is an occurrence of frothy mixture of air and a
petroleum product (e.g.,
lubricant, fuel oil)
that can reduce the effectiveness of the product, and cause sluggish
hydraulic operation, air binding of oil pumps, and
overflow of tanks or sumps. Foaming can result from excessive agitation,
improper fluid levels, air leaks, cavitation,
or contamination with water or other foreign materials. Foaming can be
inhibited with an anti-foam agent. The
foaming characteristics of a lubricating oil can be determined by blowing
air through a sample at a specified temperature and measuring the volume of
foam, as described in test method ASTM-D-892.
Also see air entrainment,
emulsion.