Few boiler fittings are found on the _Pioneer_ and it appears that
little was done to update the engine with more modern devices during its
many years of service. With the exception of the steam gauge, it has no
more boiler fitting than when it left the builder's shop in 1851.
The throttle valve is a simple slide valve and must have been primitive
for the time, for the balance-poppet throttle valve was in use in this
country previous to 1851. It is located directly below the steam dome
even though it was common practice to place the throttle valve at the
front of the boiler in the smokebox. Considering the cramped condition
inside the smokebox, there would seem to be little space for the
addition of the throttle valve; hence its present location. The dry pipe
projects up into the steam dome to gather the hottest, driest steam for
the cylinders. The inverted, funnel-like cap on the top of the dry pipe
is to prevent priming, as drops of water may travel up the sides of the
pipe and then to the cylinders, with the possibility of great damage.
After the steam enters the throttle valve it passes through the front
end of the valve, through the top of the boiler via the dry pipe (fig.
18), through the front tube sheet, and then to the cylinders via the
petticoat pipes. The throttle lever is a simple arrangement readily
understood from the drawings. It has no latch and the throttle lever is
held in any desired setting by the wingnut and quadrant shown in figure
18. The water level in the boiler is indicated by the three brass cocks
located on the backhead. No gauge glass is used; they were not employed
in this country until the 1870's, although they were commonly used in
England at the time the _Pioneer_ was built.
While two safety valves were commonly required, only one was used on the
_Pioneer_. The safety valve is located on top of the steam dome.
Pressure is exerted on the lever by a spring balance, fixed at the
forward end by a knife-blade bearing. The pressure can be adjusted by
the thumbscrew on the balance. The graduated scale on the balance gave a
general but uncertain indication of the boiler pressure. The valve
itself is a poppet held against the face of the valve seat by a second
knife blade attached to the lever. The ornamental column forming the
stand of the safety valve is cast iron and does much to decorate the
interior of the cab. The pipe carrying the escaping steam projects
through the cab roof. It is made of copper with a decorative brass band.
This entire mechanism was replaced by a modern safety valve for use at
the Chicago Railroad Fair (1949). Fortunately, the old valve was
preserved and has since been replaced on the engine.
The steam gauge is a later addition, but could have been put on as early
as the 1860's, since the most recent patent date that it bears is 1859.
It is an Ashcroft gauge having a handsome 4--4--0 locomotive engraved on
its silver face.
The steam jet (item 3, fig. 18) is one of the simplest yet most notable
boiler fitting of the _Pioneer_, being nothing more than a valve tapped
into the base of the steam dome with a line running under the boiler
jacket to the smokestack. When the valve is opened a jet of steam goes
up the stack, creating a draft useful for starting the fire or
enlivening it as necessary. This device was the invention of Alba F.
Smith in 1852, according to the eminent 19th-century technical writer
and engineer Zerah Colburn.[15]
The two feedwater pumps (fig. 20) are located beneath the cab deck (1,
fig. 17). They are cast-iron construction and are driven by an eccentric
on the driving-wheel axle (fig. 27). The airchamber or dome (1, fig. 27)
imparts a more steady flow of the water to the boiler by equalizing the
surges of water from the reciprocating pump plunger. A steam line (3,
fig. 18), which heats the pump and prevents freezing in cold weather, is
regulated by a valve in the cab (figs. 18, 27). Note that the line on
the right side of the cab has been disconnected and plugged.
The eccentric drive for the pumps is unusual, and the author knows of no
other American locomotive so equipped. Eastwick and Harrison, it is
true, favored an eccentric drive for feed pumps, but they mounted the
eccentric on the crankpin of the rear driving wheel and thus produced in
effect a half-stroke pump. This was not an unusual arrangement, though a
small crank was usually employed in place of the eccentric. The
full-stroke crosshead pump with which the _Jenny Lind_ (fig. 22) is
equipped, was of course the most common style of feed pump used in this
country in the 19th century.
[Illustration: Figure 19.--BACKHEAD of the _Pioneer_. (Smithsonian photo
48069F.)]
Of all the mechanisms on a 19th-century locomotive, the feed pump was
the most troublesome. If an engineer could think of nothing else to
complain about, he could usually call attention to a defective pump and
not be found a liar. Because of this, injectors were adopted after their
introduction in 1860. It is surprising that the _Pioneer_, which was in
regular service as late as 1880 and has been under steam many times
since for numerous exhibitions, was never fitted with one of these
devices. Because its stroke is short and the plunger is in less rapid
motion, the present eccentric arrangement is more complex but less prone
to disorder than the simpler but faster crosshead pump.
[Illustration: Figure 20.--FEEDWATER PUMP of the _Pioneer_. (Smithsonian
photo 63344.)]
The check valves are placed slightly below the centerline of the boiler
(fig. 18). These valves are an unfinished bronze casting and appear to
be of a recent pattern, probably dating from the 1901 renovation. At the
time the engine was built, it was usual to house these valves in an
ornamental spun-brass casing. The smokestack is of the bonnet type
commonly used on wood-burning locomotives in this country between about
1845 and 1870. The exhaust steam from the cylinders is directed up the
straight stack (shown in phantom in fig. 27) by the blast pipe. This
creates a partial vacuum in the smokebox that draws the fire, gases,
ash, and smoke through the boiler tubes from the firebox. The force of
the exhausting steam blows them out the stack. At the top of the
straight stack is a deflecting cone which slows the velocity of the
exhaust and changes its direction causing it to go down into the
funnel-shaped outer casing of the stack. Here, the heavy embers and
cinders are collected and prevented from directly discharging into the
countryside as dangerous firebrands. Wire netting is stretched overtop
of the deflecting cone to catch the lighter, more volatile embers which
may defy the action of the cone. The term "bonnet stack" results from
the fact that this netting is similar in shape to a lady's bonnet. The
cinders thus accumulated in the stack's hopper could be emptied by
opening a plug at the base of the stack.
While the deflecting cone was regarded highly as a spark arrester and
used practically to the exclusion of any other arrangement, it had the
basic defect of keeping the smoke low and close to the train. This was a
great nuisance to passengers, as the low trailing smoke blew into the
cars. If the exhaust had been allowed to blast straight out the stack
high into the air, most of the sparks would have burned out before
touching the ground.
[Illustration: Figure 21.--"PIONEER" ON EXHIBIT in old Arts and
Industries building of the Smithsonian Institution. In this view can be
seen the bonnet screen of the stack and arrangement of the boiler-frame
braces and other details not visible from the floor. (Smithsonian photo
48069A.)]
[Illustration: Figure 22.--"JENNY LIND," SISTER ENGINE of the _Pioneer_,
shown here as rebuilt in 1878 for use as an inspection engine. It was
scrapped in March 1905. (_Photo courtesy of E. P. Alexander._)]
[Illustration: Figure 23.--CYLINDER head with valve box removed.]
[Illustration: Figure 24.--BOTTOM of valve box with slide valve
removed.]
[Illustration: Figures 25 and 26.--CYLINDER with valve box removed,
showing valve face.]