FOAMING.
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.