25 May 2005
ppm -- Parts per million; one pound of material dissolved in one million pounds of
Precipitate -- (a) To separate a dissolved substance in the solid form by its removal
from a solution. (b) The substance in solid form that has been separated from solution.
Practical Scaling Index (PSI) -- A modified scaling index developed by P.R. Puckorius
and J.M. Brooke to provide a better and more consistent indication of scaling conditions
of cooling water. It is based on using the pH of equilibrium (pHeq) rather than the actual
pH, and is calculated as follows:
PSI = 2 pHs - pHeq.
As with the RSI, a value less than 6.0 in natural water indicates a scale-forming
tendency. A value greater than 6.0 in natural water indicates a scale-dissolving
Regeneration -- That part of the operating cycle of an ion exchange process in which a
specific chemical solution is passed through the ion exchange bed to prepare it for a
service run (i.e., return the ion exchange bed to its original composition).
Ryznar Index (stability index) -- An index classifying water as to its ability to dissolve
or deposit calcium carbonate scale. It is calculated as twice the pH of saturation minus
the actual pH (RI = 2 pHs - pH). Although in theory an RI of 7.0 should be neutral,
experiments indicate that 6.0 is a better value. A value less than 6.0 in natural water
indicates a scale-forming tendency. A value greater than 6.0 in natural water indicates a
Scale -- Deposition on a heat transfer surface of normally soluble salts. Scale is usually
crystalline and dense, frequently laminated, and occasionally columnar in structure.
Shock Feed -- The process of adding one or more water treatment chemicals in one
application rather than gradually.
Slime -- Biological growths that may accumulate to the extent that they foul equipment.
Sludge -- A water-formed deposit that will settle, and may include all suspended solids
(SS) carried by water. Sludge is commonly formed in boilers where it may be baked into
place and become hard and adherent.
Softening Water -- The process of removing from water the mineral substances that
produce a condition called hardness. There are two softening processes in general use:
chemical precipitation (lime and lime/soda softening) and the zeolite ion exchange