Improved Artificial Draft Apparatus.
Year: 1891

page_text: Date of Application, 8th June, 1891
Complete Specification Left. 27th Oct., 1891-Accepted, 8th June, 1892
PROVISIONAL SPECIFICATION.
Improved Artificial Draft Apparatus.
We, WILLIAM CROSBY MUNROE, Engineer, of 407 Temple Court, and
GEORGE WASHINGTON HALL, Engineer, of 115 Broadway, both citizens of the
United States of America, and residents of the City of New York, in the County
and State of New York, do hereby declare the nature of our invention for an
IMPROVED ARTIFICIAL DRAFT APPARATUS to be as follows:-
The purpose of the invention is to enable more heat to be produced within a
fire box of a given magnitude than would be produced by natural draft.
Forced draft is very frequently employed for this purpose but as usually
practised has been created by a blower located in front of the furnace.
Such apparatus however lacks economy in the consumption of fuel and has
various other objections which are avoided by our method which consists
1. In placing a nozzle in the draft exit beyond the furnace and connecting it
with an air blower, the operation of which causes a partial vacuum in the exit
which greatly increases the draft.
This nozzle we usually make flaring and sometimes provide two, concentric with
each other and either fed by separate blowers with conductors leading to the
respective nozzles or from one blower and a double conductor.
2. In contracting the draft exit beyond the fire box of the furnace. When this
is done we prefer to place the nozzle aforesaid a little back of the plane of greatest
contraction and to arrange the nozzle so that the current of air therefrom will just
strike the contraction at said point.
3. In causing the current of air to be intermittent, which is usually done by
placing a butterfly valve in the air conductor between the blower and nozzle and so
gearing its stem to some moving part of the machinery that it will make regular
revolutions.
The first and second or first and third or all three of the features mentioned
may be combined, the best results being attained with a blower provided with a
butterfly valve in the conductors which lead to double concentric nozzles located
in the draft exit (at the uptake) and flaring at different angles, said exit being
contracted at a point a little beyond the end of the nozzles, or where the current
issuing therefrom will strike the inner circle of the contraction.
Dated, at New York City, this 29th day of May 1891.
WILLIAM CROSBY MUNROE.
GEORGE WASHINGTON HALL.
COMPLETE SPECIFICATION.
Improved Artificial Draft Apparatus.
We, WILLIAM CROSBY MUNROE, Engineer, of 407 Temple Court, and
GEORGE WASHINGTON HALL, Engineer, of 115 Broadway, both citizens of
the United States of America, and residents of the City of New York, in the
County and State of New York, do hereby declare the nature of this invention,
and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:—
Our invention relates to forced draft apparatus and consists in the novel devices
and combinations of devices hereinafter described and claimed.
The purpose of the invention is to enable more heat to be produced within a
fire box of a given magnitude than would be produced by natural draft.

page_text: Forced draft, as it is called, is very generally employed to increase the heat
derived from the combustion of fuel within a fire box of a given magnitude. The
great difficulty with apparatus ordinarily employed is, that it lacks economy in
the consumption of fuel and for the greater heat developed a much greater
quantity of fuel is required than with a natural draft.
We have discovered however that by leading the nozzle of a blower into the
stack opening beyond the flues (if in a boiler) or equivalent position, preferably
but a short distance therefrom we attain the accelerated movement of air and gases
(the increased or forced draft) desired, without the objectionable feature named,
particularly if we contract the draft passage near the opening of the nozzle and set
that a little behind the line of the greatest contraction, and render the operation
intermittent.
In the drawings forming part hereof,
Figure 1, is a side elevation of an apparatus embodying the invention, a part of
the stack being broken away to more clearly exhibit the parts.
Figure 2, is a side elevation (partly in section) of such an apparatus with devices
somewhat differently arranged, and using but one pipe.
Figure 3, is a central vertical sectional view of a portion of the stack and a
single nozzle.
Figure 4, is a plan view of a modification whereby the draft is made to operate
intermittently.
Figure 5, is a plan view of a double blower arranged to operate the apparatus,
one blower leading to one nozzle and the other blower to the other nozzle in order
that the two jets (when two are used) may be operated independently; and,
Figure 6, is a view of an arrangement of the nozzle a little behind the line of
greatest contraction of the stack, as preferred, the stack being shown in section.
B, represents a boiler which may be of any ordinary construction, here it is a
return flue boiler the draft passage being from the firebox end F, to the rear
end R. back to the uptake U, and into the stack S, which is preferably contracted
as shown, by means of pieces set in, though the location of such contraction might
be slightly varied without departing from the spirit of the invention, and it might
be accomplished by contracting the diameter of the stack itself.
A., is the blower provided with a fan f, driven by belt b, leading from engine E.
From said fan, a delivery pipe I", leads into the stack S, and terminates in a
nozzle N', located therein, preferably centrally. In this figure the mouth of the
nozzle is at the line of greatest contraction of the stack S. Within pipe P', is a
second pipe P secured by bolts (indicated by dotted lines), leading to a second
nozzle N located concentrically within nozzle N', the air between P & P going
to N', so that it may be delivered at a different angle from that issuing from N, if
desired. If preferred, a double fan, as shown in Figure 5 may be used, connected
respectively to pipes, P, and P1, instead of one fan for both pipes. Then however
P, is extended to the fan as shown, instead of ending above the elbow of P1, as in
Figure 1.
The apparatus of Figure 2, is substantially similar to that explained, the
difference being that the blower (here a single one) is located on the side of the
boiler opposite to that on which the stack is located and the delivery pipe also a
single one, having a single nozzle, leads lengthwise of the boiler into and through
the uptake and to the nozzles which are located as heretofore described.
We have, as will be seen, arranged the nozzle to flare, that is to deflect, in the
direction of opening away from a line through their centres and believe this to be
one of the great advantages of the device, and while in some cases it is well to
locate them with the mouths in the same horizontal plane as that of the greatest
contraction, we believe that the best results are attained by locating said nozzle or
nozzles a little below said plane as shown in Figure 6, in which case it is advan-
tageous to make the angle of the mouth of the nozzle such that a line projected
from the extremity of the mouth; at the same angle from the median line, would
just touch the point of greatest contraction of the stack and thereafter the wall.

page_text: At times it may be found to be advisable to have the forced draft act inter-
mittently and to that end, as shown in Figure 4, we arrange a butterfly valve f³,
in the supply pipe P', with its shaft extending through the wall thereof and
provided with a pulley from which a belt passes to the engine E. Twice during
each complete revolution of valve f³, the supply pipe P, will be almost closed,
(the wings of valve f, fitting loosely) and twice it will be fully open, and the result.
will be an intermittent action such as is desired. Other means might be adopted
to accomplish this result.
Our method of forcing the draft may be advantageously used in combination
with the ordinary method of blowing air directly into the furnace, but we prefer
it as herein represented.
The operation of the apparatus, arranged as shown is obvious;
Fire being started in the fire box, the engine E, is put in motion and the fan at.
once produces a current or currents of air, which passing through the delivery
pipes escapes at the nozzles N, and N1, that from Ni, particularly impinging upon
the inner surface of the stack where the friction is greatest. The effect is of course
to cause or tend to cause a partial vacuum in S, at the rear of the nozzles, which
necessarily increases the difference of atmospheric pressure at the different ends of
the draft passages of the boiler. Air enters the fire box with an accelerated
movement and a forced draft is produced. Decreasing the cross area of the stack
at or near the location of the nozzle, together with the blast issuing therefrom
increases the velocity of the movement of air at that point, as must be manifest,
and to this increased velocity much of the admirable effect produced may be
attributed. Indeed the action is that of drawing air through the fuel (the natural
way) as distinguished from blowing it through, the common artificial way, and to
do it effectively and with economy it is essential to employ an apparatus sub-
stantially such as that described. When but one nozzle N is used & sometimes
with two we insert a flaring piece F as shown in Figure 3. It is closed at the
bottom, cylindrical in shape & fills the end of the nozzle somewhat so that the air
issues in annular form.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. An improved forced draft apparatus, consisting of the combination with the
draft exit of a furnace, of a nozzle located in the exit beyond the fire box, a
delivery pipe leading to said nozzle and meaus substantially as described for
intermittently forcing air into and through said delivery pipe, substantially ag
set forth.
2. An improved forced draft apparatus consisting of the combination with the
draft exit of a furnace contracted beyond the fire box of two nozzles concentric
with each other, located at said contraction within the draft exit, delivery pipes
respectively leading to said nozzles and means for forcing air into and through said
delivery pipes and nozzles, substantially as set forth.
3. An improved forced draft apparatus consisting of the combination with the
draft exit of a furnace contracted beyond the fire box of two nozzles concentric
with each other, located at said contraction within the draft exit, delivery pipes
respectively leading to said nozzles each provided with a separate device for
forcing air into and through it and its respective nozzle, substantially as
set forth.
4. An improved forced draft apparatus consisting of the combination with the
draft exit of a furnace contracted beyond the fire box of two nozzles concentric
with each other with their mouths opening at different angles, located at said
contraction, delivery pipes respectively leading to said nozzles and means for
forcing air into and through said delivery pipes and nozzles, substantially as
set forth.
5. An improved forced draft apparatus consisting of the combination with the

page_text: draft exit of a furnace contracted beyond the fire box of a nozzle located within
said exit with a flaring mouth substantially as described, a delivery pipe leading
to said nozzle and means substantially as described for forcing air into and through
said delivery pipe, substantially as set forth.
6. An improved forced draft apparatus consisting of the combination with the
draft exit of a furnace contracted beyond the fire-box of a nozzle located within
said exit but behind said plane of greatest contraction, a delivery pipe leading to
said nozzle and means substantially as described for forcing air into and through said
delivery pipe substantially as set forth..
7. An improved forced draft apparatus consisting of the combination with the
draft exit of a furnace.contracted beyond the fire-box of a nozzle located within
said exit but behind said plane of greatest contraction, with its mouth opening at
such an angle that a line projected from said mouth at the same angle to the axis
of the nozzle will touch the contraction at its immost limit, substantially as
set forth.
8. An improved forced draft apparatus consisting of the combination with the
draft exit of a furnace contracted beyond the fire box, of two nozzles concentric
with each other, located within the draft exit, delivery pipes respectively leading
to said nozzles and means for forcing air into and through said delivery pipes and
nozzles, substantially as set forth.
October 8th 1891.
WILLIAM CROSBY MUNROE.
GEORGE WASHINGTON HALL.