Glossary of Pump Terms: H
Halogen
Elements that attack carbon. Fluorine, bromine, chlorine, astatine
and iodine.
Hard face
A seal face either rotating or stationary. The most common materials
are silicone carbide, ceramic, tungsten carbide, Stellite, Ni-resist.
The hard face must be the wider seal face.
Harmonic vibration
Vibtrating in harmony with something near by. This can be a big
problem for bearings in stationary or non running equipment.
Hastelloy "C"
A nickel rich, corrosion resistant metal used for mechanical
seal springs and metal bellows because it is not sensitive to
chloride stress corrosion.
Head
The equivalent height of the liquid. 20? C. water is used as
the standard where 10 meters (33.9 ft.) of water equals one atmosphere
(14.7 psi. or 1 bar). The term head is used instead of pressure
in the centrifugal pump business.
Helium Light Band
A method of measuring seal face flatness. One helium light band
equals 0.0000116 inches or 0.3 microns. Seal faces are normally
lapped to within three helium light bands of flatness.
Horse power
33,000 foot pounds per minute. A common method of measuring work.
Hydraulic balance
A method of reducing mechanical seal face loading by reducing
the seal face closing area.
Hydraulic force
Occurs any time pressure acts on a seal face area. Force times
distance divided by time is a measurement of work done.
Hydrocarbon
A petroleum product consisting of hydrogen and carbon.
Hydrodynamic force
Generated at the seal faces because, for all practical purposes,
liquid is not compressible.
Hydrodynamic seal
Special geometric features on the seal face that provide lift
by taking advantage of the rotation of one seal face upon the
other.
Hydrogen embrittlement
A premature fatigue of metal caused by the presence of free hydrogen.
This is a major cause of ceramic breakage in hot water seal applications,
and bearing fatigue if moisture penetrates into the bearing case.
Hydronium ion
An ion formed by the transfer of a proton from one molecule of
water to another. Used to determine the pH of a substance. Each
step increases by a factor of ten.
Hydrostatic seal
Maintains a controlled gap between the seal faces by balancing
the open and closing forces. There is a small amount of leakage
across the faces when the shaft is rotating. Used in some compressor
applications, but not very practical for the chemicals found in
the process industry.
Hysteresis
The delay or lag that causes seal faces to open.
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