Face combination
The materials chosen for the lapped seal faces. Usually a grade
of carbon graphite running on a hard face material.
Face to face seals
Two seals running against a common seal face. The barrier fluid
pressure is always lower than stuffing box pressure.
Face flatness
Measured by an optical flat and a monochromatic light. The measurement
is read in helium light bands (.0000116 inches or 0,3 microns).
Face lubrication
The fluid or vapor that sometimes exists between lapped mechanical
seal faces.
Face pressure
The sum of all the loads on the seal face including the spring
load, hydraulic load and shaft axial thrust, divided by the area
of the seal face. This face load is reduced by friction between
the sliding elastomer and the shaft or sleeve.
Filled carbon
Contains organic or inorganic materials that might be sensitive
to temperature, or be attacked by the fluid you are sealing. Usually
a low cost carbon.
Filter
A devise used to remove solid particles from liquid. It removes
smaller paricles than a strainer.
Finite element analysis
A computer generated method of predicting seal face distortion.
Flashing
A rapid change in liquid state from a liquid to a gas.
Flatness
Measured by Helium light bands (0.0000116" or 0,3 microns)
as opposed to surface finish that is measured by R.M.S. or C.L.A.
Flexibility factor
Same as L3/D4 Used to predict shaft bending problems.
Flexible member
The portion of the seal containing the springs or bellows.
Flexible shaft
A shaft with an operating speed higher than its first critical
speed
Fluid
The material assumes the shape of its container. It could be
either a liquid or a gas.
Flurocarbon
Genetic term for the elastomer called Viton?. Viton is a Dupont
Dow elastomer product.
Flush
Putting an outside liquid into the stuffing box of the pump at
a pressure higher than stuffing box pressure. All of this liquid
mixes with and dilutes the pumped fluid.
Foot
Supports the wet and power end of the pump and attaches it to
the base plate.
Force
Created whenever pressure works on an area. The units are pounds.
(F = P x A)
Formed metal bellows
Manufactured by stretching and compressing the metal bellows
material. Not usually used in mechanical seals because of its
high spring rate.
F.P.M. (fpm.)
Feet per minute. When used in the context of seals it is measured
at the center of the seal face.
Francis vane impeller
The most popular impeller shape with a specific speed between
1500 and 4000.
Free length
The uncompressed axial length of a seal.
Frett or fretting
Damage or grooving caused by the removal of the protective oxide
that is formed on most corrosion resistant metals. It happens
when a softer material (rubber) rubs against a hard shaft or sleeve.
A common problem with low cost O.E.M. mechanical seals and bearing
grease or lip seals.
Fugitive emission
The government has designated certain chemicals as hazardous
to the environment. If any of these chemicals is released to the
atmosphere they are called fugitive emissions.