Glossary F

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.


  • 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.


  • A rapid change in liquid state from a liquid to a gas.


  • 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/DUsed 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


  • The material assumes the shape of its container. It could be either a liquid or a gas.


  • Genetic term for the elastomer called Viton®. Viton is a Dupont Dow elastomer product.


  • 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.


  • Supports the wet and power end of the pump and attaches it to the base plate.


  • 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.