Owing to the fact (1) that nearly, if not quite all, the impurities
which exist in feed water are set free by a high temperature attained
under pressure; (2) that these impurities are left in the boiler by
the constant use of the steam, there follows the result that the water
remaining is more and more impregnated with the residuum composed of
the foreign matters which (the water removed) constitutes mud, scale,
etc.
The custom has been and is now to regularly “blow off” one or two
gauges of this water once or twice per day replacing it with fresh
water of less density; that this is a very imperfect method for
removing the foreign matter is readily allowed, besides wasting
absolutely all the units of heat contained in the water blown off.
Now, within the boiler while in use, under the operation of the fierce
heat of the furnaces, are constant changes in the position of the
water caused by the boiling, by the withdrawal of the steam and by the
constant effort of the hot water to rise and the cold water to fall.
The water thus keeps in circulation everything within the boiler,
including the sediment, _except in places where the water is from
any cause without motion_. In these quiet nooks there is a constant
depositing of the elsewhere active foreign matters contained in the
water, which deposits, in the form of mud and scale, left undisturbed,
causes loss and danger.
It is in taking advantage of these facts, and of the principles of the
circulation of hot and cold water, that mechanical boiler cleaners are
brought into successful use.
These devices for the stilling of the water and collection of the
sediment are made in various forms and all sizes and capacities, and
are located at the sides or back of the boiler setting and even on top
of the boiler. There is a system where pipes in a coil are fixed in
the sides of the furnace and exposed to its greatest heat, and which,
owing to their enlarged area, act as most efficient reservoirs. In
all these devices there is an _upflow pipe_ connected with the lower
and coolest water, and a _return pipe_ connecting with the top of the
water where it is hottest. This arrangement assures a constant current
which is more or less rapid according to the intensity of the fire and
which keeps up as long as the firing is done. Where this current passes
through the reservoir, the enlarged area and comparative quiet is
favorable for the deposit of the sediment and in practical experience
it does deposit nearly all of it. The collection of the impurities is
helped by a _funnel-shaped appliance_ placed at the opening of the
upflow pipe, which, aided by the rapid flow of the hot water, carries
the floating scum towards it into the reservoir. Attached to the
reservoir is the blow-off pipe through which the deposited matter is
removed as often as necessary.
The use of these mechanical cleaners is readily understood: (1) they
provide a place of accumulation for the sediment; (2) they save the
necessity of opening the boilers to remove by hand, the refuse of the
boiler; (3) save fuel by avoiding the necessity of frequent blowing off
one or two gauges of water, and (4) by the preventing the formation of
scale with its attendant evils.