KEY: A small wedge or rectangular piece of metal inserted in a slot or groove between a shaft and a hub to prevent slippage.

KEYWAY: A slot cut in a shaft, pulley hub, wheel hub, and so forth. A square key is placed in the slot and engages a similar keyway in the mating piece. The key prevents slippage between the two parts.

KILO: A prefix meaning 1,000.

KINETIC ENERGY: The energy which a substance has while it is in motion.

LABYRINTH PACKING: A soft metal ring or rings arranged inside a casing throat in such a manner that the inside diametrical edges will form a series of seals along the surface of the rotating shaft. The edges fit either close to the surface of the shaft or in grooves machined in the shaft.

LAGGING: (1) A protective and confining cover placed over insulating material. (2) A term applied to the insulating material that is fitted on the outside of engine exhaust, piping, and so forth.

LAMBERT SEAL: The hydraulic equivalent of labyrinth packing.

LAP: To work two surfaces together with abrasives until a very close fit is produced; to polish.

LASH: The clearance or play between adjacent movable mechanical parts. See VALVE LASH.

LATENT HEAT: Heat that is given off or absorbed by a substance while it is changing its state.

LATENT HEAT OF CONDENSATION:

The amount of heat (energy) required to change the state of a substance from a vapor to a liquid without a change in temperature.

LATENT HEAT OF VAPORIZATION: The amount of heat (energy) required to change the state of a substance from a liquid to a vapor without a change in temperature.

LEAD: (1) The distance a screw thread advances in one turn, measured parallel to the axis. On a single-thread screw, the lead and the pitch are identical; on a double-thread screw, the lead is twice the pitch; on a triple-thread screw, the lead is three times the pitch. (2) A wire or connection.

LIFT CHECK VALVE: A valve having a guide-mounted, spring-loaded disk wherein liquid exerting pressure on the bottom of the disk will lift the disk and pass through. Pressure against the top of the disk shuts the disk and ensures only one direction of flow.

LIGHT OFF: To start; literally, to start a fire in, such as to light off a boiler.

LIMIT SWITCH: A switch that is actuated by the mechanical motion of an element.

LIQUID: A form of matter that has a definite volume but takes the shape of its container.

LOAD: (1) External resistance overcome by a prime mover. (2) The power that is being delivered by a generator.

LOADING: The act of transferring energy into or out of a system.

LOCAL MANUAL OPERATION: Direct manual positioning of a control valve or power operator by means of a handwheel or lever.

LOCKED TRAIN: A gear arrangement that has each high-speed (prime mover) pinion locked between two primary gears which cancelthe tooth loading on the pinion bearings.

LOCK NUT: (1) A thin nut that is turned down over the regular nut on a bolt to lock the regular nut against turning off. (See JAM NUT.) (2) A thin nut placed on a pipe to hold packing at a joint or used on both sides of a bulkhead through which a pipe passes to secure tightness.

LOG: (1) A ships speedometer. (2) The actof a ship in making a certain speed, as The shiplogged 20 knots. (3) A book or ledger in whichthe watch officer records data or events that occurred during the watch.

LOG BOOK: Any chronological record of events, such as the engineering watch log.

LOG ROOM: Engineers office aboard ship.LOOP SEAL: A vertical U-bend in drain piping in which a water level is maintained to create an airtight seal.

LUBE OIL PURIFIER: A unit that removes water and sediment from lubricating oil by centrifugal force.

LUBRICANT: Any material, usually of a petroleum nature, such as grease, oil, and so forth, that is placed between two moving parts in an effort to reduce friction.

LUG: An earlike projection that is frequently split, such as the clamping lug on the tailstock of a lathe.