When held at its normal point, the water line protects the flanged part
of the inner shell; but no damage can occur, either from a willful or
an accidental drawing down of the water, as the spray deflected through
the nipples of the outer tubes is sufficient to protect the flange,
although the actual water level is well down in the leg.
The steam in contact with the upper part of the shell is by no means
dry, and the heat absorbed at this point is amply sufficient to
protect it. To insure a delivery of dry steam to the cylinders, a
peculiar _“take-off” ring_ is provided at the highest part of the
steam reservoir, the same encircling the inside sheet of the shell.
The upper edge of the ring is perforated at a distant point from the
throttle, and the steam entering the ring chamber in small streams is
held in close contact with the hot shell at a point closely adjacent
to the upper line of rivets; the steam by this means is dried during
its passage to the throttle, and the heat thus absorbed serves as a
protection to the rivets just referred to.
NOTE.—The life of both water tubes and fire tubes is generally found
disproportionate to the heavier parts used in boiler construction,
and experience shows conclusively that the cost of subsequent
maintenance is measured directly by, and may be diminished by, the
facility with which these indispensable parts may be replaced or
repaired in an emergency.
The principal heating surface of the boiler is contained in the
vertical water tube sections, which comprise and will be referred to,
as _an inner and an outer tube system_.
_The outer system_, embraces the short manifold sections which
completely encircle the fire-box walls. The top end of each section
is screwed and suspended from the flanged part of the shell, and the
lower end is stayed by direct connection with the leg of the fire-box.
_The tubes are “staggered”_ in their manifolds, thereby exposing the
greatest possible surface to the fire, and filling out the space due
to the difference in the width of the water-leg and steam space of the
shell.
The direct application of heat to the tubes causes a natural and active
upward current therein, which in turn induces a corresponding downward
movement of the water in the leg of the fire-box, and promotes the flow
into the feed pipes.
_The inner-tube system_ comprises those tube sections which extend to
the upper limits of the boiler, their number and arrangement being
such as to completely fill the interior of the shell above the space
required for the combustion of the fuel. The construction of the
vertical inner-tube system is simple, and consists of the required
number of manifold sections, suitably arranged to conform to the
circular space occupied, the flat inner end of each upper manifold
being rigidly bolted to a heavy transverse beam, which in turn is
supported in suitable pockets secured to the upper part of the shell.
At the top of the boiler, each section has its own connection with
the steam space, and it is easy to remove either one of the sections
separately without disturbing the others; _or the entire inner-tube
system can be raised out of the boiler as a whole, after breaking the
proper connections_, all of which are accessible. The current of steam
and water carried over through the top connections of the inner system
is generally sufficient to keep the tubes clear of scale; and the
point of discharge and disengagement is brought down low, to prevent
its mixture with the drier steam contained in the highest part of the
shell.
When connected to a stationary boiler, as is now the general practice
in fire departments, the circulative currents of water reach all
parts of the boiler, hence its contents may be kept uniformly at any
desirable temperature.
_A stationary heater for the fire engine_ consists of a small boiler,
placed at some convenient point near the same when in quarters. It
is connected with the engine boiler by means of suitable circulating
pipes, the entire arrangement being adapted to supply hot water through
pipe connections which separate automatically as the engine leaves the
house.
[Illustration: Top View.—FIG. 401.]
Although the best types of fire engine boilers require but a few
minutes’ time to generate a working pressure from cold water, the
general adoption of many improvements has made the stationary heater an
essential part of a complete equipment.
[Illustration: Bottom View.—FIG. 402.]
Experience proves that the life of the boiler is prolonged by being
kept constantly in a state of activity, and the elevated temperature of
the water insures prompt and efficient work by the steamer at the very
time when a few moments’ delay may breed disaster.
_The pumps_ fitted and adapted to steam fire engines comprise two
separate and distinct double acting piston pumps united in a single
body and akin in many details to the duplex pump.
[Illustration: FIG. 403.]
Calling in mind the well-known fact, that, in drawing a water supply
the only power available to bring the fluid under forcing influence of
the pump’s pistons is the limited pressure of the atmosphere, therefore
the importance of all details concerned in first inducing an entry of
the water will be readily conceded. Easy and unrestricted “suction
ways” in direct communication with properly proportioned receiving
valves (and these valves suitably arranged in close proximity to the
working barrels of the pump), are the conditions that must always
remain paramount, and to which all other features must give way, to
safely attain the desirable high piston speeds. The value of perfect,
simple and direct water ways, the passages, and all which they imply,
has been studied in the design of this pumping engine. See Figs.
403-407.
The facilities provided for exposing the interior mechanism permits
all such parts to be quickly reached for examination, or detached for
renewal or repair, and this can be done without dismounting the entire
pumps or greatly disturbing their exterior attachments. It will be
seen, by reference to the cuts, that all of the valves can be easily
and quickly examined, and also replaced, by removing the caps that
enclose the chambers; all joints required for this purpose are made
between flat surfaces planed true, as shown in Fig. 404; gun metal, or
other suitable composition, is used and no part of the pump body is
subject to wear, either by friction or corrosion. _All valve seats are
screwed into place_, and either these or the working barrels of the
pump may be readily replaced with new ones, in case the same should
become worn. All stud bolts, nuts, etc., coming in contact with water,
are made of drawn phosphor or Tobin bronze; nipples, piping, etc., are
of brass.
[Illustration: FIGS. 404, 405, 406 and 407.]
Suction or hydrant connection may be made at either side of the engine;
and, in operation, the central core of the pump body is _practically
a continuation of the suction hose_, and serves to establish a direct
communication with the receiving pump valves, arranged on opposite
sides of the chamber. This chamber, as shown in the sectional view,
Fig. 408, thus _becomes the distributing center, from which the
incoming water flows to the suction valves_. The current from the
suction is not required to change its general direction, and but little
friction is encountered by the water in its diversion through the pump
valves.
The position of the suction or receiving valves, in relation to the
water cylinders, may be understood by reference to Fig. 408, which
shows the same arranged in a cluster around the open ends of the
barrels. The suction valve area is large, and the proportions adopted
contribute largely to the smooth running of the pump, under conditions
of speed seldom attempted in ordinary practice.
[Illustration: FIG. 408.]
The valves in this pump are controlled by improved springs, the
tension of which is at all times the same; and which are made of
phosphor bronze; _the force chambers_ in opposite ends of the pumps are
practically equal, and, owing to the close proximity of the valves, the
clearance is reduced to a minimum The discharging outlets are elevated
above the highest point of the valve chambers, and the communicating
passages are designed to prevent conflicting currents, and also to
permit the pump to free itself promptly of air. The pistons are of a
frictionless type, and in accordance with the usual practice of working
double pumps in unison, the cranks controlling the movements of the
pistons are placed at 90 degrees.
[Illustration: FIG. 409.]
A convenient and effective arrangement of suction strainers is shown
in Fig. 409. Perforated cages are introduced into the suction chambers
through the inlets on opposite sides of the pump. The ends of these
cages are open, and a short sleeve, which is permanently secured within
the pump, serves to support and also to establish communication from
one cage to the other.
The surface of both cages is, therefore, available as a strainer, and
any obstruction entering with the water is carried to the opposite
side, to a point where it can be removed, without first detaching the
suction hose.
The driving mechanism supplied with the American Pump is shown by Figs.
389 and 394, which are perspective views engraved from photographs. It
may be noted that the design is practically compact and well balanced,
and embodies many excellent advantages found in no other type of fire
engine.
_The pumps, steam cylinders and driving parts_ are built as a unit,
and have no direct connection with the boiler other than the necessary
stays and pipe connections, all of which are readily accessible and
visible for inspection at any time.
The steam cylinders used in connection with the pumps are of the
ordinary slide valve type. The valve chests are easily opened from
either side of the engine for examination, and the valve rods are made
from a special composition and can not corrode. The valve motion is
simple, and there is nothing connected with the steam ends that may not
be quickly understood.
[Illustration: FIG. 410.]