OFFSET SECTION: A section view of two or more planes in an object to show features that do not lie in the same plane.

OHM: The unit of electrical resistance.

OHMMETER: An instrument for directly measuring resistance in ohms.

OIL KING: A petty officer who receives, transfers, discharges, and tests fuel oil and main-tains fuel oil records.

OIL STRAINER: A strainer placed at the inlet end of the oil pump to prevent dirt and other particles from getting into moving parts.

OILTIGHT: Having the property of resisting the passage of oil.

ONBOARD PLANS: See SHIPS PLANS.OPERATING CHARACTERISTICS: The combination of a parameter and its set points. See PARAMETER.

OPERATING PRESSURE: The constant pressure at which a component is designed to operate in service.

OPERATING TEMPERATURE: The actual temperature of a component during operation.

OPERATION (AUTOMATIC): The regula-tion of a process by a controlling system without manual intervention.

OPERATION (LOCAL-MANUAL): Posi-tioning of a final control element by attending personnel from the elements manual controlstation.

ORIFICE: A circular opening in a flow passage which acts as a flow restriction.

OSCILLATION: A backward and forward motion; a vibration.

OTTO COMBUSTION CYCLE: Combustion induced by spark ignition occurring at constant volume. The basic combustion cycle of a gasoline engine.

OUTPUT SIGNAL: The pressure or flow of fluid leaving the output port of a fluidic device.

OVERHAUL: To inspect, repair, and put in proper condition for operation.

OVERLOAD: A load greater than the rated load of an engine or electrical device.

OXIDATION: The process of various elements and compounds combining with oxygen. The corrosion of metal is generally a form of oxidation; rust on iron, for example, is iron oxide or oxidation.

OXYGEN-FREE FEEDWATER: Water from which dissolved oxygen has been removed.

PACKING: A class of seal that provides a seal between two parts of a unit, which move in relation to each other.

PANT, PANTING: A series of pulsations caused by minor, recurrent explosions in the firebox of a ships boiler. Usually caused by ashortage of air.

PARALLEL CIRCUIT: An electrical circuit with two or more resistance or impedance units connected to split the current flow through both units at the same time.

PARALLEL OPERATION: Two or more units operating simultaneously and connected so their output forms a common supply, as opposed to series or independent operation.

PARAMETER: A variable such as tem-perature, pressure, flow rate, voltage, current, frequency, etc., which may be indicated, monitored, checked or sensed in any way during operation or testing.

PARTIAL SECTION: A sectional view consisting of less than a half-section. Used to show the internal structure of a small portion of an object. Also known as broken section.

PARTICULATE: Minute particles or quan-tities of solid matter resulting from incomplete combustion. Carbon, sulphur, ash, and various other compounds are all referred to as particulate, either collectively or individually, when discharged into a flue or into the atmosphere.

PERIPHERY: (1) The curved line which forms the boundary of a circle (circumference), elipse, or similar figure. (2) The outside surface, especially that of a rounded object or body.

pH: A chemistry term that denotes the degree of acidity or alkalinity of a solution. The pH of water solution may have any value between 0 and 14. A solution with a pH of 7 is neutral. Above 7, it is alkaline; below 7, it is acidic.

PHANTOM VIEW: A view showing the alternate position of a movable object, using a broken line convention.

PHASE: An impulse of alternating current. The number of phases depends on the generator windings. Most large generators produce a 3-phase current that must be carried on at least three wires.

PHYSICAL CHANGE: A change that does not alter the composition of the molecules of a substance, such as from gas to liquid.

PICTORIAL DRAWING: A drawing which gives the real appearance of an object showing general location, function, and appearance of parts and assemblies.

PILOT VALVE: A small valve disk and seat, usually located within a larger disk, which controls the operation of another valve or system.

PILOT VALVE (GOVERNOR): A hydrau-lic control valve that regulates hydraulic pressure to a piston and cylinder.

PINION: A gear that meshes with a larger gear.

PINTLE-TYPE NOZZLE: A closed-type nozzle having a projection on the end of the fuel valve which extends into the orifice when the valve is closed.

PIPE: A tube or hollow body for conducting a liquid or gas. Dimensions of a pipe are designated by nominal (approximate) outside diameter (OD) and wall thickness.

PIPING: An assembly of pipe or tubing, valves, and fittings that forms the transferring part of a system.

PISTON: A cylindrical plug which slides up and down in the cylinder and which is connected to the connecting rod.

PISTON BOSS: The reinforced area around the piston-pin bore.

PISTON DISPLACEMENT: The volume of air moved or displaced by a piston as the piston moves from BDC to TDC.

PISTON HEAD: The portion of the piston above the top ring.

PISTON LANDS: The spaces in pistons between the ring grooves.

PISTON PIN (WRIST PIN): A cylindrical alloy pin that passes through the piston bore and connects the connecting rod to the piston.

PISTON RING: A split ring of the expansion type placed in a groove of the piston to seal the space between the piston and the wall.

PISTON-RING END GAP: The clearance between the ends of a piston ring.

PISTON-RING GROOVE: The grooves cut in the piston into which the piston rings are fitted.

PISTON-RING SIDE CLEARANCE: The clearance between the sides of the ring and the ring lands.

PISTON SKIRT: The portion of the piston that is below the piston bore.

PISTON SPEED: The total distance traveled by each piston in one minute.

PITCH: A term applied to (1) the distance a propeller will advance during one revolution; (2) the distance between the centers of the teeth of a gear wheel; (3) the axial advance of one convolution of the thread on a screw; and (4) the spacing of rivets, and so forth.

PITTING: The localized corrosion of iron and steel in spots, usually caused by irregularities in surface finish and resulting in small in-dentations or pits.

PLAN VIEW: A view of an object or area as it would appear from directly above.

PLUG COCK: A valve that has a rotating plug, which is drilled for the passage of fluid.

PLUNGER: See RAM-TYPE CYLINDER.

PNEUMATIC: Driven, or operated, by air pressure.

PNEUMATICS: That branch of physics pertaining to the pressure and flow of gases.

POLAR TIMING DIAGRAM: A graphic method of illustrating the events of an engine cycle with respect to crankshaft rotation. (See figures 2-1 and 2-2.)

PORT SCAVENGING: Introducing scav-enging air through ports in the cylinder wall when they are uncovered by the piston near the end of the power stroke.

POTABLE WATER: Water that is suitable for drinking. The potable water system supplies scuttlebutts, sinks, showers, sculleries, and galleys, as well as provides makeup water for various freshwater cooling systems.

POTENTIAL: The amount of charge held by a body as compared to another point or body. Usually measured in volts.

POTENTIAL ENERGY: (1) Energy at rest; stored energy. (2) The energy a substance has because of its position, its condition, or its chemical composition.

POWER: The rate of doing work or the rate of expending energy. The unit of electrical power is the watt; the unit of mechanical power is horsepower.

PPM (PARTS PER MILLION): Concentra-tion of the number of parts of a substance dissolved in a million parts of another substance. Used to measure the salt content of water. If 1 pound of sea salt were dissolved in l,000,000 pounds of water, the sea salt concentration would be 1.00 ppm.

PRECISION INSERT BEARING: A pre-cision type of bearing consisting of an upper and lower shell.

PRECOMBUSTION CHAMBER: A portion of the combustion chamber connected to the cylin-der through a narrow throat. Fuel is injected into and is partly burned in the precombustion chamber. Heat released by this partial burning causes the contents of the precombustion chamber to be ejected into the cylinder with considerable turbulence.

PRESSURE: The amount of force distributed over each unit of area. Pressure is expressed in pounds per square inch (psi), atmospheric units, or kilograms per square centimeter, inches of mercury, and other ways.

PRESSURE DIFFERENTIAL: The dif-ference in pressure between any two points of a system or a component.

PRESSURE RELIEF VALVE: A valve designed to open when pressure in the system exceeds a certain limit.

PRESSURE SWITCH: An electrical switch operated by the increase and decrease of pressure.

PRESSURE-TIME FUEL SYSTEM: A system in which fuel is injected into the cylinders at a specific pressure in separately timed events.

PRIMARY SENSING ELEMENT: The control component that transforms energy from the controlled medium to produce a signal which is a function of the value of the controlled variable.

PRIME MOVER: (1) the source of motion- as a diesel engine. (2) The source of mechanical power used to drive a pump or compressor. (3) The source of mechanical power used to drive the rotor of a generator.

PRIMING: To fill, load, or put in working order (to fill a fuel system with fuel or a pump with water).

PROMPTNESS: The time it takes a governor to move the fuel control from a no load position to a full load position.

PROPELLER: A propulsive device consisting of a boss or hub carrying two or more radial blades. Also called a SCREW.

PROPELLER ARCH: The arched section of the stern frame above the propeller.

PROPELLER GUARD: A framework fitted somewhat below the deck line on narrow, high-speed vessels with large screws, designed to overhang and thus protect the tips of the propeller blades.

PROPELLER THRUST: The effort delivered by a propeller in pushing a vessel ahead.

PROPULSION PLANT: The entire propul-sion plant or system, including prime movers and those auxiliaries essential to their operation.

PSYCHROMETER: A form of hygrometer consisting of a wet and a dry bulb thermometer.

PULSATION: A rhythmical throbbing or vibrating.

PUMP: (1) A device which converts mechanical energy into fluid energy. (2) A device that raises, transfers, or compresses fluids or gases.

PUMP CAPACITY: The amount of fluid a pump can move in a given period of time, usually stated in gallons per minute (gpm).

PUMP RISER: The section of piping from the pump discharge valve to the piping main.

PURGE: To make free of an unwanted substance (as to bleed air out of a fuel system).

PURPLE-K-POWDER (PKP): A purple powder composed of potassium bicarbonate that is used on class B fires. Can be used on class C fires; however, CO2 is a better agent for such electrical fires because it leaves no residue.

PYROMETER: A device for measuring high temperatures such as the exhaust temperature of an internal-combustion engine.