The Cornish engines have been alluded to in connection with the
Newcomen engine. Probably no large pumping engines in the past have
held, and deservedly so, as high repute as have the Cornish engines
when used for deep mine pumping. Their construction, with the rude
appliances at hand, is not only a marvel but as well a high tribute
to the ingenuity of those who designed them and to the skill of the
workmen who built them. A rather full illustrated description of this
almost unexcelled machine will be found later on in the book.
_The next class of large steam pumping-engines which have played an
important part in the history of hydraulic engineering may be grouped
together as “rotative engines.”_ What is here meant by the term
“rotative” is engines in which there are parts which make complete and
continuous rotary motion and in which are used, in some way or another,
shafts, cranks and fly-wheels.
These engines vary greatly in their design and in the details of their
construction. They are of varying sizes, including some of the largest
and most expensive in the world. As a general thing they are employed
in supplying towns and cities with water, and in some cases freeing
shallow mines of water. The application of the power of the steam used
in the steam cylinders in this class of engines to drive the plungers
or pistons in the pumps, varies greatly, both as to the general design
upon which they are built, and in the detail of their construction. In
some instances it is through the use of long or short beams or bell
cranks, sometimes through gearing, and occasionally through the plunger
or piston of the pump direct; but in all cases the limit of the stroke
of the steam piston, and of the pump plunger, is governed by a crank on
a revolving shaft.
Attached to the revolving shaft is _a fly-wheel_ of greater or less
diameter and weight, which, in addition to assisting the crank to
pass the center at each end of its stroke, _is employed to store up
at the beginning of each stroke of the steam piston, whatever excess
of power or impulse there may be imparted to it, beyond that required
to steadily move the water column, and to give out again, toward the
latter part of the stroke, when the power of the steam is of itself
below that required to move the water column, the power previously
stored in it_. In this respect the function of a revolving fly-wheel on
a rotative engine is the same as is the weighted plunger in the Cornish
engine; both being used for the purpose of permitting the steam to be
cut off at a portion of its stroke in the steam cylinder, and expanded
during the rest of the stroke.
In short, these devices, as employed in both the classes of pumping
engines described, were used in order that the best economy in the
consumption of steam by means of early cutoff and a high grade of
expansion, might be attained.
The succeeding class of pumps to be described, driven by steam are
_direct acting steam-pumps_.
What is here meant as “direct-acting,” is a steam-driven pump in which
there are no revolving parts, such as shafts, cranks and fly-wheels;
_pumps in which the power of the steam in the steam cylinder is
transferred to the piston or plunger in the pump in a direct line_, and
through the use of a continuous rod or connection. (Fig. 82.)
_The introduction of the direct-acting steam-pump marked a point of
deviation_, and it entered the field almost without a rival, and at a
time when economy was overshadowed by its convenience.
In the brief description given of these three most prominent classes
of pumping engines, no attempt has been made to describe any of the
peculiarities of their general construction, beyond what was necessary
to describe their action and the principles upon which they operate.
[Illustration: FIG. 82.]
In pumps of this construction there are no weights in the moving
parts other than that required to produce sufficient strength in
such part for the work they are expected to perform, and, as there
is consequently no opportunity to store up power in one part of the
stroke, to be given out at another, it is impossible to cut off the
steam in the steam cylinder during any part of its stroke. The uniform
and steady action of the direct-acting steam-pump is dependent alone
on the use of a steady uniform pressure of steam through the entire
stroke of the piston against a steady, uniform resistance of water
pressure in the pump; the difference between the power exerted in the
steam cylinders over the resistance in the pump governing the rate of
speed at which the piston or plunger of the pump will move. The length
of the stroke of the steam piston, within the steam cylinders of this
class of pumps, is limited and controlled alone by the admission,
suppression and release of the steam used in the cylinders.
NOTE.—Up to the introduction of the direct-acting steam pump, all
the other pumping machinery of the world then in use was the outcome
of evolution. It had been developed by slow stages, in which one
engineer after another aided by the experience of others and of
his own, supplemented by his inventive faculties, added here and
there slight improvements to which other engineers, with increased
experience, were enabled to add still other improvements, so that
each new engine constructed under more favorable circumstances, and
with increasing expenditures, was supposed to excel all previously
built; until at this time we have, as it is fair to suppose, pumping
engines which combine all the wisdom of the past, and which leave
little or no room for further improvements in their respective
classes.
The history of the _Direct-Acting Steam Pump_ differs from all others
from the fact that it was the invention of one man, and was in the main
perfected during his lifetime. It was so strikingly different from all
that had preceded it, that there was nothing in the way of precedent,
either in ancient or modern practice, of which the inventor could avail
himself by which to aid or guide him to success.
The date of the first patent on these pumps was September 7, 1841. It
was issued on a small pump used for supplying feed water to a steam
boiler, and consisted of one steam cylinder connected to a force pump,
and so arranged that by the use of levers, trips, springs, and other
connections between the piston rod and the slide valve, the movement
of the piston rod controlled the movements of the slide valve to an
extent that not only regulated the length of the stroke of the piston,
but reversed its motion. This pump was placed alongside of the steam
boiler, and was so connected by means of pipes and levers and floats
within the boiler, that when the water fell below the proper level in
the boiler, it would start the pump, and stop it when the water rose
too high.
NOTE.—At the head of a list consisting of two names only, who, on the
foremost pages of “The American Society of Mechanical Engineers,”
are recorded as the “Honorary Members in Perpetuity” of that large
society, and standing as well at the head of that long and increasing
list of members who have accomplished their work on earth, may be
seen the name of _Henry Rossiter Worthington_, the inventor and
original builder of the “direct-acting steam pump.”
Feeling how incomplete was an invention which did not provide against
the intermittent action of the pump, Mr. Worthington devoted much time
and study to correct this trouble, and a few years later he brought
out an improved pump which, in its simplicity of parts, certainty
of action, and cheapness of construction more than rivaled the
original invention itself. This pump is now universally known as the
“_Direct-Acting Duplex Steam Pump_.”
In the main, the construction of the steam ends and the water ends of
the duplex pump differs but slightly from those of the single-acting
pump, but the mechanism which operates the steam valves is different,
and the effect on the water column was marvelously different; the
principle upon which it operates is this:
Two pumps of similar construction are placed side by side, a lever
attached to the piston rod of each pump connects to the slide valve of
the opposite steam cylinder; thus the movement of each piston, instead
of operating its own slide valve as in the single pump, operates the
slide valve of the opposite cylinder. The effect of this arrangement
is, that as the piston or plunger of one pump arrives near the end of
its stroke, the plunger or piston of the other begins its movement,
thus alternately taking up the load of the water column, producing a
regular, steady, onward flow of water, without the unusual strains
induced by such a column when suddenly arrested or started in motion.
While the “duplex steam pump” overcame one of the greatest objections
to the former single pump, there still remained in this class
of pumping machinery one other difficulty. It did not use steam
expansively.
This not only debarred it from competing with other engines where a
large quantity of water was required to be raised, and where the cost
of fuel was an item of importance, but as well prevented the pump from
taking rank among the hydraulic appliances required in supplying towns
and cities.
This objection was one which seemed insurmountable, steam in them could
not be used economically. Applied to the propulsion of the plunger or
piston of this pump it must be of sufficient quantity, and pressure,
to overcome the height of the column of water on the pump, together
with its friction through the pump and its connections, _at the very
beginning of the stroke_; and it must be maintained, both as to its
volume, and its pressure up to the very last part of the stroke. Any
diminution, either of volume or pressure, during any part of the stroke
would simply bring the pump to a stop. This apparent inability to cut
off the steam in the steam cylinder, and to complete the stroke of the
pump by the aid of the steam remaining in the cylinder, and by its
expansive force, had debarred this pump from coming into general use
for large water works. How this, the only remaining objection to their
use for such purposes, was overcome, forms an interesting chapter in
the history of the “_Direct-Acting Steam Pump_.”
It was when this question had assumed a most formidable, importance,
that the principle of _using steam in compound steam engines_ had
engaged the careful consideration of the most eminent engineers of this
and other countries; _its adjustment to the Duplex pumps was made_,
and while it was easily done, owing to their peculiar construction,
its application produced a most wonderful result in their working, and
their speedy introduction for water works use.
NOTE.—At this time the man who had invented and built the little
steam pump for the canal boat, who had watched its growth and
development, supplemented one device after another to help it on
through the trial period of its existence, had merged it at last
into the dual or duplex stage of its advancement, had added to it
the compound feature, had seen it expanding in size and importance
until, growing up and out of the day of small things, it had come to
take its well-earned place alongside those old and massive machines
whose invention and origin was lost amid the musty records of the
past—it was, at this time, and of which any man might well have been
proud, that his lifelong labors came to an end Dec. 18., 1880, at the
Everett House, New York City.
ELEMENTARY
HYDRAULICS