Particle count -- the number of particles present greater than a
particular micron size per unit volume of fluid. Selected methods of particle counting are:
automated optical, where particles are directly sized and
counted using the dispersion or blockage of light created by a solid
particle passing between a light source and a sensor;
Image analysis, where stationary particles are directly sized
and counted under the microscope by manual or automated systems;
Electrical resistance, which measures the volume of a particle
as it passes through an orifice in an electrically conductive liquid;
Flow decay,
where count and size data is
extrapolated from a standard equation applied to the rate at which flow
decreases through a screen as particles block it.
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 discolored 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.
Penetration -- consistency, expressed as the distance in
millimeters that a standard needle or cone penetrates vertically into a sample
of the material (for example, grease) under known conditions of loading, time,
and temperature.
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; may apply
to either the driving or the driven gear.
Platelet – wear analysis-specific term for a smooth-surfaced,
irregular or round-edged flake whose appearance is
"plate-like", associated with rolling element bearing fatigue;
also known as spall flakes.
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 unit of viscosity equal to
the viscosity of a fluid that would require a shearing force of one dyne to move
a square-centimeter area of either of two parallel layers of fluid one
centimeter apart, with a velocity of one centimeter per second relative to the
other layer, with the space between the layers being filled with the fluid in
question. It is the ratio of the shear stress to the shear rate of a fluid,
expressed in dyne seconds per square centimeter. 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 decreased ring seal and increased oil consumption.
Polymerization -- the chemical combination of similar-type
molecules to form larger molecules, often in chain-like structures.
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 carburetor
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.
Power unit -- a combination of pump, pump drive, reservoir,
controls and conditioning components which may be required for its application.
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 between upstream pressure (filter
inlet) and downstream pressure (filter outlet).
Pressure line filter -- a filter located in a line conducting
working fluid to a working device or devices.
Process contamination -- unwanted solids or liquids entering one
part of a process from another part of the same process, but generally not
referring to operating environment sources.
Process oil -- an oil not used for lubrication but as a component
of another material, or as a carrier of other products.
Pump -- a device which applies mechanical force and motion to a
liquid, creating hydraulic fluid power. Pumps are divided into two categories:
positive displacement and
centrifugal:
Positive displacement pumps force liquid to flow in volume
proportion to increasing and decreasing pump volume, as in reciprocating
and rotary pumps. Reciprocating pumps use pistons, plungers or
diaphragms to increase and decrease fluid volume. Rotary pumps use a rotating
gear, vane or screw to force liquid from the pump.
Centrifugal pumps, also called kinetic pumps, provide smooth
non-pulsed flow and adjustible flow velocity. Liquid flow is established through
centrifugal force created by a rotating impeller, as in radial
flow and axial flow centrifugal pumps. In a radial flow
pump, fluid enters the pump at the impeller rotational axis and is forced
outward by vanes. In an axial flow pump, a propeller or screw moves fluid down
the axis of the pump, parallel to the shaft.
Pumpability -- 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.
