P – Terminologies

PISTON SPEED – The total distance travelled by the piston in one minute, not the actual velocity at any given instant.

PORTABLE COMPRESSOR – A small compressor which is easily moved from place to place.

POWER – The rate at which work is done, that is work divided by the time in which it is done. Unit of power is horse power equal to 4500 m.kg/ minute.

POWER DRIVEN COMPRESSOR – A compressor having a separate prime mover and connected by a suitable transmission such as a belt.

PRIME MOVER – An apparatus or mechanism whereby motion and force are received directly from some natural source of energy (fuel) and transmitted into some motion by means of which the power may be conveniently applied.

PANHARD ROD – A control rod that connects the frame on one side of the vehicle to the axle housing on the other side to keep the axle housing centred under the vehicle.

PARKING BRAKES – Mechanically operated brakes that operate independently of the (hydraulic) service brakes on the vehicle. They may be set for parking the vehicle or holding the vehicle against rolling. Also called an emergency brake.

PASCAL’S LAW – A principle of hydraulics which states that pressure at any point in a confined liquid is same in every direction and applies equal force on equal areas.

PEDAL BLEEDING – A method of removing air from the hydraulic system parts by applying the brake to raise the pressure in the system to help move the air through the system when the bleeder valves are opened.

PEDAL PULSATION – A rapid up and down movement of the clutch pedal during operation.

PITMAN ARM – That part of the steering gear which is linked to the steering knuckle arms of the wheels; it swings back and forth for steering.

PITMAN ARM STOPS – On some cars (particularly those using linkage power steering), stops are used to prevent excessive pitman arm movement and thus steering linkage movement.

PITMAN SHAFT – The shaft to which the pitman arm is attached in a steering gear.

PLANETARY GEARBOX – A system of gears used in an automatic transmission, a sun gear, planet gears, a carrier and a ring gear.

PLIES – The layers of cord fabric in a tyre carcass, each layer is a ply.

PLYSTEER – The tendency of a tyre to always turn in one direction as it rolls. This is the result of the way the tyre was constructed.

PNEUMATIC TYRES – Tyres that are filled with air to the required pressure.

POWER BOOSTER – A device used to increase the drivers brake pedal force going to the master cylinder, without an accompanying increase in pedal travel.

POWER BRAKE – Conventional brake system that utilizes engine vacuum to operate vacuum power piston. Power piston applies pressure to brake pedal, or in some cases, directly to master cylinder piston. This reduces the amount of pedal pressure that the driver must exert to stop the vehicle. Also called POWER ASSISTED BRAKE.

POWER RACK – In the saginan power steering unit, a rack that meshes with a sector on the pitman shaft and transmits to the shaft, power from the power cylinder.

POWER STEERING – A device that uses hydraulic pressure to multiply the drivers effort as he turns the steering wheel so that less steering effort is required.

POWER TRAIN or DRIVE TRAIN – The group of mechanisms that carry the rotary motion developed in the engine to the vehicle wheels, it includes the clutch, transmission, drive shaft differential and axles.

PRESSURE CAP (radiator) – A radiator cap with valves that causes the cooling system to operate under pressure and thus at a somewhat higher and more efficient temperature.

PRESSURE PLATE – That part of the clutch which exerts pressure against the friction disc, it is mounted on and rotates with the flywheel.

PREVENTIVE MAINTENANCE – The systematic inspection, detection and correction of failures in a engine, or in a vehicle, either before they occur, or before they develop into major defects.

PRIMARY SHOE – A brake shoe moved by a wheel cylinder to apply the brake.

PROPELLER SHAFT – A shaft in the power train that extends from the transmission to the differential and transmits power from one to the other.

PROPORTIONING VALVE – A valve used to maintain the correct proportion of fluid pressure between the front disc or drum brakes and rear drum brakes. Usually the rear brake pressure is a fraction of front brake pressure.

PUNCTURE SEALING TYRES AND TUBES – Tyres and tubes coated on the inside with a plastic material. Air pressure in the tyre or tube forces that material through holes made by punctures. It hardens on contact with the air to seal the puncture.

PENETRATION – The distance through which fuel particles are carried by the kinetic energy imparted to them when they leave the fuel nozzle.

PHYSICAL DELAY PERIOD – The time that elapses between the beginning of fuel injection and the begining of pre-flame reactions.

PILOT INJECTION – is the early injection of a small quantity of fuel to initiate combustion of the injected main fuel, in a diesel engine.

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

PRECOMBUSTION CHAMBER – Part of the combustion space located in the cylinder head, into which fuel is injected, and combustion starts here and spreads into the main chamber via the interconnecting orifices.

PARTING COMPOUND – Material dusted or sprayed on a pattern or mould to prevent adherence of sand.

PATTERN – Model of wood, metal, plaster or other material used in making a mould.

PATTERN ALLOWANCES – The dimensions on the pattern differ from those on the drawing to allow for metal shrinkage, distortion, core shift, draft and machine finish. Such allowances are made by the pattern-maker.

PEEN – Small end of a moulders rammer.

PERMANENT MOULD – A long life mould into which metal is poured by gravity.

PILOT CASTING – Usually the first casting made from a production pattern and examined for dimensional accuracy, quality and other features before the pattern is placed on the line.

PIT MOULD – Mould in which the lower portions are made in a suitable pit or excavation in a foundry floor.

PLASTER MOULDING – Gypsum or plaster of Paris is mixed with fibrous talc, with or without sand, and with water to form a slurry, that is poured around a pattern. In a short period of time, the mass sets or hardens sufficiently to permit removal of the pattern. The mould so formed is baked at elevated temperature to remove, all moisture prior to use.

PLASTICITY – The ability of the sand mixture to acquire the outlines of a pattern or corebox under the action of external forces and retain the shape acquired without destruction.

PLASTIC PATTERN – Pattern made from any of the several thermosetting type synthetic resins such as phenol formaldehyde, epoxy etc. Small patterns may be cast solid, but large ones are usually produced by laminating with glass cloth.

POURED SHORT – Casting which lacks completeness due to the cavity not being filled with molten metal.

POURING CUP – Part of the mould that receives the molten metal from the pouring ladle and transfers it further into the cavity of the mould.

PRINT – Wooden projection put on to a pattern to provide supports for the cores in a mould.

PROGRESSIVE SOLIDIFICATION – is the freezing of the metal from the mould metal interface toward the center of the cavity.

PUSHUP – An indentation in the casting surface due to displacement (expansion) of the sand in the mould.

PARAMAGNETIC MATERIALS – These materials are only feebly magnetic.

PARTING SAND – Fine sand used for dusting on sand mould surfaces that are to be separated.

PEARLITE – The laminar mixture of ferrite and cementite in slowly cooled iron carbon alloys as found in steel and cast iron.

PEARLITIC MALLEABLE IRON – Irons made from the same or similar chemical compositions as regular malleable iron, but so alloyed or heat treated that some of the carbon in the resultant material is in the combined form.

PERMANENT MAGNET – Special magnet steel that retains its magnetic power indefinitely.

PETROCHEMICALS – Chemicals derived from petroleum substances or materials manufactured from a component of crude oil or natural gas.

PEWTER – Alloy containing 1.8% lead, 89.4% tin, 7% antimony and 1.8% copper.

PHASE – It is a portion of matter which is homogeneous in the sense that its smallest adjacent parts are indistinguishable from one another.

PHASE DIAGRAM – Phase diagram is also called equilibrium diagram or constitution diagram, indicates the relative amount and composition of phases present in an alloy at a given temperature and pressure, when the alloy is in equilibrium.

PHOSPHOROUS – One of the elements, its chemical symbol is P. Its formula weight is 123.92, specific gravity 1.82, and melting point 44.1°C.

PHOSPHOR BRONZE – Alloy containing 78.5-81.5% copper, 9-11 % tin, 9-11 % lead, 0.05-0.25% phosphorous and 0.75% zinc, has excellent antifriction properties. Used as bearing material.

PHOTON – The smallest possible quantity of an electromagnetic radiation that can be characterized by a definite frequency.

PIG IRON – Iron produced from iron ore in the blast furnace, basic raw material from which all cast iron, wrought iron and steel are made. Usually contains about 4.5% carbon and impurities such as phosphorous, silicon and sulphur.

PITCH – Usually coal tar pitch obtained in the manufacture of coke and distilled off at about 175°C.

PLASMA – An ionized gas of extremely high temperature achieved by passing an inert gas through an electric arc. Plasma arcs are used in welding, cutting and machining processes.

PLASTIC – A certain group of natural and synthetic resins and their compounds that can be moulded, cast, extruded or used for coatings and films.

PLASTIC ELASTOMERS – Plastic elastomers are materials which exhibit the characteristics of rubber, but are of a basic chemical structure that is decidedly different from that of natural rubber.

PLATINUM – It is a silver-white heavy metal, unaffected by acids, air, or a great variety of chemical agents. It is extensively used, either solid or clad, for chemical equipment.

POLYESTERS – Polyesters are a reaction product of polyhydric alcohol and a dibasic acid plus monomer styrene or diallyl phthalate. In combination with glass fibres they form a product which has an outstanding strength weight ratio.

POLYETHYLENES – The product of straight chain polymerization of ethylene and are obtainable as viscous liquids, gums, and tough flexible solids suitable for moulding.

POLYMER – A chemical compound or mixture of compounds formed by polymerization and consisting essentially of repeating structural units.

PORCELAIN – Porcelain is a ceramic product made up of clays, quartz, and feldspar used as high voltage insulator.

POWDER METALLURGY – Forming parts out of powdered metal by compacting the powder into a mould under great pressure and heating it.

PRECIOUS METAL – One of the relatively scarce and valuable metals gold, silver and platinum groups of metals.

PROTON – The positively charged particle in the nucleus of an atom.

PRUSSIAN BLUE – A blue pigment, obtainable in tubes which are used to find hot spots in a bearing.

PAD LUBRICATION – A part of the bearing surface upon which there is no pressure is dispensed with, and its place is taken by a soft pad, which is kept saturated with lubricant.

PICKUP SCREEN – A screen in the oil pan that prevents any large particles from entering the oil pump.

PIVOT BEARING – Pivot portion (flat or conical) which is on the end of a shaft, that takes up the thrust produced along the axis of the shaft.

PLAIN BEARING – A one or two piece assembly consisting of a hard metal backing piece with a softer metal mated to it.

PLUNGER OIL PUMP – An oil pump that uses a piston or plunger and check valves to move oil.

POUR POINT OF OIL – The temperature at which the oil will not flow when cooled under specified conditions, due to formation of wax.

PREMIX – Two stroke cycle engine lubrication is provided by oil, mixed with fuel in the fuel tank.

PRESSURE RELIEF VALVE – A spring loaded valve used to regulate the pressure in the lubrication system.

PRESSURIZED FEED OIL SYSTEM – A type of engine lubricating system that makes use of an oil pump to force oil through tubes and passages to the various engine parts requiring lubrication.

PROFILOMETER – Instrument used to measure the surface irregularities.

PARTICULATES – Small particles of lead and other substances occurring as solid matter in the exhaust gas.

PEAT – A substance of vegetable origin always found more or less saturated with water in swamps and bogs.

PETROLEUM – Crude oil as it comes out of the ground, which consists of 83-87 percent carbon, and 10-14 percent hydrogen, plus traces of oxygen, nitrogen and sulphur. From the crude oil, gasoline, diesel, lubricating oil and other products are refined.

PHOTOCHEMICAL SMOG – The result of sunlight reacting with hydrocarbons and nitrogen oxides in the atmosphere.

PING – The sound resulting from sudden auto ignition of the air-fuel charge in a SI engine combustion chamber. Characteristic sound of detonation.

POLLUTANTS – Any gas or substance in the exhaust gases from the engine or that evaporates from the fuel tank or carburettor. These gases or substances add to the pollution of our atmosphere.

POLLUTION – The presence of matter or energy whose nature, location or quantity produces undesirable environmental effects.

POSITIVE CRANKCASE VENTILATION – PCV system-A crankcase ventilating system which produces the circulation of air through the crankcase, thus clearing it of water vapour, unburned hydrocarbons, and blow by, the air passes into the intake system of the engine and hence into the combustion chambers where they are burnt.

POT TYPE BURNER – It is a hot plate burner in which the fuel oil drops into a hot plate and vaporizes.

POUR POINT OF FUEL – is the temperature at which crystals begin to appear and the fuel flow will be interrupted, as the fuel is being cooled.

PREI-GNITION – Ignition of air fuel mixture in the SI engine cylinder (by any means) before the (ignition) spark occurs at the spark plug terminals.

PRIMARY AIR – The air mixed with the fuel at or in the burner. It ensures instant combustion as the fuel enters the furnace.

PRIMARY POLLUTANT – A pollutant emitted directly from a polluting source.

PROPANE – A type of LPG that is liquid below –42°C at atmospheric pressure.

PULSATION – A panting of the flames in a furnace, indicating cyclic and rapid changes in the pressure in the furnace.

PURGE – The evacuation of air or any other designated gas from the duct line, pipe line, container or furnace. Purging may be done in some instances simply by the use of a fan or blower, in others by driving out the air or gas by means of an inert gas, such as nitrogen, under high pressure.

PARALLEL FLOW HEAT EXCHANGER – A heat exchanger in which both compressed air and gases let out by the turbine flow in the same longitudinal direction. Also called UNI DIRECTIONAL or COCURRENT HEAT EXCHANGER.

PARTIAL ADMISSION – Admission of gas stream over only a part of the blade circumference, since the nozzles are covering only a fraction of the inlet blade circumferential annulus. This is the case in impulse turbines.

PLANE SHOCK WAVE – Shock wave in which the variables of flow ego pressure, temperature and velocity are constant along the wave front.

POLYTROPIC EFFICIENCY – The isentropic efficiency of an elemental stage of the compression which is constant throughout the process. Also called the SMALL STAGE EFFICIENCY.

POSITIVE DISPLACEMENT COMPRESSOR – Type of compressor in which a fixed amount of working fluid is being positively contained during its passage through the machine.

POWER INPUT FACTOR – For a compressor this is the ratio of the actual work to the theoretical work of compression. Represents an increase in the work input the whole of which is absorbed in overcoming frictional loss and which is therefore degraded into heat energy.

POWER RATIO – Ratio of useful or net horse power of the cycle compared with the power developed by the turbine of the system. Also called WORK RATIO.

PRESSURE COMPOUNDED IMPULSE TURBINE – The turbine in which the pressure range available for expansion is broken into a series of steps or stages. Each stage consists of a nozzle or bank of nozzles (which increase the kinetic energy) followed by a row of turbine blades or buckets (which absorb the kinetic energy).

PRESSURE RATIO – Ratio of pressure of air at the end of compression to the pressure of air at the begining of compression.

PREWHIRL – Whirl velocity (tangential component of the absolute velocity at intake), imparted to the air that enters the centrifugal compressor impeller, by allowing the air to be drawn into the impeller eye over curved inlet guide vanes attached to the impeller casing.

PRIMARY AIR – Part of the air which flows through the core of the combustion chamber, in just sufficient quantity for combustion.

PRIMARY ZONE – Portion of the combustion chamber wherein about 15 to 20% of the air is introduced around the jet of fuel and the burning of this rich mixture provides the high temperature necessary to prepare the mixture for further reaction and burn it almost completely in a very short time.

PROPELLER JET ENGINE – The unit in which the gas turbine develops power in excess of that required to drive the compressor and employs this excess power to drive a propeller through reduction gearing and the leaving jet also contributes to the thrust power.

PROPULSION EFFICIENCY – Ratio of thrust power to the jet power.

PARKERIZING – A coslettizing process in which a patented mixture of iron and manganese phosphates is used in solution to provide a rust proof surface on iron and steel parts.

PHOSPHATE COATING – Coating produced by converting the surface of iron or steel parts to insoluble phosphate, such as iron phosphate or zinc iron phosphate.

PICKLING – Treatment of objects with an acid solution to remove all oxide, scale or dirt. Usually done to clean and brighten the surface, although sometimes used for etching.

POWDER COATING – Surface coating of almost any metal or alloy applied to another by powder method.

PRECIPITATION HARDENING – A process of hardening an alloy by heat treatment in which a constituent precipitates from a supersaturated solid solution while at room temperature or at some slightly elevated temperature.

PANCAKE ENGINE – An engine with two rows of cylinders which are opposed and on the same plane, usually set horizontally in a vehicle.

PISTON – A cylindrical part, closed at one end, which moves up and down in the cylinder. Open end is attached to the connecting rod. Combustion pressure is exerted on closed end of piston, causing connecting rod to move and crankshaft to turn.

PISTON CROWN – Top of piston, directly exposed to combustion pressure and heat.

PISTON DISPLACEMENT – The cylinder volume displaced by the piston as it moves from the bottom to the top of the cylinder during one complete stroke.

PISTON PIN – Also called wrist pin. The cylindrical or tubular metal piece that attaches the piston to the connecting rod.

PISTON PIN BOSS – A strengthened section of piston wall extending to inside of piston crown. It supports piston pin.

PISTON PIN HOLE – Machined hole through piston wall where piston pin and retaining circlips are mounted.

PISTON RINGS – Rings fitted into grooves in the piston. These are two types: Compression rings for sealing the compression into the combustion chamber and oil rings to scrape excess oil off the cylinder wall and thereby prevent it from working up into and burning in the combustion chamber.

PISTON RING COATINGS – of relatively soft substances such as phosphate, graphite, and iron oxide aid effective wear in and prevents rapid wear of the ring.

PISTON RING COMPRESSOR – A special tool used in engine overhaul work to compress the piston rings inside the piston grooves so that the piston and rings assembly may be installed in the engine cylinder.

PISTON RING END GAP – Distance between ends of a piston ring when installed in the cylinder. The clearance is measured with a feeler gauge, keeping the piston at BDC.

PISTON RING GROOVE – Grooves machined in the piston external surface to accept piston rings.

PISTON SEIZURE – Overheating of piston to the point where it will no longer move freely in the cylinder.

PISTON SKIRT – The lower part of the piston below the piston pin hole.

PISTON SLAP – A hollow, muffled, bell like sound made by an excessively loose piston slapping the cylinder wall at dead centre positions.

POPPET VALVE – A mushroom shaped valve widely used in internal combustion engines.

PORT (cylinder) – In an engine, the valve port or opening in which the valve operates and through which the charge or burned gases pass.

POWER – Rate at which work is done.

POWER PLANT – The engine or power producing mechanism in the vehicle.

POWER STROKE – The piston stroke from TDC to BDC during which the charge burns and forces the piston down so that the engine produces power.

PRESSURE TESTER – An instrument that clamps in the radiator filler neck, and is used to pressure test the cooling system for leaks.

PREVENTIVE MAINTENANCE – The systematic inspection, detection and correction of failures in an engine or in a vehicle, either before they occur, or before they develop into major defects.

PUSH ROD – In the I head engine, the rod between the valve lifter and rocker arm.

PARALLEL BLOCK – Steel or cast iron block used when setting up work for machining, marking out or measuring.

PIN GAUGES – End measuring pins for determining bore diameters.

PLUG GAUGE – A gauge on which the outside measuring surfaces are designed to test the specified dimensions of holes. May be straight or tapered, plain or threaded, and of any cross-sectional shape.

PLUMB BOB – Weight hung on the end of a cord so that when the latter is supported at its top end the cord will hang vertical.

PNEUMATIC MICROMETER – An instrument designed to measure, among other things, the errors in the size, shape and alignment of bores, with compressed air.

PROTRACTOR – Instrument graduated so as to enable the measurement of angles to be made in degrees.

PYROMETER – Specified type of thermometer used to measure high temperatures in the production and heat treatment of metals and alloys.

PARALLEL JAW VICE – Type of vice in which the gripping faces between the sliding and fixed jaws are always parallel, irrespective of the gap between them.

PILOT – A guide at the end of a counter-bore which fits freely into the drilled hole to hold and align the body of the counter-bore while cutting takes place.

PINION – The smallest of a pair of gears regardless of the size or type.

PIN VICE – Small vice with self centering jaws useful for gripping small rods, wires, drills and files.

PIPE THREAD – A 60° thread form having flattened crests and roots which are cut on a taper having 3/4 inch taper per foot. Pipe thread is used on piping and tubing.

PIPE VICE – Clamping device designed to hold work of tubular or circular section.

POWER ASSISTED CHUCKS – These are used where great holding power is required. These are operated with auxiliary power such as compressed air or oil pressure. Where simplicity of chucking is the first consideration, magnetic chucks are used.

PULLEY – A wheel having a plain or V groove rim over which a belt runs for the transmission of power from one shaft to another.

PEEN – The end of the head of a hammer opposite the face, such as ball, straight or cross peen, and used for peening or riveting.

PILOT – A guide at the end of the counter bore which fits freely into the drilled hole and align the body of the counterbore while cutting takes place.

PILOT SHAFT – A shaft positioned in or through a hole of a component as a means of aligning the components.

PILOT VALVE – A valve used to control the operation of another valve.

PINION – The smaller of the pair of gears regardless of the size or type.

PIPE THREAD – A 60° thread having flattened crest and roots which are cut on a taper. Pipe thread is used on piping and tubing.

PITCH – In screw threads, the distance from a point on one thread to a corresponding point on the next thread measured parallel to the axis. In the case of spur gears, indicates the size of the gear teeth and is correctly called diametral pitch.

PITCH DIAMETER – For screw threads, the diameter of an imaginary cylinder, the surface of which would pass through the threads at such points that would make the width of the groove and width of the land equal to one half the pitch.

PLAY – The movement between two components.

PULLEY – A wheel having a plain or V groove rim over which a belt runs for the transmission of power from one shaft to another.

PLAIN MILLER – Milling machine in which milling can be carried out in a direction parallel with the axis of the arbor or at right angles to it , but no swivelling of the worktable is possible.

PLANING MACHINE – Machine for removing material from plane surfaces by means of cutting tools fixed in the machine. It comprises a bed, a travelling worktable on which the parts to be planed are carried, standards, a cross slide, tool box and gearing. Also called PLANER.

PLANOMILLER – Milling machine, sometimes called a slab miller, similar in shape and appearance to a planing machine, but having cutter hands instead of clapper type tool boxes.

PLUNGER PUMP – A pump which operates and displaces fluid by means of a plunger.

PNEUMATIC TOOL – Design of hand tool operated by air pressure e.g., pneumatic drill, pneumatic hammer or riveter.

POWER HAMMER – Machine for shaping metal while hot, grouped into three classes, according to the power supplied: compressed air, steam or hydraulic pressure.

POWER PLANT – The engine or power producing mechanism.

PRESS – Machine designed to manipulate sheet and strip metal so as to produce a given shape or form.

PROFILING MACHINE – Form of milling machine designed to produce delicate parts whose form or contour is irregular, particularly for mass production by the use of jigs and so on, of small machine and other parts, or where the production of interchangeable parts is desired.

PRONY BRAKE – A friction brake used for engine testing.

PUMP – Mechanical device in which a fluid, gas or liquid, is lifted or forced against an external pressure, main types are reciprocating or piston pumps, centrifugal pumps and rotary displacement pumps.

PUNCHING MACHINE – Machine designed to cut metal blanks from the sheet. It may be of the crank or eccentric variety; the frame of the C or double sided type. Also called PUNCH PRESS.

PALLET – A standard platform on which material is placed for storage and movement. The platform has an upper and lower flat surface with space between for the forks of an industrial lift truck.

PIGGYBACK (TOFC) – Transportation of highway trailers or demountable trailer bodies on specially equipped cars.

PIN WHEEL PLATFORM – A pallet pattern used for the arrangement of items of unequal length or width.

PIPE LINES – Specialized carriers that transport petroleum or natural gas.

PLATE CLAMP – Handling attachment which is an eccentric clamp used for handling steel sheets and plates in the vertical position.

PNEUMATIC CONVEYING – Method of transporting bulk materials in the form of powder, short fibre and granules over a pipe line as a mixture with air or due to the pressure of air, e.g., suction or vacuum type systems, pressure type systems, combination systems.

PNEUMATIC DRIVE – System in which compressed air is admitted into direct acting cylinders under pressure, the piston rods are linked with the business end.

PORTABLE PLATE – A loading ramp that can be moved to any loading position on the deck.

POSITIONER – A device that orients and positions the part for the next operation.

POWER DRIVE – Drive provided in the form of electric motor, steam engine, internal combustion engine, hydraulic or air motor. Includes combinations such as diesel electric, electro hydraulic, electro pneumatic drives.

POWER SHOVEL – An earth digging machine with an operating member (bucket) which digs soil, carries it over a small distance and dumps it in a pile or onto transporting facilities.

PREFORMED WIRE ROPES – The ropes in which the wires and strands, before being laid, are preformed to fit the shape they carry in the rope.

PEARLITE – A micro constituent of iron and steel consisting of alternative layers of ferrite and iron carbide or cementite.

PEEL LOAD – In metal, plastics or composites, the force that acts to peel apart joined pieces.

PH – The negative logarithm of the hydrogen ion activity. It denotes the degree of acidity or basicity of a solution.

PERMEABILITY – In casting of metals, the term is used to define the porosity of foundry sands in moulds and the ability of trapped gases to escape through the sand.

PERMANENT SET – When a metal remains deformed from its original dimensions after the forces applied to it have been reduced to zero, it is said to have undergone plastic deformation, and the amount of deformation is called the permanent set.

PHASE – A portion of an alloy, physically homogeneous throughout, that is separated from the rest of the alloy by distinct BOUNDARY surfaces. The following phases occur in the iron carbon alloy, molten alloy; austenite, ferrite, cementite, and graphite.

PHYSICAL CHANGE – A change which does not alter the composition of the molecules of a substance.

PIEZOELECTRIC EFFECT – The reversible interaction, exhibited by some crystalline materials between an elastic strain and an electric field. The direction of the strain is dependent upon the polarity of the field.

PLASTICITY – The quality of material such that it can be deformed without breaking. Clay is completely a plastic material. Metals exhibit plasticity in varying amounts.

PLASTIC DEFORMATION – Deformation that does or will remain permanent after the removal of load which caused it.

POISSON’S RATIO – When a rod of elastic material is elongated by stretching (strain), the lateral (crosswise) dimensions will contract. Poisson’s ratio is the ratio between the strain and the amount of lateral contraction.

PROPORTIONAL LIMIT – Proportional limit is the value of stress at which the stress strain curve first bends to the right. The proportional limit is high for steels and low for cast iron, copper, and aluminium.

PROOF LOAD – A predetermined load, generally some multiple of the service load, to which a specimen or structure is submitted before acceptance for use.

PROOF, RESILIENCE – Maximum amount of elastic energy that may be stored without permanent deformation in the material during its first loading cycle.

PEENING – Work hardening the surface of metal by hammering or blasting with shot (small steel balls). Peening introduces compressive stresses on weld surfaces that tend to counteract unwanted tensile stresses.

PERFORATING – Piercing many small holes close together.

PICKLING – Process of cleaning (that is removing oxide film from) castings by dipping them into an acid bath prior to plating, painting or further cold working.

PIERCING – Producing holes in a blank by driving a punching tool into the mass of the metal, while at the same time forcing the displaced material into the particular form required by the part, this is known as deep piercing.

PINNING – Scratching of the work surface during a filing operation caused by small particles of metal getting wedged in front of the teeth of the file.

PLANING – Producing flat or plane surface on a moving or other part by removing metal from them by means of a cutting tool used in a planning machine.

PLANISHING – Hammering operation by which the surface of a metal component is brought to a first class condition for such operations as polishing, plating and spraying.

PLATE MOULDING – Specialized form of moulding which consists of one or more patterns mounted on a plate with the runner and ingates being allowed for in the pattern.

PLATE EDGE PLANING – Smoothing and generally making true and accurate the edges of large plates.

PLATING – The process of depositing a layer of one metal on another, often done electrically, for the purpose of corrosion protection, appearance, improved electrical conductivity, and other engineering requirements.

POWDER METALLURGY – Forming parts out of powdered metal by compacting the powder into a mould under great pressure and heating it.

PRESSING (hot) – Process of shaping a metal article by pressure and while the metal is hot, and without any interstate forging.

PRESSURE WELDING – Method of uniting two sheets of metal by squeezing them between heated dies.

PROFILING – Method of milling irregular forms by reproducing the form of a master template, form or pattern.

PULTRUSION – A process that is opposite to extrusion and is used in composite part manufacturing.

PUNCHING – The operation of cutting a hole in sheet metal using a die. The whole material is scrapped. It is a shearing operation carried out in a press.

PUSH FIT – Class of fit which allows two parts to be assembled under hand pressure.

PAIR – Two bodies in contact constitute a pair. LOWER PAIRING exists when two surfaces are in contact. HIGHER PAIRING refers to the contact which exists at a point or along a line.

PANTOGRAPH – Mechanism used to reproduce to an enlarged or reduced scale and as exactly as possible the path described by a given point.

PARALLEL MECHANISMS – Linkages which give parallel motion (e.g., pantograph which is used for reducing or enlarging drawings and maps, also used for grinding cutting tools or cutting torches to duplicate complicated shapes).

PATH OF CONTACT – The path traced out by the point of contact between a pair of teeth (may be divided into approach and recess).

PINION – The small of the two mating gear wheels.

PITCH CIRCLES – Equivalent rolling circles for a pair of mating gears.

PITCH CIRCLE DIAMETER – The diameter of a circle which by a pure rolling action would transmit the same motion as the actual gearwheel.

PITCH LINE – The point of contact of two circles.

PITCH SURFACES – The cylindrical surfaces of the equivalent rolling circles for a pair of mating gears.

PLANE MOTION – A body has plane motion if all the points move in planes which are parallel to some reference plane (called plane of motion).

POSITIVE DRIVE – The drive that exists in a direct contact mechanism if motion of the driving link compels the follower to move (e.g., cam and follower).

POWER – Rate of doing work or work done in unit time.

PRECESSIONAL MOTION – The change in the direction of the plane of rotation of a rotating disc.

PRESSURE ANGLE – Angle between the common normal and the tangent at the pitch point in a gear drive. Also called ANGLE OF OBLIQUITY.

pH VALUE – Logarithm to base 10 of the reciprocal of the concentration of hydrogen ions. Measure of the acidity or alkalinity of a solution.

PRESSOSTAT – An automatic switch connected by a small bore tube to the suction of the compressor, stopping the latter when the pressure falls to a certain value and starting it again after a definite rise in pressure.

PRESSURE RELIEF VALVE – Used to minimize the possibility of explosion when air temperature surrounding a refrigeration system may rise to a point where it causes the pressure of the refrigerant gas to increase to a danger point.

PRIMARY REFRIGERANT – A substance used as the working fluid in the vapour compression cycle, as distinct from a secondary refrigerant, which in some cases is used as an intermediate conveyor of heat between the substance to be cooled and the primary refrigerant.

PSYCHROMETRIC CHART – A graph, the coordinates of which are usually either dry bulb temperature and absolute humidity, or enthalpy (total heat) and absolute humidity. Families of lines are there showing constant dry bulb temperatures, wet bulb temperatures, enthalpies, absolute humidities, relative or percentage humidities and specific volumes.

PURGING – A method of removing air and moisture from a refrigerating system by means of the refrigerant gas pushing some of the air ahead of it and out of the system.

PERCOLATION – A condition in which the fuel actually “boils” due to excess heat. Percolation prevents proper atomization of the fuel causing rough running.

PERFORMANCE NUMBER – is the ratio of knock limited imep with the fuel in question to the knock limited imep with iso-octane when the inlet pressure is used as the dependent variable.

PING – A metallic rattling sound produced by the engine under acceleration. It is usually due to incorrect ignition timing or poor grade of gasoline.

POST COMBUSTION ACTIVITY – The last phase of combustion, during which the piston descends, the volume inside the cylinder increases, and the cylinder eliminates spent gases.

POWER PISTON – In some carburettors, a vacuum operated piston that allows additional fuel to flow at wide open throttle to permit delivery of a richer air fuel mixture to the engine.

PREIGNITION – Abnormal combustion that occurs when the air fuel mixture ignites before the spark plug fires and this is due to some hot spot.

PRIMARY IGNITION CIRCUIT – Section of the ignition circuit including contact points, condenser and primary winding of ignition coil, power supply (battery or ignition generating coil), ignition switch and related wiring.

PRIMARY WINDING – Part of an ignition coil, a separate winding of heavy wire wound a few hundred turns around a laminated steel core.

PACKAGED BOILER – A completely factory assembled boiler either water tube or fire tube, including boiler firing apparatus, controls and boiler safety devices.

PALM STAY – A round rod having forged on one end a plate or palm.

pH VALUE – It is a number between 0 and 14 indicating the degree of acidity or alkalinity.

PITTING – A form of corrosion resulting in a series of minute holes or pits eaten into the surface of the metal to a depth of sometimes 6 mm.

POP SAFETY VALVE – A valve so constructed that it opens very suddenly like a cork popping out of a champagne or sparkling burgundy bottle and remains open until the pressure is reduced a predetermined amount.

PORCUPINE BOILER – A boiler having a vertical drum into which are screwed a multiplicity of horizontal radial short tubes.

PORTABLE BOILER – A boiler mounted on a truck, barge, a small river boat, or any other such mobile apparatus.

POSITIVE INJECTOR – One with a hand operated overflow valve, which permits operation at high pressure by stopping the drizzle from the overflow.

POWER BOILER – A power boiler is a steam or vapour boiler operating above 15 psig and exceeding the miniature size boiler.

PRIMING – It lifts the water level and delivers steam containing spray of water. It is usually caused by forcing a boiler too hard or by a too high water level or a combination of both these causes.

PARTIAL ADMISSION TURBINE – An impulse turbine in which the nozzles occupy only a part of the circumference leading into blade annulus and therefore admit steam over part of the blade annulus.

Impulse turbines are partial admission turbines.

PORT – The entrance at the valve seat to either a steam passage leading to the cylinder or an exhaust passage leading to the exhaust pipe.

PRESSURE COMPOUNDED IMPULSE TURBINE – Steam turbine in which the total pressure drop of steam is divided into stages in a number of rings of fixed nozzles and the velocity produced by a ring

of nozzles is utilized almost fully in the immediately following row of moving blades attached to the rotor.

PRESSURE VELOCITY COMPOUNDED IMPULSE TURBINE – Steam turbine in which the total pressure drop of steam is divided into stages and the velocity thus obtained in each stage is also compounded i.e utilized in two or more rings of moving blades.

PARALLEL FLOW HEAT EXCHANGER – A heat exchanger in which the warm and cool fluids flow in the same direction but separated from one another.

PERFECT GAS – Gas which behaves in accordance with the gas law PV = MRT, where P-absolute pressure, V-volume, M-mass, T-absolute temperature and R-constant for the particular gas depending on its molecular weight.

PERPETUAL MOTION MACHINE OF FIRST KIND – is a machine which will give continuous work without taking any energy from other system or surrounding.

PERPETUAL MOTION MACHINE OF SECOND KIND – is a machine which abstracts heat continuously from a reservoir and converts it completely into work or 100% efficient engine.

PERPETUAL MOTION MACHINE OF THIRD KIND – is applied to devices that, once set in motion, continue in motion for an indefinitely long time without slowing down.

PHASE OF A SUBSTANCE – It refers to a quantity of matter which is homogeneous or uniform throughout its physical structure and chemical composition.

PHASE DIAGRAM – is a pressure temperature diagram showing more than one of the saturation lines (liquid-vapour, liquid-solid, solid-vapour and other of a pure substance).

PATH FUNCTIONS – depend on which path is followed between the states 1 and 2. Examples are heat, work, internal energy and entropy.

POINT FUNCTIONS – are the properties of a system at a state.

POLYTROPIC PROCESS – follows the law Pvn = constant. In this process, heat is supplied in such a way there is some work done by the gas (i.e., during expansion) and there is also a change in internal energy.

PROCESS – It is the transformation of a system from one state to another.

PROPERTY OF A FLUID – is its characteristic such as pressure, volume, temperature, internal energy, enthalpy and entropy which are measurable directly or indirectly.

POTENTIAL ENERGY – Energy possessed by a substance by virtue of its position with respect to a datum.

POWER – The rate at which work is done, i.e., 1 HP = 4500 Mt.kg/ minute.

PRESSURE – As defined by Rankine-A force of the nature or a thrust, distributed over a surface measured as kg/sqcm.

PURE SUBSTANCE – is any material of single chemical structure or of homogeneous and invariant chemical structure.

PISTON (brake system) – A movable part of a master cylinder or wheel cylinder. Master cylinder piston produces pressure and caliper (wheel cylinder) piston applies that pressure to brake disc, slowing or stopping the wheel rotation.

PISTON PORT SYSTEM – The two stroke intake system that uses the piston to open and close the intake and exhaust ports.

PLY RATING – A rating given to a tyre which indicates strength (but not necessarily actual number of plies).

PORTS – The passage ways cut into a two stroke engine cylinder, that channel gases into and out of the engine. Also called PORT WINDOWS.

POWER TO WEIGHT RATIO – Ratio of horse power to weight of a vehicle.

POWER TRANSMISSION – A system of gears, chains, sprockets and shafts that transfer power from the crankshaft to rear wheel in varying ratios.

PREMIX – Two stroke cycle engine lubrication provided by oil mixed with fuel in fuel tank.

PRIMARY CHAIN DRIVE – A primary drive design that uses a chain and sprockets to transmit engine power from crankshaft to clutch.

PRIMARY DRIVE SYSTEM – A system of gears, chains or belts that transmits power from the crankshaft to the transmission, includes the clutch.

PRIMARY KICKSTART – A kick-start system which connects kick-start lever to crankshaft through clutch basket. Gearbox can be in gear for starting if clutch is disengaged.

PRIMARY REDUCTION – A gear reduction usually about three to one, accomplished by primary drive.

PLASMA ARC CUTTING – Process that severs metal by melting a localized area with a constricted arc and removing the molten material with high velocity jet of hot, ionized gas issuing from the constricted orifice.

PLASMA ARC WELDING – Process that produces coalescence of metals by heating them with a constricted arc between an electrode and the workpiece (transferred arc) or the electrode and the constricting nozzle (non-transferred arc). Shielding is obtained from the hot ionized gas issuing from the orifice which may be supplemented by an auxiliary source of shielding gas.

PLUG WELD – A weld made in a circular hole or one member of a joint, fusing that member to another member.

POROSITY – Cavity type discontinuities formed by gas entrapment during solidification.

POST HEATING – Application of heat to an assembly after a welding, brazing, soldering, thermal spraying or thermal cutting.

PRE HEATING – Application of heat to the base metal immediately before welding, brazing, soldering, thermal spraying and cutting.

PRESSURE GAS WELDING – An oxyfuel gas welding which produces coalescence simultaneously over the entire area of faying surfaces by heating them with gas flames obtained from combustion of a fuel gas with oxygen and by the application of pressure, without the use of filler metal.

PROJECTION WELDING – is a modification of spot welding in which the current and pressure are localized at the weld section by the use of embossed, machined, or coined projections on one or both pieces of the work.

PROTECTIVE ATMOSPHERE – Gas or vacuum envelope surrounding the work-pieces used to prevent or facilitate removal of oxides and detriment surface substances.

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