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Suction

conditions

4.1 General

The suction conditions have to be considered the key element of a
successful pump installation and operation. If the liquid to be pumped
does not arrive at the impeller eye under the fight set of conditions, the
pump will be unable to provide the performance for which it was
designed. Consequently an understanding of the necessary suction
conditions is necessary, as well as an overview of some pump design
considerations that affect these conditions.
The most predominant of all suction problems is Cavitation. More
paragraphs have been penned on this topic than on every other aspect
of pumping combined, yet the vast majority of the world's pumps have
never experienced the problem. However, there are enough of those
who have been subjected to cavitation for us to review the matter in
some detail.

4.2 Vapor pressure

Cavitation is particularly related to a condition referred to as vapor
pressure which is that pressure below which a liquid will vaporize. For
example, water at 212 ~ F. will vaporize when the pressure falls to 14.7
p.s.i. The layman's term for this phenomenon is 'Boiling'. Similarly,
water at only 100 ~ F. will boil or vaporize if exposed to a vacuum of 18
inches of mercury. (18" Hg)

4.3 Cavitation

To anyone who works with pumps, the symptoms of cavitation are