The causes are—dirty water, trying to evaporate more water than the
size and construction of the boiler is intended for, taking the steam
too low down, insufficient steam room, imperfect construction of
boiler, too small a steam pipe and sometimes it is produced by carrying
the water line too high.
Too little attention is paid to boilers with regard to their
evaporating power. Where the boiler is large enough for the water to
circulate, and there is surface enough to give off the steam, foaming
never occurs.
As the particles of the steam have to escape to the surface of the
water in the boiler, unless that is in proportion to the amount of
steam to be generated, it will be delivered with such violence that the
water will be mixed with it, and cause foaming.
For violent ebullition a plate hung over the hole where the steam
enters the dome from the boiler, is a good thing, and prevents a rush
of water by breaking it, when the throttle is opened suddenly.
In cases of very violent foaming it is imperative to check the draft
and cover the fires.
The steam pipe may be carried through the flange six inches into the
dome—which will prevent the water from entering the pipes by following
the sides of the dome as it does.
A similar case of priming of the boilers of the U. S. Steamer Galena
was stopped by removing some of the tubes under the smoke stack and
substituting bolts.
Clean water, plenty of surface, plenty of steam room, large steam
pipes, boilers large enough to generate steam without forcing the
fires, are all that is required to prevent foaming.
A high pressure insures tranquillity at the surface, and the steam
itself being more dense it comes away in a more compact form, and the
ebullition at the surface is no greater than at a lower pressure. When
a boiler foams it is best usually to close the throttle to check the
flow, and that keeps up the pressure and lessens the sudden delivery.
Too many flues in a boiler obstruct the passage of the steam from the
lower part of the boiler on its way to the surface—this is a fault in
construction.
An engineer who had been troubled with priming, finally removed 36 of
the tubes in the centre of the boiler, so as to centralize the heating
effect of the fire, thereby increasing the rapidity of ebullition at
the centre, while reducing it at the circumference. The effect of the
change was very marked. The priming disappeared at once. The water line
became nearly constant, the extreme variation being reduced to two
inches.