplied in a continuos stream at low pressure and subsequently drains away.

LUBRICATION, FULL FILM - A type of lubrication wherein the solid surfaces are separated completely by an elstohydrodynamic fluid film.

LUBRICATION, MAGNETO HYDRODYNAMIC Hydrodynamic lubrication in which a significant force contribution arises from electromagnetic interaction.

LUBRICATION, MELT - Lubrication provided by steady melting of lubricating species. Also phase-change lubrication.

LUBRICATION, MIST - Lubrication by an oil mist produced by injecting oil into a gas stream.

LUBRICATION, OIL FOG - (see mist lubrication).

LUBRICATION, OIL RING - A system of lubrication for horizontal shafts. A ring of larger diameter rotates with the shaft and collects oils from a container beneath.

LUBRICATION, PAD - A system of lubrication in which the lubricant is delivered to a bearing surface by a pad of felt or similar material.

LUBRICATION, PRESSURIZED GAS - A system of lubrication in which a gaseous lubricant is supplied under sufficient external pressure to separate the opposing surfaces by a gas film.

LUBRICATION, SOLID-FILM - Lubrication by application of a solid lubricant.

LUBRICATION, SPLASH - A system of lubrication in which the lubricant is splashed onto the moving parts.

LUBRICATION, THICK FILM - (also known as flood lubrication).

LUBRICATION, THIN FILM - (also known as boundary lubrication).

LUBRICATION, VAPOR-PHASE - A type of lubrication in which one or more gaseous reactants are supplied to the vicinity of the surface to be lubricated and which subsequently react to form a lubricious deposit on that surface.

LUBRICATION, WASTE - A system of lubrication in which the lubricant is delivered to a bearing surface by cloth waste or yarn.

LUBRICATION, WICK - A system of lubrication in which the lubricant is delivered to a bearing surface by means of a wick.

LUBRICITY - The ability of a lubricant to reduce wear and friction, other than by its pure viscous properties.

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