P.E. - Professional Engineer (licensed or registered by each U.S. state)
P - The abbreviation of poise, the CGS derived unit of dynamic viscosity of a fluid.
Packed Column - A tower filled with small objects, designed to obtain large surfaces per volume between rising vapors and a
Packing - Material made usually of woven animal, plant, mineral or metal fiber and some type of lubricant, placed in rings
around the shaft of a pump and used to control leakage from the stuffing box
Packing Gland - The metal part that compresses and holds packing in place in a pump stuffing box
Panel Hammer - A special hammer for metalworking.
Paris Bronze - A term given to brass containing 88% copper, 10% zinc and 2% lead used to produce trinkets and souvenirs.
Partial Pressure - When two or more gases occupy a space and each one creates part of the total pressure.
Particulates - Soluble and insoluble dusts and fumes, including submicrons, pyrophorics, hydrocarbons, and toxic metals
Pascal's Law - Pressure imposed upon a fluid is transmitted equally in all directions
Passivation - The changing of the chemically active surface of a metal to a much less reactive state
PCB - polychlorinated biphenyls; until 1977 PCB's were used as coolants and lubricants in transformers, capacitors and other
electrical equipment because they did not burn easily and were good insulators;
Peck - An old unit of volume (approximately 8 quarts)
Peen Hammer - A body hammer with a pein of triangular section with a fairly sharply shaped end.
Peening - The mechanical working of metals by means of hammer blows.
Peierls Stress - The stress required to move a dislocation.
Pein Hammer - A body hammer with a pein of triangular section with a fairly sharply shaped end.
Peltier Effect - When a current flows through a thermocouple junction, heat will either be absorbed or evolved depending on
the direction of current flow. This effect is independent of joule I2 R heating.
penetrant inspection - A method of nondestructive testing for determining the existence and extent of discontinuities that
are open to the surface in the part being inspected.
Peritectic - An isothermal reversible reaction in metals where a liquid phase reacts with a solid phase to produce a single
(and different) solid phase upon cooling.
Permeability - Passage / diffusion of a gas, vapor, liquid, or solid through a material without physically or chemically affecting it
Petrochemical - An intermediate chemical derived from petroleum, hydrocarbon liquids or natural gas: ethylene, propylene,
benzene, toluene and xylene.
Petrol Engine - An internal-combustion engine in which the fuel is petrol that is drawn or injected into the cylinder along with
air and ignited with an electric spark.
Pewter - Tin-base white metal containing antimony and copper: 1 to 8% Sb and 0.25 to 3% Cu.
PFD - Process flow diagram
pH - The negative logarithm of the hydrogen-ion concentration of a solution; simply a measure of the relative acidity or
alkalinity of a water solution
Phase Diagram - Graphical representation of the temperature and composition limits of phase fields in an alloy or ceramic
Phase Transformation - Changes that can occur within a given material system.
Phonon - A single quantum of vibrational or elastic energy.
Photovoltaic Cell — The smallest semiconductor element within a solar module to perform the immediate conversion of light
into electrical energy. Also called a solar cell.
P&ID - Piping & instrumentation diagram
Pick Hammer - A hammer with a round head for conventional planishing and a small pick-shaped head for working away in
sharp or tight corners.
Pickling - The chemical removal of surface oxides and other contaminants from a material by immersion in an aqueous acid
Piezoelectric - Any material which provides a conversion between mechanical and electrical energy.
Pilot Hole - A starting hole for large drills to serve as a guide.
Pin Connection - In two dimensions, a pin connection restrains two translation degrees of freedom but does not restrain
Pin Spanner - A spanner with pins on forked ends, used to turn an adjustable cup on the bottom bracket of a bicycle.
Piping Stress Analysis - Calculations which address static and dynamic loads on process pipe due to the effects of
temperature, pressure, weight, etc.
Piston - A cylindrical part which reciprocates in the cylinder bore of an engine and transmits the force of the gas pressure
through the connecting rod to the crankshaft.
Piston Pin - A pin that rests in two bored holes in the piston and passes through the eye of the connecting rod, to join the
two together flexibly.
Pitch - Pitch is the distance between the teeth on a gear.
Pitch Circle - The effective working circle of a gear which would be obtained if a pair of gears were replacedwith disks that
transmitted the same motion in the same package space through contact friction.
Pitot Tube - An open ended tube arrangement to face against the current of a stream of fluid; used in measuring the velocity
head of a flowing medium
Plain Cutter - A milling cutter with cutting teeth on the periphery only.
Plastic - A solid material in the primary ingredient of which is an organic polymer of high molecular weight.
Plastic Deformation - Deformation that is permanent or nonrecoverable after release of the applied load.
Plasticine - Modelling Clay.
Plasticity - The inverse of elasticity. A material that tends to stay in the shape or size to which it is deformed has high
Plasticizer - A low molecular weight polymer additive that enhances flexibility and workability and reduces stiffness and
PLC - Programmable-logic controller, used to automate industrial operations
Pneumatic - Operated by air pressure
Point Mobility - The velocity at a point per unit force at the same point and same direction.
Poise - Named after the physicist Poiseuille this is the CGS derived unit of dynamic viscosity.
Poissons Ratio - Ratio of strain in the lateral direction to strain in the axial direction.
Polymorphism - Different crystal structures at different temperatures or pressures for a single compound.
Poppet Valve - A valve opened by the action of a cam and closed by a spring.
Porcelain - Made from china clay, a clay consisting mainly of kaolinite.
Porosity - The presence of gas pockets within a solid material.
Potential Energy - The energy, that a body has by virtue of its position or state, enabling it to do work
Power Density - Characteristic parameter of a battery/electrical power source indicating its electrical power per unit weight or
Power Factor - A quantity that relates the volt amperes of an AC circuit to the wattage
Power Spectral Density - A method of scaling the amplitude axis of spectra of random rather than deterministic signals.
Power Stroke - The working stroke of a piston.
PPM - Parts per million
Pre-cast Concrete - Concrete products that have been manufactured off-site as opposed to being cast-in-place.
Pre-stressed Concrete - The steel reinforcement within concrete is “stretched” as the concrete is poured into the mold and
allowed to cure. Releasing the pressure on the steel results in an increase of the compression strength of the concrete.
Prandtl Number - A dimensionless group often used in heat exchange calculations.
Precession - A modern term, derived from the precession of the equinoxes and meaning a motion around a cone of the
rotation axis of a spinning body.
Precision Casting - Also known as investment or lost wax casting, it is based on the use of a mould that is only used once.
Prepreg - A continuous fibre reinforcement pre-impregnated with a polymer resin which is then partially cured.
Pressure - Force exerted per unit area.
Pressure Coefficient - A dimensionless value which acts as a means of indicating the local pressure at some point of interest
around a body, and which is independent of velocity.
Pressure Welding - Any welding process or method in which pressure is used to complete the weld.
Pressure Zone - As sound waves strike a solid surface, the particle velocity is zero at the surface and the pressure is high,
thus creating a high-pressure layer near the surface.
Prick Punch - A solid punch with a sharp point, used to mark centres or other locations on metal.
Profile - The gear tooth profile is the line which defines the tooth shape in a cross-section of the gear perpendicular tothe
plane of rotation.
Profile Drag - This is drag from the three-dimensional shape of the aircraft or vehicle.
Projectile Motion - A type of motion that occurs near the surface of the Earth when the only force acting on the object is that
Proportional Limit - The point on a stress-strain curve at which the straight line proportionality between stress and strain
Propulsion - Process by which something can be moved by producing a reaction with a force of thrust.
PS - Metric horsepower
psi - An abbreviation of pounds per square inch, a British imperial unit of pressure. 1.0 psi = 6894.757 Pa
psia - Gauge pressure plus local atmospheric pressure.
psid - Difference between two pressures.
psig - Difference between the measuring point and the local pressure.
psisg - psi sealed gauge; difference between a chamber of air sealed at atmospheric pressure and the pressure at the
psivg - psi vented gauge; difference between the measuring point and the local pressure.
Psychrometer - An instrument used for measuring the water vapor content of the atmosphere
Pulley - A disc with a groove around its circumference to locate a rope or cable and is used to change the direction of a force
and/or multiply the force.
Punch List - In construction, list of incomplete or unacceptable items when project is nearly complete.
PV Diagram - A plot of pressure vs. volume.
PVC - Polyvinyl chloride
Pyrometer - A device for measuring the high temperatures in a furnace.
Engineering Glossary, Engineering Dictionary P
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