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The following definitions are intended to give basic understanding of the terms
commonly used in the pump industry. Some industry standards, or customer
specifications, may have specific meaning of certain terms that may be different
from their common usage - in such case the terms should be interpreted in the
context of the standards, or specifications, being referred to.
L10 bearing life - The number of hours that ninety percent (90%) of a group of
bearings shall attain or exceed prior to the onset of bearing fatigue failure.
L^3 / D^4 - The mathematical expression known as shaft flexibility factor (SFF).
Labyrinth seal - A non-tight fluid seal that restricts flow and induce turbulence
by means of a tortuous path.
Lantern ring - A rigid ring with radial flow passages that is inserted between the
packing rings in a stuffing box to allow the injection of flush liquid into the box.
Lapping - A finishing operation to produce extremely flat and smooth surface on
a mechanical seal face using small free-floating abrasives or diamond charge
Lateral critical speed - a resonant frequency associated with the lateral
deflection of a rotor; not to be confused with torsional critical speed which is
associated with the torsional or angular deflection of a rotor.
Leakage concentration - The concentration of a volatile organic compound,
or other emissions, to the atmosphere immediately surrounding a seal measured
in parts per million (PPM) using a calibrated analyzer.
Leakage rate - The volume of liquid passing through a given part - such as
across a wear ring, sleeve, seal, etc. - for a given period of time(Typically
measured in gallons per minute in US customary units.)
Liner - A replaceable circular plate installed in a casing to protect it from wear.
In a pump with open-type impeller, the liner is used to obtain a close clearance
between the impeller face and the pump casing to prevent excessive flow
leakage back into the impeller suction. Liners are commonly used in pumps
handling liquids with slurry or abrasive materials. In radially-split case pumps,
both the casing and the casing cover are usually provided with liners.
Lip seal - An elastomer or metallic seal that prevents leakage by a scraping or
wiping action with a controlled interference fit between the lip and its mating
Load E - The equivalent load impressed on a bearing, including radial and axial
loads, usually expressed in pounds -force.