Foaming is the violent agitation of the volume of water in the boiler;
it occurs only in dirty boilers and where dirty feed water is used,
which causes the water to become saturated with foreign matter, such as
lime, sediment, mud, oil or grease, etc.
The steam trying to escape through the scum formed by these
impurities, raises the whole mass from the surface of the water in
large bubbles, and causes a general frothing or foaming condition of
the water level, which is indicated by the dirty appearance of the
gauge cocks and joints and the cutting of piston rod and cylinder by
the gritty matter carried over by the steam. Foaming does not result in
carrying over so much water, but a foamy boiler does not produce as dry
steam as one that is kept perfectly clean.
Q. How do you prevent a boiler from foaming?
A. To remedy foaming, or prevent it, requires frequent blowing off from
the surface of the water the scum which causes it, and the use of pure
feed water. It may be stopped for a while by closing the throttle valve
for an instant, to give the water and scum a chance to settle.