Paper chromatography

A method, which involves placing a drop of fluid on a permeable piece of paper and noting the development and nature of the halos, or rings, surrounding the drop through time. The roots of this test can be traced to the 1940s, when railroads used the "blotter spot" tests.

Paraffinic

A type of petroleum fluid derived from paraffinic crude oil and containing a high proportion of straight chain saturated hydrocarbons. Often susceptible to cold flow problems.

Particle count

The number of particles present greater than a particular micron size per unit volume of fluid often stated as particles > 10 microns per millilitre.

Particle density

An important parameter in establishing an entrained particle's potential to impinge on control surfaces and cause erosion.

Particle erosion

Occurs when fluid-entrained particles moving at high velocity pass through orifices or impinge on metering surfaces or sharp angle turns.

Particle impingement erosion

A particulate wear process where high velocity, fluid-entrained particles are directed at target surfaces.

Patch test

A method by which a specified volume of fluid is filtered through a membrane filter of known pore structure. All particulate matter in excess of an "average size," determined by the membrane characteristics, is retained on its surface. Thus, the membrane is discoloured by an amount proportional to the particulate level of the fluid sample. Visually comparing the test filter with standard patches of known contamination levels determines acceptability for a given fluid.

Permeability

The relationship of flow per unit area to differential pressure across a filter medium.

pH

Measure of alkalinity or acidity in water and water-containing fluids. pH can be used to determine the corrosion-inhibiting characteristic in water-based fluids. Typically, pH > 8.0 is required to inhibit corrosion of iron and ferrous alloys in water-based fluids.

Pinion

The smaller of two mating or meshing gears; can be either the driving or the driven gear.

Pitting

A form of extremely localized attack characterized by holes in the metal. Pitting is one of the most destructive and insidious forms of corrosion. Depending on the environment and the material, a pit may take months, or even years, to become visible.

Pleated filter

A filter element whose medium consists of a series of uniform folds and has the geometric form of a cylinder, cone, disc, plate, etc. Synonymous with "convoluted" and "corrugated".

Pneumatics

Engineering science pertaining to gaseous pressure and flow.

Poise (absolute viscosity)

A measure of viscosity numerically equal to the force required to move a plane surface of one square centimetre per second when the surfaces are separated by a layer of fluid one centimetre in thickness. It is the ratio of the shearing stress to the shear rate of a fluid and is expressed in dyne seconds per square centimetre (DYNE SEC/CM2); 1 centipoise equals .01 poise.

Polar compound

A chemical compound whose molecules exhibit electrically positive characteristics at one extremity and negative characteristics at the other. Polar compounds are used as additives in many petroleum products. Polarity gives certain molecules a strong affinity for solid surfaces; as lubricant additives (oiliness agents), such molecules plate out to form a tenacious, friction-reducing film. Some polar molecules are oil-soluble at one end and water-soluble at the other end; in lubricants, they act as emulsifiers, helping to form stable oil-water emulsions. Such lubricants are said to have good metal-wetting properties. Polar compounds with a strong attraction for solid contaminants act as detergents in engine oils by keeping contaminants finely dispersed.

Polishing (bore)

Excessive smoothing of the surface finish of the cylinder bore or cylinder liner in an engine to a mirror-like appearance, resulting in depreciation of ring sealing and oil consumption performance.

Polymerisation

The chemical combination of similar-type molecules to form larger molecules.

Pore

A small channel or opening in a filter medium, which allows passage of fluid.

Pore size distribution

The ratio of the number of effective holes of a given size to the total number of effective holes per unit area expressed as a percent and as a function of hole size.

Porosity

The ratio of pore volume to total volume of a filter medium expressed as a percent.

Positive crankcase ventilation (PCV)

System for removing blow-by gases from the crankcase and returning them through the carburettor intake manifold to the combustion chamber where the recirculated hydrocarbons are burned. A PC valve controls the flow of gases from the crankcase to reduce hydrocarbon emissions.

Pour point

Lowest temperature at which an oil or distillate fuel is observed to flow, when cooled under conditions prescribed by test method ASTM D 97. The pour point is 3°C (5°F) above the temperature at which the oil in a test vessel shows no movement when the container is held horizontally for five seconds.

Pour point depressant

An additive, which retards the adverse effects of wax crystallization, and lowers the pour point.

Power unit

Combinations of pump, pump drive, reservoir, controls and conditioning components, which may be required for its application.

Predictive maintenance

A type of condition-based maintenance emphasizing early prediction of failure using non-destructive techniques such as vibration analysis, thermography, and wear debris analysis.

Pressure

Force per unit area, usually expressed in pounds per square inch.

Pressure, absolute

The sum of atmospheric and gage pressures.

Pressure, atmospheric

Pressure exerted by the atmosphere at any specific location. (Sea level pressure is approximately 14.7 pounds per square inch absolute.)

Pressure, back

The pressure encountered on the return side of a system.

Pressure, cracking

The pressure at which a pressure operated valve begins to pass fluid.

Pressure, rated

The qualified operating pressure, which is recommended for a component or a system by the manufacturer.

Pressure, system

The pressure, which overcomes the total resistances in a system. It includes all losses as well as useful work.

Pressure Drop

Resistance to flow created by the element (media) in a filter. Defined as the difference in pressure upstream (inlet side of the filter) and downstream (outlet side of the filter).

Pressure gage

Pressure differential above or below atmospheric pressure.

Pressure line filter

A filter located in a line conducting working fluid to a working device or devices.

Preventive maintenance

Maintenance performed according to a fixed schedule involving the routine repair and replacement of machine parts and components.

Proactive maintenance

A type of condition-based maintenance emphasizing the routine detection and correction of root cause conditions that would otherwise lead to failure. Such root causes as high lubricant contaminant, alignment and balance are among the most critical.

PSIA

Pounds per square inch absolute. (PSIG + 14.696)

PSID

Pounds per square inch differential.

PSIG

Pounds per square inch gauge (PSIA - 14.696)

Pump

A device, which converts mechanical force and motion into hydraulic fluid power.

Pump ability

The low temperature, low shear stress-shear rate viscosity characteristics of an oil that permit satisfactory flow to and from the engine oil pump and subsequent lubrication of moving components.

Pump, fixed displacement

A pump in which the displacement per cycle cannot be varied.

Pump, variable displacement

A pump in which the displacement per cycle can be varied.