Packing: deformable substance used for sealing between locations at which fluids are present under different conditions, usually where relative motion occurs at the boundary between the fluids.

Packing box: the portion of the casing or cover through which the shaft extends and into which a seal or packing is placed to limit leakage; also known as a stuffing box.

Packing gland: an adjustable follower that compresses packing in a stuffing box.

Packing gland assembly (lube systems): assembly that is screwed into the measuring valve body.

Pad lubrication: see oil pad.

Panel coker: a testing device that involves dripping cold fluid onto a hot panel to determine the detergency and deposit-forming tendencies of the test fluid.

PAO: see polyalphaolefins.

Paraffin wax: a high-VI crystalline substance removed from paraffinic crudes after distillation, composed of unbranched straight chain hydrocarbons that are solid at room temperature. Waxes are primarily used for water proofing and candles; in small quantities, they degrade the low-temperature properties of lubricants.

Paraffinic base: characterizes certain petroleum products prepared from paraffinic crudes (crudes that contain high percentages of straight chain aliphatic or paraffin hydrocarbon molecules).

Partial bearing: see journal bearing.

Particle count: the object of various test procedures employed in condition monitoring. The ISO Solid Contaminant Code rates the number of particles (per volume) larger than five microns (silting condition) and the number of particles (per volume) larger than 15 microns (presence of wear material); the two rating numbers are separated by a slash. The ISO standard supersedes most other methods, but some utilize ISO codes to report particles larger than two microns.

Pascal’s Law: axiom stating that the pressure on a confined fluid is transmitted undiminished and with equal force to all equal areas of the container.

Penetration (grease): (ASTM D-217) the depth, in tenths of a millimeter, that a standard cone penetrates a semisolid sample under specified conditions. Test methods include undisturbed (sample tested in its container); unworked (sample transferred to worker cup); worked 60 X (transferred to worker cup and worked with 60 strokes); prolonged worked (worked more than 60 X) and block (sample of block grease cut into a cube) (see consistency).

Penetrating oil: usually a solvent based oil; loosens rusty nuts or bolts by penetrating the rust barrier, thereby facilitating disassembly without destruction.

Penetrometer: instrument for measuring the penetration of semisolid substances like greases.

Pensky-Marten Closed Cup test: closed cup test for determining the flash point of fuel oil or open gear lubricant; sometimes used for lubricants suspected of being contaminated with fuel or solvent.

Pentane insolubles: see insolubles.

Petrolatum: product made from the residuals of paraffinic crudes, consisting primarily of high molecular weight amorphous waxes, with some grades containing microcrystalline waxes. It is pale to yellow in color, with oily or grease-like characteristics, used in some lubricants and rust preventives or a lay- up lubricant for some kinds of wire rope.

Petrolene: a petroleum naphtha containing asphalt, used in protective coatings.

Petroleum: oily liquids or semisolids found in the earth, composed of hydrocarbons and primarily such nonmetallic elements as sulfur, oxygen, nitrogen, etc. Though the composition of these dark, highly complex mixtures varies, they are often lighter than water and highly flammable. Only a small percentage of crude petroleum can be processed for lubricants.

Petroleum spirits: solvents obtained from petroleum with boiling ranges from 300-400°F and flash points exceeding 100°F (see mineral spirits).

Phenols: a class of aromatic chemicals used chiefly as antioxidants in lubricating oils like hydraulic fluids and circulating oils. Because of its biotoxicity, the EPA prohibits discharge of the parent chemical (“free phenol” or C6H5OH) into waterways; therefore, most phenols utilized in lubricants are sterically hindered. However, some refining extraction processes still use free phenol to remove aromatic, naphthenic and unsaturated hydrocarbons from lube base stocks.

Phospate esters: a class of synthetic esters with superior fire resistance; used primarily as FR fluids, they are formulated with these general properties: specific gravity greater than one, good lubricating capability, fair high-temperature stability, poor hydrolytic stability, and poor viscosity-temperature linkage. Though they are harmful to paints and some seal materials, one such ester, tricresyl phosphate, has long been used as an anti-wear additive in lubricating oils.

Pillow block: denotes bearing support on a site other than the machine itself.

Pilot-operated: in hydraulics, the technique of using a small valve to control a much larger one.

Pinion: the smaller of two mating or meshing gears, usually the driving gear. In the steel industry, the term “mill pinions” describes a mating pair of gears in a one-to-one ratio, each of which is coupled to a mill roll, one above the other in the mill stand; employed in both unidirectional and reversing mills, they are driven by a mill motor and mill drive coupled to the pinion stand.

Piston (lube systems): sliding part contained in the cylinder of the injector, consisting of a rod, extension and packing.

Piston stop plug (lube systems): the lower portion of the adjusting assembly.

Piston rings: used in engines to maintain a gas-tight seal between piston and cylinder, to assist in cooling the piston and to control cylinder wall lubrication; the three rings include a fire ring, a compression ring and an oil ring.

Pitch (gears): used in gear geometry to characterize features governing tooth size, shape, spacing, etc.; common terminology includes pitch circle, pitch diameter, pitch point, normal circular pitch and normal diametrical pitch (see Section 7).

Pitch circle (gears): curve where the imaginary pitch cylinder and plane normal to the axis of rotation intersect.

Pitch diameter (gears): diameter of the pitch circle of mating gears in imaginary line contact along the centerline between the two shafts.

Pitch line: corresponds in the cross-section of a rack to the pitch circle in the cross-section of a gear.

Pitch line velocity (gears): linear speed at the pitch line, measured in fpm or m/s.

Pitch point (gears): point of tangency of the two pitch circles of the mating gears, lying on the common centerline between them.

Pivot bearing: axial-load, radial-load bearing that supports the end of a shaft or pivot (as on the balance wheel of a watch).

Pivoted pad bearing: an axial or radial-load bearing with a surface consisting of one or more pads or shoes pivoted to tip, thereby promoting the establishment of a hydrocarbon film.

Plain bearing: any simple sliding bearing, as distinguished from fixed pad, pivoted pad or rolling bearings. Depending on the direction of the load on the bearing surface, plain bearings are classified as guide bearings, journal bearings or thrust bearings.

Planetary gear: a train of internal gears consisting of a sun gear, to which input power is applied, and planet gears that give the output power.

Plunger (lube systems): slide valve that controls the valve port.

Plunger spring (lube systems): spiral spring in the injector body cylinder.

Poise: the standard unit of absolute viscosity in the cgs system; expressed in dyne-s/cm2.

Polar compounds: chemical compounds whose molecules exhibit positive electrical charges at one end and negative charges at the other. This characteristic, known as “polarity”, endows such compounds with an affinity for metal surfaces. As lubricant additives, they serve as “oiliness agents”; they have good metal-wetting properties and some polar compounds promote emulsification between water and oil.

Polyalphaolefins (PAOs): a class of synthetic lubricant bases formed by polymerization of an olefin monomer, such as ethylene or propylene, whose properties after polymerization include good oxidation stability at high temperatures, good hydrolytic stability, compatibility with mineral oils and low volatility. They have found service in turbines, gears, compressors and automotive engines.

Polybutene: synthetic lubricating oil, a polymer of butene (C4H8); principal uses include insulating oils, gas compressor oils and process oils in the aluminum industry.

Polyglycol: a polymer of ethylene glycol (C2H602) used as a synthetic base stock; water-soluble polyglycols serve as thickeners or anti-freezes in FR fluids; insoluble forms are used as heat transfer and hydraulic fluids or high- temperature bearing oils.

Polyesters: synthetic resins, usually obtained from polymerization of a dibasic acid with a dihydric alcohol, not usually used as lubricant stocks. (see diesters).

Polymers: organic compounds created by polymerization that become progressively heavier and acquire diverse properties as the multiple linkages increase. The original monomer may be a gas or a liquid; according to the extent of polymerization, the final product will be a high molecular weight liquid or solid that retains the same proportion of elements as the original monomer.

Polymerization: the chemical combination and recombination of the same unsaturated hydrocarbon with itself to form an extensive chain; the chemical process of combining similar molecules to form larger molecules.

Polyolesters: a class of synthetic esters formed by reacting fatty acids with a polyol such as glycol; physical properties vary according to the polyols and acids used. Polyolesters formulated as lubricants have low volatility and good oxidation stability at high temperatures: they are used as base oils for turbines, compressors, jet engines and automotive engines and as base fluids for certain greases.

Polyureas: polymeric thickeners for grease, made from isocyanates and amines. Greases thickened with polyureas have high oxidation resistance and high dropping points; they work well in ball bearings for electric motors.

Porous bearing: bearing made from porous material such as compressed metal powders; the pores serve as reservoirs or passages for lubricant.

Positive displacement oil pumps: vane, gear or piston pumps that build up high pressure on the discharge side because the capacity output of the pump is positive. If the discharge is not utilized, the oil pressure regulator or by-pass prevents damage (see controlled volume pump, gear pump).

Pour point: (ASTM D-97) the lowest temperature at which a lubricant will pour or flow under specified conditions.

Pour point depressant: an additive in lubricating oil that lowers the pour point, by preventing any wax present from crystallizing to form a solid mass. ppm: parts per million.

Precipitation number: (ASTM D-91) the number of milliliters of solid matter precipitated from a mixture of oil and petroleum solvent under specified conditions; chiefly used to determine the presence of asphalts in semi-refined or black oils, or to examine sludge in used oils.

Precision: see tolerance.

Preloading: procedures employed during assembly and mounting to remove all looseness or play in a bearing, usually performed on shafts or spindles in machine tools and precision machines that must rotate without clearance in either the axial or radial direction. Preloaded bearings are not used where deflection is excessive.

Pre-lubed bearings: bearings lubricate by the manufacturer to preserve their integrity during storage.

Pressure angle (gears): angle between the line of action and a line tangent to both pitch circles. This angle remains constant with involute form teeth at any point in the contact path. Common pressure angles are 14.5° and 20°; when stronger teeth are needed, larger angles are used. Pressure angles increase with center distance.

Pressure, atmospheric: see normal pressure.

Pressure control valves: devices that control the pressure in a hydraulic system, including relief, unloading, counter balance, sequence and pressure-reducing valves and, occasionally, brake valves.

Pressure drop: loss of pressure caused by restriction in a hydraulic system, where restriction includes valves, orifices and pipes; synonymous with “pressure differential” or “upstream minus downstream pressure” across any device in a hydraulic system.

Pressure, gauge, (psig): pressure differential above or below atmospheric pressure.

Pressure-reducing valve (hydraulics): device that keeps pressure in a branch of a hydraulic circuit below the pressure in the remainder of the circuit.

Pressure viscometer/viscometer (grease): a capillary instrument used to determine apparent viscosity.

Preventive and predictive maintenance (PM and PDM): two basic programs that use selected features of condition monitoring procedures in managing maintenance practices and costs to increase plant productivity; PM programs schedule maintenance at regular intervals, while PDM programs schedule maintenance on the basis of information obtained from sophisticated condition- monitoring tests.

Priming: in pump operation, filling the liquid end of a pump with liquid to remove vapors and eliminate the possibility of becoming vapor bound.

Principal reference planes (gears): pitch plane, axial plane and transverse plane, all intersecting at a point and mutually perpendicular.

Process oil/process lubricants: in the steel industry, materials used in direct contact with the product being produced, e.g., rolling oils in hot and cold rolling mills, wire drawing compounds, forging compounds, slushing oils for rust protection, stamping and drawing compounds, quenching oils, wire rope laying- up lubricant, etc.

Profilometer: a device that profiles or measures surfaces to determine smoothness.

Proportional valve (hydraulics): a hydraulic valve that produces an output proportional to its input signal, that can be adjusted electronically, remotely; uses proportional solenoids with constant force for a given signal.

Proximity switches (lube systems): magnetic (dry contact) switches that detect divider valve piston movement without a cycle indicator pin attached to the piston.

Pumpability: see mobility.

Pycnometer: a device for measuring densities of liquids.

Pyrolysis: chemical decomposition by the action of heat.

Pyrometer: a device for recording high temperatures that uses a thermocouple or an infrared pyrometer to measure invisible light emitted by the hot object.